Mechanical property of new concept about Cu core bump formation For high reliability PKG

Nowadays, 2D structure of PKG needs to change to 2.5D or 3D structure for high performance of PKG. The standoff property was required to prevent the Si chip damage and electrical short when solder joint is located between substrate and interposer. So, CCSB (Cu Core Solder Ball) is the most popular candidate of interconnection material for 2.5D PKG. However, controlling of plated solder composition has limitation due to difficult deposition over 3 elements by electroplating system. So, SAC305 composition was plated for CCSB product. In this paper, we studied Cu bump formation of new concept. At first, Cu bump was formed with combination with 1st reflowed solder bump and specially controlled Cu ball which is the surface treatment layer to get good wetting property of liquid solder by additional reflow. The applied solder is the Sn-2.5Ag-0.8Cu-0.05Ni-1Bi (MXT02) for high reliability. New concept Cu bump showed higher joint strength than general CCSB product. Therefore, new concept of Cu core ball will show higher reliability, easy application and more fine pitch then general CCSB product.