2-D Fluid Simulation Approach for Miniwave Soldering

Abstract

Design reviews are a key bottleneck of fast product development processes. In order to judge manufacturability, reliable models of the design and the manufacturing process are essential. This paper presents a 2-D fluid simulation model as a manufacturability check for lead free mini wave soldering and evaluates it against soldering experiments. Miniwave soldering is a widely applied process to automatically solder THT-components onto mixed SMT/THT circuit board assemblies. The vertical hole fill is the acceptability criterion defined by the IPC-A610 and depends on the copper layer design of the THT solder joints due to thermal diffusion during the soldering process. With increasing copper content in high performance multilayer PCBs, the thermal diffusion increases likewise and causes significant soldering problems with respect to insufficient hole fill. To mitigate the design reviews as critical bottleneck for the time to market, in this paper a numerical 2-d model is implemented in ANSYS Fluent to predict hole fill of potential critical solder joints and validate the model against respective soldering experiments. The parametrized copper layer design of the solder joints are automatically generated by a python script, meshed and solved in ANSYS Fluent. This allows easy configuration of different copper layer designs with respect to board thickness, layer count and thickness as well as pin and hole diameter, solder nozzle diameter and the relevant soldering parameters. Temperaturedependent material models of the solder alloys to describe density, viscosity and wetting angle are derived from literature and applied to the simulation model. The simulation methodology is divided in two steps, first the flow field of the solder fontain has to be calculated. In the second step, the soldering process can be simulated based on the stable flow field including capillary action, heat and mass transfer based on the volume of fluid method. The simulation results show good agreement with soldering experiments. With this developed and validated simulation method the understanding of heat transfer and fluid mechanical effects during miniwave soldering can be improved.