CRACK GROWTH RATE MEASUREMENT AND ANALYSIS FOR WLCSP Sn-Ag-Cu SOLDER JOINTSAuthor: Paresh Limaye et al.
Company: IMEC and Katholieke Univ.
Date Published: 9/25/2005 Conference: SMTA International
In this paper we have attempted to measure crack growth rates in Sn/Ag/Cu solder joints subjected to thermal cycling with dye penetration tests and crack area image analysis. The devices used were stiff wafer level CSP’s which were daisy chained for in-situ electrical monitoring. The solder joints were ~0.2 mm in height. The crack growth rate measurements have been conducted for 3 temperature profiles, -40°C to +125°C, 0°C to +100°C and -65°C to +100°C with a frequency of 1 cycle per hour, resulting in an estimated strain range of 0.01 to 0.1. For each imposed strain value, a total of 8 joints were analyzed.
In all the test conditions, increase in crack area was observed to be a linear function of number of thermal cycles while crack initiation was observed at less than 5% of the total fatigue life. We have correlated the crack growth rate results with the average inelastic strain and strain energy density accumulated in a single cycle with the help of finite element analysis.
Key words: Crack Growth Rate, Lead free solder joints, reliability and fatigue models, SnAgCu Solder
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