Effect of Reflow Profile on SnPb and SnAgCu Solder Joint Shear Force

Reflow profile has significant impact on solder joint performance because it influences wetting and microstructure of the solder joint. The degree of wetting, the microstructure (in particular the intermetallic layer), and the inherent strength of the solder all factor into the reliability of the solder joint. This paper presents experimental results on the effect of reflow profile on both 63%Sn 37%Pb (SnPb) and 96.5%Sn 3.0%Ag 0.5%Cu (SAC 305) solder joint shear force. Specifically, the effect of the reflow peak temperature and time above solder liquidus temperature are studied. Nine reflow profiles for SAC 305 and nine reflow profiles for SnPb have been developed with three levels of peak temperature (230o C, 240o C, and 250o C for SAC 305; and 195o C, 205o C, and 215o C for SnPb) and three levels of time above solder liquidus temperature (30 sec., 60 sec., and 90 sec.). The shear force data of four different sizes of chip resistors (1206, 0805, 0603, and 0402) are compared across the different profiles. The shear force of the resistors is measured at time 0 (right after assembly). The fracture surfaces have been studied using a scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS).
The purpose of this experiment is to study the effect of the reflow peak temperature and time above liquidus on solder joint shear force. Nine reflow profiles for SAC 305 and nine reflow profiles for SnPb have been developed with three levels of peak temperature (230o C, 240o C, and 250o C for SAC 305; and 195o C, 205o C, and 215o C for SnPb) and three levels of time above solder liquidus temperature (30 sec., 60 sec., and 90 sec.). The shear force data of four different sizes of chip resistors (1206, 0805, 0603, and 0402) are compared across the different profiles. Note that 1206 means a component with a nominal length of .12 inch (3.0 mm) and a nominal width of .06 inch (1.5 mm). The shear force of the resistors is measured at time 0 (right after assembly). The fracture interfaces are inspected by a scanning electron microscopy (SEM) in order to determine failure mode and failure surface.