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January 2004

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From:
"d. terstegge" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Mon, 19 Jan 2004 17:19:55 +0100
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Hi Bill,

Several years ago we stopped using 1812's on the wave solder side for
all our new designs, based on recommendations of componentvendors and
fellow Technetters. For older designs and for some our subcontracting
customers we still have to wave solder 1812 caps, and fortunately
without any reported problems.
We've had our share of cracked capacitors, but that was always with
smaller parts.

Daan Terstegge
Thales Communications
Unclassified mail
Personal Website: http://www.smtinfo.net

>>> [log in to unmask] 01/15/04 08:26pm >>>
Hello folks,

I've posted this question (similar) to this forum a couple of time only
to
get a few responses.

So, here goes......

Most data sheets for Ceramic Capacitors advise against wave soldering
any
surface mount ceramic caps whose size is larger than 1812. I have
board
designs that have ceramic 1825's on the backside. We used to wave
solder
them with great solder results. About a year or so ago, we received
notice
that we should not be wave soldering larger ceramic caps due to their
susceptibility to cracking from thermal shock. I've always blamed
failed
caps due to handling problems. As a result, I've had to convert the
second
side soldering from wave soldering to reflow soldering. I've always
been
nervous about second side reflow "re-melting" the solder joints already
on
the topside so, I've always used fixtures to protect that side from
"re-melting". The process works but the drawback is that any leaded
parts
that remain must be hand soldered. (Or re-design the board to allow
intrusive soldering. I have no experience with this.) We've also
improved
our handling practices as well and we haven't seen any failed caps. (I
still
say it was the handling.)

So, are most folks wave soldering any sized ceramic caps or does
everyone
follow the 1812 limit?

I've even thought about pre-heating the board prior to wave soldering
in an
oven in addition to the regular pre-heat of soldering. This would help
solve
the problem of the steep temperature gradient.  But the drawback is
that the
flux would be dried out before the wave. So the work around for this is
to
use water based organic flux that would remain active as the board
passes
over the wave. This remains an option but requires a lot of convincing
to
get approval.

Thanks.

Bill Kasprzak
Moog Inc., Systems Group, Process Engineer

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