Here are some relevant links that I copied from a recent posting on SMTnet's
forum, it includes the AVX pages that were already referred to:
http://www.kemet.com/KEMET/web/homepage/kechome.nsf/vapubfiles/f2106/$file/f
2106.pdf
http://www.avxcorp.com/docs/techinfo/cracks.pdf
http://www.avxcorp.com/docs/techinfo/paramimp.pdf
http://www.avxcorp.com/docs/techinfo/assembly.pdf
http://www.avxcorp.com/docs/techinfo/smzero.pdf
http://www.kemet.com/KEMET/web/homepage/kechome.nsf/vapubfiles/f2111/$file/f
2111.pdf
Daan Terstegge
http://www.smtinfo.net
----- Original Message -----
From: "ME Magnin" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 12, 2003 5:29 PM
Subject: Re: [TN] TH capacitor on SMT pads
> Hi Jean-François,
> we have faced two major crisis with cracked multilayer capacitors in the
> past.
> the first one, at the very beginning of our SMD experience and very easily
> solved, was when we were separating panalized boards by hand and was
solved
> by using a CAB machine. Rule : never bend a board.
> the second was really tricky and took us weeks to find the real
explanation.
> the basic reason was the same : boards were flexed during insertion of a
28
> pins EPROM into a socket. the board had some 40 caps on the bottom side,
but
> the borken ones were distributed on the line of maximum flexion.
>
> to find more explanations, please visit AVX website (i saw it a few weeks
> ago, but I cannot remember the URL, try with Google).
>
> Regarding your option to move to TH caps, we did this sometimes, but
because
> the pitch is quite narrow, you take the risk of shorts, cracked bodies,
> etc...
> And second, depending on the quantity of caps you have to change, it will
> cost your company at lot
>
> good luck
>
> Marie Magnin
>
> FIRSTEC SA
> Rue du Grand Pré 70
> CH 1211 Genève 2
>
> Tél. : +41(0)22 918 36 85
> Fax : +41(0)22 918 36 93
> mailto:[log in to unmask]
> http://www.firstec.ch
>
>
> > -----Original Message-----
> > From: TechNet [mailto:[log in to unmask]]On Behalf Of Bissonnette,
> > Jean-Francois
> > Sent: mercredi, 12. février 2003 16:25
> > To: [log in to unmask]
> > Subject: [TN] TH capacitor on SMT pads
> >
> >
> > Hi Technetters,
> >
> > We're having problem with some multilayer ceramic capacitors
> > (SMT), they
> > crack. We have a
> > high level of rejects from the field and we're thinking of
> > replacing them.
> > However, the
> > best that the design team came up with so far is to use
> > regular ceramic
> > capacitor (TH)
> > (... please don't ask why they don't chance supplier... I
> > already did and
> > well, forget it!)
> >
> > I'm not too confortable with that, but on the other hand, a
> > design change on
> > the board
> > would be very costly and we want to avoid that.
> >
> > Did anyone ever changed a SMT part for a TH part? What
> > problems should we
> > expect
> > if we decide to go that way? Of course assuming that the
> > leads would be
> > bent properly, the
> > cap would be bonded to the board, every applying rule for
> > soldering would be
> > respected and
> > Murphy won't show its ugly face... then again we all know
> > what appends when
> > we assume...
> >
> > I'd prefer to go another way but my way will cost a lot of
> > money and I'm
> > told that we have to
> > keep it to a minimum.
> >
> > Any thoughts?
> >
> > Jean-François Bissonnette
> > Vérificateur, Contrôle de la Qualité
> > Électronique
> >
> >
> >
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