During the heating stage, the entire assembly placed in a furnace and its temperature increased from room temperature to below the eutectic temperature. When the assembly is heated, some solid-state penetration occurs between the interface layer and the base metal. The amount of penetration depends on several factors, including the surface roughness and cleanliness of the surface and the pressure exerted on the surface. In most cases, it expected that the amount of particle penetration of this stage is low. However, the amount of mass transferred in this step depends on the eutectic temperature, heating rate and diffusion coefficient. The longer the heating stage, the more penetration of elements that reduce the melting point in the base metal. If the heating rate is too low and the heating step is too long, the maximum concentration of the soluble element in the interlayer may be lower than its required value for melting, and therefore, by increasing the heating step too much, there may be no Do not form a liquid. After the dissolution and expansion phase, the melting point lowering elements permeate across the solid/melt interface in the base metal during an isothermal holding period. This infiltration process is similar to multiphase infiltration coupling. To maintain thermodynamic equilibrium, the melt composition at the solid/melt interface remains constant at CLα. Therefore, the composition of the melt assumed uniform throughout the width of the liquid. Since diffusion is faster in the melt than in the solid, the thickness of the melt is too thin for this assumption to consider accurate. The direction and rate of movement of the solid/melt interface should create a mass balance in the solid/melt interface, so that the direction of movement of the two solid/melt interfaces is towards the center of the connection.