Research On Application Of Insulated Gate Bipolar Transistor(IGBT) Module Fabrication By Pressureless Low Temperature Sintering Of Nanosilver Paste

Nanosilver paste is emerging as a promising lead-free die-attach material in power electronics,especially for high-temperature applications.It has also been applied as an alternative to traditional electrical and structural interfacial materials,e.g.,solder alloys and conductive epoxies,due to its superior performance,such as high melting point?961??,high electrical and thermal conductivity(4.1×10⁷ S/m and229 W/mK,respectively)and low sintering temperature?lower than 260??.In this paper,relevant work was carried out based on sintering mechanism,large-area die attachment and application of high power IGBT module fabrication by pressureless low temperature sintering of nanosilver paste.The main research results were listed as follows:Firstly,the pressureless low temperature sintering and its densification behavior of nanosilver paste were studied.Test results show that the pressureless low temperature sintering of nanosilver paste could be divided into three stages:evaporation of thinners and solvent,connection and densification among silver particles.The formation of necks was strongly dependent on the sintering temperature,while prolonging the holding time and decreasing the heating rate were beneficial to neck growth.Secondly,the IGBT chip was bonded onto the DBC substrate by optimizing the pressureless low temperature sintering of nanosilver paste.The bondline thickness was controlled by a designed fixture,and the cross pattern of as-printed nanosilver paste was optimized.The relationship of cross shape factor parameters was achieved by theoretical calculation,and the database of these parameters was obtained.The effect of drying time,sintering temperature and sintering time on die-shear strength was studied so as to obtain the optimum sintering parameters.Thirdly,a high power 1200V/150A IGBT module was fabricated with the proposed large-area die attachment.The electrical and thermal characteristics of the IGBT module using presssureless sintered nanosilver have been measured and compared with the commercial one using soldered Sn5Pb92.5Ag2.5.Test results show that the on-state voltage drop and switching characteristic of these two kinds of IGBT modules agree with each other,while the thermal resistance of the IGBT module using pressurless sintered nanosilver were 0.022^oC/W lower than that of commercial one,respectively.Finally,the reliability of the 1200V/150A IGBT module using pressureless sintered nanosilver was evaluated by power-cycling and thermal-cycling tests.By second-level power cycling test?junction temperature:25¹25?,case temperature:25⁵5??,the lifetime of IGBT module with soldered Sn5Pb92.5Ag2.5 was 30 K cycles lower than the one with pressureless sintered nanosilver.After 35 K minute-level power cycling test?junction temperature:25¹25?,case temperature:25¹05??,the thermal resistance,on-state resistance and total switching energy of IGBT module using pressureless sintered nanosilver were 2.1%,9.0%and 13.4%lower than that of commercial one,respectively.The temperature profile of thermal cycling test ranges from-55 to 150?.After 300 thermal cycles,the thermal resistance and on-state resistance of IGBT module using pressureless sintered nanosilver were4.1%and 7.0%lower than that of commercial one,respectively.