The Cu/Sn–49Bi–1Ag/Sn–3.0Ag–0.5Cu/Ni–P hybrid solder joints for customer electronics were assembled by low-temperature soldering at 170–200°C. The relationship between microstructural evolution and board-level drop failure mechanism of these solder joints during aging at 110°C was investigated. The Bi-rich zone increased from 24.98to 78.85% with increasing soldering temperature from 170 to 200°C. The growth rate of intermetallic compound (IMC) in 170-SAC/SB solder joints was approximately 3 times faster than that in 200-SAC/SB solder joints. The drop failure mechanism was explained that the drop-induced crack propagation path shifted from Bi phases in the as-soldered joints to the solder/Cu6Sn5 interface in the aged joints, since the interfacial Cu6Sn5 IMC grew thicker with increasing aging time.
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