Characterizations Of A Medium-and-high Voltage IGBT Module Packaged With Nanosilver Paste

The press-pack IGBT module used in smart grid realizes heat dissipation through pressure contact.However,as power electronics equipment ratings increase,the current and voltage of press-pack IGBT getting higher,generates much heat as well as causes uneven pressure and temperature distribution resulted from mismatch of coefficient thermal expansion within different materials,which undermines the reliability of the module.In order to overcome the heat dissipation problem and enhance the long-term reliability of IGBT modules,we put forward to use nanosilver paste as thermal interface materials to replace pressure contact by forming electrical contact with chip in press-pack IGBT module.We named this improved IGBT module as sinter-pack IGBT module to distinguish with press-pack IGBT module.In this paper,we mainly focused on the as-sintered specimen sintering at collector side under different hydrostatic pressures,and applied the specimens to the press-pack IGBT module to verify its feasibility.In addition,the double-side sintering process and its characterization are also explored.We firstly studied the process of low-temperature sintering nanosilver paste and finally realized large-area die attachment with few voids by double-print nanosilver paste assisted with pressure.For an optimal applied pressure,the mechanical,thermal and electrical properties and reliability of as-sintered silver joints under 1,3,5,10MPa are characterized.It is concluded that with the increase of applied pressure,the die-shear strength and porosity increases,thermal impedance(Z_th)reduces,contributing to the higher reliability.Based on the results,we analyzed the effect of applied pressure on improving the bonding quality from microscopic.Secondly,considering the mechanical,thermal,and electrical properties of the as-sintered joints,low pressure was insufficient for achieving robust and stable joints with few defects and high density;however,high pressure might damage the power chips owing to microcracks.Therefore,a pressure of 3 MPa was selected for use in the sintering process;sinter-pack IGBT modules were packaged using the as-sintered specimens sintered at 3 MPa for characterizing the thermal resistance and static characteristics.The results indicate that thermal resistance(R_th)of the sinter-pack IGBT module is15.8%lower than that of the press-pack,indicating a significant improvement in the thermal dissipation.The nearly identical electrical characteristics of these two types of modules?sinter-pack and commercial press-pack?prove the feasibility and applicability of nanosilver paste as interfacial material in medium-to-high press-pack IGBT modules.The silver sputtering process was studied by measuring the thickness of the coatings under different air pressures to realize the double-side sintering process and it concluded that 0.8 Pa was the optimal working air pressure.Then by comparing once sintering and secondary sintering methods from non-destructive test and die-shear strength test,the better double-side sintering process was determined and its feasibility was proved by the ultra-low Z_th which was only 1/4 of that of single-side sintered joints and the good static electrical properties of the double-side sintered joints.