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22 SMT Magazine • March 2017 Fraser: First, it is important to ensure the board hasn't absorbed moisture prior to running through SMT process. Second, the pallet de- sign must be appropriate for running the board through the SMT process and work with the test fixture. Third, it is important to develop a de- tailed handling plan that considers every step from when someone takes the board out of the out of the package through placing it in the fin- ished goods package. Finally, finished goods packaging design needs to protect the product in shipment and be easy to load and unload without stressing solder joints. Las Marias: How do assemblers address these chal- lenges? What parameters should be considered? Fraser: The reflow soldering process is straight- forward. If you are running double-sided reflow, you really need to have your profiles dialed in. But for the most part, if you have good process in place, it isn't significantly more challenging. Las Marias: How different is the flex circuit assem- bly from the standard PCB assembly, and what are the important factors to consider? Fraser: Support and handling are more com- plex. In test, you need to design fixtures that will accommodate a carrier to lift the flex pan- el from the fixture without stressing it. Verify- ing stress and strain requirements at test is also critical. Las Marias: What about the challenges with re- spect to flexible circuit materials? Fraser: Moisture sensitivity can be an issue with the bonding material. Las Marias: Do customers call out a specific brand name of material to use when dealing with flexible printed circuits? Fraser: Yes, most of our customers specify mate- rial and board house. Las Marias: What has the greatest impact on the quality of flexible circuit assemblies? Fraser: When you are doing final assembly, you need to make sure that the board functions properly before beginning the mechanical as- sembly process and that the final mechanical assembly process doesn't damage it. The more a flex circuit is handled, the higher the probabili- ty of operator incurred defects or stress fractures that could cause failures in the field, so mini- mizing the possibility that a mechanical assem- bly step must be reworked is far more important than with a traditional PCBA. Las Marias: In which end markets are you seeing increasing use of flexible circuits? Fraser: In our case, exterior and interior auto- motive lighting. Las Marias: What should OEMs consider when choosing an assembly partner for their flex circuit assemblies/projects? Fraser: Does that partner have demonstrated capabilities in that application? Also, it is im- portant to understand that less defects are like- ly to occur if the contract manufacturer does fi- nal assembly as compared to shipping the flex Steve Fraser STRATEGIES FOR ADDRESSING FLEX CIRCUIT ASSEMBLY PAIN POINTS