Ming Hu, Lee Kresge, and Ning-Cheng Lee
Clinton, NY USA
Epoxy flux works well without the need of solder paste at assembly. However, when the area array packages warp upon heating, solder paste is indispensable in order to prevent opens. Use of solder paste caused a challenge when applying epoxy flux at the same time, mainly due to oozing of the solder paste at reflow when immersed in the liquid epoxy flux.
Here the epoxy flux was not specifically formulated for compatibility with the solder paste. The glass slide was used to mimic the body of the BGA. As a result, upon heating on a 250C hot plate, the wet flux of the solder paste dissolved in the liquid epoxy flux, with solder powder being carried everywhere by the wet flux. The widely dispersed solder powder still remained highly scattered at the end of solder coalescence.
In this study, a newly developed epoxy flux, which is compatible with solder paste, was evaluated for assembly and reliability. Results of the assembly process with epoxy flux on top of solder paste, drop test, temperature cycling, and SIR are presented and discussed.
Initially Published in the IPC Proceedings