Insert Molding of Aluminum Alloy A7075 and Alumina Plate by Semi-Solid Forging

Abstract

Industrial, electric railway, and automotive applications of inverters and converters use case-type semiconductor packages called power modules. Power modules have multiple joint points, and among them, from the viewpoint of reliability and bonding strength, many studies on metal-ceramic substrate bonding have been reported. Alumina Al203 or aluminum nitride AIN are mainly used for ceramics, and copper or aluminum are mainly used for metals, although alumina and aluminum have a price advantage. The joining methods are generally brazing and AMB (Active Metal Brazing), but there is a need to improve the joint strength, heat dissipation characteristics, and productivity, i.e., a joining method that does not use brazing material. The purpose of this study is to achieve direct joining of alumina A1203 and aluminum alloy A7075, and semi-solid forging [1, 2, 3, 4, 5, 6] was used as the method. The A7075 used in this study is considered to be suitable for this application because of its high strength and thermal conductivity among aluminum alloys. In this study, solid phase ratio 30 % semi-solid forging was actually performed using a servo press and a die, and the results were evaluated by observing the cross section of the fabricated specimens. The punches and dies were circular in shape to ensure uniform spreading of the molten material, and carbon steel S50C with high thermal conductivity was used to quickly dissipate the heat of the semi-solid slurry during the pressing process. The thickness of 99.6 % Al2O3 alumina plate was 2.5 mm. The semi-automatic stirring device was modified to stir the molten metal by attaching a 1000 mm round bar to the rotating part of a tabletop drilling machine and attaching a stirring blade to the tip of the bar. Debonding between aluminum alloy and alumina plate was not confirmed. There was no gap between the aluminum alloy and the ceramic plate.