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50 DESIGN007 MAGAZINE I FEBRUARY 2023 Article by Anaya Vardya AMERICAN STANDARD CIRCUITS Introduction One of the biggest challenges facing PCB designers is not understanding the cost drivers in the PCB manufacturing process. e next final finishes to discuss in this series is OSP. As with all surface finishes there are pros and cons with the decision of which to use. It is a combi- nation of application, cost, and the properties of the finish. OSP is RoHS-compliant as there is zero lead content in the finish. Final Finishes OSP (Organic Solderability Preservative) OSP is a thin organic coating, typically 5.9 to 11.8 µin [0.15 to 0.30 µm] thick, designed to prevent the oxidation of copper to maintain solderability over an extended period. Com- pared with other surface finish technologies, OSP is somewhat different. It uses a chemi- cal process to produce an organic film on the bare copper surface which acts as a barrier to copper oxidation. OSP is organic, not metallic, and its cost is lower than most surface treat- ment technologies. As with all surface finishes, the primary pur- pose is to protect the solderable surfaces on the PCB from oxidation and to aid in assembly soldering. is process coats a very thin coat- ing of an organic material that inhibits copper oxidation. It is so thin that it is nearly impos- sible to see and measure. e organic material is removed by the assembly flux. Boards that have been OSP coated will have bright cop- per pad coloration. OSP is specially designed for mixed metal applications, such as electro- less nickel immersion gold (ENIG). e OSP selectively deposits on copper while leaving gold connectors or metallic heat sinks free of contamination. ere are a couple of common OSP finishes widely used in the industry: ENTEK CU-56: is is used for assemblies that will only go through a single reflow process. is finish is not being utilized much anymore DFM 101 Final Finishes: OSP

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