Diffusion anisotropy induced uneven regional growth of Cu6Sn5 IMC in Cu/SAC305/Cu micro solder joints under temperature gradient

Distinct uneven regional growth of interfacial Cu6Sn5 intermetallic compound (IMC) in Cu/Sn-3.0Ag-0.5Cu/Cu micro solder joints under temperature gradient (TG) was reported. The results revealed that thick and thin Cu6Sn5 IMC evenly formed at the whole cold end interface in the joints with small and large theta angle (the angle between the c-axis of beta-Sn grain and the direction of TG) beta-Sn grains, respectively; however, for the joints with medium theta angle beta-Sn grains, distinct uneven regional IMC growth with thick Cu6Sn5 IMC region and thin Cu6Sn5 IMC region was detected at each cold end interface. After aging for 600 h, the average IMC thickness in the thick Cu6Sn5 IMC region gradually decreased as the theta angle increased and presented a linear relationship with cos(2)theta, while that in the thin Cu6Sn5 IMC region always stuck to 4.5 +/- 0.5 mu m regardless of theta angle. The uneven regional growth of the Cu6Sn5 IMC was attributed to the strong diffusion anisotropy of Cu atoms in beta-Sn grains. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

The study reported distinct uneven regional growth of interfacial Cu6Sn5 intermetallic compound in Cu/Sn-3.0Ag-0.5Cu/Cu micro solder joints under the influence of temperature gradient. The uneven growth was attributed to strong diffusion anisotropy of Cu atoms in beta-Sn grains, leading to variations in IMC thickness at different theta angles.