A hydrostatic model of solder fillets part I: Axisymmetric model

Despite its wide use and long history as a metal joining technique, soldering until today remains as much an art as a science. Although there are some general characteristics that can be used to describe a good solder joint or fillet, no precise definition of a good solder fillet exists. With the increasing application of mass soldering methods for manufacturing large numbers of identical parts, it becomes desirable to have a precise definition of a good solder fillet. Such information would be useful in quality control and component design and it would also contribute to the basic understanding of soldering. An analytical model based on the balance of surface tension and pressure forces in solder at the molten state is formulated to predict fillet shapes. The paper deals mainly with the fillet formed by a pin and the land area of a plated-through-hole. The model can also be adopted to other geometries.