Studies of the Thermal Conductivity and Thermal Resistance of Solder Layers with Lead-Free Pastes by the Photodeflection Method

The processes of heat removal from multijunction solar cells on a germanium substrate to AlN ceramics through a solder layer were studied by thermal wave photodeflection methods. Two types lead-free solder based on SnBi and SnAgCu were used under various pressure soldering conditions. The thermal conductivity and thermal resistance of the solder layers are compared. It is shown that the thermal conductivities of the solder layers differ from the reference data for the corresponding metal alloys, and in some cases may depend on the pressure during the brazing process.