In 217Plus, the solder joint failure rate is included at the component level. Specifically, the failure rate model at the component level contains a solder joint term consisting of a base failure rate and an acceleration factor, which is dependent upon the temperature excursion between the non-operating and operating states. This is rolled up along with the operational, non-operational (environmental), temperature cycling and electrical overstress failure rates to yield the overall failure rate for a component. Therefore, it is not necessary to include a separate PCB failure rate in the manner of MIL-HDBK-217, unless one wants to include the raw (unpopulated) board. In this case data from NPRD/EPRD publications should be used. Note, the solder joint failures described here are those related to “random” causes, that is, due to the occasional defect that might be expected to be present in a population. This term does not apply to solder joints which have failed due to wear-out. The model is only valid when the equipment is operating within its solder joint life.
2011-11-11T21:09:18-05:00November 11th, 2011