Dave,
Yes, that is what piqued my curiosity – just where that temp threshold would
be….
In the microelectronics arena it is not uncommon to have ready access to
-40°C [and even -80°C] freezers. Academically, I was curious if the more
mundane temps such as -40 or -80°C were even low enough to reasonably quench
the diffusion process to a reasonable extent. Was curious to plug the
activation energy into the Arrhenius equation I use for wire bond time/temp
equivalencies – just for grins of course, and see what came out.
Now then, if liquid nitrogen temps [or colder] were required to suppress the
diffusion process to a reasonable degree, that would not be considered too
practical from my point of view.
Hey! I’m watching the winds howl outside. Have had whiteout conditions all
morning. Needed something to stimulate the mind other than hot chocolate!
Steve C – free spirit!
From: [log in to unmask] [mailto:[log in to unmask]]
Sent: Thursday, December 10, 2009 8:34 AM
To: TechNet E-Mail Forum; Steven Creswick
Subject: 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
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steven Creswick <[log in to unmask]>
To
[log in to unmask]
cc
Subject
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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<[log in to unmask]>
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Subject
[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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