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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