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March 2003

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Mon, 24 Mar 2003 15:14:31 +0800
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Daan,

As a supplement to my previous mail, I should say that our boards have an
alchromated (alodined) aluminiuim strip between board and chassis on one
side and wedgelocks (card retainers) on the other side. Each pair of
interfacing surfaces is filled with a thin thermal tape to take up the
irregularities between the surfaces, so that the different metals are not
actually in contact with each other, but are connected thermally as well as
possible.

Peter



Brian Ellis <[log in to unmask]>      18/03/2003 08:54 PM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to Brian Ellis

              To:  [log in to unmask]
              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: Re: [TN] Heat transfer from ENIG board to aluminium casing








Daan

I would have thought exactly the opposite! An uneven HASL surface will
have fewer contact points to the aluminium than a flat ENIG surface.
That having been said, I would have thought that both would be bad,
electrochemically speaking, if subjected to humidity. From very poor
memory, the Al-Au couple is somewhere about 4 V, roughly double that of
Al-Sn/Pb.

Brian

d. terstegge wrote:
> Hi Technet,
>
> We are in the process of converting some of our boarddesigns from HASL
> to ENIG conductor finishing. Now one of our designers is worried about
> the effect that this change may have on heat transfer from the plated
> board-edges to the aluminium casing on which the board is mounted. He
> feels that the heattransfer from leadtin to aluminium is better that for
> nickel/gold to aluminium, possibly resulting in heat problems in the end
> product.
>
> Any ideas on this ?
>
> Daan Terstegge
> Thales Communications
> Unclassified mail
> Personal Website: http://www.smtinfo.net
>
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