With respect have we not done this subject to its full - we now digress from the forum's intent.
Chris
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Wenger, George M.
Sent: 10 December 2008 16:04
To: [log in to unmask]
Subject: Re: [LF] Pro's and Con's of using Immersion Silver
The differences I see are due to who we are and what we're
Dave,
The differences I see are due to who we are and what we're chartered to do. Werner is a consultant who is hired by clients who want someone to help them make the right decision. Although there are some customers are rather syphiscaated and want information so they can make an informed decision, many of the customers that are out there what to pay someone to make the right decision for them. I my case, I as well as all of my customers, who are typically RF designers, work for the same employer and what they want from me is a direction based on my years of experience doing FMA and Reliability and Quality analysis. We do have a few simple products that use ENIG and I would certainly not recommend to my customers to switch away from ENIG for those products or tried and tested PCB suppliers. However, if they need to change PCB suppliers for some reason or their product designs start to change and become very dense and incorporate fine pitch, BGAs, QFN's, that I have would, and do, steer them away from ENIG and on to the most trouble-free path, and that is ImAg.
Regards,
George
George M. Wenger
Andrew Wireless Solutions
Senior Principle FMA/Reliability Engineer
40 Technology Drive, Warren, NJ 07059
(908) 546-4531 (Office) (732) 309-8964 (cell)
[log in to unmask]
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Werner engelmaier
Sent: Wednesday, December 10, 2008 10:11 AM
To: [log in to unmask]
Subject: Re: [LF] Pro's and Con's of using Immersion Silver
Hi Dave,
As a consultant, I frequently have to give advice to people that are newbies--obviously, old hands at this do not need my advice. Thus, I need to steer them on the most trouble-free path, and that is ImAg.
Werner
-----Original Message-----
From: [log in to unmask]
To: (Leadfree Electronics Assembly Forum) <[log in to unmask]>; Werner engelmaier <[log in to unmask]>
Sent: Wed, 10 Dec 2008 8:59 am
Subject: Re: [LF] Pro's and Con's of using Immersion Silver
Hi Werner - the only area we differ
would be that I would not advise a design team to not use ENIG - I would
give them the advantages and disadvantages of the ENIG finish, make sure
that they fully understood what could go wrong and what could go right,
and then let make their choice. We typically also spell out the other surface
finish possibilities at the same time so a design team can view the full
picture of surface finish opportunities. I am not a fan of ENIG (I am a
fan of Immersion silver which should bring a smile to George Wenger) but
I don't prescribe to steering a design team away from ENIG but instead
allow them to make the decision.
Dave
Werner engelmaier <[log in to unmask]>
Sent by: Leadfree <[log in to unmask]>
12/09/2008 05:10 PM
Please respond to
"(Leadfree Electronics Assembly Forum)" <[log in to unmask]>;
Please respond to
Werner engelmaier <[log in to unmask]>
To
Leadfree@IPC
.ORG
cc
Subject
Re: [LF] Pro's and Con's
of using Immersion Silver
Hi Dave,
So, where is our disagreement?
Werner
-----Original Message-----
From: [log in to unmask]
To: (Leadfree Electronics Assembly Forum) <[log in to unmask]>; Werner
engelmaier <[log in to unmask]>
Cc: [log in to unmask]
Sent: Tue, 9 Dec 2008 8:17 am
Subject: Re: [LF] Pro's and Con's of using Immersion Silver
Hi Werner! I respectfully disagree with
your overall surface finish summary. All surface finishes have their disadvantages/advantages
and just because a surface finish can be produced "bad" doesn't
mean it shouldn't be considered for use on a printed wiring design. If
I were to take the conservative approach, we probably wouldn't have used
HASL due to its inconsistency of thickness and solderability characteristics.
Precious metal embrittlement (aka gold, silver, palladium) occurs if the
plating is too thick and/or the soldering process is out of control - root
causes that can be corrected and prevented without eliminating the use
of a specific surface finish. I am a big fan of the immersion silver surface
finish and I typically recommend that design teams do not use ENIG because
of the possibility of black pad and the attributes of soldering to nickel
- but, we successfully use ENIG on a number of
product designs by working
with our board fabricators and enforcing specific process requirements.
All of the printed wiring board surface finishes should belong in a design
team's tool box and as technoweenies, we should provide the design teams
the complete picture of positives and
negatives for using a particular
surface finish in a product use environment.
As always, printed wiring board surface
finishes seems to be a great forum discussion topic.
