The Research On Reliability And Pb Contamination Of Microelectronic Assembly Solder Joints

With the development of electronic industry, the integrated level has become higher and higher. The demand for higher performance, higher power, smaller outline devices are in progressing. And the higher power with smaller outline device generates larger heat in unit area. So the reliability of assembling joints under high temperature has become a big problem. And as the environment protection ideas become more profound around the world, the Pb elimination is considered to be the general trends. In this special period of time for the transition from Pb to Pb-free, the Pb contamination of Pb-free solder joints has become a new problem for the electronic assembling.MARC finite element analysis software was used in this paper. The 3D model was established according to the geometric property of an actual plastic ball grid array package assembling system. The material property of the solder joints was defined with non-linear material user subroutine of steady creep. The creep strain, equivalent stress, regional deformation of solder joints array under temperature cycling was simulated. And the reason of creep strain distribution was found with the analysis of stress and deformation. The optimization methods to prevent creep failures were presented. The creep situations of two kinds of solder joints, Sn-3.8Ag-0.7Cu and 63Sn-37Pb, were compared during thermal cycling. The shear creep strain and shear stress were calculated. The low cycle fatigue lives of the two solder joints were predicted with the help of an empirical equation, and the reliabilities of the two solder in this case were evaluated. The work can to some extent be a guideline for the device design and material selecting. The establishment of 3D model and definition of non-linear material guarantee the analyzing accuracy.Solder alloys were melted by High frequency inducing method. Different amounts of 63Sn-37Pb solder alloy were added to Sn-3.8Ag-0.7Cu alloy to obtain the Pb contaminated Pb-free solder alloys. The melting points of the Pb-contaminated solder in different extents were measured, and the effect of the Pb-contaminations on the melting temperature was analyzed. The Pb-contaminated solder joints were fabricated by the computer programmable SMT soldering machine, and the joints were aged in different temperature. The effects of Pb-contamination on micro-hardness, microstructure and intermetallic compound were analyzed.