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Reliability Analysis of Low-Silver BGA Solder Joints using Four Different Failure Criteria
Keywords: low-silver BGA assembly, failure criteria, solder joint
The estimated reliability life of solder joints would be different if different failure criteria are used. Currently different researchers have used different criteria in their solder joint reliability studies, for example, a resistance threshold of 450 Ω, an increase in resistance of 10Ω or greater, the resistance change of 5 Ω, and a resistance threshold of 1000 Ω or 20% resistance increase defined in IPC-9701A. Thus, it is difficult to compare the results from published studies. The objective of this study is to compare estimated reliability life under four different failure criteria. The four failure criteria are a 20% resistance increase defined in the IPC-9701A standard, a resistance threshold of 500Ω, an infinite resistance (hard open), and a failure criterion proposed by J. Pan and J. Silk [1] based on X-bar and R charts. The accelerated thermal cycling data are from the low-silver lead-free BGA study by G. Henshall, et al. [2]. Low-silver, lead-free BGA sphere alloys are gaining popularity largely due to lower material cost and improved drop shock performance. The study included accelerated thermal cycling for mixed Sn-Pb/Pb-free solder joints with varying Ag and "micro alloying" elements as well as Sn-Pb/Sn-Pb joints. Thermal cycling conditions included 0 to 100 °C and -40 to 125°C with ten minute dwell times. Over 2 Gb data are analyzed. The results shows that the life estimation based on the failure criterion proposed by J. Pan and J. Silk [2] is similar to the life estimation when a 20% resistance increase defined in the IPC-9701A standard is used. It seems that the reliability life would be overestimated if the failure criterion of a resistance threshold of 500Ω or an infinite resistance (hard open) is used. [1] J. Pan and J. Silk, "A Study of Solder Joint Failure Criteria," proceedings IMAPS, 2011. [2] G. Henshall, et al., "Low-Silver BGA Assembly Phase II - Reliability Assessment Seventh Report: Mixed Metallurgy Solder Joint Thermal Cycling Results," proceedings SMTAi, 2011.
Erin Kimura, Student
California Polytechnic State University
Moorpark, CA

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