Investigating the effect of applied pressure on reactive multilayer foil joining

This paper describes the effect of applied pressure on reactive joining of stainless steel specimens and Al alloy specimens using nanostructured Al/Ni foils and AuSn and AgSn solder layers. For a given material system, higher applied joining pressure enhances the flow of the molten solder and thus improves wetting and bonding. Shear strengths of the reactive joints are shown to increase as the pressure that is applied during joining rises to a critical value. At higher applied pressures joint shear strengths remain relatively constant. The critical applied joining pressure is shown to be dependent on the foil thickness (or total heat of reaction), and the properties of the solder material and components, which determine the duration of melting of the solder and the maximum temperature at the solder/component interface. Longer durations of melting and higher interface temperatures enhance the flow of solder, improve wetting conditions and result in lower critical applied pressures.