Shapes and residual forces of BGA interconnects for optimal design in aerospace applications

A model for the shapes and residual forces for an individual, axisymmetric BGA solder interconnect is developed from the basic assumption that the surface bounding the solder possesses constant mean curvature. The inputs for the model are the geometric design parameters: pad radius, stand-off height, and volume of solder. The model is contrasted with simpler ones to identify the combinations of parameters for which more relaxed assumptions regarding the shape of the interconnect (e.g., a cylinder, truncated sphere, or circular arc meridian) may lead to unacceptable errors when designing for the demanding requirements of aerospace applications. The parameter combinations include situations when there exists a large stand-off height in conjunction with residual tension in the interconnect and when there is considerable compression or tension in the interconnect. The errors can be especially significant if one is designing around presumed surface contact angles at the solder/pad/PCB junction