Dynamic wetting behavior and solder ball spattering formation of Sn-Bi solder pastes during reflow soldering process

The dynamic wetting behavior and formation of solder ball spattering of Sn-58Bi solder paste on Cu substrate during reflow soldering process were studied by the soldering interrupt test method; meanwhile, the formation mechanism of solder ball spattering was analyzed. Further, the effect of reflow process parameters on the severity of solder ball spattering defect during reflow soldering process was investigated by a modified solder ball test. Results show that solder ball spattering mainly takes place during the second ramp-up stage of the reflow profile, in which the oxidation of solder alloy elements on the surface of molten solder pool is deoxidized into high Bi content liquid solder ball by redox reactions, then the liquid flux film breaks up and pushes the liquid Bi-rich solder balls to the edge of the solder pool, this finally results in the formation of solder ball spattering. The results of solder balling test show that a higher ramp-up rate significantly increases the severity of solder ball spattering, and a longer dwelling time can also increase the severity of solder ball spattering for the high volatility solder paste.