Built-in Reliability Design of Highly Integrated Solid-State Power Switches With Metal Bump Interconnects

Abstract

A stacked substrate-chip-bump-chip-substrate assembly has been demonstrated in the construction of power switch modules with high power density and good electrical performance. In this paper, special effort has been devoted to material selection and geometric shape of the bumps in the design for improving the thermomechanical reliability of a highly integrated bidirectional switch. Results from 3-D finite-element simulation indicate that for all design cases the maximum von Mises stresses and creep strain accumulations occur in the solder joints used to join bumps on IGBTs during a realistic mission profile, but occur in the solder joints used to join bumps on DBC substrates during accelerated thermal cycling. The results from both the simulation and the accelerated thermal cycling experiments reveal that selection of Cu/Mo/Cu composite brick bumps in the stacked assembly can significantly improve the thermomechanical reliability of both the solder joints and the DBC substrates when compared to Cu cylinder bumps and Cu hollow cylinder bumps reported in previous work. Such results can be attributed to the effective reduction in the extent of mismatch of coefficients of thermal expansion between the different components in the assembly.Index Terms-Cu/Mo/Cu composite, finite-element (FE) method, integration, thermal cycling, wirebond-less packaging.

Thermal Design of Stacked Power Modules for Electric Drive Applications

“…The two substrates in each of the four IGBT modules are 0.3/0.32/0.3 Cu/Si 3 N 4 /Cu substrates because of sufficiently high thermal conductivity and good thermo-mechanical reliability [7]. The conductive shims are made of 1/4/1 Cu/Mo/Cu sandwiched structure, which has coefficients of thermal expansion compatible with IGBT and FRD chips [8]. All the power and signal/control terminals are made of oxygen-free copper (OFHC) with high thermal and electrical conductivities.…”

Thermal management and packaging of wide and ultra-wide bandgap power devices: a review and perspective

“…Junction-and double-side cooling have been pursued for SiC devices by replacing the traditional wire bonds with interconnect methods that enable direct heat transfer from the device junction to the substrate or lead frame. Examples of such interconnect methods include soldering lead frames or substrates directly to the die topside contacts [20,76,92], soldering or sintering Cu, Mo or Cu-Mo posts or bumps between the die and the substrate [93][94][95][96], and drilling and electroplating Cu-filled vias for PCB-embedded packages [97][98][99]. As an example, the use of Cu and Mo posts in a double-side cooled configuration was utilized to achieve an overall R th,j-c of just 0.17 • C W −1 for a 10 kV, 25 A SiC MOSFET [85].…”