SMTA International Conference Proceedings

The Effect Of Coating And Potting On The Reliability Of QFN Devices

Authors: Greg Caswell and Cheryl Tulkoff
Company: DfR Solutions
Date Published: 10/13/2013   Conference: SMTA International

Abstract: The fastest growing package types in the electronics industry today are Bottom Termination Components (BTCs). While the advantages of BTCs are well documented, they pose significant reliability challenges to users.

One of the most common drivers for reliability failures is the inappropriate adoption of new technologies. This is especially true for new component packaging like BTCs. Obtaining relevant information can be difficult since information is often segmented and the focus is on design opportunities not on reliability risks. Most users have little influence over component packaging and most devices offer only one or two packaging styles. And, when faced with challenges, users typically fall back on tried and true solutions that may not work for new packaging. This has already occurred with BTC components. Commonly used conformal coating and potting processes have resulted in shortened fatigue life under thermal cycling conditions.

Why do conformal coating and potting reduce fatigue life? This paper details work undertaken to understand the mechanisms underlying this reduction. Verification and determination of mechanical properties of some common materials are performed and highlighted. Recommendations for material selection and housing design are also given. Basically, the lack of a compliant lead structure makes BTC devices more susceptible to PCB warpage related failures so proper precautions must be taken to ensure adequate fatigue life for high reliability applications.

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