Glass PCB Material Properties
Printed circuit boards are generally made up of flat laminated non-conductive materials with layers of copper on all surfaces. In the manufacturing of glass PCB( printed circuit board), these are the following material that is used.
1- Piece of Glass
2- UV photoresist
4- Copper foil
5- Chloride of iron
6- OHP printout
These above mention materials are used in making glass PCB. Here we will discuss in detail.
Piece of Glass
Glass serves as the foundation of glass PCB manufacturing. The substrate of PCB glass is ultra-clear float glass. Glass should be waterproof, moisture-free, best resistance of corrosion, high thermal dissipation, high reflectivity, low expansion coefficient, feasibility to laminate with other materials. Glass PCBs are used in those fields which have demands of high thermal dissipation and light transmittance.
UV light is used for transferring the image from a plotted film onto a bare copper clad laminate. There are two types of UV resist film i.e., positive and negative. Negative is when the developer added to the resist, exposed parts remain undissolved and others dissolved. Positive is the reverse of negative. UV box has a case with organic glass, panel, UV lamps ballasts and starters, and Controllers.
Baking soda has qualities of alkalinity and abrasive that are good for PCB glass. Baking soda is used as the cleaner for PCBs corrosion. To eliminate the corrosion, it is used. Baking soda cleans and eliminates all the corrosion without damaging the PCB. Use the solution of baking soda, about 150ml, and water. If baking soda is not available then use rinse powder.
Choose a copper foil whose thickness is almost 0.05mm, that is perfect for PCB. The high thickness of the copper foil is very expensive that is sometimes not affordable. There are two types of copper foil used in glass PCB: ED( electrodeposited) and RA( rolled-annealed) copper. The manufacturing of both coppers is different, and different treatments are given to them.
Chloride of Iron or Iron Chloride
Chloride of iron or Ferric chloride powder is also involved in making glass PCB. FeCl3, one iron part, and three chloride parts are available in both forms i.e., powder and liquid. Powder costs less, but it’s dangerous if not used carefully. For PCB liquid is used. About 150ml of ferric chloride powder is added to water to make the solution. Ferric chloride powder is used in all unwanted copper.
The design of PCB (printed circuit board) is usually printed on OHP print. After making the layout of the PCB design then print the design through OHP transparent sheet. OHP sheet is the thinnest sheet, it is easy to use the thinnest sheet. The thinnest sheet facilitates ironing on PCB without crumpling. OHP print is important to blocks the UV light exposure of the resist in unwanted regions.
PCB glue or adhesive would be a two-part epoxy. They are inexpensive and average volume is required. It protects and saves the PCB from moisture and a harsh environment. Curing would take one day at normal temperature.
China PCB Glass Board: FXPCB
Printed Circuit board is used in LCBs and LEDs. It uses glass as raw material and then the construction of the process is started. We use masks that are UV curable and this is an essential part of the process. When people produce PCB in bulk manufacturing this methodology is adopted. When uncured etches are exposed to UV radiation they got tough.
An opaque film is used in which there is a photo of the circuit. UV light is subjected to a copper board using a UV light output. The circuit design is created and the circuit is now started for the imprinting process.
UV films are of too kind Positive and Negative UV films. In the process, the Photoresist remains and the other portions are melted when the developer is added. This is a symbol appositive of negativity and the negative one will be used in different ways
People who have skills according to PCB and know how to create circuits are very demanding in the market. The process of Glass PCB production is not easy and has the same alert as other different types of PCBs. Specialists can use optical methodologies based on glass substrates and different types of materials are used in glass printed circuit board production.
Different types of Glass PCB:
Different experts use substrates and materials of different types to create PCB. These materials have shown different kinds of properties during the performance of the product. Here are the most common types of glass PCB. These are widely used all over the world.
1. Sapphire Glass:
Usage of Sapphire crystals has shown the marvelous performance in thermal characteristics of glass PCB. Not only these features but also the product is inert chemically, good in structure, and extraordinary in electronics. The infrared conduction of sapphire glass makes it an amazing material to adopt.
1. Tempered Glass:
Tempered Glass is tough to break and it is a very strong material usually we can say in a common language that it is a glass reprocessed by the glass. Experts suggest that it is the best material to use in military devices like cameras, infrared viewing systems, high precision devices, and much more.
2. Quartz Glass:
Experts suggest that Quartz crystals should be used when the glass PCB is to be used in microelectronics. Quartz is a low thermal coefficient because of its resistance to the mold process. It is observed that it is very stable to UV and infrared rays.
Materials Used in making Glass Printed Circuit Board:
There are different materials but experts prefer using a printout of OHP, copper foil, iron chloride solution, piece of glass (UV resistant material), UV photo resistance, baking soda, and different types of glue.
Benefits of Glass PCB:
Glass PCB is commonly used in LED and LCD along with other purposes like making clear glass invisible wiring for decoration purposes. It is also used in circuits in which transparency is important like on a lead set. It is also used in making packaging that emits light at 360 degrees. PCB glass is used in solar plants in the production of solar cells.
A huge benefit of glass PCB is observed in making 3D printers and LED screens. Due to the high heat resistance and opacity of the glass substrate, it is amazing to use when operations are to be performed at high temperatures because of its capability of less deformation.
What is glass PCB etching? Best Guide 2022
PCB (printed circuit board) on glass is a recent development, although it is quite quick, and it is convenient to print. These days etching of PCB on glass is affordable and through several services, this is done. For decades, people did PCB at home with the chemical etching process. But today, because of many services, people do not go through this troublesome work.
There are many ways to do etching on the glass, the most common way is to print the pattern of the circuit on the copper clad board and then etch on the unwanted copper. There is a method that is most useful to etch PCB on any desirable surface. It will be suited on every surface. It is reliable and awesome to transparent PCB on glass.
Step 1: Technique
The toner transfer method is most effective and it is also used in the mass production of PCB. In this method, UV curable glass is used to transfer the circuit on the copper board. Even with the smaller width, it provides fine and amazing output.
Step 2: PCB Glass Material
Piece of glass/ glass, UV photoresist, baking soda, copper foil, ferric chloride, super glue (cyanoacrylate), OHP printout (overhead projector printout ). These are the material that is required in etching the PCB on the glass. These are very effective tools in etching the circuit on the glass.
Step 3: Design the circuit design
After getting the material, firstly, there is a need to prepare the design of the circuit which is going to transfer on the transparent sheet. Many platforms help make designs, one of them is EASY eda. This online circuit design software is very easy to use and free of cost. After sketching the circuit, model the PC B layout. With the autoroute tool, root the path of the circuit. When you satisfy with your circuit then export the image as PNG.
Step 4: Printing the circuit
OHP printing is used to print the circuit and the advantage of using OHP printing is that it makes a layer that blocks UV light to expose the unwanted areas. Black parts or block parts of OHP do not allow the light to pass through them. But one layer of OHP print does not stop the light to pass that’s why three print attached with glue, is used.
Step 5: Gluing the Copper Foil to the GLASS
After printing the circuit, then copper foil is glued on the glass. A thickness of 0.05mm is perfect for gluing because more thickness of the copper foil is very expensive. Clean the copper foil and glass thoroughly and press the copper foil on the glass with glue. Make sure there are no bubbles between them. If any then remove the extra glue.
Step 6: Applying photoresist
The photoresist has two transparent covers which covered both sides, firstly cutting off the required size piece. Because of sticky material, when covers are removed the photoresist is easily attached to the copper board. Press gently to attached the photoresist with a copper board and make sure there are no bubbles between them.
Step 7: Expose the setup to the light
After photoresist, OHP print attached with the copper board. Make sure to print is attached with the board tightly and use two clips to keep them tight. Then expose the setup to light.
Step 8: Exposure of light
Expose the setup in the front of artificial UV light, sunlight is the natural source of UV light. 5min exposure to sunlight is good. 5-7minute exposure of setup to UV light dissembles everything. And you can see the print cured on the resist.
Step 9: Develop the resist
Resist film has another layer of cover, remove this layer by using baking soda. Make baking soda and dip in it and keep it in for a while. Remove the cover gently. Wash the unexposed areas and in the end, you will end up with a copper board with tracks of cured resistance.
