Black pad is not caused by gold being too thin. Gold plating skips or
thicknesses less than 3-4 uinches causes other problems related to
nickel oxide barriers, but not BP.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Rick Smith
Sent: Wednesday, November 29, 2006 9:11 AM
To: [log in to unmask]
Subject: Re: [LF] black pad
Don't forget thin gold coverage problems which is a major issue with PCB
suppliers trying to save money on gold application. This can be
inspected with SEM/Backscatter method, but it is very hard to inspect
with the naked eye or even under magnification. XRF will tell you gold
is there & thickness, but not show the holes in the surface that are
typically found when suppliers scrimp.
Remember the gold is supposed to be only "flashed" on; thin enough to
keep the nickel from oxidizing because solder won't stick well to nickel
if it is oxidized. If the nickel is not covered on the PCB, then in
assembly solder joint integrity is adversely affected and we see more
black-pad.
Too much gold is the enemy, embrittling solder joints.
Gold boards also have limited reworkability because of the nickel.
The key is to select a board supplier that has good process controls and
the right equipment to verify gold coverage, and for the PCBA process
engineer to control the solder process effectively to limit rework.
my thoughts, sorry for rambling.
Rick Smith
Product Engineering
Celestica Aerospace Technologies Corporation
4616 West Howard Lane
Building One Suite 100
Austin, Texas 78728
Phone: 512-615-8591
"Wenger, George M." <[log in to unmask]> Sent by: Leadfree
<[log in to unmask]>
11/29/2006 06:56 AM
Please respond to
"(Leadfree Electronics Assembly Forum)" <[log in to unmask]>; Please
respond to "Wenger, George M." <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [LF] black pad
I think that the fear of brittle failures with ENIG surface finish stems
from the fact that there isn't a known root cause for the failure.
Unfortunately, it appears that this research report doesn't calm those
fears because the root cause is still unknown. I haven't read the
report but it appears from the information Wolf-Dieter provided that we
know exactly what we knew years ago:
1. ENIG Chemical Suppliers Provide Good Chemistry 2. Solder / Paste
Suppliers provide Good Solder 3. Assemblers Use Good Soldering Processes
4. Therefore the problem must be some inaccuracies of cleaning and
surface plating by some PCB fabricators.
Regards,
George
George M. Wenger
Senior Principle FMA / Reliability Engineer Wireless network Solutions
Andrew Corporation, 40 Technology Drive, Warren, NJ 07059 (908) 546-4531
[log in to unmask]
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of SCHMIDT,
WOLF-DIETER - PFHO
Sent: Wednesday, November 29, 2006 3:19 AM
To: [log in to unmask]
Subject: [LF] black pad
Hello Gaby,
a few weeks ago the research report on that topic, carried out by Andus
(PCB-manufacturer) and Fraunhofer Institute, was published. The result
based on technical analysis and a poll asking a lot of PCB manufacturer
as well as assembling companies showed that neither the type oc
chemistry (e.g. the chemistry supplier) nor the type of solder nor the
soldering process itself is the reason for black pad. The only remaining
root seems to be some inaccuracies during running the board production
process - mainly the chemistriy of cleaning and surface plating.
The same information I received two years ago from Eric de Kluizenaar
(ex Philips Eindhoven).
Best regards
Wolf-Dieter Schmidt
-----------------------------------------------------------
THALES Defence Deutschland GmbH
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Land & Joint Systems
Ostendstrasse 3
D-75175 Pforzheim - Germany
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Phone: +49 7231 15 3386
Fax: +49 7231 15 3390
mailto: [log in to unmask]
http://www.thalesgroup.com
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