Ioan,
While happier people than me and you are able to joke about this, I am not
at all.
We lost thousands of dollars because of this issue, and tried both the epoxy
and the permanent kapton stencil.
http://www.all-spec.com/1/viewitem/650-101/ALLSPEC/prodinfo/i=rss
Both can work on one condition:
If you can spot all the bad solder mask areas and aquire an excellent
adhesion between the applied material and the -sometimes very short
conductor between the BGA pad and the through hole.
It is important to clean thoroughly these conductors of solder, but it is a
sisific work.
If the through holes are solder filled or coated after pad surface
preparation the chances of success are smaller.
The solder on and in the holes reflows and the epoxy fill will float on
them, allowing new solder to seep through.
Applying the epoxy by non trained operators can result in a height
difference on the surface of the circuit which alters the paste deposition
through the ministencil and may lead to shorts after reflow.
Epoxy may bleed on solder pads too and you get opens.
I don't want to tell you how many X-rays I performed on such repairs.
You are right, reworking Lead free BGA's was even harder.
It was interesting for me to see that not all the circuits were badly
damaged during BGA removal and rework, and the difference was made by the
circuit manufacturer and/or the circuit design.
If hole plugging was required and done correctly , the chances of solder
flow were drastically diminished, and the loss of solder on the small
conductors was almost not important for reliability.
After rework we always check it by X-ray.
Sometimes , minor solder flow outside the pads causes smaller ball image
seen from above, but if you see a hourglass shape by tilting, you still may
have a connection.
My 2 cents.....
Good luck,
Gaby
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ioan Tempea
Sent: Friday, February 20, 2009 3:47 PM
To: [log in to unmask]
Subject: [TN] Repair soldermask
Hello Technos,
What kind of soldermask do you use for repair jobs under BGAs? You know, the
original SM goes away when wicking the pads after BGA removal and we need to
cover the vias back. And I'm talking lead-free.
Thank you,
Ioan Tempea, ing.
Ingénieur Principal Fabrication / Sr. Manufacturing Engineer
30 ans déjà! - Already 30 years!
950 rue Bergar, Laval, Québec, H7L 5A1
t : 450-967-7100 ext : 244
Mtl : 514-990-5762
f : 450-967-7444
[log in to unmask]
www.digico.cc <http://www.digico.cc/>
P N'imprimer que si nécessaire - Print only if you must
---------------------------------------------------
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
-----------------------------------------------------
---------------------------------------------------
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
-----------------------------------------------------
|
