The Thermo-Mechanical Effects of Lead and Lead-Free Solder Alloys on the WLCSP Packages

• Main Author: 辛震
• Other Authors: 蔡新春
• Format: Others
• Language: zh-TW
• Published: 2009
• Online Access: http://ndltd.ncl.edu.tw/handle/55527538364217986249

碩士 === 明新科技大學 === 精密機電工程研究所 === 97 === The removal of lead (Pb) from electronic products necessitates the replacement of the classical eutectic Sn-Pb solder by an adequate material. Among alternative lead-free solders the Sn-Ag/Sn-Ag-Cu materials seem to have the most promise as lead-free solders in the IC industry. The plastic-creep analyses of solder-bumped IC on substrate or printed circuit board (PCB) assemblies subjected to the different temperature cyclic loadings are presented. For example, the melting point of Sn-Ag/Sn-Ag-Cu solders is higher than that of Sn-Pb solders by 30℃ in particular. These in turn lead to significant divergences in plastic and creep behaviors. This research uses the validated finite-element analyses to study the elastic-plastic-creep behaviors of the 96.5Sn-3.5Ag, 95.5Sn-3.8Ag-0.7Cu and 95.5Sn-3.9Ag-0.6Cu lead-free solders and the classical 63Sn-37Pb solder bumped wafer level chip scale package on PCB assemblies subjected to two different temperature cyclic loadings. The behaviors of shear stress-strain hysteresis loops and strain energy density are examined on the key upper-right spot at the outmost corner solder joint. It can be seen that, (1) the effect of the elastic strain is slight on the thermo-mechanical behavior of these four solder alloys; (2) the shear strain range of the 96.5Sn-3.5Ag solder alloy derive almost from the plastic strain, that is, it can sustain more creep than others; (3) the plastic or creep strain effect of the 95.5Sn-3.8Ag-0.7Cu solder alloy is close to the 63Sn-37Pb solder respectively; (4) the effect of the strain energy density on these solder alloys is consistent with that of the shear strain range; (5) the 95.5Sn-3.9Ag-0.6Cu solder alloy is the most significant on the Bauschinger effect among the four solder alloys and the secondary is the 95.5Sn-3.8Ag-0.7Cu solder, then is the 96.5Sn-3.5Ag. Besides, the 63Sn-37Pb solder is not noticeable.