Microstructure of solder joints with micron stand-off height in electronic packaging

In present paper the microstructural change was studied when the stand-off height(SOH) of solder joints with Cu/Sn/Cu sandwich structure was reduced from 100μm to 50μm, 20μm and 10μm. With the reducing stand-off height, the Cu content increases in the solder bulk, and the Cu₆Sn₅ intermetallic layer formed at both sides decreases in thickness; while the proportion of IMC thickness to solder joint stand-off height increases. The thickness of the copper layer consumed by solder joints with different stand-off heights was calculated according to the formed IMC layer and Cu content in the solder bulk. It is found that the consumed copper thickness decreases with the reducing stand-off height. In the aging, the solder joint with lower SOH increases faster in IMC thickness and IMC proportion, leading to more dramatic microstructural change.