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November 26, 2012

Solder Joint Strength

Which surface finish provides the best solder joint bond strength for a leaded assembly, HASL or ENIG? Is there enough of a difference in strength to make either a better choice for a high-vibration military application?

E.H.

Experts Comments

When soldering to ENIG, you are bonding to a nickel surface and forming a nickel-tin intermetallic. With HASL, the intermetallic is formed to a copper surface resulting in a copper-tin intermetallic. The copper-tin intermetallic is typically more robust than the nickel-tin intermetallic. Therefore, from a solder bond perspective, you would expect to have a more reliable solder joint on the HASL surface.  However, there are many other things to consider. For example, the planarity of the HASL surface is not as good as ENIG. That can result in poorer printed paste transfer efficiency. A bad print can more than offset any gain achieved by the improved intermetallic bond.
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Tim Jensen
Product Manager, Advanced Assembly Materials
Indium Corp.
Timothy Jensen is the Product Manager for Indium Corporation's PCB Assembly Materials and has spent over a decade troubleshooting and optimizing SMT process lines. Having worked directly on hundreds of surface mount lines, and building thousands of different products, Tim understands each customer's unique requirements, and tailors Indium's products and services to meet or exceed those needs.
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