Steve,

I would still be concerned about moisture absorption. Polyimide is known 
for it's moisture absorbtion. The moisture content could affect the 
electrical performance of the assembly, specifically at the time of 
applying the power. Furthermore, the components will also be affected in 
a similar way. I believe if the assembly is properly stored, eg. in 
sealed wrap, and/or, controlled environment, you would have a better 
chance at meeting the long term storage requirement, and still be able 
to sleep at night.

Gary

Steve Kelly wrote:
> 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
> 
> [log in to unmask]
> 
> cc
> 
> 
> 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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