Numerical study of vapour concentration reduction in a vacuum vapour phase soldering oven

The vapour concentration reduction process in a vacuum type Vapour Phase Soldering (VPS) oven was investigated by numerical simulations. The low vapour pressure is applied to decrease the number of voids during the formation of solder joints. This paper contains the preliminary preparations of a detailed numerical modeling of the vacuum VPS oven and the scientific examination of the problem. A three-dimensional simplified numerical gas flow model based on the Navier-Stokes equations was established to describe the vapour concentration reduction. The model was solved by Finite Difference Method (FDM) and by explicit Forward Time Central Space (FTCS) algorithm. The reduction of the vapour concentration was studied at different vacuum pump settings. It was found that considerable vapour concentration gradient can form during the reduction at the suction pipe which might have effects on the heat transport processes of the oven and via this on the forming of the joints microstructure. The decrease of the vapour concentration showed negative exponential characteristics.