Step 10: Final PCB Glass Etching
Mix ferric chloride powder and 150ml water, the solution will be dark. Dip the board in the solution and shake the board to etch. With acetone and warm water, you can remove the extra resist from the board. Now you have the final product of PCB on glass. It is a very awesome and creative method of PCB on glass.
You can apply glue, fluxes, and solder paste to a printed circuit board in any of the following 5 Surface mount pcb ways:
- With rods.
- Screen printing.
- pulsation pump.
- screw pump.
- piston pump.
The use of these types of pumps, using a dosing mechanism, makes it possible to point the application of materials to the board. The first 2 methods (using rods and screen printing) are designed to simultaneously apply material to several areas at a time. Each of these 5 methods has both pros and cons.
Rod method Surface Mount PCB
This is the easiest way, suitable for both glue and flux. Although the rod can only be applied at a single point in 1 application, you can use the rod matrix to do this at several points at the same time.
In the process, the rod is lowered into a container with glue. The length and thickness of the rod directly affect the volume of material collected from the container.
Next, the rod is lowered onto the board at the desired point, and due to surface tension, a small drop of glue remains on the board. It is required to avoid touching the rod with the board, because this will change the shape of the drop. The use of a matrix of rods will make it possible to apply glue to an already installed board.
Best Method to Apply Flux On PCB Board
The same method is used when applying the flux to the solder balls of DCA/FC packages. The crystal is immersed in a container with a thin film of flux. Because of this, only solder balls get wet, as a result they play the role of rods for transferring flux droplets to the board.
A serious problem with the rod method is the use of open containers filled with material prepared for application. The fact is that the glue quickly absorbs atmospheric moisture, and fluxes, on the contrary, quickly lose their main carrier (water or alcohol) and other components as a result of evaporation.
All this leads to the loss of the initial properties of the material and has a great influence on the volume of material collected on the rod, or the volume of the drop remaining on the board. This places higher demands on the quality of adhesives and fluxes.
Screen printing method
This method is suitable for both adhesives and pastes. The low viscosity of many fluxes prevents them from being applied in this way. Screen printing is based on the fact that the material is applied through holes in the stencil, called apertures.
These holes are placed over the areas of the board where the material is to be applied. The application itself is carried out with a squeegee, which, when passing over the stencil, squeezes out a certain amount of material into the apertures.
There are 2 types of stencils: with partially closed (mesh) and open apertures. These stencils are designed for use in different areas.
Mesh structures have 2 layers: emulsion and emulsion-preserving film. Holes through which the material is applied are formed by photochemical milling. In this case, the material simply flows through the mesh covering the apertures.
The design with open apertures looks like a metal sheet (molybdenum, nickel, brass or steel) with holes. To obtain apertures, the following methods or their combination are used:
- photochemical milling
- laser cutting
A specific technique is selected based on the required diameter and aperture placement density. Mesh stencils have largely replaced open aperture designs, as they are simpler and suitable for boards with a large number of small elements.
In addition, in the manufacture of a printed circuit board, the application of the paste can be performed using stepped stencils. Similar designs come in 2 types of different thicknesses. They are used if it is necessary to fix on the board many components of various configurations with different pitches.
Pump applications on PCB Board
In a pulsating pressure pump, the dosed application of the material (glue or paste) occurs due to the application of a pressure pulse to the container with the material for some time.
A strictly measured volume of material is squeezed out of the nozzle of the device of the required diameter and remains on the board. Often, the material is sold in pre-packaged form – in syringes designed to be inserted into the assembly machine.
As with other application techniques, the characteristics of the adhesive and paste are of the utmost importance as they affect the stability of droplet volumes in different areas.
The storage conditions and shelf life of materials must be strictly observed, as they quickly decompose. The optimum viscosity of the materials is in the range of 100-400 cps.
Functions of Automatic Machines
Automatic machines with piston pumps allow you to apply the material as droplets of different volumes. To do this, nozzles or syringes of different diameters are mounted on one head, while equal pressure is applied to them.
There is another method, which consists in pre-programming the duration and power of pressure in the pump, which allows you to apply drops of different volumes without changing the diameter of the nozzle or syringe.
This technique requires more time in the manufacture and development of printed circuit boards than screen printing, but it can be used to strictly control the number and location of drops of glue or paste.
The screw pump uses an Archimedean screw to extrude a given volume of material through a nozzle. The rate and duration of the turn of the screw, and in addition, the diameter of the nozzle, affect the amount of material remaining on the board.
In a screw pump, as in a piston pump, you can use different heads and programming to change the speed of the rotating screw or the duration of its rotation, thereby changing the size of the droplets of material without changing the diameter of the nozzle.
Output printed circuit boards
The main task of each of the considered methods is to apply droplets of material of a precisely defined and constant size to the entire surface of the printed circuit board. A very small drop of glue in the manufacture of printed circuit boards will not allow you to fix the part on the board, and too much glue will spread and lead to poor soldering.
The PCB board is a component present inside various everyday objects, such as computers or smartphones. This element represents the vital fulcrum of many tools used in everyday life: entrusting its production to a reliable partner means ensuring a functional and quality finished product.
Each project, to be perfect in every detail, requires a detailed and very precise design. However, it may be necessary to make changes or refine some details during manufacturing. To this end, it is essential to be able to have rapid and effective communication with the customer.
In this article, FX PCB explains the advantages of choosing a Chinese partner for the production of your PCB boards.
FX PCB: A single point of contact for your project
The Chinese reality of companies specializing in the design and manufacture of PCB boards is developed in a network of medium-sized companies, ideal for the production of printed circuits intended for very particular products.
Given the singularity of these productions, a lot of attention and care is required from the very beginning of the project itself. Having a partner capable of following your project from A to Z , from the design of your idea to delivery, is a considerable advantage : having the possibility of dealing with a single team avoids having to transfer information elsewhere , reducing the risk of misunderstandings and additional critical issues.
Given the uniqueness of the products made, the relationship between customer and partner becomes fundamental: choosing a company located in China allows you to reduce the physical distance between them, ensuring faster and more effective communication.
Furthermore, the difficulties of linguistic comprehension are certainly reduced: opting for a contact person who shares the same mother tongue eliminates the risk of misunderstandings that, otherwise, one would risk encountering. In fact, the PCB boards are made up of components named with specific terms, which must be well known in order to avoid misunderstandings and consequent complications during the processing phases.
Less distance, more services
Difficulties can be encountered during the different stages of production, for which it is necessary to communicate with the customer: the reduced distance allows, also in this case, a rapid and efficient communication, aimed at the rapid realignment of the production line.
In addition, it should be remembered that in order to have products equipped with technology in step with the times, it is essential to carry out the correct updates to their software and that this delicate operation is carried out by a qualified and specialized team.
Always having a competent partner available, reachable in a short time, means saving time on the shipment and collection of correctly updated products. Furthermore, given the use of constantly evolving components, it is important to have a team always available: this will allow you to never be left with obsolete technology.
Quick and competent assistance
Should system bugs or anomalies that cause software malfunctions emerge, the proximity between the client company and FX PCB allows you to move quickly throughout the national territory, guaranteeing rapid and effective inspections and debugging services.
For FX PCB, ensuring rapid response times to the customer is an aspect of fundamental importance: from the awareness that a bug in a PCB board can cause sudden interruptions in the operations of a company, the need arises to be able to solve any problem quickly and effective.
Choosing to entrust the design and production of your PCB boards to a Chinese partner allows you to benefit from numerous advantages such as a lean and fast communication, an effective assistance service, able to move easily throughout the national territory, and rapid resolution of complications or criticalities that emerged during the different stages of production.
Are you looking for a qualified Chinese partner to entrust with your project? Contact us: the FX PCB team is at your disposal to bring your ideas to life.
2. 1. –Introduction to PCB Board Design
When starting the design of a pcb board, the functional requirements imposed by the system, by the client, etc. must be taken into account. , as well as the commercial economic aspect of the project.
But there are also a series of factors limited by the rules of making and by the facilities available to the factory (machinery, tools, etc.), to be taken into account when choosing the pcb board.
