Process and Material Characterization of Die Attach Film (DAF) for Thin Die Applications

The main drivers for die attach film (DAF) implementation are package miniaturization and die thickness reduction, especially in applications requiring die thickness <100 mum. However, processing of DAF materials presents certain difficulties, especially in dicing of DAF-laminated wafers. This work outlines the challenges in terms of material selection and processing optimization to incorporate DAF into the assembly of a 100 micron thin die Ball Grid Array (BGA) package. Process characterization with material modification was conducted to provide insights on influence of material on assembly processes such as wafer lamination, dicing and die attach. Reliability testing was also conducted to evaluate the robustness of the DAF incorporated package. To achieve void-free lamination, it was found that increasing the lamination temperature reduces the occurrence of voids between the DAF and wafer. Due to the additional layer of soft DAF material present, dicing parameters optimization becomes critical to reduce side wall chipping. It was found that minimum chipping and whisker formation can be achieved using a 2-step dicing process with optimized cutting depths and feed rate. It was also observed that whisker formation can be overcome with proper material modification. Optimum adhesion of the DAF material to both the dicing tape and die backside is critical to prevent "flying die" during dicing and die pick-up problem during die attachment. Reliability tests results demonstrated the robustness of DAF material to meet moisture sensitivity level 3, unbiased highly accelerated temperature and humidity stress test, and temperature cycling. In summary, this study demonstrates that good processibility and robust performance with DAF can be achieved with proper material selection and optimized process parameters.