Flip-chip Assembly and Reliability Testing

Abstract

This thesis investigates the assembly and reliability processes of two different flip chip technologies, C4 solder bumps and gold stud bumps. The thesis mainly focuses on how underfill affects the mechanical and electrical reliability of the flip chip assemblies when going through temperature cycling. The reliability of the assemblies were tested using various methods such as measuring resistance, performing shear tests and cross sections. The result of the project clearly shows that underfill significantly improves both mechanical and electrical reliability. This was especially clear on the C4 chips were the ones with underfill seemed almost unaffected by the temperature cycling while the chips without underfill deteriorated significantly over time. For the Au stud bumps assemblies, problems with underfill application were observed, mainly because of low standoff height. Even though there were challenges the underfill still improved the mechanical reliability of the Au stud bump assemblies. The thesis concludes that the underfill process is crucial to achieve reliable flip chip assemblies and recommends further improvements of the assembly processes to reduce defects.