Quality and Reliability Considerations for the Assembly of Implantable Medical Electronics

Category: Medical Electronics
Post Date: January 3, 2005
Author(s): Peter Borgesen, Universal Instruments Corporation, Binghamton, NY; Eric Cotts, Physics and Materials Science, Binghamton University, Binghamton, NY

Description
Implanted electronic devices face an unusually benign environment in many respects. However, mechanisms still exist by which an occasional device may degrade and fail in service. Because of the extreme financial and ethical liabilities often involved these warrant careful consideration in terms of how to test for them and, in particular, how to minimize the associated risk. We discuss long term degradation phenomena active in solder based assemblies at body temperature such as Kirkendall voiding and the growth of various intermetallics and whiskers. Depending on materials selection, supplier process control, and contamination these may lead to significant reductions in the resistance to mechanical loads common in service, or possibly even to failure in the absence of a significant load. Underfilling may reduce and/or eliminate the risk of most such failures but introduces alternate risks which must be minimized by optimized materials selection and substrate design.