Hi Bob - yes, we have experience with VCI materials, vapor barrier bags,
and "silver saver" type materials. All of these materials work very well
in the disruption of the oxidation process (yes, the 18-24 months is a
reasonable statement). However, that is only part of the recipe that will
cause a tin coated copper sheet to lose it solderability. None of those
materials inhibit the diffusion of the copper and tin metals. Once a
copper/tin intermetallic has formed and that intermetallic phase can be
oxidized, then you lose solderability. The thicker the tin plating, the
longer it takes for intermetallic phase to be present on the surface and
be oxidized. However, there are practical limits on how much tin can be
deposited and retain its expected properties. A rough order rule of thumb
is that 40 uinches of immersion tin will provide a printed wiring board 12
months of shelf life when stored in an office environment. Good Luck.
Dave
bob wettermann <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/14/2009 12:13 PM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
bob wettermann <[log in to unmask]>
To
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cc
Subject
Re: [TN] Storing of Copper Sheets
Dear Technettters:
Thanks for your previous grim assessment of the possibility of extending
the shelf life of the tin-coated copper sheets.
Since then we have discovered that there may be several commercial
products-namely corrosion inhibiting bags and papers, that could help in
this particular circumstance. Their chemistry allegedly "coats" and
"protects" the surface of the metals to inhibit rust and oxidation.
The recommendation from several
corrosion barrier bag companies is to place several of the approx 1mil
tin-coated
(at some point it may be soldered to) sheets into a specially-formulated
PE bag. This bag through volatilization and
contact will protect the sheets against rust, oxidation. Allegedly it
inhibits corrosion as well
as oil, water and moisture. The manufacturers are telling us
that one can expect efficacy of 18-24 months after heat sealing each bag
which
could contain no more than 50mm thick in materials. Some manufacturers
suggested
interleaving similar "saver papers" every 3-5 sheets. They will be stored
in a
temperature-controlled approximately 68-72F low humidity level
environment.
Does anyone have experience with some of these products? Do we believe
what we are being told?
Regards
Bob Wettermann
PH 847-767-5745
--- On Thu, 12/10/09, Douglas Pauls <[log in to unmask]> wrote:
From: Douglas Pauls <[log in to unmask]>
Subject: Re: [TN] Storing of Copper Sheets
To: [log in to unmask]
Date: Thursday, December 10, 2009, 10:55 AM
Nope, been a resident of Deweyville for many years now. Been thinkin' of
runnin' fer mayor next year.......
Doug Pauls
Steven Creswick <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/10/2009 10:06 AM
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Subject
Re: [TN] Storing of Copper Sheets
Doug,
You are treading into Dewey's territory now... :-)
Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Douglas Pauls
Sent: Thursday, December 10, 2009 9:16 AM
To: [log in to unmask]
Subject: Re: [TN] Storing of Copper Sheets
Though one would have to ponder if this would lead to cold solder
joints......
Doug Pauls
"David D. Hillman" <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/10/2009 07:33 AM
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Re: [TN] Storing of Copper Sheets
Hi Steve! Not off the top of my heat. I am pretty sure I have the
activation energy in my database somewhere but it would take some time to
dig it out. As Syed pointed out, there is going to be a diffusion limit or
at least a practical limit point where which would make freezing copper
sheets an action worth taking.
Dave
Steven Creswick <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/09/2009 07:24 PM
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Re: [TN] Storing of Copper Sheets
Dave,
Any idea what the average net activation energy might be??
Steve C
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Syed Ahmad
Sent: Wednesday, December 09, 2009 6:53 AM
To: [log in to unmask]
Subject: Re: [TN] Storing of Copper Sheets
Depends upon activation energy?!
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, December 08, 2009 4:59 PM
To: [log in to unmask]
Subject: Re: [TN] Storing of Copper Sheets
Yes, freezing would extent the time some length but I don't know
specifically how long without running the numbers thru the diffusion
equation.
Dave
"John Burke" <[log in to unmask]>
12/08/2009 04:55 PM
To
<[log in to unmask]>
cc
"'TechNet E-Mail Forum'" <[log in to unmask]>
Subject
RE: [TN] Storing of Copper Sheets
But will push the time frame out right?
John Burke
(408) 515 4992
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Tuesday, December 08, 2009 2:51 PM
To: John Burke
Cc: 'TechNet E-Mail Forum'
Subject: RE: [TN] Storing of Copper Sheets
Hi John - yes, if that deep freeze is in liquid nitrogen - otherwise
diffusion is still going to progress on its merry way to the same end
result. Standard freezing temperatures will not slow down the diffusion
process enough to prevent degradation.
Dave
"John Burke" <[log in to unmask]>
12/08/2009 04:48 PM
To
"'TechNet E-Mail Forum'" <[log in to unmask]>, <[log in to unmask]>
cc
Subject
RE: [TN] Storing of Copper Sheets
Unless of course he stores them in the deep freeze........
John Burke
(408) 515 4992
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, December 08, 2009 2:40 PM
To: [log in to unmask]
Subject: Re: [TN] Storing of Copper Sheets
Hi Bob - unfortunately you are going to lose the solderability of those
sheets somewhere in the 6-12 month time frame depending on which immersion
tin formulation you are using and due to diffusion issues will lose the
solderability of the sheets on a permanent basis somewhere in the 12-24
month time frame depending on the thickness of the immersion tin plating.
You may be able to "reactive" the surface for some other operation but you
will need to somehow make sure the surfaces to not passivate (aka oxidize)
preventing the next process operation. My recommendation is talk to your
favorite plating supplier. Good Luck.
Dave Hillman
Rockwell Collins
[log in to unmask]
bob wettermann <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>
12/08/2009 11:11 AM
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[TN] Storing of Copper Sheets
Dear Technetters:
If you planned on storing 10z copper sheets with a bright immersion tin
coating for several years in 24 x 24" sheets-how would you do it?
We have several internal opinions from interleaving of saver paper to
moisture barrier bags to other types of bags.
Thanks!
Bob Wettermann
PH 847-767-5745
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