Dependence of condensate thickness on the substrate properties during Vapour Phase Soldering

In this paper, the average and the range of the condensate layer thickness was investigated in the function of different substrate properties with numerical simulations of Vapour Phase Soldering (VPS). The condensate layer thickness is the main influencing factor during the heat transfer of the VPS process. The phase change on the substrate and the transfer mechanisms in the condensate layer were included in a three-dimensional numerical model. Stationary and saturated vapour conditions were applied as boundary conditions, in order to separate the effects of the substrate properties from the effects of the realistic unsteady and nonhomogeneous vapour conditions. Three different substrate materials was studied: FR4, 94% Alumina and Insulated Metal Substrate (IMS). The effect of the substrate shapes and thicknesses was also studied. It was found that the thermal properties of the substrate has considerable effects on the formation of the condensate layer and consequently on the heat transfer of the VPS. It was also proven that shape of the substrates has non-ignorable effects since it affects the movement of the condensate on the surface of the substrate.