Just as Cinderella’s 12:00 deadline turned her coach into a pumpkin in the famed children’s fairy tale, at midnight on June 30th all electronics manufacturing will magically transform to lead-free. Well, not quite. But, the anticipatory build-up to the RoHS deadline would certainly lead one to believe that was the case. Quite the opposite is true and, in fact, there are many products that will be exempt from the legislation – at least in the short-term – meaning that numerous electronics firms will still be running tin-lead processes. The big question, though, is how these companies will cope with the inevitable interaction of lead-free terminated components and board finishes within a SnPb process. Will they scour the kingdom in search of elusive tin-lead terminated devices? Doubtful.

Herein lies the challenge. While manufacturers may still be using SnPb processes, suppliers of printed circuit boards (PCBs) and components have completely switched or are migrating products to lead-free. In many cases, these vendors are not identifying the changes in plating, are supplying boards that contain different finishes on the same PCB or are supplying components with varying lead finishes (pure Sn, SnBi or AuPdNi). The result? Companies that are exempt under the RoHS legislation will most likely have to use lead-free components (many times unbeknownst to them) in their tin-lead processes.

Traditional tin-lead materials are not compatible with lead-free device finishes. Because proper reflow for lead-free materials can only be achieved with higher temperatures, attempting to process lead-free terminated devices in 183°C tin-lead conditions leads to incomplete wetting and the related issues of voiding and opens. In order to compensate for this gap in process temperatures, many assemblers have attempted to adjust the reflow profile, only to discover that the higher temperatures exceed the capability of most SnPb materials. In one such case, a manufacturer of power devices was experiencing wetting problems with an SOIC device and attempted to “fix” the problem by adjusting the reflow profile to a higher temperature than that conducive to SnPb pastes. But, the adjustment was not sufficient to achieve the necessary wetting required to pass inspection.

Different problems exist in the case of area array devices. When processing a SnPb bumped BGA or CSP device in a tin-lead process, the results can be disastrous. For bfree
bumped devices, the SAC alloys generally used require a melting temperature of 217°C, but SnPb solder pastes achieve liquidus at 183°C. So, when lead-free BGAs and CSPs are processed at lower temperatures, the bumps usually do not completely melt or collapse, which can lead to undue solder joint stress and, ultimately, failure.

In order to address this materials mismatch, the experts at Henkel have developed a tin lead solder paste material that is capable of withstanding the elevated lead-free processing temperatures. Multicore® MP218 is a halide-free, no-clean solder paste developed specifically for compatibility in higher-temperature processes. Comprised of similar raw materials, activators and components used in the company’s award-winning lead-free solder pastes, Multicore MP218 effectively achieves lead-free performance within a tin-lead system. The extra activity and wider process window of this extraordinary material overcomes the now common wetting challenges caused by the interaction of SnPb solder and lead-free device finishes. What’s more, Multicore MP218 also has a high resistance to humidity -- another condition that is problematic and exacerbated in a SnPb – Pb-free mixed environment. The properties of Multicore MP218 alleviate many of the humidity-related challenges of pre-mature drying or undue moisture absorption and are suitable for varied global climactic conditions.

The visionary Henkel team identified this dual-process condition as a potential problem long before assembly firms even began lead-free paste evaluations. This is what Henkel does best – anticipate, evaluate and develop solutions well before the market knows it even needs them. It’s not magic or fairy dust…..just expertise and know-how that keep Henkel at the forefront of materials leadership.

For more information on how Henkel’s Multicore MP218 can optimize your process, log onto www.goleadfree.com or call the company’s Irvine, California headquarters at 949-789-2500.
 

Keywords : Henkel, Multicore, SnPb, tin lead

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