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.

Expert Panel Responses

Whensoldering to ENIG, you are bonding to a nickel surface and forming a nickel-tinintermetallic. With HASL, the intermetallic is formed to a copper surfaceresulting in a copper-tin intermetallic. The copper-tin intermetallic istypically more robust than the nickel-tin intermetallic. Therefore, froma solder bond perspective, you would expect to have a more reliable solderjoint on the HASL surface. However, there are many other things toconsider. For example, the planarity of the HASL surface is not as goodas ENIG. That can result in poorer printed paste transferefficiency. A bad print can more than offset any gain achieved by theimproved intermetallic bond.

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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