Surface Mount Attachment Reliability and Figures of Merit for Design for Reliability

Abstract

Surface Mount (SM) assemblies in the field are subject to complex thermal fluctuations. The cyclic thermal expansion mismatch between SM components and the substrates to which they are attached may lead to fatigue or wearout of solder joints during the useful life of a product. Attachment reliability is the ability of solder joints to provide electrical and mechanical connections under stated conditions and for a specified duration. Packaging engineers and physical designers thus bear the responsibility to design SM attachments that will survive the desired product life. This is achieved by proper design of the attachment and soldering according to recommended Workmanship Requirements (e.g., reference1). While several companies have gathered attachment reliability data for generic SM components, the data often remain proprietary or are not readily available for less common or emerging packaging technologies. Reliability evaluation can then be an involved process2 ,3including the design and assembly of test vehicles, accelerated testing, data, and failure mode analysis, all of which require the appropriate expertise and adequate commitment of time and resources. This process amounts to a 6-month to 1-year effort while design cycles for SM packages or electronic assemblies are as short as 1 month, sometimes less. Clearly, design tools are needed to build in attachment reliability throughout the design process and provide reliability information quickly, based on critical design and assembly parameters.