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20 SMT Magazine • March 2017 by Stephen Las Marias I-CONNECT007 In an interview with SMT Magazine, Steve Fraser, VP of Operations at Firstronic, discuss- es the challenges they face in flex circuit assem- bly and strategies to ensure the reliability of the products. Stephen Las Marias: What do you think are the major challenges in flex-circuit assembly? Steve Fraser: We are predominately working with rigid-flex circuit automotive lighting appli- cations. One of the issues we are seeing is that while these boards used to be shipped in a rig- id panel, they are increasingly coming in non- rigid panels. This is because LEDs tend to use metal backing rather than FR4. The cost of met- al is high enough that to reduce material cost, panels are shipped in flex format. However, the tradeoff is that when this is done, the flex pan- els must be palletized. This drives added tooling cost since it requires 25–30 pallets to run prod- uct on an SMT line without impacting through- put. Post-SMT, panels/boards then require flat trays and carts for movement among produc- tion operations, which may or may not be com- patible with a manufacturer's existing PCBA handling equipment. An additional challenge is that the bond- ing material used to bond to the rigid portion is moisture sensitive, which means the product needs to be kept in sealed-in bags until ready for use in production. Typically, they must pass through the SMT process within four hours of opening to prevent unacceptable moisture ab- sorption. Consequently, if you have serializa- tion requirements, you have serialize product inline or run small batches. In lieu of this, pre- SMT baking is required which adds time and cost and is a non-value added process. Finally, we have some applications that have bend and form requirements for the rigid portions. We re- ceive them flat, bend them first and then run them through the line formed, which increases the complexity of the required pallet. Las Marias: What specific steps in a flexible circuit assembly process have the biggest effect on yields? Strategies for Addressing Flex Circuit Assembly Pain Points FEATURE INTERVIEW