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80 PCB007 MAGAZINE I JANUARY 2022 per surface with a non-uniform topography. is non-uniformity will invariably lead to less than optimum photoresist adhesion. e potential for resist to "lock" into some of the non-uniform areas on the foils is quite high, mainly due to the extreme peaks and valleys in the surface profile. e best remedy to prevent this situation is to completely remove the chro- mate film. In the past, tarnish resistance was accom- plished by immersion of the copper foil into a solution containing chromate ions. Yates and others further improved upon this method with an electrolytic technique to enhance the oxidation resistance of the copper foil 1 . Others later improved upon this invention with the introduction of zinc chromate 2 . One should never underestimate the tenac- ity of the chromate film. is is precisely why I recommend a strong mineral acid cleaning step prior to pumice, aluminum oxide or chem- ical microetching. It is much more effective to enhance the resist adhesion when a good chro- mate removal process is online prior to these additional processes. Chemical Cleaning and Microetching First, a review of various chemical cleaning methods is warranted. It is well known that the definition of cleaning is "making the soil soluble in a solvent." I don't remember who is respon- sible for this quote, but it is something I have not forgotten. Basically, one should under- stand what the composition of the soils is and what the proper solvent or solvents are best suited to remove those soils. Chemical compo- sitions designed to remove soils are endless. As an example, Table 1 provides a succinct sum- mary of those processes. One should also con- tact the chemical supplier to extract advice and counsel on proper operating parameters, equipment compatibility and costs. ere are some suppliers that provide one-step chromate remover/microetchants.