A circuit or a family of printed circuits that meet an optimal design will be obtained, when these requirements have been combined, in a detailed analysis. Many times from this analysis the conclusion is drawn that it is difficult or impossible to arrive at the ideal design. Below are the most important considerations that must be taken into account, in the choice of pcb board, to find consistency and interactions between design rules, manufacturing facilities and the final economic result:
- a) Specification of the product and estimate of its cost.
- b) Equipment Life.
- c) Electronic requirements (voltages, gains, impedances, etc.).
- d) Manufacturing methods:
- dl) Compatibility with the existing Factory Plant.
d2) Size of the order to be produced
d3) Degree and type of mechanization used.
- e) Subsequent operations:
- f) Maintenance
f1) Operational requirements.
f2) Repair requirements.
f3) Minimum degree of maintenance required.
- g) Materials and Components
- gl) Acquisition sources
g2) Delivery dates
In the design of a pcb board, it will be necessary to start by choosing the simplest category according to its density, attending to the requirements expressed in the corresponding specification. Electrical and environmental factors and the use or destination of the circuit board must be taken into account.
The lower the category of the board, the lower the cost and the less important in terms of quality and quantity the problems that arise in design and manufacturing.
The orientations on the use of the methods of design and distribution of the elements of the circuit in the base circuit board, must be presided over by the DISTRIBUTION RULES stated in this chapter.
2.2. – DISTRIBUTION METHOD. BASIC MODEL DRAWING.
Knowing the schematic, with the greatest precision and clarity possible, the distribution of the components of the circuit will be drawn in its simplest form, placing the elements with the idea of reducing the crossing points of the interconnections to zero.
The distribution will be made based on successive initial drafts or sketches, which gradually incorporate improvements, until the next step in drawing generation can be carried out. It is not uncommon to specify 3 or 4 sketches, and even more, in circuit boards of higher categories.
It is useful to use templates that serve as a basis for the assembly of components and that, together with the point-to-point connection of the schematic, help organize the interrelationships of the circuit, trying to comply with the design rules expressed in the chapter.
For an initial sketch it is common to start from a paper copy of a Basic Model Drawing that contains elements common to a family of pcb boards, thus saving time in this design step.
This mode of operation is used both for the manual production of model drawings, and when preparing sketches for digitization, prior to the use of plotting machines.
The Basic Model drawing generally records the following impressions:
a)circuit board outline.
- b) Reference Systems (with all their indications and marks).
- c) Printing and labeling of the connectors.
- d) Position of the support hole.
- e) Normalized configuration of holes.
- f) Ground and power planes.
- g) Connector outlet positions, as specified by the product.
- h) Test knots, as assigned by the product test specification.
These impressions can be common, repetitive or fixed and as such are expressed in the drawing.
In the method of distribution of a pcb board, the following steps can be followed as a guide, which can be completed in the order indicated or in another, increasing or reducing their number.
- a) Study of the schematic and the complete and detailed list of the components of the circuit.
a.1) Dimensional parameters (templates) of the circuit board and components
a.2) Electrical and mechanical parameters
- b) If a paper copy of the Basic Model Drawing is available, it will be taken as a starting point. If it is not available, assign their positions to all the fixed elements of the circuit (list of components) making the distribution bearing in mind the Distribution Rules for pcb boards.
- c) Find the repetitive parts of the Circuit and place them looking, in principle, for a uniform geometric distribution, coupling, on the other hand, the mechanical components (switches, pins, etc.).
- d) Decide on the type of base material for thecircuit board. This depends on its density, external environmental conditions, assembly conditions, recipient equipment, etc.
- e) Set the sizes of holes and knots and the widths of the conductors.
- f) Keep in mind the density classification, trying to avoid limit configurations.
- g) Locate components according to their input and output requirements
- h) Consider all the electrical, mechanical, structural and environmental requirements, especially taking into account:
h.1) Insulation resistance and/or dielectric properties of the base material for higher frequency or impedance circuits.
h.2) Voltage drops and temperature rise of the conductors.
h.3) Environmental operating and storage conditions (humidity, dust, temperature, vibrations, shocks, etc.)
h.4) Mutual coupling and inductive and capacitive effects.
h.5) Uniform distribution of the weight of the components on the surface of the base circuit board.
- i) Special reinforcements, special insulation, critical ground connections, temperature dissipation.
- j) Optimum use of the useful space of the circuit board for the routing of the conductors, remembering that they must be as short as possible.
- k) Take into account in the placement of the components, the necessary separation of the same to make feasible the use of the tools and devices that must be used in the assembly operations. Of course the components must not interfere physically, in accordance with electrical, thermal and repair requirements.
- l) The most delicate components must be placed in the correct place, to avoid harmful electrical couplings in the operation of the circuit.
All these requirements must be taken into account as a guide to follow in design, in accordance with the product specification. They serve both for manual processes and for digitization processes, as mentioned above.
The identification and accuracy of the finished pcb board can be, at most, equal to that of the Original Model Drawing.
The designer must be aware of the most important manufacturing parameters and reprographic processes of the pcb boards that can be used.
23. -DISTRIBUTION RULES.
Usually when a printed board is designed, there is a product specification that meets all the necessary requirements for the engineer to be able to generate all the information needed to manufacture it:
- a) Geometric characteristics of the circuit boards: External dimensions, details of their contour (notches). Hole blocks, their location relative to the contour or to a reference point. circuit board thickness and flatness limits.
- b) Conductive printing, its configuration on one or both sides, components that must be welded. Dimensions of nodes and conductors. Identification Records.
- c) Base material (your specification). Metallic holes. Protective finishes.
All this with the precise detail and for all kinds of circuit boards. both for the repetitive and for the special ones.
Below are a series of numerical data and design rules that the engineer needs to know to generate Model Drawings. This in turn, in the Factory, will be the starting material to begin the production process of the pcb board.
The smallest possible number of different sizes of holes is usually used for assembly and connection. The attached table shows the nominal diameters and their tolerances.
|Nominal diameters in mm.||non metallic||metallic|
To obtain a certain economy in drilling or punching operations, it is recommended not to use more than 3 diameters for ordinary holes.
The thickness of the metallic coating film will be for copper:
20 µm. min for holes diam. <= 1/2circuit board thickness.
25μm. min for holes diam. > 1/2circuit board thickness.
For tin/lead: 10µm. minimum.
Position of the center of the mounting holes, of the components with respect to the separation from the origin. tolerances.
Spacing <= 150mm. – Tolerance 0.1mm.
Separation > 150 mm. – Tolerance 0.2mm.
The distance between holes is expressed in the following table, with its tolerances.
|Distance between holes (d)||Distance tolerance (mm.)|
|Classes 11 and 21||Classes 12, 22 and 23|
|50 <= d < 100mm.||±0.2||±0.1|
The tolerance on grooves and notches is ±0.1 mm. in its two dimensions, whether or not they are metallic.
The following table specifies the nominal diameters of the conductive nodes corresponding to the nominal diameters of the holes. The nominal welding reserve node is also indicated. All this in the different types of circuit board.
|mm.||Lessons||diam. hole rating
of the node
of the node
The tolerances on the minimum widths of the conductors for the model drawings and different classes of circuit board are indicated in the attached table.
|Printed board class||eleven||twenty-one||12||22||13||23|
|min width in mm||0.8||0.8||0.6||0.5||0.4||0.4|
|Tolerance in mm.||±0.04||±0.04||±0.03||±0.03||±0.02||±0.02|
In the finished printed board and after the etching processes the conductors must have the following widths and tolerances.
|Nominal width in mm.||0.4||0.5||0.6||0.8||1.0||1.3||2.6|
|Maximum reduction in mm.||0.05||0.05||0.06||0.08||0.10||0.13||0.26|
Separation between conductors in the model drawing.
|PI class||11 and 21||12||13||22||23|
between conductors in mm.
Separation between conductors in finished pcb board and after the etching processes.
It must not be less, throughout the pcb board, than the following minimums in mm.
|PI class||11 and 21||12||13||22||23|
between conductors (mm.)
Distance of the conductors to the edge of thecircuit board: It will not be less than 2mm.
