Achieving Successful Flex Circuit Assemblies

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Flexible circuits are increasingly being used in most end-markets amid the growing miniaturization trend and functionality needs of electronics products. “Flex circuits facilitate product miniaturization through 3D and that is a growing trend in most markets,” says Yousef Heidari, vice president of engineering at EMS firm SigmaTron International.

When it comes to assembly, the challenge varies based on the details of the all-flex or rigid-flex-rigid mechanical design, as well as the components that need to be assembled. The solder paste printing step is also one of the key challenging operations for designs that have multiple areas with fine-pitch components.

Heidari notes that there is no specific new equipment needed to address the challenges for typical flex circuit assemblies once the design details of handling the flex circuit during assembly have been worked out. The design must ensure that the different areas of the flex circuit get registered and are well supported.

Since the assemblies are moisture sensitive, one needs to ensure that the flex circuits and components are dry prior to going through the correct reflow process. He adds that they must be handled appropriately and baked prior to use. Handling is a concern throughout the assembly as inappropriate handling can cause delamination.

Do customers call out a specific brand name of material to use when dealing with flexible printed circuits? Heidari says they deal with a lot of mission critical products, and typically, those customers do have preferences in all aspects of defining the stack up material and details.

Overall, the design for the flex circuit assembly as well as the subsequent handling of the assembly before final product integration have the greatest impact on the quality of flexible circuit assemblies, according to Heidari, while the flex circuit panel design is the biggest contributor to yields.

For successful flex circuit assemblies, OEMs need to work closely with the design house, the fabricator, and the contract manufacturer, especially on the design for manufacturability, says Heidari. He stresses that having a good flex fabricator is also critical.

This article was originally published in the March 2017 issue of SMT Magazine.