Shear strengths and fracture behaviors of Cu/Sn37Pb/Cu soldered joints subjected to different displacement rates

Abstract

The effects of displacement rate and reflow duration on the shear strengths of the Cu/Sn37Pb/Cu soldered joints as well as the interfacial microstructure were investigated after reflowing. The samples were reflowed at 300°C for different durations (5min, 15min and 30min) and then shear tested with different displacement rates ranging from 2.5×10−3 to 5×10−2mms−1. The intermetallic compounds (IMCs), including Cu6Sn5 and Cu3Sn phases were observed between Sn37Pb solder and Cu substrate, and their thicknesses increased with increasing reflow duration up to 30min. The single lap shear test results indicated that the shear forces of the joints increased with increasing displacement rate, but decreased with increasing reflow duration. Failure mechanisms of soldered joints in different displacement rate regimes were investigated based on the fractography analysis. After reflowing for 5 and 15min, the fractures of the Sn37Pb soldered joints mainly occurred inside the bulk solder irrespective of the displacement rate. While some broken Cu6Sn5 particles could be observed at the bottom of dimples in solder bulk as the high displacement rates were adopted (such as 1×10−2 and 5×10−2mms−1). In case of reflow duration of 30min, as the low displacement rates (such as 2.5×10−3 and 5×10−3mms−1) were adopted, the fracture patterns of soldered joints were similar to that of soldered joints reflowed for 5 and 15min. In contrast, little solder and many IMCs were detected on the fracture surface under high displacement rates condition (such as 1×10−2 and 5×10−2mms−1), which indicated that the fracture mainly occurred in the interior of Cu–Sn IMC layer. The displacement rate sensitivities of the soldered joints reflowed for different durations were also investigated, and it is found that the displacement rate sensitivity decreased with increasing reflow duration due to the increased interfacial IMC layer thickness.