The conductive crowns on the faces must comply with their limitations, with respect to the holes that correspond to them, as follows:
|IP class||Minimum radius width (a) of the conductive ring,
formed by a node and its hole (ignoring edge defects).
|21,22 and 23||0.05mm|
Conductor thickness (for non-metallized circuit boards).
|Nominal thickness in mm.||Minimum thickness at reception||Minimum thickness before welding|
2.4. –LIMIT CONFIGURATIONS OF THE CLASSES ACCORDING TO THEIR DENSITIES
The dimensions that appear in the following examples have been obtained using the data from the previous sections.
2.4.1. –Limit configurations for circuit boards. Class 11.
Figure (a) shows the minimum possible gap between two holes of 1.2mm. in diameter, located in the grid of a module. Also listed is the only possible node size for that configuration.
Figure (b) shows the only configuration in Class 11 that allows the passage of a conductor between two 1.2 holes separated by 2 modules.
2.4.2. – Limit configurations for circuit boards. Class 12.
Figure (c) shows the minimum separation allowed between two holes located in a ½ or 1 module grid. For said separation, the maximum nodes and holes that can be used are listed.
Figure (d) shows the passage of a conductor between two 0.8 mm holes. located on a 1½ module grid.
2.4.3. – Limit configurations for circuit boards. Class 21.
Figure (e) shows the minimum distance allowed between two holes located in a 1-module grid. Likewise, the maximum holes and nodes compatible with said separation are indicated.
Figure (f) shows the passage of a conductor between two 1.2 mm holes. located in a grid of 2 modules. For this configuration, the only possible node is indicated, as well as the maximum width of the conductor.
2.4.4. – Limit configurations for circuit boards. Class 22.
Figure (g) indicates the minimum separation allowed between two holes located in a 1-module grid. The maximum possible nodes and holes are also listed.
Figure (h) shows the passage of a conductor between two 1.2 mm holes. located on a ½ module grid. For this configuration, the minimum node and the maximum conductor allowed are indicated. If the width of the conductor is reduced to another value within the margin indicated in the section corresponding to circuit boards without metallized holes, the diameter of the nodes or the separation between conductors can be increased.
Figure (i) shows the passage of a conductor between two 1.2 mm holes. located diagonally in a 1-module grid. The only supported node and conductor sizes for that configuration are also listed.
2.4.5. – Limit configurations for circuit boards. Class 23 and 33.
Figure (j) shows the only configuration that allows the passage of a conductor between two 0.8 mm holes, located in a 1-module grid.
2.4.6. – Typical applications of the different types of circuit boards.
The class of a printed board is fundamentally determined by the type of compactness of the components mounted on it.
The following tables indicate the possible limit configurations for each class, as well as the type of components that define them.
2.5. – RULES OF DISTRIBUTION OF COMPONENTS ON THE BASE CIRCUIT BOARD.
The rules below are to be followed on manually or computer-aided boards, and are specifically observed by technicians involved in printed board design.
A large number of the design rules depend on the direction in which the board is carried on the solder wave (molten tin bath over whose surface the board with its assembled components is passed to be soldered). That direction of travel is called the “transport direction in the circuit board weld.”
2.5.1. –Space between components.
The maximum size of the body of the components, admitted in the specification, must be taken into account. This will be the starting point to study the space between components.
In general, a minimum distance of 0.5 mm is allowed around the components for the purpose of inserting them. However, under certain circumstances (heat dissipation, high voltages, etc.) it may be necessary to space the components further, depending on the requirements and size of the components.
In that case, the special distances required must be defined by the designer on the printed board assembly drawing.
In the cases of high-density printed boards that do not have special requirements, isolated components with diameters less than 5 mm can be assembled without special precautions.
Example: Let there be two components A and B. (See fig. below).
It will be T(min)= ½ max. body diameter of A + ½ max. body diameter B + x(0.5 mm.). The value of T must always be rounded to the modulus dimension (M) or ½ (M).
Fig.2.5.1. Greater space, than the nominal, between components for isolation purposes.
2.5.2. –Overlapping of components.
The overlapping of components on the printed board, as indicated in the figure, is not allowed. This restriction is necessary in order to allow the replacement of a particular component without the need to move other adjacent components. In this sense, the wires used as bridges are also considered components.
Fig.2.5.2. Overlapping between components.
2.5.3. -Space between components and location holes of the circuit board.
The following figure shows the distances between centers that must exist between the locating holes and the closest mounting holes for speakers in the automatic mounting of components.
Fig.2.5.3. Placement in location hole circuit board.
2.5.4. -Layout of components.
Correct component orientation on the printed board also makes it easier to trace tracks later and reduces the overall cost of the printed board.
In order of preference, here are four different ways to arrange the axial components:
Configuration A. -All the axial components are mounted with their larger side parallel to the side of the circuit board that carries the connector and the same for the polarized components (diodes, etc.), with their polarity oriented, in all of them, in the same direction. In configuration 1A (less preferred) the polarized components could be oriented differently.
Configuration B. -All axial and polarized components have their larger side vertical to the side of the circuit board that carries the connector. The polarized components all have the same orientation. In Configuration 2B (less preferred) the polarized components may have different orientations.
Configuration C. -(Little preferred) .Most of the components are oriented parallel to the side of the board with connectors, but some are vertical to this side. The polarized components are not all oriented in the same direction.
Configuration D. -(Should be avoided). Most of the components are parallel or perpendicular to the side of the board that carries the connectors; but some of them are placed perpendicular to thecircuit board, that is, standing up. This Configuration makes the board considerably more expensive and should only be used when absolutely necessary.
Layout of Integrated Circuits (DIP). They should all have their polarity oriented the same way and the preferred orientation is with the polarity marking facing the connectors side of the board.
LAYOUT OF COMPONENTS
|A. PREFERRED ARRANGEMENT||B. PREFERRED ARRANGEMENT IF ‘A’ IS NOT POSSIBLE|
|C. LITTLE PREFERRED PROVISION||D. NON-PREFERRED ARRANGEMENT, MUST AVOID|
LAYOUT OF COMPONENTS
INTEGRATED CIRCUITS (DIP)
LOCATION OF THE HOLES IN THE GRID
TO REACH THE MAXIMUM DENSITY OF COMPONENTS ON THE CIRCUIT BOARD:
– All holes in the Y direction must be on the grid (1M=2.54mm.)
– All holes in the X direction in multiples of ½ M=1.27 mm.
– Typically: X1=1 ½ M.
2.5.5. -Mounting distance for axial terminations of components.
The following values will be used to determine the minimum mounting distance.
The axial terminations of the components will be submitted as indicated in figure 2.5.5. respecting parallelisms and forms.
- a) Non-glass body components with terminations of diameter <= 0.8 mm.
Min. distance “S” = max. body length s/spec. + 4 mm. Round to the next multiple of the module (M = 2, 54 mm).
- b) Glass body components and all components with conductor diameter > 0.8 mm.
Min. distance “S” = max. length of the body s/spec. + 5 mm. Round up to the next multiple of the module (M = 2.54 mm).
2.6. -TRACKING RULES.
The quality of a printed board, from the point of view of metallization, weldability of the circuit board holes and flatness, depends on the shape and distribution of the conductive print. The original drawing must satisfy the following rules:
2.6.1. -Conductive printing and shape.
- a) On each face of the circuit board the conductors must be distributed in the same direction and as long as possible. On the weld face, – whenever possible, the conductors should be oriented in the direction in which the circuit board moves in the welding machines, that is, parallel to the longest edges of the circuit board.
- b) The changes of direction of the conductors must be forming angles not less than 45º. Acute angles are not allowed.
- c) The width of the conductors must be as wide as possible, narrowing only in special and necessary cases.
2.6.2. -Distribution of conductive printing.
- a) The conductive print must be distributed over the entire surface of the circuit board in a uniform manner.
- b) Conductive printing areas on double-sided boards should be as equal as possible. To satisfy points a) and b), additional areas must be included in the model drawing. These areas are not part of the electrical circuit but ensure a good distribution. During metallizing processes these additional areas aid in current distribution so that the electrodeposition is more evenly distributed.
2.6.3. -Configuration of aids for current distribution.
- a) Current distribution aids consist of blind traces or crosshairs with lines approximately 6 mm apart. and 1mm wide. These blind zones should be positioned as close as possible to the conductive print, but never closer than 1mm. away.
A typical distribution of blind lines is indicated in the figure.
