Numerical simulation of condensate layer formation during vapour phase soldering

• Refined numerical model of VPS is developed with dynamic condensate layer.
• Condensate layer changes have considerable effect on the heating during VPS process.
• Considerable temperature gradient can form on the assembly during the VPS process.
• Suggested to fit the soldering profile to the demands of the bottom of the assembly.

This paper presents a modelling approach of the condensate layer formation on the surface of printed circuit boards during Vapour Phase Soldering (VPS) process. The condensate layer formation model is an extension to a previously developed board level condensation model, which calculates the mass of the condensed material on the surface of the soldered printed circuit board. The condensate layer formation model applies combined transport mechanisms including convective mass transport due to the hydrostatic pressure difference in the layer and the gravity force; conductive and convective energy transport. The model can describe the dynamic formation and change of the condensate layer after the immersion of the soldered assembly into the saturated vapour space and can calculate the mass and energy transport in the formed condensate layer. This way the effect of the condensate layer changes on the heating of the soldered assembly can be investigated. It was shown that the numerical modelling of the VPS process becomes more accurate with application of dynamic condensate layer instead of a static description.