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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