Thanks to everyone for the prompt responses, it validated my
concerns (I was right, nyah, nyah, nyah!). We're getting another stencil
burned right now with 12mil aps, the 1:1 stencil originally specd was a
disaster, 4-6 bridges every board.
Now to another topic: What are your experiences with mask
dams/webbing and fine pitch? In previous lives, I tried to specify mask
between pads on 25mil and under. This seemed to help minimize bridging
potential. However, I am now dealing with people higher up that have had
bad experiences with this practice, and I want to bring about a dialog
to pursue some process experiments.
Step up to the pulpit and tell it like it is, brother (or
sister). Amen!
Mike McMonagle
PCA Process Engineering Supervisor
K*Tec Electronics
1111 Gillingham Lane
Sugar Land, TX 77478
(281) 243-5639 Phone
(281) 243-5539 Fax
[log in to unmask]
> -----Original Message-----
> From: Stephen R. Gregory [SMTP:[log in to unmask]]
> Sent: Friday, August 21, 1998 6:14 PM
> 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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