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April 2015 • The PCB Magazine 57 tainly, the low thickness is cause for concern. With such a low thickness, the OSP would not effectively protect the copper from oxidation. However, what other process variations could be the cause for the low thickness? One possi- bility is the micro-etch step. It has been stated in the literature that a clean active copper sur- face is necessary in order to allow for a more uniform deposit of the OSP film. In addition, one should avoid an overly aggressive micro- etch as there are concerns about insufficient thickness of the organic film in deep crevasses (Figure 3). Surface roughness does have an impact on OSP film thickness and is directly connected to solderability. trouble In your tAnk COPPER DISCOLORATION AND OTHER CONCERNS WITH OSP continues Figure 3: uniform micro-etch leads to uniform oSP film (left). non-uniform micro-etch leading to thin oSP film thickness in some areas (right). Figure 4: Top side view of oSP chemical chamber. (Courtesy of Shikoku Chemical Corporation/Glicoat)

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