Packaging Reliability Enhancement Of An Insulated-Gate-Bipolar-Transistor Module

Attachment is usually a weak point of power module packaging due to complex electrical-thermo-mechanical loads.Fatigue failure was considered as one of the dominated failure modes for power module packaging.This work presents a packaging strategy for reliability enhancement of IGBT modules using sintered nanosilver as die attachment instead of high-lead solder.Thanks to the high melting point（961℃）,high thermal conductivity,and low elastic modulus of the sintered nanosilver,the low-cost high-temperature solder can be used as substrate attachment instead of low-temperature solder,e.g.,Sn Ag3.0Cu0.5,which was susceptible to thermo-mechanical stress fatigue.Moreover,current-assisted sintered nanosilver is proposed as an improvement of die attachment because of much shorter processing time and extremely fine grain microstructures,which can also significantly improve the resistance to thermo-mechanical stress fatigue.The proposed method is quite suitable for high-temperature applications,e.g.,electrical vehicles.Firstly,the module topology,the packaging materials,and the packaging processing of a 1200-V/50-A IGBT module are introduced at the beginning.The current-assisted sintered nanosilver is used as die attachment,and the high-temperature solder is used as substrate attachment to demonstrate the preparation of the proposed 1200-V/50-A IGBT module.Then,in order to verify the feasibility of the reliability enhancement,this work compares the electrical performance and transient thermal impedance of the proposed IGBT module.A commercial IGBT module with the sample power rating and topology is used as benchmark.The results show that the collector-emitter saturation voltage(V_ce（sat）)of the enhanced IGBT modules is 1.72 V and 1.91 V at 25℃and125℃,respectively.The static and the switching electrical characteristics are consistent with those of the benchmark commercial IGBT module.The enhanced packaging strategies has not caused any chip degradation during the packaging processing.Furthermore,the thermal resistance of the benchmark commercial IGBT module is about 0.407℃/W,while the thermal resistance of the enhanced IGBT module is only 0.337℃/W,which is 17.2%lower than that of the commercial IGBT one.Finally,a thermal shocking test（-40℃to 150℃）is carried out to verify the reliability enhancement in this work.The failure criterion is defined as 20%increase of the thermal resistance of IGBT modules.The degradation of the thermal resistance and the microstructures of the substrate attachment are recorded by transient thermal impedance measurement and scanning acoustic microscopy,respectively,for further comparisons and proposal of a failure mechanism.The results show that the thermal resistance of the proposed IGBT module degrades much more slowly rather than the benchmark commercial IGBT module,due to the excellent thermo-mechanical fatigue resistance of both the current-assisted sintered nanosilver and high-temperature solder.Therefore,it is a feasible way to enhance the reliability of the IGBT module using the current-assisted sintered nanosilver as die attachment,and the low-cost high-temperature,e.g.,Sn5Pb92.5Ag2.5,solder as the substrate attachment.