Development status of advanced packaging copper pillar bump interconnection technology and reliability

With the development of lightweight electronic components, copper pillar bumps (CPBs) have emerged as a flip-chip interconnection solution that combines high performance and high reliability, owing to their high-aspect-ratio structure, which enables finer pitch and higher interconnection density within the same area. A comparison was presented between traditional C4 bumps and CPBs, highlighting the unique structural characteristics of CPBs and their advantages in thermal, electrical, and mechanical properties, while also addressing existing challenges and issues associated with this technology. The electroplating process for fabricating CPBs was discussed, with a detailed explanation of how electroplating solution composition and electroplating parameters affect bump quality. Optimization of the types and concentrations of additives, as well as the electroplating conditions, could enable CPBs with excellent surface planarity and uniformity. Furthermore, the reliability performance of CPBs under thermal cycling and electromigration conditions was analyzed, including morphological and microstructural changes observed during thermal aging, thermal cycling, and electromigration tests. The influence of factors such as bump shape, surface treatment, and underfill on reliability was also examined. Finally, the future development direction of CPBs was summarized and projected.