Description
Flex PCB Assembly manufacturing Process
Many people think that Flex PCB assembly is tough to deal with. But as long as you understand the basics, it’s not so difficult. Now, let’s look at some key aspects of Flexible PCB assembly.
Pre-Treatment of Flex PCB
FPC boards are flexible and usually shipped in a non-vacuum package. They can absorb moisture from the air during transportation and storage, so the flexible PCB needs to do the pre-baking before SMT(Surface Mount Technology) to get rid of the moisture. If you don’t do this step, the absorbed moisture will evaporate quickly during the high-temperature reflow process, which will cause problems such as delamination, bubbles, etc.
How do we do the pre-baking before the Flex PCB (FPC) Assembly?
Pre-baking conditions are normally at 80-100°C for 4-8 hours, but you can adjust the temperature higher to 125℃ in some special cases while shortening the baking time.
FX PCB would suggest you do a sample test before baking, which can ensure whether FPC can stand the baking temperature. However, you can also ask the FPC material manufacturer for the right baking conditions. Some Flexible PCB manufacturers like to place paper between each flex PCB panel for isolation, so you need to remove them before FPC PCB baking. When we are baking the FPC board, we shouldn’t stack the flex PCB too many (10-20 Panels are ideal). After baking, the IPQC needs to check whether the Flex PCB has problems like discoloration, deformation, warping, etc.
Mounting and Fixing before Flex PCB Assembly
Flex PCB is a thin and soft material, and it will be easily misalignment and damaged during assembly and handling if we don’t use the fixture. The fixture can ensure accurate placement and improve production efficiency and quality.
Solder Paste Printing for FPC board
Even after fixing the FPC board in the fixture, the flex PCB may not be completely flat due to its deformation; adhesive thickness, stiffener, or reinforcement layers. This unevenness can cause problems like solder bridging, insufficient solder, or too much solder
Flex PCB assembly manufacturers don’t have special requirements for solder paste composition, but the paste should have excellent thixotropy for easy printing and adhesion. These can avoid the poor demolding to clog the stencil openings, or collapse after printing.
A flexible PCB’s printing surface won’t be the same flat and hard as a Rigid PCB, So it is not suitable to use metal squeegees. Instead, a polyurethane squeegee with a hardness of 80-90 degrees is more suggested.
Meanwhile, the Flex PCB solder paste machine should have with optical positioning system, which is important for the printing quality.
Adhesive Application (Optional)
For double-sided Flex PCB assembly, the adhesive is applied to prevent components from falling off during wave soldering or reflow soldering.
Component placement
Component placementThe Flex PCB components assembly uses an automotive pick-and-place machine to accurately place the components on the FPC PCB. The Flexible PCB Assembly complexity and efficiency requirements will decide whether medium or high-speed placement machines are used. As we know now the Flex PCB can’t be the same flat as the rigid PCB, there will be a gap between the Flexible PCB and carrier board or fixture. Then the setting for nozzle height, air pressure, and speed are crucial.
Pre Soldering and Post soldering of Flex PCB Assembly Inspection
Flex PCB assembly manufacturers need to inspect for proper component placement and alignment before reflow soldering.
Reflow Soldering for FPC PCB
Use forced convection infrared reflow ovens to ensure the temperature of FPC PCB is more uniform and reduce the soldering defects.
Component Insertion
For through-hole components or some surface mount parts that cannot be placed by machine, for example, the DIP capacitor, connector, switch, MELF, etc. Which will need to be assembled by manual insertion or automatic insertion equipment.
Wave Soldering
Wave soldering is used for through-hole components for flexible PCB.
Cleaning
Clean the assembled FPC PCB to remove flux residues.
Repair
This is an offline step that involves repairing defective solder joints or replacing faulty components.
Testing
Use magnification of 5 times or more to check the FPC for visual inspection, and the key checking is residual adhesive on the surface, discoloration, tin contamination of the gold fingers, solder balls, unsoldered IC pins, and solder bridges. As the FPCB PCB surface is not so flat, it will cause a high rate of false positives in automated optical inspection (AOI), So It is not suitable for AOI inspection on Flexible PCB assembly. However, we can use the X-ray machine to inspect the internal solder joints.
Meanwhile, the assembled FPC PCB can still undergo ICT(In-circuit test) and Functional test.
Since Flexible PCBs are normally produced in panels, we need to do depaneling before doing the ICT and function test. You can use scissors or blades to cut it, but the efficiency is low and defect rate is high. FX PCB would suggest you make FPC PCB stamping molds for the separation, as the stamping molds can significantly increase the operational efficiency, and the edges of the stamped FPCs will be more neat. What is more important is that the internal stress generated during the stamping is very low, which can prevent the solder joint damaged
Quality Management
Implement in-line quality control and final product assurance before delivery.
Packaging and Sampling Inspection
Finally, package the components and conduct sampling inspections to ensure high-quality delivery.
How to find the Right Flex PCB assembly supplier?
There are many factors you need to consider when you are choosing the right flex PCB assembly manufacturers:
Equipment and Technical capabilities：
Advanced equipment can improve the efficiency of production, reduce the defect rate, and ensure product quality.
Technical Capabilities: customers need to evaluate whether the flexible PCB assembly factory has mastered the latest SMT technologies, such as whether they can handle 01005 components, irregular-shaped components, double-sided mounting, and multi-layer board processing.
Production Capacity:
Check how many production lines and employees in the flex PCB assembly factories, and you can evaluate whether the manufacturer has sufficient production capacity to finish your order on time.
Quality Control Process
The flex PCB assembly manufacturer must have strict quality control at every stage (from component procurement to final product delivery).
The factory should conduct strict inspections on all incoming components and PCB boards to ensure raw material quality,and it also need to monitor and inspect each key process, such as measuring solder paste thickness and controlling reflow soldering temperature, in real time.
Finally, the factory should have the capability to conduct comprehensive testing, including functional testing and X-ray inspection, to ensure the final product meets quality standards
Flex PCB Assembly cost:
The price for the flex PCB assembly is an important part of the customer’s decision-making, so the factory should have effective cost-control measures to help customers get a better price without compromising quality.
Delivery time and Customer Support
Whether the factory can deliver the order on time is important, as prompt delivery will ensure the customers’ smooth production and sales plan. Meanwhile, it can avoid the production pause or inventory shortages caused by delays.
A good customer support team should be easy to communicate with, quickly respond to your questions, and be willing to help you meet your needs. these can ensure smooth operations, build trust, and bring the success of your business.
Conclusion
Flex PCB assembly manufacturing is more complicated than Rigid PCB assembly, and we not only need to take care of the precise fixing, right fixture, pre-baking, printing, assembly, and reflow. Meanwhile, strict process control is also needed. The workers must follow SOPs(Standard Operating Procedures) and be continuously monitored by the engineers and IPQC, so any issues found during assembly can be controlled earlier.
Choose FX PCB as your flex PCB assembly manufacturer, an ISO9001 certificated Supplier, and we have strict quality control on each production process. Send us your Gerber file and Bom list to get your flex PCB assembly price today!
