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June 2009

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Subject:
From:
John Burke <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Burke <[log in to unmask]>
Date:
Fri, 26 Jun 2009 08:53:37 -0700
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text/plain (156 lines)
Genny, I do not believe there is a "limit" to this but obviously you would
not want to keep doing it..... The numbers for storage normally quoted are
for "room temperature"

The formation of the intermetallic between your plated tin and the copper
will follow the general rule of an Arrhenius equation.

So if you intend to store for a long time and do not want to keep sending
them back I suggest that they be vacuum packed and put in a freezer, which
if you do the math will give you many years of "shelf life".

Kind regards,

John Burke
(408) 515 4992

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Friday, June 26, 2009 8:20 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Tin solderability eval

 One last question, then.  Is there a point of no return - or can they
always be refreshed by this process no matter how long the boards have
sat?


Genny 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Dorothy Lush
Sent: June 24, 2009 11:10 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Tin solderability eval

Genny,

I have customers that when their immersion tin PCB has sat so many
months on the shelf no matter how well it is stored it is sent back to
the PCB maker to be re-tinned/plated. It takes only one pad to ruin your
day. The smaller the pad the more likely a problem.

Dorothy Lush
Fine Pitch a Flextronics Company

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Whittaker, Dewey
(EHCOE)
Sent: Wednesday, June 24, 2009 9:43 AM
To: [log in to unmask]
Subject: Re: [TN] Immersion Tin solderability eval

Genny,
You have to go with the flow. Sometimes localized hand soldering will
give you a false positive. If you want to know whether to use them or
not, sacrifice a few and run them though all the subsequent processes
(especially thermal excursions) they would be exposed to in order to
establish an expected level of success. If you have to have an official
reason; test them per IPC J-STD-003 for solderability.
Dewey 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Wednesday, June 24, 2009 9:16 AM
To: [log in to unmask]
Subject: [TN] Immersion Tin solderability eval

We have some Immersion Tin boards that are several years old.  From
everything I have read here or elsewhere, ImmSn is supposed to have a
short shelf life.  6 mos to a year.  No one wants to scrap the boards
without testing them, though.  
How would you verify whether they are still good?  We hand-soldered some
pads and actually had no problems which surprised me, considering the
age of the boards, but I don't know if that is a valid test.

Genny 

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