A traditionally bonded sputtering target experiences a wide range of temperatures over its life cycle. It is bonded at over 200°C – usually almost 300°C for Sn/Ag/Cu bonding. Since this is the temperature it is bonded at, all changes in temperature will expand or contract the materials. Next, it cools down to room temperature. It is then operated at temperatures around 100°C and repeatedly cycled over the course of its usable life.
In an alternative approach to traditional sputtering target bonding, NanoFoil® can be used as described in Eliminating Bond Stresses of Sputtering Targets at Operating Temperatures:
“Incoming aluminum and molybdenum pieces were initially tested for flatness as a gauge for the expected deflection after bonding. In preparation for bonding, the aluminum and molybdenum pieces were coated with solder, as is standard procedure for bonding with reactive multilayer foils. The aluminum was coated with 96.5Sn/3.0Ag/0.5Cu using mechanical agitation. The molybdenum was media-blasted to roughen the surface, then coated with 96.5Sn/3.0Ag/0.5Cu solder using an ultrasonic soldering iron and an adhesion layer of activated solder. These solder layers on the two pieces of metal were then machined flat to provide coplanar surfaces for bonding.”
More information regarding the NanoBond® Process can be found here.