Hi rudy,
    thanks for the resist stripping summary.  I've heard many numbers thrown around and had
difficulty getting a straight answer.  Your outline was very informative and gave me a better
understanding of the whole picture.  I was especially surprised at the level of Cu.  I always
thought it was less than that.  I did however had a question about tin/tinlead.  I was under the
assumption (not THAT word!!) that some tin/tinlead was also removed and in turn generated a
potential for a Hazardous material.  Where is the industry on this situation?   JOHN WAITE

RSedlak wrote:

> David:
>
> You gave a great paper at the PCMI, and now you have asked one of the more
> fascinating, and difficult to answer questions to appear on Technet, and since
> we like to think of ourselves as experts in exactly this field, I am going to
> reply, with more detail than you likely want.
>
> First, an easy part of of the question, about rinse water.
>
> It turns out that resist strippers pickup Copper during stripping, and in
> most, but not all, cases, it tops out at around 250 PPM.   With a stripper
> containing 250 PPM of Copper, the rinse waters are going to have more than an
> allowable level of Copper, thus they must be waste treated, and this is
> expensive, especially since the strippers are usually chelated.
>
> Some stripper chemistry vendors are getting around this matter by using feed
> and bleed, and feeding enough stripper chemistry through the system to keep
> the Copper levels down, thus keeping the rinse waters legal to dump.  This is
> simply a keep-the- --stripper-chemistry-rich concept, but there are some folks
> who buy into it.
>
> It is possible, by using the proper inhibitors in the stripper chemistry, to
> keep the Copper levels down to less than 50 PPM, no matter how deeply you go
> into the chemistry, but of course, I am too modest to tell you those suppliers
> that can supply this kind of chemistry.
>
> Now about actual stripping costs.
>
> First, understand that because of overplating issues, the outerlayer strippers
> have to be real high performance, compared to innerlayer strippers,  and this
> high performance can cost a whole lot, or not so much more, depending on the
> chemistry in the stripper.
>
> To be specific, the cost of stripping can vary from a low of around US$0.006
> per square foot (and this is for a fully formulated proprietary stripper) to
> as high as US$0.12 per square foot, for folks using really badly formulated
> strippers in a feed and bleed mode.
>
> Some facts to remember about costs of stripping:
>
> 1.) The faster you want to strip at, the higher the cost of stripping, this
> means that the longer the strip chemistry is in contact with the resist, the
> deeper into the chemistry you can go.  Thus the longer the strip chamber, the
> lower the chemistry costs, because the longer the chamber, the longer the time
> the chemistry is in contact with the resist, for a given throughput.
>
> 2.) The higher the temperature you strip at, the faster the stripping, thus,
> this really means that the higher the temperature you strip at, the lower the
> cost, as long as the stripper does not tarnish the Copper because it is being
> used so hot.
>
> 3.) The issue of tarnishing the Copper is crucial, especially in the
> innerlayer line, as in the US, most innerlayers go to AOI after stripping, and
> for most AOI, any tarnish slows the AOI dramatically.  This is so important,
> that some people throw out stripper chemistry when it starts to tarnish.  And
> the propensity to tarnish increases as the Copper level in the stripper
> increases, unless you have a properly designed anti-tarnish system in the
> stripper chemistry.
>
> 4.) Feed and Bleed generally increases the cost of stripping by a factor of
> 2+, because good chemistry is thrown out with the bad.
>
> I think that I have given you more than you asked for, but if you have further
> questions, get back in touch.
>
> Regards,
> Rudy Sedlak
> RD Chemical Company
> Mountain View CA
>
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