Modelling approaches of Vapour Phase Reflow Soldering

Abstract

Vapour Phase Soldering (VPS) is a condensation based heat-transfer method for reflowing electronic assemblies in electronics manufacturing. VPS is still not widespread in the industry, despite its comeback and clear advantages. This is mainly due to the general use of convection type reflow, the lower throughput of VPS type ovens and the complex process, which is difficult to monitor both by measurement and modelling approaches. Our research focuses on investigating the modeling of the process, to aim for better control and improved soldering quality. The process is sensitive to any perturbing measurements, involving sensors, so carefully validated modelling software may help to understand the details of this reflow method. In order to investigate the process, three different modelling approaches were elaborated with different focuses. The first approach presents an explicit and fast modelling method of the Printed Circuit Board level, involving the abstraction of condensation on horizontal plates and discs. The second approach extends the view by focusing on the component, using heat transfer coefficients extracted from experimental data. The method can reveal specific effects of heat transfer on SMD components with different structures. The third approach involves the volume of the work zone, the vapour blanket inside, the surface and the structure of the assembly. With a multi-physics (heat- and mass transfer) and additional co-simulation approach - based on a custom Finite Difference Method (FDM) solver - the work zone and the board level can be modelled simultaneously. This brings the possibility to monitor the state of the vapour, to investigate the effects of assemblies on the vapour blanket, and the state of the condensate combined, affecting heat transfer on the assembly. The modelling approaches are presented in the paper with a general summary of our recent works, discussion on the validation and the achieved results, highlighting possible rooms for improvement. The findings may also help improving oven design aspects pointing to the requirements of future factories.