Ultrasound-induced interinhibitive dissolution-precipitation evolution and significantly improved mechanical properties of Kovar/SnSb10 assembly

Ultrasound-assisted Kovar/SnSb10 assemblies are promising candidates for high-precision electronic devices; however, limited research has been conducted on the effect of ultrasonication on its interfacial evolution and mechanical properties. In this study, the microstructure evolution, orientation relationships (ORs), interinhibitive dissolution-precipitation mechanism, and mechanical properties of a Kovar/SnSb10 assembly with/without ultrasonication were systematically investigated. The morphology of the intermetallics (IMCs) evolved from a newly-formed, lash-type to a block-type morphology with an increasing reflow duration, and dentation-type IMCs appeared after ultrasonication. The interfacial IMC without ultrasonication mainly contained FeSn2 and a minority of Ni3Sn2, whereas the strong disturbance caused by ultrasound led to the formation of FeSn in the peripheral FeSn3 and NiSn IMCs. Furthermore, high-resolution transmission electron microscopy (HRTEM) analysis revealed that the ORs of IMC/solder and IMC/Kovar transformed from coherent and semi-coherent to incoherent relationships after ultrasonic treatment. The ORs of the IMC/solder growth front after ultrasonication were [0 1¯ 1]Sn∥[1 1 0]FeSn3, (0 1 1)Sn∥(0 0 1¯)FeSn3 and [0 1¯ 1]Sn∥[5¯ 1 0]NiSn, (0 1 1)Sn∥(0 1¯ 0)NiSn. Additionally, 60 s ultrasonic treatment promoted the growth of IMCs, and increased the ultimate shear strength by approximately 20 MPa, despite the emergence of incoherent interfaces. This phenomenon was primarily attributed to the dispersion strengthening effect of the abundant ultrasound-induced nano-Ni3Sn2 precipitates. This study substantiates the feasibility of ultrasonication-assisted Kovar/SnSb10 assemblies and introduces a novel concept for low-cost, high-efficiency, and high-performance packaging.