Impact of in situ current stressing on Sn-based solder joint shear stability

This paper reports experimental observations showing that a current flow produces an effect of strengthening a solder joint against a shear load. This conclusion is found from a single-joint shear test conducted on Sn-1Ag-0.5Cu wt% (SAC 105) joints with in situ current stressing varied from 700 to 1400 A/cm(2) at room temperature. To isolate the current effect from the Joule heat effect, the same type of tests were conducted at room temperature, 40, 50, and 80 degrees C, without current applied to the joint, thus mimicking the condition of steady-state temperature resulting from Joule heating. Comparative testing was also conducted after aging the samples at 150 degrees C for 200 h. These tests produced indications suggesting that the current flow causes the maximum shear load to increase, while the rise in temperature by the Joule heat effect results in the opposite effect. Experimentally, as much as a 9.5% increase in the maximum shear load was observed from the isothermally aged sample tested under a current density of 700 A/cm(2), while an similar to 25% reduction was estimated to result from a temperature increase by Joule heating. The potential mechanism for these observations is discussed.