iNEMI project on process development of BiSn-based low temperature solder pastes: Part III: Mechanical shock tests on POP BGA assemblies

Lowering peak reflow temperature from the current 240°C+ level for SnAgCu (SAC) solder paste during the assembly of electronic board products has economic, environmental and technical benefits. The Bi-Sn solder system is one low melting metallurgical system of interest, but the inherent brittleness of bismuth is its major drawback. Recently, solder suppliers have developed ductile Bi-Sn metallurgical and resin reinforced formulations of solder pastes to overcome this drawback. In this study, many of these newly developed solder pastes systems were evaluated by assembling SAC ball Package-on-Package (POP) components with these pastes on boards having the new JEDEC Standard design and then subjecting them to mechanical drops until failure. Result showed that though there was significant improvement in the mechanical shock resistance of the solder joints formed using the ductile metallurgy and resin reinforced formulations over those formed with the baseline eutectic Bi-Sn formulations, this improvement was still not up to par with that of the SAC solder paste.