Neil,
Depending on how the glass frit in the termination thick film paste was
fired to the ceramic body you can see end caps come loose. Usually when
this occurs there will be a slight discoloration on the capacitor body
where glass diffusion had started but not completed the process resulting
in a very weak bond between termination and ceramic body. This is typical
of some larger case sizes (1206 and up) but I have seen some hints on 0805
sized chips also.
When I was a consultant I loved soldering irons and V scoring, they put my
wife and oldest son through university along with making the house payment.
John
At 09:23 AM 10/8/01 +0100, you wrote:
>I have seen this in the past and you must be very careful during
>de-panellising PCBs as well.
>
>We banned 'v' scoring of FR4 surface mount PCBs because of the risk of
>cracking surface mount capacitors. The time to failure can be anything from
>hours to months depending on environment - temperature, moisture etc.
>
>I have another question - has anybody out there seen chip capacitors fail
>open circuit when operated in a circuit which runs quite hot?
>
>Can the end caps become loose through temperature cycling causing the
>capacitors to go open circuit at elevated temperatures?
>
>Neil
>
>-----Original Message-----
>From: KK Chin [mailto:[log in to unmask]]
>Sent: 05 October 2001 17:15
>Subject: Re: Leaky Capacitors
>
>
>We has banned manual soldering for leadless chip capacitors. Years ago we
>experienced exactly the same problem. Microsectioning revealed that cracks
>are
>formed across several layers of the interleaved electrodes. Even bigger
>problem
>was that the cracked capacitor would not be detected in the initial test.
>After
>operating for a while, metal migrated across the crack and shorted the
>layers.
>We glad the problem was caught in burn-in rather than in the field. The
>shorted
>capacitor burnt some of our assemblies badly.
>
>Manual soldering was not the only cause of capacitor cracking. AVX and Kemet
>published some articles about precautions in design and assembly processes.
>
>K.K. Chin
>Artesyn Technologies,
>Fremont, CA
>
>###########################################################################
>##########
>Attention:
>
>This message is for the named person's use only. It may contain confidential,
>proprietary or legally privileged information. No confidentiality or
>privilege
>is waived or lost by any mistransmission. If you receive this message in
>error,
>please immediately delete it and all copies of it from your system,
>destroy any
>hard copies of it securely and notify the sender. You must not, directly or
>indirectly, use, disclose, distribute, print, or copy any part of this message
>if you are not the intended recipient. STADIUM GROUP PLC and any of its
>subsidiaries
>each reserve the right to monitor all e-mail communications through its
>networks.
>Any views expressed in this message are those of the individual sender,
>except where
>the message states otherwise and the sender is authorised to state them to
>be the
>views of Stadium Group Plc. or one of its subsidiaries.
>
>Although this message has been scanned by MailMarshall for known viruses and
>inappropriate content, we recommend that recipients employ appropriate
>measures on
>their systems to intercept any such material.
>
>Thank You - Stadium Group Plc., IT Department - Tel: +44 (0)1429 266544
>###########################################################################
>##########
>
>---------------------------------------------------------------------------
>------
>Technet Mail List provided as a free service by IPC using LISTSERV 1.8d
>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 delivery of Technet send the following message: SET
>Technet NOMAIL
>Search previous postings at: www.ipc.org > On-Line Resources & Databases >
>E-mail 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 1.8d
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 delivery of Technet send the following message: SET Technet NOMAIL
Search previous postings at: www.ipc.org > On-Line Resources & Databases > E-mail 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
---------------------------------------------------------------------------------
|
