Die-attach Process Of Double-sided Cooling SiC MOSFET Modules

Nanosilver paste has high melting point,low young's modulus and excellent thermal and electrical conductivity,making it the preferred chip interconnection material for wide-bandgap semiconductor devices.In the past,the research on the connection between nano-silver and substrates was mainly based on gold-plated or silver-plated substrates,which increased the cost and generated new difficulties in coating technology.Therefore,the bonding on bare copper substrates has caused extensive attention.However,the oxidizability of copper impedes the connection between nanosilver and copper substrate.To solve this problem,this paper explores the proper process atmosphere to realize the reliable connection between the power chip and the bare DBC substrate surface.Firstly,in this paper,the sintering mechanism of nano-silver paste based on the DBC substrate was studied under different process atmospheres and then the process curve was optimized to obtain reliable joint.Results show that when the sintering atmosphere is formic acid,the sintered joints own the lowest porosity and the best performance?shear strength 22 MPa,porosity 12.29%?at the formic acid injection temperature of 200?and the sintering temperature of 280?.This is related to the decomposition mechanism of formic acid.The main decomposition products at low temperature are H₂+CO₂,and at high temperature are CO+H₂O.H₂ decomposed at low temperature can promote the densification of nanosilver paste.In order to improve the sintering ability of nano silver and avoid surface oxidation,we use the process of combining air and formic acid atmosphere.Experimental results show that when the oxygen content is 100×10³ ppm,the sintered joint has the best comprehensive performance?shear strength 32.5 MPa,the transient thermal resistance0.12?/W,saturation voltage 2.01 V,wire bonding strength 99 gf?.Microscopic analysis shows that the existence of oxygen is the prerequisite for the densification of silver nanoparticles.Secondly,this paper explores the influence of wire bonding process parameters on bonding quality in order to obtain stable wire bonds.The results show that when the arc height is 1 mm,the bonding power is 1.2 W,the bonding time is 40 ms and the bonding pressure is 50 g,the bonding strength is the highest.At the same time,the influence degree of each factor on the experimental results was bonding power>bonding pressure>bonding time.Finally,based on the above sintering process and wire bonding parameters,the thermal and electrical properties of double-sided SiC MOSFET module with nano-silver packaging are tested.Result indicates that the thermal resistance of the module ranges from 0.05 to 0.1 C/W;the static withstand voltage of the module is1200V;when the gate drive resistance is 10?,the turn-on switching loss E_on is 82.89mJ,the turn-off loss E_off is 88.97 mJ,and the peak voltage is 708 V.The result shows that the sintered nanosilver SiC MOSFET module own good thermal and electrical properties,which verifies the feasibility of the sintering process,structure design and performance of the sintering module.