Since the self-aligning effect compensates the positional error occurred in BGA (ball grid array) soldering, it is useful in the electronic packaging application. The self-aligning action is investigated in this work by modeling the solder profile using the second-order polynomials. The solder profile is predicted by minimizing the surface and potential energies exerted on the solder, and corresponding restoring force and spring constant are calculated numerically. The effects of soldering parameters are analyzed using the non-dimensional numbers and the factors influencing the aligning error are estimated. The spring constant increases with smaller solder volume and larger pad size. As the spring constant in the lateral direction is much smaller than that in the vertical direction, the positional accuracy is influenced more easily by the disturbances in the lateral direction. Among several factors such as non-uniform solder volume, pad size, drag force and wetting condition, the non-uniform wetting condition appears to be the main cause of the aligning error.
