AN APPROXIMATE MODEL FOR PREDICTING THE SIZE AND SHAPE OF WAVE-SOLDERED SURFACE-MOUNT JOINTS

An approximate method is developed to determine the effect of pad dime nsions, component dimensions, conveyor angle and solder properties (su rface tension and density) on the size and shape of solder joints form ed during a wave soldering process. The model uses a dipping analogy t o simulate the wave soldering operation, and is thus also applicable t o dipping processes for soldering, pre-tinning or bumping. The study r epresents an extension of previous work by the authors in which the ef fect of conveyor angle was not included and the exact solution for the molten solder capillary surface was utilized. In the present investig ation a constant curvature approximation is introduced in the dipping sequence as well as in the find joint configuration. This reduces the problem to one of a geometrical nature only. The results of the model are presented in dimensionless form, compared with the exact theoretic al results for a horizontal conveyor, and compared with data from actu al production joints. The fundamental concept upon which the model is based may also be extended to through-hole and leaded surface-mount co mponents.