Root Cause of Analysis on the FCCL Delamination of Rigid Flexible Board

As the high-end rigid flexible board (R-F board) widely used in the automotive electronics, industry control systems and smart medical products, the reliability of R-F board is becoming more and more important. FCCL is a very important material in the stack up of R-F board. As we know, PI has excellent heat resistance, electric property, mechanical property and flame retardancy, because of the amazing physical property and chemical property, PI is broadly applied in all kinds of situation. However, the biggest disadvantage of PI is that it is easy to absorb moisture. When the R-F board undergoes reflow of SMT, the water in PI will tum into water vapor at high temperature, resulting in the delamination between PI and copper foil because of rapidly increased stress of water vapor. In this situation, not only it brings serious economic loss but also affect efficiency. This study is aiming at the root of delamination of FCCL. We mainly study the type of PI, design of grid copper, water absorption and baking before SMT with DOE analysis, to find how these factors affect the delamination of FCCL. We hope this paper can provide reference for engineers in the industry of PCB and SMT.