High-temperature joint materials are indispensable to realizing next-generation power modules with high-output performance. However, crack initiation resulting from stress concentration in semiconductor chips joined with high-temperature joint materials remains a critical problem in high-temperature operation. Therefore, clarifying the quantitative influence of joint materials on the stress generated in chips is essential. This study investigates the stress behavior of chips joined by Ni–Sn solid–liquid interdiffusion (SLID), which results in a high-temperature joint material likely to generate cracks after joining or when under thermal cycling. The results are compared with those fabricated using three types of solders, Pb–10%Sn, Sn–0.7%Cu, and Sn–10%Sb (mass %), which are conventional joint materials with different melting points and mechanical properties. Using Ni–Sn SLID results in the generation of high compressive stress (500 MPa) without stress relaxation after the joining process in contrast to the case of solders in which the compressive stresses are low (<300 MPa) and decrease to still lower levels (<250 MPa). In addition, no stress relaxation occurs during thermal cycling when using Ni–Sn SLID, whereas stress relaxation is clearly observed during heating to 200 °C using solders. Different stress behaviors between Ni–Sn SLID and other joint materials are illustrated by their mechanical strength and resistance against plastic and creep deformation. These results suggest that stress relaxation in a chip is key in suppressing crack initiation in highly reliable modules during high-temperature operation.

Highly reliable operation at high temperatures is required for next-generation power modules in electric vehicles. We propose a joining concept involving nickel-tin (Ni-Sn) double solid-liquid interdiffusion with an aluminium (Al) sheet (Ni-Sn DSLID/Al), which enables the production of modules with high thermal reliability. The use of Ni-Sn DSLID/Al joint as bonding layers for a large thermal coefficient mismatch [silicon (Si) chip: 3.9 × 10 −6 K −1 , copper electrode plate: 16.5 × 10 −6 K −1 ] effectively decreased the compressive stress to 250 MPa in the Si chip, compared with that of a conventional Ni-Sn SLID joint (500 MPa) after joining. Moreover, the stress was relaxed when heating to 200°C during thermal cycling (from −40 to 200°C), due to the plastic and creep deformations of the inserted Al sheet. In addition, Ni-Sn DSLID/Al joint suppressed crack propagation during thermal cycling and exhibited higher thermal durability than Ni-Sn SLID and Sn-10% antimony solder joints up to 500 cycles, due to the higher resistances of the plastic and creep deformations of the inserted Al sheet. The present concept demonstrates great potential for use in fabricating joints for next-generation power modules.

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