HI Mike,
We specify dams on all fine pitch. I can't live with out it. If you don't
get it on fine pitch you better have an automated stencil for registration.
Otherwise it is solder bridge city. Specifying LPI for Soldermask will work
fine. You may get few broken dams but that is the price you pay for having
14mil pads.
Hector Valladares
Honeywell -SASSO
Production Staff Engineer
727.539.3683 voice
727.539.4469 Fax
[log in to unmask]
-----Original Message-----
From: McMonagle, Michael R. [SMTP:[log in to unmask]]
Sent: Saturday, August 22, 1998 8:48 AM
To: [log in to unmask]
Subject: Re: [TN] Stencils for Gold Boards -Reply
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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