Solder joint structure and reliability of board level BGA package using no-clean curable solder paste

In the SMT(surface mount technology) process, the cleaning process of flux residue is getting difficult due to the decrease of interconnection pitch. In this study, the curable type no-clean solder paste containing resin instead of rosin was formulated and its effectiveness on the reflow process accessibility and the thermal cycling and dynamic bending reliabilities were evaluated for the board level ball grid array package. It was found out that the solder joint and cured adhesive fillet could be properly formed after reflow process. The flux was cross-linked with epoxy resin to form the thermoplastic cured product. Although the formation of cured adhesive fillet at the only bottom side of solder joint seemed to be detrimental to the dynamic bending reliability, it was considered to be helpful to the thermal cycling reliability due to the reinforcement of ball and die shear strength.