Package to Board Interconnection Shear Strength (PBISS): Effect of Surface Finish, PWB Build-Up Layer and Chip Scale Package Structure

摘要

The package to board interconnection shear strength (PBISS) of two different area array packages with Sn62Pb36Ag2 solder balls are characterized as a function of pad finish, board build-up layer type and package structure. Results indicate that the measured PBISS value is sensitive to the quality of surface finish and build-up layer on the board, but the sensitivity is dependent on the package structure. In general, the presence of hypercorrosion of the Ni layer (blackpad) on the board results in lower mean strengths and wider variation in the strengths than for organic solderability preservative (OSP) surface finish. Further, the usage of aramid reinforced build-up layer results in a lower measured PBISS values primarily because of a higher incidence of fractures within the build-up layer. The combination of OSP with resin coated copper (RCC) build-up layer appears to yield the highest interconnection strength. The finite element simulation results and fracture surface analysis together indicate that the stress field within the solder joints is primarily shear. The PBISS test method proposed here has potential applications in evaluation of the quality of interconnection of an area array package after final assembly.