- b) On the welding face, the lines of the blind grid must form 45º angles with the direction of movement of the welding machine. A typical case is shown in the figure.
- c) A blind line of 1 mm. wide can completely surround the conductive print. This blind trace should be located as close as possible to the conductive print but outside the outline of the finished board. The figure shows a typical case of application of the blind outline outline of thecircuit board.
- d) The blind lines must not be constituted by a filled area. This is done because if the blind traces occupy a larger area than the areas of the conductive print, it can lead to non-uniformity in the metallics. The purpose of the blind traces is to protect the current distributions in the conductive print throughout its entire area. The mesh of the grid is therefore recommended to be 6 mm. Figures a , b and c show several typical cases with this technique.
Fig. a)circuit board with correct application of blind lines.
Fig. b)circuit board whose design does not require blind lines.
Fig. c)circuit board whose design is not correct. Filled areas should be gridded.
2.6.4. -Influence of the conductive print on the weldability of the holes.
A circuit board hole will have good weldability when its conductive area on the weld face is greater than on the component face. This is achieved in two ways:
- a) By an appropriate method of connecting the conductors to the node. Two examples are shown in the figure:
If a certain number of conductors start from a node, they must be arranged, on the component face, so that they start from a point separated from the node, as indicated in the figure.
- b) By selection of the size of the node. On the weld face an isolated hole must be surrounded by a larger node than on the component face; or, it must be connected to a blind conductor, as indicated in the figure.
Improved weldability by selecting the diameter of the node.
2.6.5. -Contacts for edge connectors.
Edge connectors allow PCBs to be connected quickly and easily. They can be of the direct or indirect connection type.
188.8.131.52. -Direct connection connectors.
The female connectors receive the edge connector printed on the board by simple plugging. For this purpose the connector contacts must be gold circuit board and. so specially made to fit the female connector. Tolerances in circuit board thickness must be taken into account.
184.108.40.206. -Indirect connection connectors.
In this case the multiple contacts of the connector are soldered to the board. The circuit board does not require a special shape and the tolerances are not so critical.
220.127.116.11. -Comparison between the types of connectors.
From the point of view of printing, the indirect connector is cheaper. The contacts do not need to be gilded and therefore the metallizing process is easier. The dimensions of the circuit boards are not critical and there is no special requirement regarding the thickness of the circuit board. The direct connector, on the other hand, requires tighter thickness tolerances. This is sometimes difficult and therefore the reason for a higher rejection rate.
The disadvantages of indirect compared to direct is that it requires more space in addition to its cost and the assembly operation.
To perform electrolytic gold plating of the edge connector, it is necessary to connect all its contacts to a conductive strip located outside the contour of the printed board. This interconnecting bar must be shown on the model drawing.
2.7. – METHOD OF CONNECTION BETWEEN LAYERS
The methods used for electrical interconnection between faces of a printed board are reflected in the attached table and must be selected for each particular case. The following table indicates the different methods to be used, depending on the type of circuit boards and the insulating support.
|connection method||insulating support||multilayer circuit boards||Lead allowed in the same hole|
|Phenolic paper||epoxy paper||epoxy glass|
|Thread in “C”||X||X||X||X|
Any of the three methods can be placed under components as long as they are properly insulated and separated from the printed board surface.
2.7.1..- Connection method in “C”.
It consists of a bare wire passing through a hole in the pcb board , folded over each face of the pcb board and soldered to the conductive print on both sides. The wire is not welded to the nodes immediately adjacent to the hole, but its ends are positioned so that the difference between the thermal expansions of the wire and the base material causes a slight additional bending of the wire, rather than lifting. (detachment) of the nodes or a breakage of the welded joint.
The figure shows a transverse connection section with “C” thread.
There are automatic and semi-automatic machines for inserting and forming “C” wires.
The design of the pcb boards to use the connection between faces with “C” wires must meet the following requirements:
- a) The nominal diameter of the holes must be 1.2 mm.
- b) No point of conductive printing on both sides of the pcb board, electrically connected to the wire or insulated from it, will be less than 1.5 mm nominal distance from the center of the hole.
- c) The shape and nominal dimensions of the nodes for the connection of the “C” wire, on both faces of the circuit board, are indicated in the following figure.
- d) The “C” wires of a printed board must be oriented according to the direction of the simultaneous welding, as indicated in the figure. However , it is recommended that all the threads in “C” be aligned in one direction only.
- e) In order to leave enough space for the “C” wire insertion tool, no holes should be placed within the oval area indicated in the figure. For example, once hole A is located, hole B will be allowed but hole C will not.
- f) The base materials in which the “C” thread connection can be used are the following:
– Phenolic paper.
– Epoxy paper.
– Epoxy glass.
2.7.2. -“V” connection method.
It is a preformed “V” thread that is inserted into a hole in the printed board. The wire is folded over the component side and soldered onto the conductive print on the component side. Bonding with the conductive print on the solder face is made by the solder position that fills the space between the “V” wire and the conductive foil. Such a section is shown in the figure.
The design of the pcb boards to use the connection between faces with thread in “V”. must meet the following requirements:
- a) The nominal diameter of the holes for “V” threads must be 1.2 mm.
- b) A hole used for the passage of a “V” wire cannot also be used for the passage of a component terminal.
- c) On the weld face of the circuit board there should be a circular node around the hole. The diameter of this node will be in accordance with the standards, that is, the minimum nominal diameter of the node for each class of circuit boards is the
|Class||Minimum Nominal Node Diameter|
- d) The spacing between adjacent “V” wires is limited by the normal rules governing the spacing of nodes, holes, and conductors.
- e) The “V” threads of a printed board must be oriented according to the direction of the simultaneous welding.
- f) The base materials in which the “V” thread connection can be used are the following:
– Phenolic paper
– Epoxy paper.
– Epoxy glass.
2.7.3. -Method of connection by metallized holes.
The most widely used interlayer connection method for double-sided and multilayer PCBs is circuit board holes. It consists of a hole on whose walls metal is deposited by chemical and electrolytic procedures, making the different layers through which the hole passes conductive.
On a printed board, if a connection between layers is made using this method, the rest of the connections between layers must be made using this same procedure.
The requirements that must be met in the design of circuit boards with circuit board holes are as follows:
- a) The circuit board holes can be used not only to connect the layers to each other but also to house the terminals of the components.
- b) The diameter of the holes must be selected according to the specified diameters. As a general rule, the diameter will never be less than one third of the nominal thickness of the circuit board. If the hole is also used for the passage of component terminals, its diameter must meet the appropriate requirements.
- c) The metallized holes must have a node in each of the outer layers. In the inner layers (multilayer circuit boards) a node will only be placed if an electrical connection with this layer is required. The minimum nominal sizes of the nodes will correspond to those specified for the type of circuit board.
- d) circuit board holes should only be used in epoxy fiberglass base material.
Main functions of circuit board holes.
The main functions of a circuit board hole are as follows:
1) Improve the fixation of the components.
2) Electrical connection between layers.
- a) When a hole in a printed board is not metallized, the only bonding force between the component terminal and the conductive print (node) is the adhesive that joins the conductive area with the insulating support. (See Figure).
If the density of the circuit board is high, when the diameter of the nodes is reduced, their adhesion force is reduced, thus not guaranteeing the fixation of the component terminals.
The metallization of the hole provides greater adhesion force in the soldering of the terminal of the components. See figure below.
- b) The electrical connection between layers is the fundamental basis of the circuit board hole as well as keeping the component terminal available for welding.
The circuit board holes must meet the following requirements:
In single-sided circuit boards, the function of the metallized hole is only to provide a better union of the component, although in this type ofcircuit boards it is uneconomical.
In double-sided circuit boards made with paper base material, the metallized hole can be made only in order to improve the union of the component, but not for continuity purposes, due to the low reliability that exists in this type of material, with respect to metallized. There is only a guarantee of continuity through the component terminal. Therefore, the union of the hole with the terminal must be visible and accessible or by making a hole parallel to the previous one that remains outside the component. The figure shows a detail of these procedures.
These methods are not recommended.
In double-sided circuit boards made of fiberglass base material, not only a connection between faces but also a good bond between component and hole is achieved.
The possibility of metallizing the holes in a uniform way, with an adequate thickness, depends on this compromise between the diameter and the thickness of the circuit board.
