Ian

As Mike has already suggested, it is almost certainly silicone residues.

My best recommendation is to call HumiSeal because they have masking tapes
that are specifically designed for coating applications - non-silicone
adhesives.

I am dismayed at the suggestion of changing the coating after all, it is a
permanent product to do a permanent job - not a temporary product to do a
temporary job. Further, silicone does not stick to other silicone so
easily - usually not at all.

You need to specify a high temperature tape with no silicone adhesive. We
actually found that paper masking tape works OK but requires far too much
re-work time cleaning off the adhesive residues.

BTW, I operate a conformal coating service here handling around 1000 boards
per day - the HumiTape works great - and I don't care if that is regarded by
some as spamming.

Regards,
Graham Naisbitt

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WEB: http://www.concoat.co.uk

CONCOAT Ltd
Alasan House, Albany Park
CAMBERLEY GU15 2PL UK

Tel: +44 (0) 1276 691100  Fax: +44 (0) 1276 691227
----- Original Message -----
From: Ian Slater <[log in to unmask]>
To: <[log in to unmask]>
Sent: 25 November 1999 16:44
Subject: [TN] Board Contamination


> We're having contamination problem which is impacting our
> conformal coating process.  Here's the story:
>
> We use  "Kapton" style tape to guard the edges of a circuit board
> while the board is processed in our wave solder machine.   The
> board/tape reaches a peak temperature of 220C for three seconds.
> The temperature ramp keeps the board above 120C for
> approximately three minutes.
>
> After passing through the wave solder machine, the board is allowed
> to cool to room temperature.  The tape is then removed.  No visible
> residue is left on the board.  However, when we attempt to conformal
> coat the board, the coating is repelled from areas where the tape
> was applied.  No manner of cleaning (alcohol, water, acetone...) will
> remove the contamination and allow the conformal coat to bond to
> the board.
>
> Are you aware of what the source of contamination could be?  We
> have managed to rule out flux. Boards have been taped and tested
> prior to heating and no residue was found.  Four different brands of
> tape were tested with identically poor results.
>
> Ceramic edge stiffeners have been tried.  The edge stiffeners clamp
> mechanically over the edges of the board.  Some contamination was
> found when edge stiffeners were used, though not as much as with
> the tape.
>
> Boards run without protection show no contamination.
>
> I would appreciate any insight you could provide into the nature of
>
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