Column Grid Array Rework for High Reliability

The probability of removal and replacement of these devices on the actual flight printed wiring board assemblies is deemed to be very high because of last minute discoveries in final test which will dictate changes in the firmware. The questions and challenges presented to the manufacturing organizations engaged in the production of high reliability electronic assemblies are, “Is the reliability of the PWBA adversely affected by rework (removal and replacement) of the CGA package?” and “How many times can we rework the same board without destroying a pad or degrading the lifetime of the assembly?” To answer these questions, the most complex printed wiring board assembly used by the project was chosen to be used as the test vehicle, the PWB was modified to provide a “daisy chain” pattern, and a number of bare PWB’s were acquired to this modified design. Non-functional 624 pin CGA packages with internal “daisy chained” matching the pattern on the PWB were procured. The combination of the modified PWB and the daisy chained packages enables continuity measurements of every soldered contact during subsequent testing and thermal cycling. Several test vehicles boards were assembled, reworked and then thermal cycled to assess the reliability of the solder joints and board material including pads and traces near the CGA. The details of rework process and results of thermal cycling are presented in this paper.