Hi Anna,
This is obvious case of mis-handling.
Even application of strain relief (at flex-rigid intersection) being step in
the right direction, there are other locations I can see where the flex will
tear due to mis-handling
1) Most imp is training personal in handling flex.....we have seen this at a
few customers who start using flex...training personal is the biggest help.
One of our customers uses a lot of flex that bend into tight spaces (twists
and turns invloved)....they have training for handling each flex assy.
2) making the flex a bit thicker also helps....e.g. use 2 mil thick kapton
instead of 1 mil...use coverlayer on both sides instead of 1 side.. In my
opinion, when flex is 8 mils of thicker, tendency to tear is greatly reduced.
We have a few customers that donot use strain-relief because they want tight
bend radius (strain relief gets in the way)
Rush
Accurate Engg Inc
_www.accueng.com_ (http://www.accueng.com)
In a message dated 2/22/2007 11:22:03 AM Pacific Standard Time,
[log in to unmask] writes:
Hi Anna!
I've got your pictures posted. Go to:
http://stevezeva.homestead.com/files/FlexBroken.JPG
http://stevezeva.homestead.com/files/FlexBroken2.JPG
Yep, it sure looks like to me that you stand a real good chance of
ripping the flex when you depanel it. I don't see a bead of epoxy for
strain relief at any of the flex-to-rigid junctions either. That makes a
TON of difference on how robust the assembly is to any sort of handling.
We build quite a few rigid-flex assemblies here, and almost all of them
use something like Eccobond 45 at the flex-to-rigid junctions...the fab
vendor does that of course. Here's one of the assemblies that we build
that shows the Eccobond fillets:
http://stevezeva.homestead.com/files/RigidFlexAssy.jpg
I can't remember when the last time was that we damaged a flex here...it
very rarely happens. We always keep the assemblies in their panel until
the last moment before we ship too.
The panel layout and break-away tab placement needs to be well thought
out as well. For instance, I don't know if I would have two break-away
tabs on that small piece of rigid board where the flex broke on your
assembly...you might get by with just one on the top edge since it's the
piece is so small. Eliminating one tab would reduce the chance of
tearing the flex by 50%.
I think your biggest improvement would be to fillet the flex-to-rigid
joints with Eccobond 45 or equivalent. Yes it will increase the board
cost, but it's worth it...
-Steve Gregory-
-----Original Message-----
From: Anna Seredovaya [mailto:[log in to unmask]]
Sent: Thursday, February 22, 2007 8:38 AM
To: Steve Gregory
Subject: FW: [TN] Disconnections in transition zone in rigid-flex boards
Thank for you answer.
I guess it happens during nesting separation and removing the board from
a panel. There are some photos attachted.
Thanks'
Anna Seredovaya
Kodak IL Ltd.
-----Original Message-----
From: Stadem, Richard D. [mailto:[log in to unmask]]
Sent: Thursday, February 22, 2007 1:08 PM
To: TechNet E-Mail Forum; Anna Seredovaya
Cc: Steve Gregory
Subject: RE: [TN] Disconnections in transition zone in rigid-flex boards
We need more information. What is the assembly process where you suspect
the opens are happening? If you have a picture of the assembly it may be
helpful. Steve Gregory posts pictures on his website for Technet
viewing. Send the picture to him at [log in to unmask]
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Anna Seredovaya
Sent: Thursday, February 22, 2007 5:55 AM
To: [log in to unmask]
Subject: [TN] Disconnections in transition zone in rigid-flex boards
Hello Techneters,
We have some boards disconnected in transition zone: between rigid and
flex segments. This happens during an assembly process. What is
recommended to add to manufacture process in order to strengthen the
area.
Thank you,
Anna Seredovaya
Kodak IL Ltd.
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