Cracking near the termination is often the result of thermal shock of the
component during reflow or soldering profiles, where in my experience, flex
cracks are often in other locations. Many times the corrective action can
take the simple route of adjusting profiles to allow adequate ramp to
compensate for the component sensitivity to internal CTE stresses. Some are
more delicate than others. Larger components are more susceptible than
smaller ones and none survive hand soldering with any grace at all. Part of
the difficulty issue is related to the fact that crack may not cause a fail
until metalization forms across the crack during operation, long after test.
Best of luck.
Mel Parrish
Director, Training Materials Resources
Soldering Technology International
102 Tribble Drive
Madison, AL 35758
256 705 5530
256 705 5538 Fax
[log in to unmask]
www.solderingtech.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Bissonnette,
Jean-Francois
Sent: Wednesday, February 12, 2003 10:11 AM
To: [log in to unmask]
Subject: Re: [TN] TH capacitor on SMT pads
I'll see what I can do for the pictures.
The cracking are near the end terminasion. They are called "flex-cracks"
apparently due
to flex of the boards but the boards they're soldered on are rather thick
we're not sure.
And there is a variety of reasons why these appeared. What we're facing now
is more
can we do it another way so these cracks are not appearing? The TH part
seems to be
the most economical way, on short term that is. But I've seen more than
enough situation
where economical way turn out to be "pay now or pay (more) later".
I want to know if anyone tried it the way I said before and what they came
up with.
Here is a link to a report on these cracks. It may interest some of the
technetters.
http://www.syfer.com/ta_02.htm
-----Original Message-----
From: James TerVeen [mailto:[log in to unmask]]
Sent: Wednesday, February 12, 2003 10:48 AM
To: TechNet E-Mail Forum.; Bissonnette, Jean-Francois
Subject: Re: [TN] TH capacitor on SMT pads
I guess coming from a Chip manufacturers side I need to ask Why you do not
change suppliers. What kind of cracking are you talking about. I ask
this because I just did a long process of tracking down a cracking problem
with a customer and the final result was they had to much pressure in
placing the component and were cracking it there. Very small cracks but
they were there and when they fired up the board the cracks got much
larger. Can you supply a picture of the cracks to Steve so we can take a
look.
"Bissonnette,
Jean-Francois" To: [log in to unmask]
<JBissonnette@WAB cc:
TEC.COM> Subject: [TN] TH capacitor
on SMT pads
Sent by: TechNet
<[log in to unmask]>
02/12/03 10:24 AM
Please respond to
"TechNet E-Mail
Forum."; Please
respond to
"Bissonnette,
Jean-Francois"
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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