TECHNET Archives

March 2003

TechNet@IPC.ORG

Options: Use Monospaced Font
Show Text Part by Default
Show All Mail Headers

Message: [<< First] [< Prev] [Next >] [Last >>]
Topic: [<< First] [< Prev] [Next >] [Last >>]
Author: [<< First] [< Prev] [Next >] [Last >>]

Print Reply
Subject:
From:
"FOX, Ian (York Rd)" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Wed, 26 Mar 2003 08:02:25 -0000
Content-Type:
text/plain
Parts/Attachments:
text/plain (154 lines)
Steve, yes, pretty much IPCesque lands. As I said in an earlier reply, we
actually bonded components to the bare PCB surface such that no solder joint
could form. The pick-up of solder on the end terminations from the wave was,
as you would expect with this config, relatively light ie some pick-up but
not a bulbous end by any stretch of the imagination. There was no evidence
of resolvable thermal damage after the soldering op but cracking occurs
during screen

Ian

-----Original Message-----
From: Steve Thomas [mailto:[log in to unmask]]
Sent: 25 March 2003 17:53
To: [log in to unmask]
Subject: Re: [TN] Cracking Capacitors


Ian,

A question, and a comment....are you using the standard IPC recommendation
for land size and spacing?  The reason I ask is that I've heard of research
that suggested that reducing the land size may reduce the tendency towards
cracking.  Apparently it's a function of the decreased rigidity of the
land/pcb interface as it's size decreases. This in turn reduces the affect
of CTE mismatches. If my memory serves me
right, the research was performed with FR-4, but I can't verify that.
Unfortunately I don't
have references to these studies...just word of mouth and a hazy
recollection.

The bottom line was that an 0603 pad size may be a better size for an 0805
component
with respect to reducing ceramic capacitor cracking. Whether it's better in
all aspects (contrary to what you might guess, given the support of IPC to
the contrary) is anybody's guess unless they've done research themselves.

I'd like to know more, if anyone's got a source for information along those
lines.

Regards,

Steve

-----Original Message-----
From: FOX, Ian (York Rd) [mailto:[log in to unmask]]
Sent: Tuesday, March 25, 2003 9:41 AM
To: [log in to unmask]
Subject: Re: [TN] Cracking Capacitors


Joyce, thanks for that, I haven't seen that publication before. Similar
failure mode, but significantly less solder on ours than shown by TDK. We've
actually cracked them on cycling with only the build up of solder from
contact with the wave (bonded them to the surface of the PCB without
associated pads) so we aren't talking bulbous joints.

Regards
Ian

-----Original Message-----
From: joyce [mailto:[log in to unmask]]
Sent: 25 March 2003 16:38
To: 'TechNet E-Mail Forum.'; 'FOX, Ian (York Rd)'
Subject: RE: [TN] Cracking Capacitors


Seen that before... You should not use excessive solder (bending
stress)...see tdk...
http://www.component.tdk.com/components/commoncrackingmodes.pdf
                                                               jk

>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of FOX, Ian (York Rd)
>Sent: Tuesday, March 25, 2003 11:37 AM
>To: [log in to unmask]
>Subject: [TN] Cracking Capacitors
>
>
>Technetters, have a little problem with capacitors that I'd be grateful
>for comments on. We've been wavesoldering 0805/1206 chip caps onto the
>underside of both FR4 and poly/glass PCB's for the best part of 15
>years and we've been experiencing a low failure rate of devices
>in-house after ESS and burn-in. On top of this however we've had some
>early life in-service failures. Process and assembly trials together
>with FEA analysis we've carried out suggests that the thickness of
>solder left on the topside of the device after the soldering
>operation is critical. Too much and the devices nucleate
>cracks relatively quickly, as during the negative part of the
>temperature cycle, the solders modulus increases to the extent
>that the stress imposed on the termination/body interface is
>in excess of that the titanate capacitors can withstand. My
>question to the forum therefore, is has anyone else found
>similar issues? I know we've seen posts before with regard to
>cracking caps, but this failure mode isn't anything to do with
>assembly stresses or thermal shock during the soldering
>operation (we've artificially increased the solder volume on
>convection reflow soldered components using dispensed paste
>and generated exactly the same failure
>mode)
>
>Regards
>Ian Fox
>Goodrich Engine Control Systems
>
>---------------------------------------------------
>Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
>To unsubscribe, send a message to [log in to unmask] with following text
>in the BODY (NOT the subject field): SIGNOFF Technet To temporarily
>halt or
>(re-start) delivery of Technet send e-mail to
>[log in to unmask]: SET Technet NOMAIL or (MAIL) To receive ONE mailing
>per day of all the posts: send e-mail to
>[log in to unmask]: SET Technet Digest Search the archives of previous
>posts at: http://listserv.ipc.org/archives Please visit IPC web site
>http://www.ipc.org/html/forum.htm for additional information, or
>contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
>-----------------------------------------------------
>

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in the
BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/html/forum.htm for additional information, or
contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e To
unsubscribe, send a message to [log in to unmask] with following text in the
BODY (NOT the subject field): SIGNOFF Technet To temporarily halt or
(re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet
NOMAIL or (MAIL) To receive ONE mailing per day of all the posts: send
e-mail to [log in to unmask]: SET Technet Digest Search the archives of
previous posts at: http://listserv.ipc.org/archives Please visit IPC web
site http://www.ipc.org/html/forum.htm for additional information, or
contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------

---------------------------------------------------
Technet Mail List provided as a free service by IPC using LISTSERV 1.8e
To unsubscribe, send a message to [log in to unmask] with following text in
the BODY (NOT the subject field): SIGNOFF Technet
To temporarily halt or (re-start) delivery of Technet send e-mail to [log in to unmask]: SET Technet NOMAIL or (MAIL)
To receive ONE mailing per day of all the posts: send e-mail to [log in to unmask]: SET Technet Digest
Search the archives of previous posts at: http://listserv.ipc.org/archives
Please visit IPC web site http://www.ipc.org/html/forum.htm for additional
information, or contact Keach Sasamori at [log in to unmask] or 847-509-9700 ext.5315
-----------------------------------------------------

ATOM RSS1 RSS2