Nickel solder ball performance for Pb-free LFBGA assembly under oxygenous reflow

Due to the technology improvement of ball-grid-array (BGA) package, the high-pin count concept was derived to the mass production. The low profile fine pitch BGA (LFBGA) package was employed to gain the assembly competition. The smaller diameter of solder ball, 0.3 mm, must be incorporated and the composition of solder ball needs to be modified such as including nickel to strengthen the adhesion capability in IMC layer. Since the oxygen concentration in flow process usually works upon the quality of solder joint such as oxidation causing aged effect and quality of inter-metal compound, the oxygen variance is checked in this study. Furthermore, the flux as solder assistance is also a cardinal factor affecting the solder adherence between LFBGA substrate and solder ball. Adopting the temperature cycling test, shear test and drop test to understand the adhesion ability for lead-free solder balls on LFBGA substrate assisted with several fluxes, the optimal process recipe was obtained. The soldering performance was promoted well.