I didn't pose the original question, just offered my opinion.

Colin McVean
Production Manager
Artetch Circuits Limited
Tel: 01903 725365
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Pete menuez
Sent: 03 May 2005 21:36
To: [log in to unmask]
Subject: Re: [TN] Via contamination

Colin,

In some of the pictures it looks like the contamination is actually
flowing
on top of the mask. Is it?  Also is this contamination solid or is it
like a
gelatin? Did you see any indication of this in the unpopulated boards?

I can't really make out the white contamination.  It looks similar to
the
nomenclature ink but it's darker. What is its consistancy. (solid or
gelatin)

I think you wouuld be better off with FTIR analysis over the cross
section.
The cross section may help if the cause of the contamination is
originating
in the hole but I can't imagine what would be in there that would cause
the
contamination.  Flux residue that burned on after vaporphase/reflow?

You may want to buddy up with the board shop that supplied these (if
they
are local to you).  Their laminate supplier may have the equipment
(FTIR) to
do the analysis and may provide the service at no charge.  Otherwise
there
are a number of labs that provide this service.

Good luck - if you do solve this let the Technet know what it was.

Pete


>From: Colin McVean <[log in to unmask]>
>Reply-To: TechNet E-Mail Forum <[log in to unmask]>,              Colin
McVean
><[log in to unmask]>
>To: [log in to unmask]
>Subject: Re: [TN] Via contamination
>Date: Tue, 3 May 2005 17:01:35 +0100
>
>This looks like a case of over-plating, (nodules on pads) where the
>current density is either too high for the board in question, or they
>are isolated via pads, which will incur a high CD. Remedies for this
are
>low CD and/or thieving. Other possibility is that they have been in the
>plating tanks too long, but if the CD was correct, then all that should
>happen is that the plating just gets thicker and stays smooth.
>Subsequent etching will show an overhang, which could trap dry film
>resist.
>
>Colin McVean
>Production Manager
>Artetch Circuits Limited
>Tel: 01903 725365
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Al Onderick
>Sent: 03 May 2005 16:40
>To: [log in to unmask]
>Subject: [TN] Via contamination
>
>Greetings Tech netters,
>
>
>
>             In the past we've had problems with tented vias not
>completely
>tenting and trapping liquid.  The liquid would boil and find its way to
>the surface of the board.
>
>
>
>While this looks similar these vias were not tented.
>
>
>
>
>
>http://www.texas-gold.org/PCB/
>
>
>
>Al Onderick
>
>National Instruments
>
>
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