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   TO:         I4235700 IBMMAIL   new address for ipc technet 25.6.96

   FROM:       DSTEWART EX2       D.Stewart        - Product Development Manager.

   DATE:       8 April 1997
   SUBJECT:    re:resist adhesion test
   REFERENCE:  why it's wanted

    I was interested to see that someone else is looking for a way to
    measure resist adhesion. We have tried to follow this route as
    well, because in our continuous improvement program, we try to
    optimise processes by Taguchi methodology, and require real data
    rather than attribute data at the end of the process. To optimise
    the preclean and lamination process, it is neccessary to have a
    measure after lamination - the interference of additional processes
    can and does have an influence on the results of the process ie.
    exposure level, developing conditions, printing cleanliness,
    laminate resin spots, etching parameters -  all affect the "yield"
    that is measured at AOI.
    We have asked our dry film suppliers for a measure such as that
    which was requested, but have been unable to convince these guys of
    how important it is and that they should have a measure. On the
    other hand, we have also had to educate our process staff to
    differentiate between inner and outer layer adhesion requirements -
    on inners, you need the adhesion to prevent lift during etching -
    stripping is easier because the resist is on the surface - in outer
    layers you need the resist to be easily removed if not exposed to
    avoid residues, and it must also be easily strippable between
    plated tracks.
    Having said all that, it would still be useful to have a good
    measure that is based on values rather than attributes for the
    adhesion of dry film after lamination !

    Dougal Stewart
    Exacta Circuits
    Scotland

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