IMPACT OF LEAD-FREE PCB SURFACE FINISHES ON MICROVOIDINGAuthors: Guhan Subbarayan, Purushothaman Damodaran, Krishna
Company: Department of Systems Science and Industrial Engin
Date Published: 9/24/2006 Conference: SMTA International
A full factorial statistically designed experiment was conducted to determine the main and interaction effects of lead-free surface finishes and peak reflow temperatures on microvoiding. PCBs with Immersion Silver (0.15 micron and 1 micron silver thickness), Electroless-Nickel Immersion Gold (ENIG) and Organic Solder Preservative (OSP) surface finishes were investigated at two different lead-free peak temperatures: 235ºC and 250ºC. After assembly, electrical resistance test was performed on a daisy chained test vehicle to detect failures on the assembled leadfree packages. The BGAs were then inspected using a high resolution digital X-ray system for microvoids. Microsectioning of the solder joints were later performed to corroborate the X-ray findings.
The findings of this work are expected to help understand the root cause for microvoids and to select the optimum lead-free surface finish and peak temperature that minimizes microvoids. This paper discusses, in detail, the important factors which affect microvoids, the experimental setup, the findings of this research, and the recommendations to minimize or eliminate microvoids in a lead-free assembly.
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