Stress analysis of pressure-assisted sintering for the double-side assembly of power module

Abstract

Purpose: Crack and stress distribution on dies are the key issues for the pressure-assisted sintering bonding of power modules. The aim of this research is to build the relationship among the stress distributions, the sintering sequences, and the sintering pressures during the sintering processes. Design/methodology/approach: Three sintering sequences, S(a), S(b) and S(c), have been designed for the double-side assembly of power module in this paper. Experiments and finite element method (FEM) analysis are conducted to investigate the crack and stress distribution. Findings: The sintering sequence had significant effects on the crack generation in the chips during the sintering process under 30 MPa pressure. The simulation results revealed that the module sintered by S(a) showed lower chip stress than those by the other two sintering sequences under 30 MPa. In contrast, the chip stress is the highest when the sintering sequence follows S(b). The simulation results explained the crack generation and prolongation in the experiments. S(a) was recommended as the best sintering sequence because of the lowest chip stress and highest yield rate. Originality/value: This study investigated the stress distributions of the double-side sintered power modules under different sintering pressures. Based on the results of experiments and finite element method (FEM) analysis, the best sintering sequence design is provided under various sintering pressures.

Brief review of silver sinter-bonding processing for packaging high-temperature power devices

“…In recent times, some suppliers have developed pressure-assisted sintering equipment, and the sintering pressure and temperature range from 0.5-30 MPa and 220-270 ℃, respectively [33] . The selection of sintering pressure, which is an important factor for sintering efficiency, yield and cost management [34][35] , highly depends on the scale of the silver particle in the silver-sintering materials [36] . Tab.…”

“…Pressure-assisted sintering could ensure the reliability of sintered silver attachment effectively. However, compared to bonding the discrete devices, the pressure-assisted sintering would lead to lower yield for fabricating high-density power modules integrated with multiple bare devices because it is difficult to obtain a uniformly distributed auxiliary pressure for each bare devices [34,56] . In addition, the pressure-assisted sintering requires a large investment in the sintering equipment and customized molds for different packaging cases.…”

“…Therefore, those SiC modules with the pressure-less sintered nanosilver are believed to be approximately 40% better in heat-dissipating capacity than that of the traditional wire-bonding case. Considering that expensive SiC-based devices have higher Young's modulus than Si-based devices [15] , the pressure-assisted sintering is prone to damage the power devices, resulting in a low yield for multi-chip SiC power modules [34] . Therefore, using the pressure-less sintering for bonding SiC-based power chips with the small chip size is preferred for massive production.…”

Joints realized by sintering of pressureless Ag paste

“…At present time, joints realized by sintering of pressureless silver paste is a progressive trend in the field of power electronics (Bai, 2005;Chua and Siow, 2016;My sliwiec and Kisiel, 2015;Liu et al, 2018aLiu et al, , 2018b. Silver paste is promising bonding material that can be sintered at low temperature (175°C or 200°C) within curing time ranging from 30 to 90 min) and also without the necessity to apply external pressure while curing (Roh et al, 2017;Steen, 1984).…”

“…This new nanoscale high thermal conductive die attach silver paste is promising low-temperature sintering material because of its possibility not only to improve the performance and reliability of power electronic devices but because of its possibility for increasing the density of integrated circuits and decreasing the dimension of interconnections in microelectronic systems as well (Lukacs et al, 2017;Liu et al, 2018aLiu et al, , 2018bSiow, 2012). This high electrical and mainly thermal conductive material has great potential for new generation of joints in power electronics.…”