Study on Solder Joint Reliability of Fine Pitch CSP

摘要

Today's consumer electronic products are characterized by miniaturization, portability and light weight with high performance,especially for 3G mobile products. In the future more fine pitch CSPs (0.4mm) component will be required. However, theproduct reliability has been a big challenge with the fine pitch CSP. Firstly, the fine pitch CSPs are with smaller solder balls of0.25mm diameter or even smaller. The small solder ball and pad size do weaken the solder connection and the adhesion of thepad and substrate, thus the pad will peel off easily from the PCB substrate. In addition, miniature solder joints reduce thestrength during mechanical vibration, thermal shock, fatigue failure, etc. Secondly, applying sufficient solder paste evenly onthe small pad of the CSP is difficult because stencil opening is only 0.25mm or less. This issue can be solved using the high endtype of stencil such as Electroforming, which will increase the cost.For this analysis, we focus on the following areas: Reliability performance of different SMD or NSMD pads Bigger pad size with higher adhesive strength IMC thickness analysis and the results(such as Ni crack or thick IMC) Improvement with underfill on CSP Improvement of solder paste deposition on pad with vacuum support Optimized reflow profile and reliable solder joint relationship