Rudi,
Let me add my two cents to Your message :
Rinse water quality :
I am in doubt , that stripping solution contain so high levels of copper (
250 ppm ) , especially the systems , that are operating on feed and bleed
base .
To my opinion , there is basic difference between stripping photoresist used
as etch resist and used as plating resist :
1 ) etch resist : photoresist is above surface of the copper . Quality of
the copper depends not only on stripping chemistry , but also on quality of
the copper under the photoresist ( e.g. - if photorists is laminated on
oxidised copper , with the best stripper the copper after striping will be
oxidised ) . A lot depends on rinse water quality and efficiency of the dryer .

2 ) plate resist . In most of the cases the problem are related to
oveplating and to potential damage to etch resist ( tin or tin lead ) . The
spent stripper is contaminated by tin or tin-lead .
Decision regarding feed and bleed or batch-wise operation depends not only
on the direct costs of the chemistry but on process considerations : feed
and bleed is steady state process ( constant operation parameters ) while in
batch wise mode operation parameters must be adjusted as the chemistry is
loaded . For plate resist stripping oxidation is also crucial for the next
process , which is normally alkaline etching .

Regarding costs considerations :
Apart of the choise of mode of operation , stripping machine is of the most
importance , especially skin removal capacity .This is important for
propertiary strippers : if chemistry is working on dissolution of removed
skin instead on stripping , this is the best way to loose money .


At 14:10 10/05/98 EDT, you 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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Shalev Shabtay
Eltek Ltd - Israel
Tel  972 3 9395050
Fax 972 3 9309581
E-mail :  [log in to unmask]

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