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July 2009

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Subject:
From:
Steve Kelly <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Steve Kelly <[log in to unmask]>
Date:
Tue, 14 Jul 2009 17:12:28 -0400
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Hi Inge,
Thank you - good common sense. I can work with this. Regards Steve

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Inge
Sent: July-14-09 5:08 PM
To: [log in to unmask]
Subject: Re: [TN] Storage life for rigid flex

Steve,
I think there would be no problem with the storage in itself, however, what 
happens when the part is to be used after 20 years. It might depend, as a 
certain person use to say, parts are used differently. A part that is 
vibrating or is part of moving function will react to small changes more 
than a 'stiff' one. I have seen flexes with sharp bends delaminate after 
long use. On the other side, non movable and fixed flexes in e.g. cameras 
seem to live for ever. And finally an example from a copiator used in one of

our vehicles for 'desert' use. The machines had been half filled by sand, 
had been frequently  used and under awful conditions. There was absolutely 
no problem with the large flex that operates the head. So, PI is very tough.

The answer to your question is probably dependant of the application. 
Interesting case, I recognise your situation. Missiles, grenades and a lot 
of other mil stuff is often stored for many years, and are supposed to work 
instantly despite the long storage time. In such cases, there will be little

wear with operational time only seconds or minutes and hence no problems.  I

suppose you get  the best information from the PI manufacturers themselves. 
Would be surprised if someone at TN can give a real safe answer to  your q.
Good Luck. Who seekest will find.
/Inge


----- Original Message ----- 
From: "Steve Kelly" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, July 14, 2009 10:28 PM
Subject: Re: [TN] Storage life for rigid flex


Hi Dave and all,

1)The rigid flex would be assembled

2) I have read all of the multitude reports on kapton and airplanes and the 
problems. In my opinion the problems where associated with kapton wiring 
(wire wrapped with kapton) - never seen any major problems with a flexible 
printed circuit board anymore than a standard rigid board. Build it right 
like the people at Rockwell for example expect and it will last a long, long

time.

So I go back to my question is polyimide rigid better in long term storage 
conditions than a high end FR-4. The operative word is storage - a finished 
assembly never used sitting in some bunker in the desert or Arctic  that 20 
years from now has to turn on.



Regards Steve Kelly





From: [log in to unmask] [mailto:[log in to unmask]]
Sent: July-14-09 3:30 PM
To: TechNet E-Mail Forum; Steve Kelly
Cc: [log in to unmask]
Subject: Re: [TN] Storage life for rigid flex




Hi Steve - Wow, if you really are going to sit around for 20 years, I would 
make the pwb surface finish bare copper and apply an OSP treatment right 
before assembly. A good tin/lead finish might make 20 years self life but 
you are really on the edge. Good Luck.

Dave Hillman
Rockwell Collins
[log in to unmask]




Steve Kelly <[log in to unmask]>
Sent by: TechNet <[log in to unmask]>

07/14/2009 02:11 PM

Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
Steve Kelly <[log in to unmask]>

To

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Subject

[TN] Storage life for rigid flex








Good Afternoon,

We have a program for some reasonably simple rigid flex (4-8 layer) where 
the requirement is a 20 year life in storage conditions from -40C to +125C. 
Is there any evidence that polyimide rigid material and pre-pregs would be 
better than a good FR-4 (170C) for long term reliability. Thanks. Steve 
Kelly



Steve Kelly (PLEASE NOTE NEW E-MAIL ADDRESS)

(416) 750-8433 (work)

(416) 750-0016 (fax)

(416) 577-8433 (cell)




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