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December 2009

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Subject:
From:
Joe Fjelstad <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, [log in to unmask]
Date:
Tue, 22 Dec 2009 13:03:17 -0500
Content-Type:
text/plain
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Hi Steve
 
Thanks for the clearer picture. I was pondering off line about the benefits 
 of making it a rigid-flex. Why not do so at both ends? Seems that the  
prospective benefits are evident in your current findings. 
 
That aside, the cycling is pretty radical. Where on (or off) earth can this 
 be duplicated and what hurdle, in terms of numbers of cycles must be  
cleared to claim success? If there are to be components soldered on this, I  
would fret for their future under such conditions.
 
Best wishes, 
Joe  
 
 
 
In a message dated 12/22/2009 9:51:09 A.M. Pacific Standard Time,  
[log in to unmask] writes:

Hi  Joe,
3 pieces of AP 8525 - DuPont. Bondply - polyimide adhesive 35  micron,
apical- 12 micron, polyimide adhesive- 15 micron. Cracks start in  the 15
micron polyimide adhesive- no total failures yet - drill size 10  mils -
aspect ratio - nothing special. About 200 vias per part.   Thermal - +200c-
-60C as fast as they can cycle the chamber. This is one  end of the flex -
the other end is a rigid flex - same flex build then  added 2 layers of
polyimide rigid either side - this end shows none of the  cracking so I
assume somehow the GI is stopping the polyimide adhesive from  expanding as
much. Regards Steve

-----Original Message-----
From:  TechNet [mailto:[log in to unmask]] On Behalf Of Joe Fjelstad
Sent:  December-22-09 11:58 AM
To: [log in to unmask]
Subject: Re: [TN] Via fill  on flex

Hi Steve

Are all vias impacted or just some? If the  latter, any common  
characteristics? (i.e aspect ratio, stack up,  location in stack, etc.) For
shared 
edification, what are the materials  in the set and  what are the cycling 
conditions and requirements? (at  least so we can all  get a sense of what
kind of 
unreasonable  requirements might be out there looming  on the horizon) 

Season's  best, 
Joe






In a message dated 12/22/2009 8:26:57  A.M. Pacific Standard Time,  
[log in to unmask]  writes:

Hi  All,

We have a 6 layer flex that my customer  has to thermal cycle at  
temperatures beyond the rated Tg's of the  material- the end use environment
is  about 
as bad as it gets.  After repeated thermal cycles we start to see cracks  
develop in the  glue layer used to bond the adhesiveless layers together.
Will   
some kind of via fill help this issue?

Thanks in   advance.

Regards 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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