I forgot to mention two additional important factors;
11) Solder joint/pad size
12) Cool down rate after exiting the wave

John Maxwell

At 09:06 AM 8/17/01 -0400, you wrote:
>Last thought on this topic:
>
>Over the past 18 months, CALCE has seen a significant increase in ceramic
>capacitor failures (thermal shock cracks, flex cracks, manufacturer flaws)
>among its customers. In terms of pure speculation, its possible that the
>huge demand for capacitors during the boom may have lead to some relaxation
>in process control.
>
>What this implies is that your process was borderline to begin with, and
>then the addition of caps with larger flaws or a lower fracture toughness
>simply lead to the introduction of failures where there were none before.
>
>Best Regards
>Craig
>
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]]On Behalf Of Bartkowaik Christine
>Sent: Friday, August 17, 2001 6:56 AM
>To: [log in to unmask]
>Subject: Re: [TN] To wave or not to wave, that is the question...
>
>
>Kevin:
>
>We have no problem with 1uf caps (TANT). Thus I suspect:
>1-      thermal shock
>2-      too long a time in the wave >2 s
>
>I would not suspect moisture if the boards have already been thru a reflow
>oven and have not sat long.
>
>Chris
>
>         -----Original Message-----
>         From:   Kevin Stokes [SMTP:[log in to unmask]]
>         Sent:   Thursday, August 16, 2001 4:26 PM
>         To:     [log in to unmask]
>         Subject:        [TN] To wave or not to wave, that is the question...
>
>         Old problem: mounting ceramic capacitors to the bottom side of an
>assembly and your customer wants you to wave them on.
>
>         We are having problems with 0805 0.22 uF and 0.1 uF caps going
>through wave and cracking during the process.  We are following all of the
>standard protocols (preheat, etc.).  My understanding is that 0805s are
>typically capable of handling this process.
>
>         Anyone got any ideas short of moving the cap to the top or doing a
>double sided reflow?
>
>         Kevin
>
>         Kevin Stokes
>         Reliability Manager
>         Kimball Electronics Group
>         (812) 634-4207
>
>
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