We wrap all of our boards with base of anti-static bubble pack and then
seal with a 250um anti-static polythene cover layer, performed in a heat
shrinking vacuum unit. All packs contain a gel type desiccant pouch. We
use the process to simply transport and contain the packs, but don't
rely on the pack to maintain vacuum, as it is subject to movement within
a box, handling etc etc.
Colin McVean M.Inst.C.T.
Production Manager
Artetch Circuits Limited
Main: 01903 725365
DD: 01903 712926
Email: [log in to unmask]
www.artetch.co.uk
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kane, Amol (349)
Sent: 19 May 2006 12:24
To: [log in to unmask]
Subject: Re: [TN] Question about ENIG and other surface finishing
A question - While reading thru this article I came across the following
line "shrink-wrapped in a
special low-outgassing wrap that seals the air out of the package, along
with a dessi-pak."
If the package is vacuum sealed, I think the desi pack will be of no use
as any ingress of moisture into the shrink wrap from an area away from
the desi pack will never reach the desi pack (as the remaining bag area
will be sealed shut). Even if there is some moisture remaining in the
sealed bag during sealing, same would be the case there also. We receive
boards this way and I have always wondered if this was the right way to
do this versus putting the boards in a MBB (with silver saver if needed)
and just sealing them with the correct amount of desiccant in units in
the bags.
Any diverse opinions about this??....would be interested to hear what
others think about this
Amol Kane
M.S (Industrial Eng.)
Process Engineer
Harvard Custom Manufacturing
941 Route 38 Owego, NY 13827
Phone: (607) 687-7669 x349
[log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard
D.
Sent: Tuesday, May 16, 2006 12:17 PM
To: [log in to unmask]
Subject: Re: [TN] Question about ENIG and other surface finishing
Yes, it depends...
To use ENIG instead of immersion silver finish as a means of mitigating
storage issues is a bad reason to switch, unless there are other
compelling reasons, such as having a storage environment with a high
chlorine content (sea salts) or other contaminants in the air that can
potentially react with the immersion silver finish on the pwb's.
Potentially, the ENIG is going to cause you a lot more problems than any
issues with storage and tarnishing of immersion silver boards ever will.
If you choose to solder to ENIG, you are soldering to nickel, not gold
as many think. The gold is absorbed into the solder and you form your
solder joints to the nickel underneath.
However, soldering to nickel is much more difficult than soldering to
the copper traces and pads on an immersion silver board, where the
silver is absorbed into the solder joint and you form your solder joint
directly with copper, which can be dissolved into the intermetallic
formation with the tin/lead solder alloy (or just tin in the case of a
Pb-free process) much easier than with nickel.
The solder joint formed with the nickel is inherently much more brittle
than one formed with copper, and is not as strong.
That is if the ENIG is plated properly. If it is not done properly,
which it often (still) isn't, then you will really regret ever
switching.
Packaging of immersion silver boards should be done with silver saver
paper between each board, and the entire brick is shrink-wrapped in a
special low-outgassing wrap that seals the air out of the package, along
with a dessi-pak. In a previous life, I had immersion silver solder
coupon boards that sat under my desk for 5 years exposed to the air. We
needed some working scrap assemblies for test set-up. Even though the
boards were somewhat discolored (slightly tarnished) they soldered right
up, and have been in use for three years as calibration units without
any failures. But there is very little sea salt in Minnesota air, and
most factories control their air quality very well.
If you do choose to change your finish, qualify the process before you
jump into changing them over. I would suggest performing an evaluation
using a small quantity of immersion silver boards and a small quantity
of ENIG, and then running durability studies that include thermal
cycling and perhaps some type of shock or stress testing.
Werner can provide more information on the appropriate types of testing
than I can.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Roger Stoops
Sent: Tuesday, May 16, 2006 9:34 AM
To: [log in to unmask]
Subject: Re: [TN] Question about ENIG and other surface finishing
I just received a question from someone inside my organization asking
about why not use ENIG instead of Iag because of storage issues...
Doing a quick Internet search took me to a paper at
http://www.mse.uiuc.edu/Faculty/Shang/Preprints/1997-2006/JMR00-pilin.pd
f#search='tin%20nickel%20intermetallic%20strength'
discussing "a comparative fatigue study of solder/electroless-nickel and
solder/copper interfaces." It's dated from 2000 and does not include
any study using Pb-free solders. Final thought is that Sn-Ni SJs do not
behave well under high stress environments after aging.
Found a few others, Daan's website was also very helpful, but time does
not permit further discussion.
We have used ENIG, Iag, HASL, Pb-free HAL, and it seems our choices (as
far as I have anything to say about it) will likely be Iag and Pb-free
HAL, due to our operating environment and quality requirements.
So, should one use ENIG instead of other SFs? In the now immortal words
of (can't remember who, sorry), "It Depends"...
Roger
-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Monday, May 15, 2006 4:50 PM
Subject: Re: Question about ENIG and other surface finishing
Good points, George.
Trouble is, in order for the temperature under a large BGA to reach 220C
for any duration, the rest of the component leads on the assembly will
be close to what? 235C? Not a good process for some components.
The problem with the logic that the ENIG will work better at higher
reflow temperatures seen with Pb-free processes is this:
The plating issues that cause the nickel oxide formation during the
immersion gold step (related to the phosphorus content, amongst other
variables) are exacerbated by subsequent temperature excursions. If the
plating is properly done, then yes, perhaps the IMF formed to nickel
will be more easily accomplished. However, if NOT done properly, the
higher temperatures will make the Black Pad and other nickel plating
process-related problems much, much worse.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of George Milad
Sent: Monday, May 15, 2006 2:15 PM
To: [log in to unmask]
Subject: Re: [TN] Question about ENIG and other surface finishing
I believe one of the key issues in assembling ENIG parts is that the
inter-metallic formed is a Ni/Sn. Ni/Sn inter-metallic requires higher
peak assembly temperature and a longer dwell at peak temperature. The
right re-flow temperature profile is a must.
The recommendation of ENIG assembly is 220 C for 20 seconds.
Some of the failures with ENIG may be attributed to colder assembly
temperatures.
The transition to Pb-Free should favor ENIG as the assembly temperature
for Pb-Free is going to be higher and the Ni/Sn inter-metallic will
always be formed successfully.
Best regards
George Milad
[log in to unmask]
National Accounts Manager for Technology Uyemura International
Corporation Technical Center 240 Town LIne Rd Southington CT 06489
(516) 901 3874 (mobile)
(860) 793-4011 (office)
(860) 793-4020 (fax)
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