Determination of Equilibrium Shapes and Optimal Volume of Solder Droplets in the Assembly of Surface Mounted Integrated Circuits

Abstract

The equilibrium shape of a liquid meniscus at a liquid-gas phase boundary of a system in which solid, liquid, and gaseous phases coexist is given by a balance of forces acting on the system. A method of calculation was introduced in Part I of this series for determining this equilibrium shape. Here, this method is used to calculate the equilibrium shapes of solder joints surrounding gullwing and jbend type lead wires present in surface mounted integrated circuits. A study is also done to determine the optimal volume needed to produce a good solder joint. Criteria are established, dimensionless calculations are done for gullwing and jbend leads, and a method is outlined for applying these results to lead wires with different geometries.