Processing And Performance Of Joint Of Instantaneous Low Temperature Sintering For Attaching High Power IGBT Chips

Sintering of nanosilver paste has been extensively studied as a lead-free die-attach solution for bonding semiconductor power chips.It has excellent mechanical properties,high temperature properties,good electrical conductivity,thermal conductivity,which can meet the requirements of high temperature and high power density packaging of high power electronic devices.Based on its excellent performance,which make it is expected to replace the traditional solder as one of the key connecting materials to achieve the packing of semiconductor device.However,nanosilver paste was mainly sintered by the traditional hot pressing sintering process,which needs complicated process conditions,such as a long sintering time(~1 h).In recent years,we tried to use nanosilver paste to realize metal dummy chips and metal substrate connection by rapid sintering method.However,the rapid sintering of power semiconductors and ceramic copper substrate(DBC)cannot be realized,which greatly limits the nanosilver paste and its fast sintering method in the power module package applications.Then,we designed an integrated device for rapid sintering of nanosilver paste.The current assisted sintering method and the densification mechanism of nanosilver paste were studied.The current-assisted sintering process was developed,which successfully achieved connection between the IGBT devices and silver-plated copper substrate connection(150 s)and DBC(10 s),respectively.The influence of sintering current and current on time on the microstructure of sintered silver joint was studied.It describes the qualitative or semi-quantitative relationship of twin organization produced during sintering process and thermal and electronic properties of joints.Firstly,we designed and manufactured a system,which can achieve the connection of a semiconductor chip and substrate.And the temperature distribution and evolution of the solder paste layer during the rapid sintering process were recorded by infrared thermography.The results show that the peak temperature of the solder paste layer is determined by the sintering current value,while the holding time of the peak temperature is controlled by the current-on time.Then,the effects of sintering current,current on time,preheat temperature and preheating time on the shear strength,shear fracture,cross section,thermal resistance and electrical properties of the sintered joint during the bonding process between the semiconductor chip and the silver plated copper or DBC substrate were studied.The experimental results show that high sintering density of nanosilver paste can be achieved when the sintering current is 2.0 kA and the current on time is 150 s,and the reliable connection between the semiconductor chip and the silvered substrate can be achieved.The heat dissipation of DBC is much lower than that of silver plated copper.And the Joule heat generated when the current flows through the substrate will increase with the distance between the electrodes increases.Therefore,a reliable interconnection of IGBT chips and DBC was achieved by rapid sintering method at sintered current of 1.1 k A and current on time of 10 s.Finally,the TEM was used to analyze the microstructural characteristics of sintered nanosilver paste with a sintering current of 1.1 kA and current on time of 10 s.And it was found that a lot of twins were formed during sintering.The influence of twin structure on the thermoelectric properties of the fast sintered joint is described by studying the twin structure.