Solder joints properties as function of multiple reflow Vapor Phase Soldering process

The continuous trend towards high density and miniaturization of electronic devices involves the use of multiple reflow processes in assembling technologies for second level of interconnections in electronic packaging hierarchy. According to the “4P” Soldering Model concept (4PSMC), considering the Pad-Paste-Pin-Process elements as Key Process Input Variables (KPIV), the solder joints are the result of KPIV synergistically interactions and correlations with consequences over their microstructure. In the paper, taking into consideration the cooling rate influence over intermetallic compounds (IMC) formation and microstructure, there was described the investigations over electrical and mechanical properties of solder joints resulted from multiple reflow Vapor Phase Soldering (VPS) process, in terms of 4PSMC. Maintaining the pad, pin and paste of KPIV as references measurements of solder joints resistances and shear forces were perform as function of VPS process´s number for two values of cooling rate, respectively IMC microstructures and stereofractography studies. The results of the studies performed and presented in the paper will be use for improving process control in order to assure the solder joints reliability, to minimize losses on VPS lines, to reduce defects number and rework time.