Gallium-based diffusive-hardening solders do not contain lead. These alloys have specific rheological properties. Their synthesis includes, as a rule, mechanical mixing of such initial components as gallium, copper and tin powders . Then the metallic paste undergoes irreversible phase transformations forming a solid alloy with a specific structure. Here, we investigated microstructures of diffusive-hardened Cu-Ga-Sn alloys by SEM and EDX methods. Thermal diffusivity and heat conductivity of alloys mentioned above were studied by the laser flash method. Also differential scanning calorimetry (DSC) experiments were performed to obtain heat properties of the samples.