Mechanical Properties of Cu-Core Solder Balls with ENEPIG Surface Finish

The development of ball grid array (BGA) packages, such as the chip scale package, wafer level package and package on package, has focused on creating electronics packages that are smaller, thinner, higher-performance and capable of higher functionality, among other desirable traits. Among the interconnection materials used in BGA packages, the Cu-core solder ball (CCSB) has many advantages, such as the use of finer pitch, improved electrical conductivity and better controllability of the coplanarity of the chip. In this study, we evaluated the mechanical properties of the CCSB and Sn-3.0Ag-0.5Cu (SAC) by low-speed shear tests, and the von Mises stress distribution and plastic strain distribution were simulated using a finite element method. The diameter of each solder ball was 280 μm, and the outer layer of the CCSB was a plated SAC layer. The shear strength of the CCSB was about 10% greater than that of SAC. The maximum value of the simulated von Mises stress for the CCSB was higher than that of SAC because the Cu-core is stiffer than SAC. The fracture energy of the CCSB decreased by about 50% compared to that of SAC. The maximum value of simulated plastic strain, which is associated with fracture surfaces, was higher with the CCSB than with SAC. We can thus conclude that the Cu-core in the CCSB affects the shear strength and fracture behavior of solder joints.