________________________________
From: Stadem, Richard D.
Sent: Monday, August 25, 2008 4:10 PM
To: 'Paul Edwards'
Subject: RE: [TN] ENIG White paper
No. Again you should print a very small amount of solder paste on the
top and bottom annular rings. It will flow down inside the barrel and
provide good electrical contact to the hardware assembled later. You do
not need to have the stencil aperture be a full ring connected by two
spokes, it can be any size you need to get enough solder on the ring and
down onto the hole wall without filling it or reducing the size of the
hole such that the hardware does not fit. I use a C-shaped aperture in
the design library for this purpose. You should always use a Bellville
washer and a star washer to ensure continued electrical contact. Our
standard lug termination is a stainless steel screw, through the
Bellville washer, through the star washer, through the lug terminal,
through the PWB, through a flat washer and into a nylock nut with a
torque callout. We have never had a failed ground connection using this
configuration. On some configurations we use a Bellville washer on both
sides of the PWB.
________________________________
From: Paul Edwards [mailto:[log in to unmask]]
Sent: Monday, August 25, 2008 2:48 PM
To: Stadem, Richard D.
Subject: RE: [TN] ENIG White paper
No problem with reliable ground connections through the mounting
holes???
Paul
Paul Edwards
Surface Art Engineering
________________________________
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Monday, August 25, 2008 12:37 PM
To: Paul Edwards
Subject: RE: [TN] ENIG White paper
Solder them. Some tarnish on unused pads is not a reliability issue, and
is certainly not a solderability issue if nothing is going to be
soldered there.
If you wish to keep SMT pads solderable for future use, simply include
those pads in your stencil artwork and print/reflow solder paste to
them.
Once soldered, the pads cannot tarnish.
________________________________
From: Paul Edwards [mailto:[log in to unmask]]
Sent: Monday, August 25, 2008 1:49 PM
To: TechNet E-Mail Forum; Stadem, Richard D.
Subject: RE: [TN] ENIG White paper
Richard,
How do you eliminate the Ag tarnishing on completed PCAs?
Paul
Paul Edwards
Surface Art Engineering
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Monday, August 25, 2008 6:25 AM
To: [log in to unmask]
Subject: Re: [TN] ENIG White paper
Dave,
You write as if you are not at all familiar with IAg, which is totally
understandable. However, IAg has been around in full production mode for
many years now, and is rapidly becoming the most-used finish in the
market. Do not confuse it with immersion tin finish, which has little or
no shelf life.
IAg-finished circuit boards have a recommended shelf or storage life of
about 1 year. However, if packaged properly in a hermetically sealed bag
with silver saver paper liners, and stored away from sulfates, it is
possible to use boards up to 5 years old or even longer with no issues
whatsoever. All you need to do is call out the packaging on the
fabrication drawing per IPC 4553.
I have soldered IAg boards that sat around exposed to the elements for
more than 4 years in previous lives, and they soldered up just fine, no
change in the DPMO.
Some of the bare boards we use here at GD are 34" by 40", 48 layers,
1/2" thick, cost is about $48,000 each. Their finish is IAg.
I have had a lot of experience with IAg over the past 10 years or so,
having seen at least 150,000 IAg boards assembled and soldered with
every type of component you can think of, and I have never experienced
any issues with them. I have experienced many, many issues with ENIG,
however, and that is the finish that would keep me up at night waiting
for the bomb to go off. There are many reliability issues associated
with ENIG such as black pad, brittle nickel, etc., etc, but just think
about the fact that you are soldering to nickel, which has a dissolution
rate about 50 times slower than copper.
Should you ever have a solderability issue with IAg, you can have the
fabricator rework the finish. If you have an issue with ENIG, the only
thing you can do is rework your scrap account.
However, you need to take the end-use environment into consideration
when you select a circuit board finish. ENIG (unfortunately) may be your
best choice. I would fully qualify just one assembly at a time, and I
would fully qualify it. For Space use, I would not suggest IAg.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dave Connitt
Sent: Thursday, August 21, 2008 3:22 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG White paper
Hi Werner,
Well, we seem to like to buy all the circuit boards for a production run
at one time which could be thousands and I worry about the special
handling. Some of the boards could end up being in stores for 9-12
months. We also have to do pretty comprehensive incoming inspection
which would keep me up at night wondering if the bare boards are being
handled (or not handled) correctly.. Setting of a time bomb of bad
boards.
Dave Connitt
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Thursday, August 21, 2008 3:10 PM
To: [log in to unmask]
Subject: Re: [TN] ENIG White paper
Hi Dave,
Why ENIG? Have you considered imAg?
Werner
Future workshops:
Reliability Issues with Lead-Free Soldering Processes, September 22,
Schaumburg Failure Mode and Root Cause Analyses Reliability (Fatigue,
Brittle Fracture, ENIG), September 22, Schaumburg Solder Joint
Reliability: Parts 1 & 4, Oct. 9, Moscow, Russia Solder Joint
Reliability: Part 4, Oct. 17, Timisoara, Rumania Solder Joint
Reliability: Parts 1 & 4, Oct. 22, Tallinn, Estonia
**************
It's only a deal if it's where you want to go. Find your travel deal
here.
(http://information.travel.aol.com/deals?ncid=aoltrv00050000000047)
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