There are no holes, its merely an etch and coverlay. Its simple traces going from one end to the other. I will speak with the fabricator about the direction.
Thanks
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly
Sent: Friday, May 15, 2009 6:17 AM
To: [log in to unmask]
Subject: Re: [TN] FLEX question
Hi John,
If the part was built as a pattern plate versus a button or selective plate it will most likely fail. If copper is plated on the top of the tracks you now have approx. .0014 of RA copper with probably about .0007 - .001 of plated copper on top AP 9121 should be specified as AP 9121R for rolled annealed. Good luck. Steve Kelly
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of John Foster
Sent: May-14-09 10:08 PM
To: [log in to unmask]
Subject: Re: [TN] FLEX question
Hi Werner
1. When I looked up pyralux AP-9121 it said it was a 2 mil core 1/1.
2. This should be the normal bend radius. I have to look into the mechanical situation
More tomorrow. That’s one reason I am concerned about the number of installs and deinstalls. I have had people fold flexs in half and then wonder why they break.
3. The fracture seems to be about halfway down the middle of the flexed leg.
4. That’s why I brought up the 17 mil traces they have not fractured.
5. When I saw the datasheet from Dupont it said the material came in both electro depostited and rolled annealed copper. However I typed in AP-9121 on the internet and
The dupont pyralux material came up which claims to be annealed. However all the fabricator told me is that they used AP-9121 is this like calling out FR-4 in the rigid world. Is Ap-9121 a Dupont name or could the material have come from many different laminate suppliers?
Thanks
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Werner Engelmaier /*
Sent: Thursday, May 14, 2009 6:29 PM
To: [log in to unmask]
Subject: Re: [TN] FLEX question
Hi John,
Unfortunately, you do not give us an adequate picture of the situation.
Missing:
1) 2-mil core thickness, the critical dimension is 1/2 of core plus 2x1.4 mils=2.4 mils [not exactly small];
2) bend radius, approximately .35 inches could be an average with minimum much smaller depending on who and how the bend is made;
3) fracture location is not clear, open is about in the middle of the flexible section—does that mean half-way between the stiffener and the connector?
4) any cracks in the 17-mil wide traces?
5) While you say the CU is rolled annealed, have you confirmed the anealing—if not annealed the ductility in the rolling direction will be significantly larger than X-rolling direction—you can tell be etched x-sections showing needle-like grains in the rolling direction;
Obvious:
1) Crack propagation being roughly equal, the 8-mil trace will show an open first;
2) if not fully annealed, rolled Cu direction should be along flexed leg.
Werner
-----Original Message-----
From: John Foster <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, 14 May 2009 8:52 pm
Subject: [TN] FLEX question
I was hoping I could get some input on a problem we are having with a
flex circuit.
I have a 2 layer flex circuit that is shaped like a L. one leg is about
5 inches long the other leg is about 4 inches long
At the corner of the L is a stiffener on both sides. The stiffener
extends into both L sections a very small amount about=2
0.3 inches.
Both ends of the flex have Omnetics connectors which are designed to be
soldered onto flex circuits. The A28300 series. Some of the traces are
17 mils wide and some are 8 mils wide. The traces are spaced fairly
evenly across the flex and are spaced like the omnetics connector which
means you can't see through the circuit as the traces overlap from side
to side. One section of the L flexs the other section is stationary.
The bend radius for the flexible section is approximately .35 inches ( I
am not positive of this number and will find out tomorrow but I know it
is far more the 6X of the thickness). The flex is constructed as follows
The core is AP-9121 with 1 oz copper on both sides.
The coverlays are LF-0110
The adhesive for the stiffener is LF-0200
And the stiffeners are .028 FR-4
The edges of the stiffeners are beaded with emerson & cummings ecobond.
I have spoken with the fabricator and they assure me that the copper is
roll annealed and not electro deposited.
The flex circuit has failed after less than 1000 cycles. The cycles are
very slow and maybe 10 or 20 per day.
The current going through the traces is very low on the order of 10 mA.
We have had two circuits fail and they both have failed on the 8 mil
traces. I have scraped the coverlay off of the flex and have concluded
that the open is about in the middle of the flexible section but I can't
see it. I would have expected to see an open at the=2
0end of the coverlay
as I have seen this before. We have been potting the connectors to move
the stress point from the omnetics connector pins to further down the
flex past the end of the coverlay.
I have a couple of questions.
1. Is there a way to remove the coverlay without using mechanical
means I fear that I could screw up the sample by scraping it with a
razor.
2. Does this surprise anyone that it would fail this soon with a
bend radius that I know is large and only a 2 mil core?
The flex has been removed many times from the system and reinstalled and
I am still having a hard time convincing people that flex circuits must
be treated with care. i.e. can't be laid on benches and smashed.
Tomorrow I will get to get into the system and see the mechanicals but
the mechys assure me that at no time is the flex stretched to the point
of pulling the bend radius down. I soldered a wire onto the connector
and ran a needle up and down the scraped flex and it sure seems as
though it opens about in the middle of the flexible section.
Anyway any input will be appreciated
Thank you
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