TECHNET Archives

December 1999

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:
"Stephen R. Gregory" <[log in to unmask]>
Reply To:
TechNet E-Mail Forum.
Date:
Thu, 16 Dec 1999 21:53:48 EST
Content-Type:
text/plain
Parts/Attachments:
text/plain (61 lines)
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
##############################################################

ATOM RSS1 RSS2