Sender: |
|
X-To: |
|
Date: |
Thu, 16 Dec 1999 21:53:48 EST |
Reply-To: |
|
Subject: |
|
MIME-Version: |
1.0 |
Content-Transfer-Encoding: |
7bit |
Content-Type: |
text/plain; charset="us-ascii" |
From: |
|
Parts/Attachments: |
|
|
In a message dated 12/16/99 6:25:30 PM Central Standard Time,
[log in to unmask] writes:
> Hi everyone ... I have been looking at solder joint failures for quite a
> while and have stumbled on something new to me. I hope someone has seen
> this and can give me some insights. Here it is ...
>
> * the failures occur on a number of different component types including
> SOICs, QFPs, SMT caps (not chip caps)
> * the failure is complete interfacial failure of the mounting pad at
> the copper/IMC interface (i.e the solder, Cu6Sn5 and Cu3Sn layers stay
> with the component lead)
> * the board finish was HASL and the IMC layer appears normal (i.e. ~
> 1-2 microns total thickness)
> * the copper is heavily oxidized. However, I believe this is because
> the crack existed for a long period of time (perhaps?)
> * I see no convincing evidence of contamination at the failed interface
>
> * the failure does not appear to be related to an electroplated copper
> interface
>
> Based on past experience, this type of thing seems to be caused by gross
> thermal shock!?! Have any of you seen the type of failure I have
> described? If so, what was the conclusion as to cause?
>
> Best regards,
> Ed Hare
> VP SEM Lab, Inc.
Hi Ed,
I'm just guessing a bit, but there maybe a problem with the design of the
boards. I've run acoss problems in the past (as many other technetters have)
that there are via's that have been laid-out very close to surface mount
pads, no thermals and very little trace length to a surface mount pad. During
wave soldering, they provide very good thermal transfer to re-reflow SMT
solder joints and actually cause the solder fillets to separate from the pads
with the fillets intact to the leads...one could inspect the joints under a
microscope and you wouldn't know there was a problem unless you actually put
some side-ways force to the leads and see that there was observed
movement...there maybe enough contact to pass ICT, but fail shortly...which
may explain the heavily oxidized copper...
Just guessing...
-Steve Gregory-
##############################################################
TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c
##############################################################
To subscribe/unsubscribe, send a message to [log in to unmask] with following text in
the body:
To subscribe: SUBSCRIBE TECHNET <your full name>
To unsubscribe: SIGNOFF TECHNET
##############################################################
Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional
information.
If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or
847-509-9700 ext.5365
##############################################################
|
|
|