Mechanical and thermal board level reliability comparison between electroless NI IM. AU and solder on PAD surface finishes for large flip chip BGA packages

Large Flip Chip BGA (FCBGA) packages are needed in high pin out applications (>1800), e.g., ASIC's and are typically used in high reliability and robustness applications. Hence understanding the package reliability and robustness becomes one of paramount importance for efficient product design. There are various aspects to the package that need to be understood, to ensure an effective design. The focus of this paper is to understand the BGA reliability of the package with particular reference to comparison of the surface finish, vis-à-vis, between Electroless Nickel Immersion Gold (ENIG) and Solder On Pad (SOP) on the substrate side of the package, which are the typical solutions for large plastic FC-BGA packages. Tests, which include board level temperature cycling, monotonic bend and shock testing have been conducted to compare the two surface finish options. The results of these tests demonstrate that the mechanical strength of the interface exceeds by a factor of two for the SOP surface finish, while BGA design parameters play a key role in ensuring comparative temperature cycle reliability in comparison with ENIG packages.