We have seen this exact phenomenon (as depicted in pics 2, 3 and 4, though not as acute as the one depicted in pic 1) on thermally challenging LF BGA board. The culprit is a combination of too little flux in the solder deposit (due to the deposit size) and too long soak. The little flux that's in the deposit burns off during the soak and the oxide layer on the solder sphere does not allow them to coalesce and dissolve in the bulk solder. In our case we could minimize it by reducing the soak on the profile
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Parsons
Sent: Thursday, April 23, 2009 2:16 PM
To: [log in to unmask]
Subject: [TN] Solder Ball Problem
I am trying to get to the root of a little solder ball problem. The problem
is specific to a single part and was evident on the first run of this board
a few months ago. We are seeing it again on this run although the common
denominator here is that the PCB's are all from the same production batch.
It appears that the formation of solder balls can be reduced by pre-baking
the PCB's (100°C for 4-8 hrs) but not eliminated. The best results are
obtained by pre-conditioning the PCB's by running them through the reflow
oven first, letting them cool, then print, populate and re-flow. The
majority of balls now formed are dealt with at wash.
The PCB's are simple double sided, HASL finish. I suspect a problem with
the solder finish (HASL) but what exactly that "problem" is I am not sure.
FYI, paste is water soluble.
http://stevezeva.homestead.com/files/Solder_ball_1.jpg - this photo is of a
board that was pre-baked for about 4 hours @ 100°C, it was then printed and
re-flowed. It does not matter if the 4 hour bake improved things you can
see that the results are pretty spectacular.
The following pictures are really more of the same except that these boards
have been populated and washed.
http://stevezeva.homestead.com/files/Solder_ball_2.jpg
http://stevezeva.homestead.com/files/Solder_ball_3.jpg
http://stevezeva.homestead.com/files/Solder_ball_4.jpg
Any insight would be appreciated.
(thanks to Steve for hosting the photos)
Regards
John Parsons
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
WARNING: Export Control
This document may contain technical data within the definition of the
International Traffic in Arms Regulations (ITAR), and subject to the Export
Control Laws of the U.S. Government. Transfer of such data by any means to a
foreign person, whether in the United States or abroad, without proper export
authorization or other approval from the U.S. Department of State is
prohibited.
CONFIDENTIALITY NOTICE:
This e-mail, and any attachments, is for the sole use of the intended
recipient(s) and may contain information that is confidential and
protected from disclosure under the law. Any unauthorized review, use,
disclosure, or distribution is prohibited. If you are not the intended
recipient, please contact the sender by reply e-mail, and delete/destroy
all copies of the original message and attachments.
Thank you.
---------------------------------------------------
Technet Mail List provided as a service by IPC using LISTSERV 15.0
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/contentpage.asp?Pageid=4.3.16 for additional information, or contact Keach Sasamori at [log in to unmask] or 847-615-7100 ext.2815
-----------------------------------------------------
|
