Peter,
I do not have experience on the Black Pad issue. My mentor was dealing
with Black Pad at the start of my career. Are the non-wetting pads dark
color? Are they rich in Carbon content? If yes, it may be the result of
high carbon concentration. It can be reworked by aggressive flux, high
heat and mechanical action to remove the carbon compound before exposing
the good nickel for soldering. Please see below on Black Pad:
Phosphorous enrichment is an indicator of black pad corrosion because
the nickel is depleted at the corrosion sites leaving that portion of
the plating phosphorous rich. Roger Jay & Alfred Kwong, "DEALING WITH
THE 'BLACK PAD DEFECT'-
A FAILURE ANALYST'S PERSPECTIVE" Solectron Corporation, September 2001.
-----Original Message-----
From: Miguel Vallejo [mailto:[log in to unmask]]
Sent: March 21, 2007 5:21 PM
To: 'TechNet E-Mail Forum'; Paymon Sani
Subject: RE: [TN] Solderability problems on through holes only.
Paymon,
Isn't this phosphor starvation what causes "black pad".
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Paymon Sani
Sent: Wednesday, March 21, 2007 2:02 PM
To: [log in to unmask]
Subject: Re: [TN] Solderability problems on through holes only.
Hello Peter,
I have not looked at the suspect assemblies. However, this defect can
occur when the Nickel under the gold is oxidized prior to the TH
component assembly process. The electroless nickel is not pure and it
contains 10 to 14 percent phosphorus by weight. The nichel-phosphorus is
a good diffusion barrier to avoid corrosion of the solderable surface.
If the phosphor content is low i.e. 3 to 5% by weight then the
solderable surface will oxidize by each reflow heat application. The
oxidize nickel will then prevent soldering to the surface. The link
below is a good read on the ENIG surface finish.
http://www.pfonline.com/articles/129901.html
The assemblies should be reworkable with aggressive water soluble
fluxes, some mechanical action and a suitable soldering iron tip
temperature.
Hope this helps,
Paymon
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Peter Wong
Sent: March 21, 2007 4:18 PM
To: [log in to unmask]
Subject: [TN] Solderability problems on through holes only.
Hi Technetters,
We are having a solderability problem confined to only through hole
locations where we need some help or advice.
We are soldering a no-clean SAC305 alloy to an ENIG finished board. All
SMT solder joints (both sides) are fine. During hand soldering in our
dedicated lead free area, we are having problems with solder wetting to
some of the annular rings and barrels of through hole locations, not all
holes. The assembly is an 0.062" thick 4 layer 1"x1" board so it is not
thermally challenging.
We've built thousands of these in the past without this particular
problem.
The time lag between smt and through hole assembly is 1-2 days.
We've tried using a more aggressive flux such as OA flux with no
improvement.
The only way that we can get solder to wet is to mechanically scrape the
annular rings with a pick.
Has anyone seen this before? Why would this only occur on some of the
through hole locations and not on smt pads?
We have isolated this to a specific lot code of boards and are waiting
for some advice from our board vendor as well.
Thanks
Peter
---------------------------------------------------
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
-----------------------------------------------------
------------------------------------------------------------------------
----
-----------
Confidentiality Notice
This e-mail and any attachment(s) are intended for the individual or
entity
to which this email is addressed and may contain information that is
confidential. If you are not the intended recipient or an employee or
agent
responsible for delivering this e-mail to the intended recipient, please
be
aware that any dissemination, distribution or copying of this
communication
is strictly prohibited. If you have received this in error, please
notify
the sender by telephone at 604.430.4336 or by return e-mail, and please
delete or destroy all copies of this communication. 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
-----------------------------------------------------
---------------------------------------------------------------------------------------
Confidentiality Notice
This e-mail and any attachment(s) are intended for the individual or entity to which this email is addressed and may contain information that is confidential. If you are not the intended recipient or an employee or agent responsible for delivering this e-mail to the intended recipient, please be aware that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this in error, please notify the sender by telephone at 604.430.4336 or by return e-mail, and please delete or destroy all copies of this communication. 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
-----------------------------------------------------
|
