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| Date: | Fri, 1 Mar 1996 08:36:55 PST |
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On Fri, 23 Feb 96 14:20:11 -0800 [log in to unmask] wrote:
> From: [log in to unmask]> Date: Fri, 23 Feb 96 14:20:11
-0800
> Subject: Exposed Copper on Assemblies
> To: [log in to unmask]
>
> Item Subject: cc:Mail Text
> As mentioned in several other messages, we have found no reliability
> problems associated with exposed copper on OCC assemblies.
>
> However, I have one question which I hope someone can answer:
>
> On some assemblies, we use grounded contact pads to ground
> shields/bulkheads, etc. The contact between the shield and the board
is
> simply a metal tab on the shield that presses against a contact pad on
> the board. Is such a connection reliable if the pad is exposed copper
> (or copper with residual OCC after a couple of reflow cycles and an
> aqueous wash)as opposed to HASL? Pasting those pads is not possible in
> all applications due to the size, number of pads, etc.
>
> Regards,
>
>
> Denis Mori
> Hewlett-Packard Co.
> Roseville, CA
> [log in to unmask]
>
Denis: First of all let me say I'm a proponent of OSP coatings.We
both fabricate and assemble product using OSP as an OEM.We also have not
found any reliability issues with exposed copper.
In response to your question on the grounding I would agree with the
reply from Ralph Hersey.We had a very similar situation as yours.This PCB
required a large bright tin plated aluminum cover shield to be in intimate
contact to the board to provide EMI shielding and coupling.When tested the
tin to copper interphase did not provide adequate grounding over time.The use
of reflowed solder paste could not provide a flat enough mating surface so we
ended up going to HASL for this particular product.Unfortunately their is
still not a wonder coating that works for all applications!
Regards
Michael Barmuta
Staff Engineer
Fluke Corp.
Everett WA.
(206)356-6076
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