Paul,

I'm Speaking from the other side of the fence ie a device manufacturer.

Our standard package for optical sensors is CLCC (either 48 or 36). We make
millions a year and as far as I know wwe haven't heard of this kind of
failure for our users. Certainly none of them do anything of the sort you
suggest. many of our customers are Far Eastern contract manufacturers who
will employ 'plain vanilla' assembly techniques.

If you do have flux trapped under the device you may be getting shorting
between pads due to dendritic growth.

Regards,




-----Begin Included Message -----

Date: Tue, 20 Mar 2001 09:23:14 -0600
 From: Paul Baine <[log in to unmask]>
Subject: [TN] Solder flux under LCCs
To: [log in to unmask]



Hello.  This is the first time I have used IPC TechNet, so please forgive
me if this question has been asked before.

Our company has built some SEM Modules (Standard Electronic Modules) for a
customer who recently reported failures in the field with these Modules.
These types of Modules have Leadless Chip Carrier ICs with castellated
terminations on them.  The solder pads are underneath the IC packages.  As
part of the failure analysis performed by the customer, some of these LCCs
were removed, and they noticed an off-yellow coating on the bottom of the
LCCs which they feel is solder flux.  They theorize that the solder flux
has hardened over time and has become conductive.

Our Production Manager thinks that this problem is caused by the fact that
these LCCs sit flat on the substrate and therefore the solder flux gets
trapped under the LCC during reflow and cannot be cleaned out.  He proposes
two possible solutions:

 - put adhesive under the LCC

 - put a spacer under the LCC which is dissolvable in water (i.e. during
cleaning)

I was wondering if anyone had experienced a similar problem and knew of
an "industry standard" solution, or any solution.  Thank you in advance.

Best regards,


Paul Baine
Q.A. Manager
C-Tech Ltd., Cornwall, Ontario, Canada

----------------------------------------------------------------------------
-----
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
----------------------------------------------------------------------------
-----



---- End Included Message ----

Eric Christison

---------------------------------------------------------------------------------
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
---------------------------------------------------------------------------------