HALT and TC Reliability of QFN Assemblies with and without Urethane Coating

(22:25 + Q&A) Dr. Reza Ghaffarian, Jet Propulsion Laboratory, California Institute of Technology
From the 2024 IEEE Symposium on Reliability for Electronics and Photonics Packaging
Summary: This talk presents the effect of standard single- and double-thickness polyurethane coating on various sizes of Quad Flat No-Lead (QFN) solder joint assemblies. This coating is commonly used for high-reliability applications. The thicker coatings better mitigate tin whisker, but it may add additional significant vertical mismatch stresses resulting in premature solder-joint failures under thermal cycling. The stresses are significantly increase in an extreme cold environment, e.g., deep-space missions, because of increase in rigidity; therefore, it is of concern for these high-reliability applications. The two thicknesses are evaluated under thermal cycling tests and vibration through an innovative Highly Accelerated Life Testing (HALT) method. Aspects of this HALT method with time-to failures and failure mechanisms were presented at APEX 2024.
The temperature cycling was performed from –55°C to +125°C for the two thickness of coatings. Half of each QFN assembly was coated in order to minimize the effects of manufacturing and testing variabilities. The HALT was performed under 50g three-dimensional random vibration at -100°C, based on an analytical stress model that showed solder joints will be in an inelastic stress condition. The HALT step followed with thermal shock cycling in the range of -100°C to 125°C to detect possible latent defects due to a priori vibration. Monitoring focused on four daisy-chain QFN assemblies during HALT, followed by manual verification at RT after testing. The thermal cycle results are presented in Weibull plots, depicting the effect of conformal coating. The uncoated and coated QFN failures under sequential HALT and thermal shock cycles are also presented and failure mechanisms were compared to previous results.
Bio: Dr. Reza Ghaffarian has a few decades of technical and program management experience within JPL, industry, and academia. At NASA/JPL, he has led industry-wide consortia and R&D reliability/assurance evaluation for infusion of advanced electronic packaging technologies, e.g., CCGA in 1998. For most spaceflight projects from Mars Pathfinder to Mars 2020 Perseverance, he acted as a subject matter expert (SME) and Material Review Board (MRB) member. Received Principal Eng. Designation in 1999, achieved the top technical rank in 2021, and received >30 NASA-JPL project awards, including: “NASA Exception Service Medal” for outstanding leadership and industrial partnership”; and “2020 SMTA Founder’s Award” for exceptional contributions to the industry, SMTA, and research in the area of reliability for years. He has published/presented more than 200 technical papers and numerous NASA Guidelines, 11 book chapters, and co-edited a CSP book. He serves as technical Advisor/Committee or Chair/Member to technical societies including IPC for reliability standards, Microelectronics Reliability Journal, SMTA, and IEEE— and world-renowned in this field. He received his Ph.D. from the University of California at Los Angeles (UCLA).

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