Research On Reliability Of Bonding Wire In Automotive Power Module

As the core of the electric drive system of electric vehicle,power semiconductor modules have an important impact on system efficiency,integration and reliability.The third-generation semiconductor material SiC has excellent performance,and its devices have the characteristics of high blocking voltage,high switching frequency,high operating temperature,high thermal conductivity and low loss.However,the size of a SiC chip of the same power level is possibly less than half the size of Si chip,its operating temperature and power density are higher,and the area available for wire bonding above the chip is smaller,and the number of bonding wire is less.Therefore,the reliability challenge of wire bonding of SiC devices for automotive is extremely severe.This article focuses on the reliability of SiC power module wire bonding,using theoretical modeling,reliability testing,and numerical simulation method to systematically study the effect of key factors such as bonding parameter,bonding wire material,and geometric structure on wire bonding reliability.The main contents include:The ultrasonic wire bonding system and mechanism are analyzed.Based on the wire bonding strength shear strength test method,the influence of bonding parameters on the bonding quality was studied,and it was pointed out that friction and ultrasonic vibration in the bonding interface are the main driving force caused plastic deformation between the bonding wire and the bonded material to complete the wire bonding,and obtained the theoretical model of ultrasonic bonding,and revealed the mechanism of bonding parameters and the mechanism of improving the bonding strength,providing a design basis for the following wire bonding parameter experiments.Experimental research on wire bonding strength was carried out for Cu and Al wire.The influence of bonding parameters on the morphology and bonding strength of bonding points is clarified,and the effective window selection range of bonding parameters is found out.At the same time,the study found that temperature shock has a significant effect on the degradation of wire bonding strength of SiC chips,which has the advantages of high degree of bonding strength degradation and short test time,which can provide a reference for the optimization of bonding parameters and rapid test evaluation of bonding quality.A standard simulation model of SiC powe r module was constructed,and the influence of Cu wire replacing Al wire on module reliability,bonding wire fatigue life and chip electrothermal performance was studied.Studies have shown that under temperature shock,the fatigue life of Cu wire is about twice that of A1 wire,but Cu wire will increase the plastic strain of the chip solder layer and the stress of the DBC substrate.Under power cycle,the reliability and fatigue life of Cu wire are significantly higher than that of A1 wire,but the thin Cu wire will increase the current density and temperature of chip bonding points and bonding wire.Two SiC MOSFET power modules were fabricated using Cu and Al wire respectively,and the influence of the bonding wire on the module’s aging law,failure mechanism and fatigue life was studied through power cycle test.The experiment found that the chip junction temperature difference and the module case temperature difference of Cu wire bonding are higher than that of the A1 wire;under the same test conditions,the failure cycle of the Cu wire module is about 3 times that of the Al wire module;There is sufficient warning time for the failure of the bonding wire in the Cu wire module,and the aging process of the bonding wire is clearly segmented.This feature can also provide reference for the monitoring and protection of the module’s health status.