Advanced Procedures for Development of Weld Schedules

The author described several documents of a series of Process Control Specifications and Materials Standards for welded electronics assembly (five in all), which are being used by Sippican and its clients. They are available to the welded packaging industry. The first is Preweld Evaluation which includes selection of the weld head to be used, qualitative analysis of materials, previous weld history, and such factors as resistance, melting point, compatibility, etching techniques and electrode selection. The second part of the process is a First Approximation, where a series of sample weldments are made at predetermined increments of energy and force over the entire range in which adhesion takes place. These are recorded on a plot which shows the apparent weld point and marginal points. Next, a Second Approximation is made, using smaller increments of energy and force. This defines the extreme limits of combinations where good welds can be obtained for the materials involved. A second diagram is made which indicates the area to be used for preparation of a Search Sample. The latter permits a metallographic evaluation to be made of the weld settings obtained by the Second Approximation, and further verifies these settings. The fifth procedure, Analytic Sampling, specifies that a prescribed number of identical samples be made at the optimum and marginal points selected earlier. Standard metallographic analysis procedures, manual destruction tests, visual inspection and pull tests are used to evaluate the Analytical Samples. In conjunction with pull testing, Sippican developed a statistical analysis procedure for optimum validity and confidence level in production welding.