Dear Ken,

I noticed you subsribe to TechNet as well.  If you find it more convenient to reach me by E-Mail.  My E-Mail address is [log in to unmask]

Please let me know if I can be of further assistance with your conformal coating issue.

Best regards,

Dave Rund
Taiyo America, Inc.
----------
> We have a problem which I suspect many of you have encountered and
> satisfactorily solved.  Most of our PCB assemblies are through-hole, double
> sided or multi-layered.
>
> We have a relatively small but persistent percentage of boards that exit
> the flow solder process with  solder bridges between adjacent
> (clipped/clinched) leads on the circuit side of the board.  Visual
> examination of the bridges typically reveals them  to be between leads
> which are not bent toward each other.
>
> This phenomenon has been accepted as part of our normal process along with
> the subsequent touch up operation which removes the shorts.  I invite you
> to comment on the following two hypotheses and to add any diagnoses and
> successful corrective actions you may have taken.
>
> --The tin-lead solder ration may sufficiently differ from the eutectic
> point that the solder remains in the "semi-plastic" state too long when the
> board exits the wave and cools before the bridging material can exit the
> surface.
>
> --The preheat temperature may be too low--especially with multi-layer
> boards having heat sinking ground planes so that too rapid cooling is
> induced and bridges form.
>
> I suspect many of you have theories better informed by experience.  Please
> let me hear from you.  I am on a team tasked with reducing our fairy
> extensive after-wave touch-up operation.
>
> PS:  I thank each of you who replied to my request for resolving a
> conformal coating over LPI solder mask non-wetting and dewetting problem.
> Each of your suggestions was enlightening and helpful.  Much testing has
> determined that the problem is some still unidentified contaminant on the
> silk-screened side only, which can be removed by a sufficiently "vigorous"
> aqueous cleaning.
>
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