Medical Electronics Symposium Conference Proceedings


LEAD-FREE COMPONENT FINISHES - PROBLEMS AND MITIGATION

Author: Joseph Zaccari
Company: Corfin Industries LLC
Date Published: 5/19/2004   Conference: Medical Electronics Symposium


Abstract: The worldwide movement towards lead-free (electroplated pure tin) electronic component lead finishes re-introduces a familiar problem to the high reliability electronics community, tin whiskers. This movement to eliminate lead from electronic assemblies is driven by legislation in the EU (WEEE and ROHs) and in Japan to eliminate lead from electronic products by 2006.

While electroplated pure tin is a component surface finish that has existed in the electronics industry for decades, there is a well-known phenomenon related to pure tin plating, known as "tin whiskers". Tin whiskers are conductive, pure tin crystals that spontaneously "grow" from an electroplated pure tin surface. The growth mechanism for whiskers is not well understood and can be characterized as unpredictable in many cases. Tin whiskers can bridge to near-by conductors causing a range of failures in critical systems.

As the availability of high reliability electronic components with tin-lead terminations continues to shrink, high-reliability equipment manufacturers are being forced to use commercial products (COTS) in many applications. These are precisely the types of components targeted by the lead-free movement. More and more pure tin is finding it’s way into high-reliability electronics.

COTS components can be tested for performance and reliability using industry and government test methods. Unfortunately there is no accepted test method to determine if a component will exhibit tin whiskers in a specific application or environment. This has lead to a number of mitigation strategy initiatives in industry and various consortia investigating methods such as conformal coating, matte tin plating and hot solder dip. This paper will focus on the latter and the capabilities of current technology to efficiently and effectively replace lead-free electro plating with hot dipped solder.

Key words: lead-free, tin whiskers, pure tin, robotic solder dip.



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