2.8. -ELECTRICAL STANDARDS FOR DESIGN.
2.8.1. -Width of conductor.
This dimension depends on the following parameters.
- a) Load current.
- b) Thickness of the conductor (copper foil).
- c) Separation between conductors.
- d) Type of base material.
- e) Maximum allowable temperature rise.
- f) Component assembly method.
The first three parameters define “the amps per unit area of the conductor”.
The next two, together, determine “the current density”.
Figure 2.8.1. It serves to know the relationship between the widths of conductors and the elevation of temperatures for circuit boards of different thicknesses of copper.
It refers to the cases in which the basic insulating material of the circuit board is phenolic paper, epoxy paper or epoxy fiberglass.
General conditions for the use of the abacus in figure 2.8.1:
- a) There is good ventilation or forced cooling is provided.
- b) The ratio, conductor width to conductor separation, will be greater than 1:2.
When this condition is not met, the current level must be reduced by 30%.
- c) The thickness of the copper will be uniform and counting on the successive operations, to which it has to be subjected in the manufacturing process, it will be necessary to estimate an excess increase, for this dimension, due to possible wear.
Fig. 2.8.1.: Maximum admissible intensity of the copper conductor.
2.8.2. -Temperature rise as a function of the current through the conductor .
In figure 2.8.2. the relationship between the current through a conductor, with a given section, and for a rise in temperature in the conductor is represented. The chart provides a means of relating the conductor width of the 1:1 scale model drawing to the thickness of the copper base laminate. The sum of the maximum ambient temperature in which the circuit board will be and the temperature rise due to the passage of current in the conductor must not exceed the maximum temperature stability of the insulating support. This limit will be indicated in the specifications and physical characteristics of each insulating support.
To select the width of the conductor, once calculated using the graph, you must choose the closest value and always in excess of the previously recommended widths.
2.8.3. -Separation between conductors, and width of conductors on the Model Drawing.
When thinking about the separation between conductors, the following factors should be taken into consideration:
- a) Potential difference between conductors.
- b) Peak voltage.
- c) Surface resistance of the base material.
- d) Environmental conditions at the destination of the equipment, temperature, humidity, dust, etc.
- e) Surface coatings that must be designed and equipped.
As a general rule, the minimum width of the conductor will be 1 mm. , in all cases where there are no density problems.
For special cases in low voltage (maximum 24 V direct current), the width of the conductor can be reduced to 0.3 mm. , and up to 0.2mm. , for processedcircuit boards. In these cases, you can increase the width when the driver leaves the compromise zone, on his route.
However, conductor widths should be kept as large as possible, allowing for imperfections that always occur at the edges.
The same can be said with the separation of conductors: It will be the greatest possible to reduce rejections in the Inspection, the more frequent the smaller the separation. The Factory and Inspection processes are complicated when the separation of conductors is minimal and therefore costs and delivery times increase.
Multilayer circuit boards.
In multilayer circuit boards, the limitations in the dimensioning are complicated, so that they admit the value of the peak of the potential difference between the conductors.
2.9. –CHARACTERISTICS OF THE CIRCUIT
It is not intended to make an exhaustive study of the characteristics of the circuit that need to be considered in the design of printed boards. The information given here is not complete; Likewise, the values and equations given should be used only as a guide, for an estimate of the approximate values of each of the characteristics. All the parameters of the circuit boards have a great interdependence and therefore the values measured empirically are not easy to coincide exactly with those calculated.
This is especially true in high-frequency regions where complete analytical prediction of plaque characteristics is impossible. Thus, the data that we provide, in this regard, is not complete and only provides orders of magnitude of parameters, to be taken into account in the design.
2.9.1.- Within the varied range of qualities of insulating supports, the fundamental characteristics of those materials most widely used today are indicated below. Average thickness of 1.58 mm.
|Properties||Phenolic paper||epoxy paper||epoxy glass|
|Surface resistance M Ohm. (*)||10 3||10 3||10 3|
|Volumetric resistance M Ohm. (*)||10 4||10 5||10 6|
|Water absorption, max. on %||0.75|
In order to ensure a high quality, safe and reliable finished product, it is necessary to carefully follow each stage dedicated to the production of the electronic board.
The realization of each board requires several steps, to be carried out with meticulous precision: starting from the design of the board, in which the customer’s idea takes shape, passing through the assembly, in which the components are positioned and correctly welded on the printed circuit, arriving at the packaging, in which each card is carefully packaged, to avoid damage during transport. Each phase, therefore, is essential to obtain a perfectly functional and effective finished product.
In this article, FXPCB shows you how the soldering phase is carried out, in which each element is precisely fixed on the electronic board.
Manual Soldering of Printed Circuit Board in 2022
How FXPCB carries out the soldering phase of the pcb boards?
After having correctly positioned the components above the printed circuit during the assembly phase, the product, defined as semi-finished product, arrives at the soldering department. This phase is of fundamental importance as it guarantees the perfect seal of the individual components on the circuit, thus ensuring a safe and defect-free finished product.
The ways in which the components are permanently fixed on the printed circuit vary according to the type of assembly that has been performed: from SMT assembly to PTH assembly; in fact, both the instruments and the application techniques vary.
In PTH (Pin Through Hole) assembly, the components of the pcb board are assembled manually. The reasons may be different: either because there are non-advanced components and, therefore, there are no equivalents in SMT, or because the customer has expressly requested the use of these components and, consequently, this assembly method.
In this case, soldering is also done manually: the procedure is performed on a soldering station equipped with a stylus with an interchangeable tip, available in various sizes to be selected according to the size of the components of the board itself, capable of heating up to 360 degrees.
Used together with the tin wire, it welds the lead, which is the terminal conductor wire of the electrical components assembled with the PTH method. The tin wire used in FXPCB is lead free and is composed solely of 99% tin , with an addition of 0.5% copper and 0.5% silver. Its use allows a more performing finish, which at the same time guarantees a greater , brighter and brighter aesthetic .
In the SMT (Surface Mount Technology) department, in which the electronic boards are assembled automatically by means of the Pick & Place machine, soldering is also carried out through the use of an automated oven. There are mainly two types of furnaces for soldering components:
Vapor-phase ovens, which work by means of a liquid which, turning into a vapor, solder the elements on the circuit;
Hot air / nitrogen reflow oven, which solder through a recirculation of hot air.
FXPCB has chosen to use only vapor-phase furnaces, since they are machines that allow you to control the soldering process in detail from start to finish. A dedicated profile is created for each type of electronic board which, when inserted in the oven, allows you to understand if the calibration of the same is correct: by carefully checking the temperature variations, it is possible to avoid sudden changes that could generate thermal shocks, which could cause damage to the components. Present on the printed circuit.
Through the inserted profile, a graph is obtained that is comparable to a photograph of what happened in the furnace during soldering: during the procedure, in fact, a trace is generated with a curve that indicates the temperatures inside the furnace, the total duration of the soldering cycle and which temperatures were used .
The same graph, at the end of the realization of an electronic board, is attached to the FXPCB report, to demonstrate at any time how the soldering itself took place.
Thanks to this, in the event that problems arise on the components, it is possible to review how it were welded and if any anomalies occurred during soldering. Each component has its own data sheet, that is a card in which various information is indicated, including which types of welds this element can receive.
In both PTH and SMT soldering, however, the process occurs by means of different thermal shocks depending on the components to be welded.
What happens after soldering?
In case the project foresees it, the pcb board now passes to testing. During this phase, the electronic circuits are tested in every detail, in order to ensure that their operation is in accordance with what was determined in the design phase.
Thanks to these tests, it is possible to verify the presence of any critical issues in one of the products: in this case, the tests would be promptly interrupted and we would dedicate ourselves to solving the problem.
Alternatively, if testing is not required, the electronic boards would be transferred to the packaging: here they are packaged in special boxes equipped with internal honeycomb hives, specifically designed to guarantee the protection of the products during storage and the subsequent transport.
Soldering electronic boards is a very delicate step in the creation of a new product for your company. The precision in carrying out this procedure determines the effectiveness and safety of your new electronic board.
Are you looking for a reliable partner to entrust with the realization of your new project? Contact FXPCB: the experience gained in the electronics sector, in over thirty years, will allow us to guarantee you a finished product that meets your wishes.
