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August 1998

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From:
Paul Klasek <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Tue, 25 Aug 1998 11:30:21 +1000
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Great ; nice & shiny ; is that all what we worry about ?
Any reliability data regarding the Ag influence in the alloy ?
Does not have to be cycling ; would anybody shear identical assemblies
with both options ?

Thanks a lot folks (& Steve)                  paul
> ----------
> From:         Stephen R. Gregory[SMTP:[log in to unmask]]
> Sent:         Saturday, 22 August 1998 9:14
> To:   [log in to unmask]
> Subject:      Re: [TN] Stencils for Gold Boards -Reply
>
> In a message dated 8/21/98 2:44:24 PM Pacific Daylight Time,
> [log in to unmask]
> writes:
>
> <<  Just one note, all reflowed solder joints have dull or
> gray-looking
> appearance.  That's normal.  Gold diffuses into melting solder causing
> dull or
> gray-looking solder joints. >>
>
> Hi Mike!
>
>      Matthew gives you good advice about your apertures. About his
> comment of
> the solder joints looking dull and grainy on gold boards, I got a tip
> for you
> to make em' look better, use a 2% silver solder with them (62/36/2).
> It lowers
> the melting temp a little...I think liquidous is 179 C. vs. 183 C.
> with a
> 63/37, and that ain't all that different, it's still eutectic, and it
> shouldn't cost much different (if you get charged anything different
> at all)
> from a regular ol' 63/37.
>
>      I worked at a memory company a couple of years ago where we had
> quite a
> few gold boards and that's what we used and our vendor charged us the
> same
> price...I'm not a metallurgist, so I can't tell you PRECISELY why the
> joints
> look better with a 2% silver, but they do, I'm not pulling your leg
> either...
>
>       I do remember reading something quite a while back that there
> was a
> mistaken belief floating around that if you used silver in your solder
> that it
> would prevent the leeching of the gold into the joints during
> reflow...something about the silver in the solder being a noble metal
> like
> gold is, raises the percentage of noble metal in the solder joint
> which
> reduces the leeching of the gold. We all know now that's not true, but
> I'm
> thinking maybe where that belief may have gotten started was
> difference in the
> solder joint appearance...someone may have thought back then that the
> addition
> of silver really did stop the gold leeching.
>
> -Steve Gregory-
>
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