Research on the Thermal Cycle Test Performance Improving in Automotive R-F PCB

With the invention and development of PCB and FPC, Rigidflexible (referred as R-F in the following text) board was designed and realized naturally by engineers. We combine flex and rigid materials by laminating with certain stack-up, these materials contain FCCL, CVL, LF PP, CCL and so on. Due to the great difference of CTE (coefficient of thermal expansion) between these materials, the defect of hole copper crack happens frequently during thermal cycle test (as known as TCT) for R-F board. Normally rigid PCB can survive after more than 1000 cycles of TCT test with condition of - 40°/30min to 125°/30min, however the R-F board will fail within 600 ~ 700 cycles. After a change of resistance more than 10% detected, engineers will find out the crack of copper mainly in the contact surface of LF PP and PI layer of FCCL, which is resulted from the obvious difference between CTE of LF PP and PI. This paper mainly starts from three factors, different kinds of PP with different CTE, through hole copper thickness and copper elongation, to research how these factors affect the life of R-F board enduring TCT with DOE method. Through this paper, we hope to give some suggestions to engineers who wants to enhance the cycles of TCT test of R-F board in PCB industry.