Solder Joints in Electronics: Design for Reliability

The emerging new technologies provide ever more challenges to assure the reliability of electronic products. The ever increasing demands in electronic products for higher performance, lower cost, less space (weight) is leading to ever denser interconnection needs. This makes solder joint reliability an even more important issue with the advent of new surface mount packages and the use of surface mounted electronics in such hostile environments as the automobile and space. The new packages are characterized by larger sizes, finer pitches, and/or problematic materials which require an up-front ‘Design for Reliability (DfR)’ to meet reliability requirements. The hostile environments can include thermal excursions over temperature ranges in which multiple interactive damage mechanisms are operative. The reliability of electronic assemblies requires a definitive design effort that has to be carried out concurrently with the other design functions during the developmental phase of the product. There exists a misconception in the industry, that quality manufacturing is all that is required to assure the reliability of an electronic assembly. While of course, consistent high quality manufacturing—and all that this implies is a necessary prerequisite to assure the reliability of the product, only a DfR-procedure can assure that the design—manufactured to good quality—will be reliable in its intended application. Explicit DfR-procedures need to be employed to account and compensate, at least in part, for the prevalent damage mechanisms. This needs to be complemented with ‘Design for Manufacturability (DfM)’ which widens the process windows and takes into account the manufacturing capabilities. These demands put an increasing burden on the designers who will require a heightened technical understanding of the underlying issues and more sophisticated design tools. It is for this reason that IPC-D-279, Design Guidelines for Reliable Surface Mount Technology Printed Board Assemblies, has been developed. The ‘Design for Reliability (DfR)’ for solder attachments in electronic interconnections will be the emphasis of this paper.