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26 I-CONNECT007 MAGAZINE I MAY 2026 This process employs a combination of a phenyl- imidazole compound mixed in an aqueous solution with acetic acid, a complexing agent, and a water- soluble iron compound. The combination of these additives allows the uniform coating of the organic film on the copper without building any appre- ciable amount on the non-copper surfaces. After the PWB has been prepped in an acid cleaner, fol- lowed by a micro-etch, the OSP coating is applied to the PWB by dipping, spraying, or flood coating. Figure 2 illustrates the latest generation OSP active compound. The substituted phenylimidazole represents a significant improvement in solder- ability protection as well as preventing subsequent OSP film deposition on other metals such as gold. Therefore, it was imperative to develop an OSP process that would selectively deposit on the bare copper surfaces only, with low residual ionics. However, a film that forms on the copper Figure 3: OSP deposit on gold: Conventional OSP (left), as plated center), and improved OSP (right). Figure 2: Evolution of OSP technology. must have sufficient ability to maintain the solder- ability of the base copper through multiple thermal excursions and with a variety of low-activity wave soldering fluxes and pastes. The efficacy of this process is demonstrated in Figure 3. Note the discolored gold deposits on the left with the benzimidazole compound. The as-plated coupon is shown in the middle, and the gold-plated coupon processed through the im- proved OSP is shown on the right. We should not underestimate the importance of minimizing organic deposits on gold, as they can interfere with successful wire bonding. In a future column, we will take a more detailed look at OSP technology for advanced packaging. I-CONNECT007 References 1. "Understanding the Basics of the Wire Bonding Process in Semiconductor Packaging," by Ross Feng, Viasion. Michael Carano brings over 40 years of electronics in- dustry experience with spe- cial expertise in manufactur- ing, performance chemicals, metals, semiconductors, medical devices, and advanced packaging. To read past columns, click here. T RO U B L E I N YO U R TA N K