Hi Joe,
Can't be built that way - has to have a slight bend at the flex end.
Components loaded both sides of the flex and both sides of the rigid- so far
they are passing with no issues. Regards Steve
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joe Fjelstad
Sent: December-22-09 1:03 PM
To: [log in to unmask]
Subject: Re: [TN] Via fill on flex
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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