Entrusting the design and manufacturin of your pcb boards to professionals in that sector is like giving the electronic heart of your company to third parties. For this reason, in FXPCB the project of each customer is taken care of in every detail with the aim of being able to guarantee finished products that are always safe and performing.
The expertise gained by each department allows FXPCB to take your project to heart at every stage necessary for the construction of the electronic board. In this article, FXPCB explains how the creation of pcb board works.
During the design phase of the electronic board, a drawing is created with which to put the initial idea in black and white, giving it shape. A clear and detailed project is created, meticulously studied in order to make the production process more streamlined and effective and to optimize delivery times.
At this moment, on the basis of the functionality that the pcb board must have, the mounting system that will be used is defined: PTH (Pin Through Hole) or SMT (Surface Mount Technology). The first is performed manually by specialized operators, the second, on the other hand, is carried out by means of fully automated machines.
Then, the BOM is compiled, which is a file that indicates the individual components that make up the electronic board and the position in which they will be placed. It is necessary to create this document with extreme precision: all information is essential for the assembly department, in order to allow a precise and error-free construction.
Furthermore, the designer also draws up the gerber file, essential for the development of the printed circuit: in fact, it is the foundation of the electronic board. It consists of a resin layer and, depending on the degree of complexity of the product, contains different layers, called layers : these layers allow the connection between the different components placed on the board.
Before proceeding with the large-scale production of a specific type of electronic boards, a preliminary sampling is carried out. In this way, it is possible to verify the correctness of the project carried out in the initial phase.
Similarly, in the event that some elements do not prove to be optimal for the finished electronic board, they are replaced with other more performing ones. In this way, high quality electronic boards are obtained, capable of guaranteeing safe and effective finished products to each customer: customer satisfaction is one of the main focuses on which FXPCB focuses in every project.
Furthermore, the replacement of unsuitable elements or the correction of errors before the start of production of the entire batch, allows to optimize production costs, limiting the waste of materials or components to be replaced.
After having ascertained, by means of sampling, the correct functioning of the pcb board, we proceed with the production of the entire batch. The project is then sent to the workers specialized in the production of the foil, which is a perforated surface in the points where the various elements will be placed. Thanks to the use of the screen printing machine, the solder paste will be placed with precision in the placements in which they will be placed.
Following the screen printing, the electronic board is ready to receive the components: through a track, it slides and enters the Pick & Place machine, previously programmed to mount those specific elements on that given board. Once the positioning is complete, the tray slides on the track of the production line, until the operators carefully pick it up and insert it into the vapor-phase oven for the welding cycle.
In the case of PTH assembly, due to the size or particularity of some elements, it is not always possible to assemble the components using an automatic machine, as happens in SMT assembly. For this reason, we generally opt for manual assembly, during which specialized technicians personally arrange the elements on the printed circuit.
The exception occurs when the electronic board does not have SMT components mounted on the bottom side: in this case the assembly takes place automatically by means of a wave soldering machine.
After assembly, the electronic board is ready for soldering: this operation is also performed manually, using a stylus equipped with a soldering tip, designed to stably fix the elements to the printed circuit.
4. AOI optical inspection
Once the assembly is complete, we proceed with the automatic optical inspection, known by the acronym AOI (Automatic Optical Inspection). It is performed using a machine that takes several 3D photographs of the product and compares them with the initial project, previously loaded on the software by an operator.
The 3-dimensional view allows you to verify the presence of pond both in height, in width and in volume. At the end of the check, the machine signals the presence of any errors: in this way, the operators can correct the electronic board quickly and directly.
After each procedure, the electronic boards are transferred to the packaging. This step is extremely important: poorly executed and left to chance packaging risks compromising the quality of the electronic boards. The same, in fact, could be damaged during storage or during transport.
The care taken in the packaging of each product respects the quality standards that FXPCB imposes in every phase of the creation of an electronic board, from the very beginning to delivery. Mainly, we choose to use a honeycomb structure: this organization makes it possible to better fit the products together, guaranteeing maximum safety for the customer.
The pcb board is the ‘brain’ of the finished product offered by your company, so it is essential to entrust its realization to careful and expert hands. FXPCB leaves no passage to chance and, thanks to a highly specialized team, offers to create high quality products for each of its customers.
Would you like to give life to your idea? Contact us: we are at your complete disposal.
1.1. -THE BASIC FUNCTIONS OF A PRINTED PLATE ARE:
- Support your own components.
- Support your electrical interconnections.
All this following established rules in view of tolerances imposed by the nature of electronic equipment or systems.
In the design of printed circuits, we will find a series of variable factors that must be selected and combined in an optimal way in each case.
The placement of the components on the circuit base plate itself, the dielectric material of the base, the type of conductors, the number of layers of conductors, the rigidity, the density or compactness of the equipment on the plate, etc., properly combined will influence the performance, quality and cost of the product.
In the design, it will also be necessary to think about the Manufacturing conditions, creating adequate information for Manufacturing, knowing the means and costs that will intervene in the different operations to be followed, in order to find viable and profitable procedures.
1.2.- ADVANTAGES OF PRINTED CIRCUITS IN THE DESIGN OF ELECTRONIC EQUIPMENT, WITH RESPECT TO CONVENTIONAL CIRCUITS
- a) Space saving: Using printed connections takes up less space in the equipment than with the use of conventional connections.
- b) The conductors are permanently bonded to the base dielectric of the circuit, which also provides greater ease for mounting the components.
- c) It is normally impossible to break wires and produce a short circuit between wires.
- d) Given the high repeatability in the circuits, there is a uniformity of the electrical characteristics from assembly to assembly, increasing reliability?
- e) The volume and weight of the interconnections are significantly reduced.
Clear routes (tracks) of the conductors are produced that allow easy visual monitoring of them and greater organization and control of the space. This is all due to the flat shape of the conductive print.
- f) The identification of the parts of the circuit is simple and the coloring of the wires has been eliminated.
- g) Production processes in large series and highly automated techniques can be used.
- h) Operators may be employed with a minimum of training and skill.
- i) The clarity of the circuits allows, with visual aid, to simplify the verification processes as far as accuracy in the assembly of the components is concerned, thus minimizing errors.
- j) The maintenance of Electronic Equipment is more simplified, it is cheaper.
- k) In flexible plates, its flat and thin shape produces maximum savings in weight, space and cost. Up to 75% savings in volume and weight can be achieved, depending on your specific application.
1.3. -LIMITATIONS OF PRINTED CIRCUITS.
- a) The flat shape of the circuit requires a special skill in the design to locate the components and the interconnections.
- b) The long time spent in the design stage influences appreciably from the initiation of the design to the delivery of the final product.
- c) It costs too much work and money to introduce changes in the design when the established tools and manufacturing means are already available.
- d) Difficulties found in the repair of printed circuits.
1.4. – BASIC ELEMENTS OF PRINTED CIRCUITS.
- a) Insulating support.
- b) Holes for mounting components and/or interconnection.
- c) Interconnection connectors.
- d) Input and output terminals.
1.5. -CLASSIFICATION OF PRINTED PLATES.
1.5.1. – Categories of printed boards according to their density in components and interconnections.
Three basic categories are considered according to their densities in order from lowest to highest:
- a) Simple Face, with conductors on a single flat surface of the insulating base.
- b) Double Sided, with conductors on both sides of the insulating base, with metallized holes for the interconnection between sides, or other means.
- c) Multilayer with three or more layers of conductors separated by insulating material and usually interconnected through metallized holes.
1.5.2.- Densities of printed plates.
In any printed board, it is necessary to combine the limitation of its surface with the elements (components and interconnections) that must be equipped as indicated by the circuit. There are or may be a series of incompatibilities, given the diversity of sizes and shapes of its components, their number, the complexity of their interconnections, etc.
It is desirable, according to this, to know a measure that gives an idea of the order of the density of a printed plate and that allows typifying them.
The unit of density is taken as the number of holes, to mount components, per square decimeter of useful surface. This unit is not perfect, but it can serve as a reference to know, in a first approximation, the portion of the circuit that can be assembled effectively in each case.
Usually, the values indicated in the table correspond to the different classes of printed plates.