Dave Hillman
Rockwell Collins
[log in to unmask]
Werner engelmaier <[log in to unmask]>
Sent by: Leadfree <[log in to unmask]>
12/08/2008 09:18 PM
Please respond to
"(Leadfree Electronics Assembly Forum)" <[log in to unmask]>;
Please respond to
Werner engelmaier <[log in to unmask]>
To
[log in to unmask]
cc
Subject
Re: [LF] Pro's and Con's
of using Immersion Silver
Hi Bob,
Wished things would be as easy as made out in those old reports--I think
the advice from this unnamed CALCE-person is pretty much on th
e mark, with
the exception of switching if ENIG works for you and you have a stable
supplier---if it works, keep it.
However, I would not advice a client without an or a good ENIG-history,
to use ENIG. Too many pit-falls.
A lot has been called 'Black Pad'---failures showing too much P at the
surface, failures showing too little or no P at the surface, failures showing
'hyper-galvanic corrosion' along the Ni-grain boundaries, failures showing
fully etched-out Ni grain boundaries all the way down and into the underlying
Cu, even failures showing brittle interfacial separation because of20solderability
issues.
Except for the last, all of these show Ni on the PCB-side and SnNi-IMC
on the solder joint side.
Too much Pat the surface can be result from too much co-plated P in the
Ni, but also because of too much Ni disolved in the solder-Sn leaving the
P behind; too little P is clearly a Ni-plating issue.
ImAg works just fine as long as you do not expose it to sulfur-containing
paper.
Gold has not "been successfully used for decades (before SMT)",
but has caused Au-embrittlement failures. These old PCBs would indeed be
serviceable, but only if the Au was washed off prior to soldering. The
change came with the self-limiting ImAu plating. Ag, if improperly stored,
can indeed tarnish. But ImAg is also different than electrolytic Ag-plating
and also prevents
Ag-embrittlement.
=0
A
-----Original Message-----
From: Bob Landman <[log in to unmask]>
To: [log in to unmask]
Sent: Sat, 6 Dec 2008 1:04 pm
Subject: Re: [LF] Pro's and Con's of using Immersion Silver
A person I know who works at CALCE (www.calce.org) has spent a lot of years
in
studying solder joint reliability. She told me the other day that
she thinks
that IAg is better than ENIG because ENIG has "black pad" problems
and I should
switch to IAg.
Here are several article on ENIG problems
http://circuitsassembly
.com/cms/content/view/5042/95/
According to George Milad and Gerard O'Brien of the IPC Plating Process
subcommittee, "Black pad is a low-level nickel corrosion defect formed
during
the immersion gold deposition step. It takes a compromised nickel surface
and
prolonged dwell in the immersion gold bath for it to occur." Black pad
is well
known to fabricators and EMS suppliers, and as Milad and O'Brien added,
the
subcommittee "was convinced that with g
ood definition and a proper
specification, the black pad phenomenon could be virtually eliminated."
-this is not a problem IF you have a decent board vendor. We have
never seen
black pad nor has our assembler except for one time (and that vendor is
no
longer in business).
The other problem is a weakness in the nickle coating as is described in
this
article
ht
tp://www.empf.org/empfasis/feb04/0204help.htm
When an ENIG surface finished PWB undergoes soldering, the solder must
adhere to
the underlying electroless nickel plate. This is because the immersion
gold is
so thin that all of the gold dissolves into the solder upon soldering.
The
solder bonds directly to the electroless nickel.
If that nickel surface is contaminated in some way, the resulting joint
will be
weak and the locus of failure will be just below the surface of the
nickel,
leaving both nickel and phosphorous (a normal constituent of electroless
nickel)
on both the pad and the failed solder joint surface.
The EDAX analysis of the failed solder joint showed the presence of nickel
at
both the fracture surface of the solder joi
nt and the pad from which the
solder
joint had lifted (see Figures 4-1 and 4-2) This is a positive indication
that
contaminated nickel was the cause of the failure.
Our assembler (who I have used for several decades) has not had a good
experience with IAg. A client gave them boards with silver saver
paper between
each board (SMT both sides). They ran half the boards (which ran fine)
then
sealed the rest in a dry seal bag. Six months later they ran the
rest of the
boards (tried to) and the results were terrible.
Gold has been successfully used for decades (before SMT). Tektronix and
HP both
used gold plated PCBs and they were serviceable decades later (when repairs
were 0A
needed). Silver in the ceramic terminal strips in Tektronix scopes
(I'm a
former Tek and HP Field Engineer) would tarnish and require cleaning to
be used.
If a board needs to be serviced or modified at some time in the future,
or the
runs of boards are not completed when the boards are delivered, I would
never
use IAg and that is why we use ENIG.
=0
ABob Landman, President
Senior Member, IEEE PES, Reliability Society
H&L Instruments
, LLC
Electro-Optics for Industry & Science
34 Post Road, PO Box 580
North Hampton, NH 03862-0580
(tel) 603-964-1818 (fax) 603-964-8881
www.hlinstruments.com
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