Preparation And Properties Of Porous Ag Sheet Infiltrated With Sn-Based Solder For Low Temperature Reflow And High Temperature Service

With the increasing integration of electronic device and the development of automotive and aerospace industry,the chip needs to withstand greater current density and work under higher service temperature.Single-crystal Si material can not work stably above 150?.The third-generation semiconductor material,silicon carbide?SiC?,can be used in high-temperature and high-power devices.SiC materials can work properly at extreme temperatures exceeding 300?.However the traditional solder has a low melting point and is not suitable for high-temperature working conditions,and the chip package is facing challenges.The goal of this dissertation is to develop a new type of brazing filler metal that can be used for high temperature service to give full play to the high temperature resistance of the third generation semiconductor materials.In this dissertation,a kind of silver foam material with three-dimensional network structure was studied.Molten Sn-based solder fills the pores due to the capillary action so that the target of low temperature reflow and high temperature service can be achieved.Foam silver preforms with different morphologies were obtained by direct compression method,electroplating method,de-alloying method,respectively.The effects of pressure,electroplating time,alloy composition and reaction temperature on the silver foam structure were investigated.With the pressure of 4 MPa,we can get an appropriate thickness of porous Ag preform through direct compression method.The electroplating method is an improvement on the direct compression method.By depositing a certain thickness of Sn on the surface of the Ag skeleton of the original porous silver material and then compressed under 30 MPa,porous silver preforms with a uniform pore distribution and a suitable pore size were obtained.In the de-alloying method,Ag-Al alloys and Ag-Mg alloys were used as raw materials.Al and Mg atoms were etched and removed by using 7.5 wt%HCl solution to obtain porous Ag foam with pore size of 200 nm⁶00 nm.The effects of different alloy systems,alloy compositions and reaction temperature on the pore size and porosity of the porous Ag sheet were studied.The porous Ag preform was prepared and reflowed,and the reflow process parameters were determined.The properties of bondline using different porous Ag preform prepared by direct compression method,electroplating method and de-alloying method were investigated.The results show that the shear strength were 41.96 MPa,43.67 MPa and 14.91 MPa at room temperature,respectively;the value was 20.13 MPa for electroplating method at 300?;the resistivity were 6.13??·cm,4.38??·cm,8.44??·cm;the thermal conductivity of porous Ag preform produced by electroplating method at 30?and 300?were 71.63 W·m^-1·K^-1and 66.88 W·m^-1·K^-1,respectively.The preform prepared in this paper have excellent mechanical properties,low electrical resistivity and high thermal conductivity.