If you have exposed copper on a cryo instrument the normal cold
surface can cause condensate to form. This can have an adverse effect on the
copper finish on the exterior. Perhaps a nickel finish would be better or a
spray over externally with HT sealant or the PCB rework flux sealants
that we used when we only had copper finish boards in the dark ages...

Jim

Jim Thornhill
University of Liverpool
Department of Physics
Oliver Lodge Laboratory
Oxford Street
Liverpool
L69 7ZE
ENGLAND

----- Original Message -----
From: "Dee Stover" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, November 13, 2003 2:01 PM
Subject: [DC] circuit board finish


> I have a 2 layer board where one side is to be a thermally conductive.  It
> is a poured copper plane with its only connection being to the mounting
> holes where copper straps will be part of how it gets mounted.  We call
> these cold stations.  Usually connectors are mounted on both sides of the
> board.  It is basically to move signals from inside a cryo instrument out
> to the world.  We have done these with a HASL finish in the past but know
> we can get better thermal conduction if we can leave off the tin/lead
> finish and just have the bare copper.  The holes need to be plated, no
> solder mask or silk screen is applied.
>
>
>
>
> My questions:
> Is there any thing special instructions I should do on the fabrication
> drawing besides remove the finish, solder mask and silk screen
> instructions? The finish I want is the copper any special statements to
> accomplish this?
>
> Besides the oxidation problem do any other problems come to mind that I
> should be concerned with on a board that will have the copper exposed in
> this manner?
>
> Thanks for you input and time!
>
>
> Dee Stover  [log in to unmask]
> Associate Technician Design
> National Optical Astronomy Observatory
> 950 N Cherry Ave
> Tucson, AZ 85719
> www.noao.edu
>
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