1.5. 3. -Classification system
There is a system for classifying printed boards by their densities, which provides the degree of concentration of conductors, knots and holes. This data, together with other factors such as the size of the plate, determine the tolerances allowed in the different phases of the design and manufacturing processes.
The classification system consists of two digits. The first digit represents the type of plate (number of layers and type of connections through them), and the second digit is related to the maximum local concentration of conductors.
To consider the amount of density of the printed plates, the following three variables are introduced:
- a) Nominal width of the conductors.
- b) Nominal separation between conductors.
- c) Difference between the nominal diameter of the nodes and the nominal diameter of the corresponding holes.
According to this, the second digit of the classification of a printed plate in design will be the smallest number for which the minimum values corresponding to the variables indicated above are satisfied over the entire plate.
1.5.4. –Minimum dimensional limits for each class of printed plate
Below, in separate tables, the minimum limits that define each class of printed plate are established, in terms of density, by the two-digit system.
- a) Plates without metallic holes.
The first digit of the classification of this type of plates will be 1, and the second will take the values 1, 2 or 3 according to the three parameters a), b) and c) indicated.
b) Plate with metallic holes.
The first digit will be 2 and the second will take the parameter values 1, 2, 3 or 4 according to the three parameters a), b) and c) indicated.
1.6. -MATERIALS USED IN THE BASE PLATE OR INSULATING SUPPORT.
They can be chosen among the following materials: according to the application of the printed plate.
- a) Rigid phenolic resins, with paper impregnated in them.
- b) Rigid polyester, with fiberglass impregnated in it. (
- c) Epoxy resin, with paper impregnated in it.
- d) Epoxy resin with fiberglass impregnated in it.
- e) Sheet Film of “mylar”, “teflon” or polyamides.
The choice, in each case, of the type of base material to be used will be made in accordance with the application and functions of the circuit to be supported.
The most used materials are a) and d). The so-called e) will be used in the case where mechanical rigidity is not an important factor, replacing the type marked d).
Materials should always be flame resistant.
The costs of these materials vary from the cheapest (phenolic resins with paper) to the most expensive (epoxy resin with fiberglass).
The cost differences of the materials are due to the physical, thermal and electrical properties of each type of material.
Materials type (a), (b) and (c).
Types (a), (b) and (c) are susceptible to puncture. The punching operation is economical when the manufacturing series are high. The use of these materials is limited to printed circuits whose holes are not going to be metallized.
These materials are not recommended for multilayer printed circuits, due to their poor dimensional stability; in boards with high conductor densities, breaks can occur inside the holes, due to the thermal shock, the terminals of the components are welded.
Materials type (d)
These materials are the most used in circuits that have metallized holes. Its dimensional stability is acceptable for boards with high conductor densities, with minimal breakage inside the metallized holes due to thermal shock. Holes in this type of material must always be drilled. There are difficulties in drilling, if they are made with a matrix, with the thicknesses normally used for printed circuits. The cutting, to size, of the plates must be done with a saw; shear or milling cutter since using a die is not recommended.
Type (e) materials
A great deal of work is currently being done to develop new types of base materials for flexible circuits. These materials in the form of a dielectric “film” have good electrical and mechanical properties. Normally these dielectric “films” have a layer of laminated copper and their use is widespread for multilayer circuits and hybrid printed circuits, whether or not they have metallized holes.
1.7. -THE SIZE AND SHAPE OF THE PRINTED CIRCUITS .
Normally, these two physical characteristics of printed plates are limited by the dimensions of the equipment for which they are intended and also by the tools and existing manufacturing facilities (machinery, facilities, etc.)
In order to reduce manufacturing costs, it is necessary to ensure that the choice of plates is made on standardized sizes for which the corresponding tools already exist (cutting elements, templates, accessories, etc.).
1.8. – COSTS.
The differences in cost between several small plates and a large equivalent are minimal. Large plates are more expensive to replace. Small boards need more connectors and have more waste.
1.9.- THICKNESS OF THE BASE MATERIAL.
The thickness is variable; it varies between 0.8 mm and 3.2 mm. For rigid plates (epoxy glass), the thickness of 1.6 mm. is the most used, the tolerance allowed in this case is +- 0.2 mm.
When the basic material is phenol or epoxy with paper, the admissible tolerance will be +- 0.14 mm.
The measurements are normalized in the following thicknesses: 0.8 mm. 1.0 mm. , 1.6mm. , 2.4mm. , 3.2mm. These values refer to nominal thicknesses of the finished printed plates.
1.10. -DEFORMATIONS OR WRAPS.
The base plate, with its plastic material, is subjected to temperatures that warp its original flat shape. The degree of deformation is higher for phenolic materials with paper and lower for epoxy resins with fiberglass.
The degree of warping also depends on the type (one-sided or two-sided) and size of the printed board, as well as the predominance of the metallic structure (conductors) and its balance on both sides (eg there may be ground planes and one side).
It is necessary to incorporate buttresses or ribs to minimize warpage. These are conveniently placed in the center or on the sides of the plate, prior to the simultaneous welding operation. The printed circuit connectors also serve as reinforcement, if their placement is studied.
1.11 .- HOLES .
Properly metallized, they are used to mount components and establish interconnections. They can be practiced by punching and drilling.
1.11.1. – Punching.
It is the most economical method when the same configuration of holes is repeated 50,000 or more times. It is used in cases where the basic material is paper or fiberglass.
Limitations for punched hole diameter and hole center spacing depend on the type and thickness of base material used.
1.11.2. – Drilled.
It is used almost exclusively for plates with epoxy fiberglass base material. It is a more expensive process than punching but there is economy if multiple numerically controlled drilling machines are available. There is no limitation on the diameter of the holes, but it is considered in practice, as a minimum limit of 0.6 mm.
Drilling tools, with perforated tapes for machine control, require less manufacturing time than punching tools.
For metallized holes, it is recommended that the diameter is not less than one third of the thickness of the circuit base plate. Under special conditions, the diameter can be reduced to one fifth of the thickness of the material.
1.12. -CONDUCTIVE PRINT.
The simplest process to obtain the conductors of a circuit is to etch them on the base laminate sheet. This requires a minimum of process steps and has been widely used in large production runs. The attack to obtain the circuit must be applied to one or both sides of the laminate.
To achieve the interconnection between the conductors on both sides, electrochemical procedures can be used. for metallizing holes.
To increase the density and complexity of the wiring, printed circuits are used with the conductors on both sides interconnected by metallized holes. These processes are used in industry for double-sided and multilayer circuits.
This requires special equipment for drilling and metallizing. So that the final product has the circuit conductors protected by metals resistant to corrosion, such as tin, lead, gold, etc. , which favor weldability during long storage times.
The manufacture of multilayer circuits: It is a combination of several processes. First, the conductive layers are individually printed and embossed, except for the outer ones, and then they are joined to form an integral panel. This panel is then processed as if it were a double-sided printed circuit with metallized holes.
The printing or the operation of depositing the model drawing on the copper of the insulating support can be done in two ways, fundamentally by serigraphy and by photoengraving. Either procedure has its own limitations though. in principle, these limitations are defined by the size of the manufacturing lot and by the conductive print density.
There are therefore two limits to determine which of the two processes should be followed. For high-density boards, with very close tolerances, in the case of class 23 and 33 boards, the process is limited to photoengraving. In plates whose manufacturing batches are small, below 10 panels, photo-engraving is also recommended, regardless of the classes of the plates.
1.13. -ENTRY AND OUTPUT TERMINATIONS.
There are basically two methods of termination between the conductive impressions of printed circuits and the interconnection of them with the system. The other method is to solder terminals for hard wiring of the PCB to the rest of the system. The other method consists of a quick connection through connectors.
The quick connection of printed circuits with connectors can be done in two ways, one by means of discrete connectors in the form of plugs and another by printed contacts on the edge of the board.
Direct plug-in contacts can be individually mounted or multi-mounted, using flanged clips and with a dielectric sandwiched between the connector and the plate.
The printed edge contacts of the conductive print are usually covered with supplemental plating that improves wear and extends their service life. These connectors are cheaper than the previous ones, but they limit the structure of the circuit by the width of the conductor and therefore the coupling for which the connectors are useful