The file is now posted on Steve Gregory’s site. Go to [log in to unmask]">[log in to unmask] and click on Flexdata.pdf

Actual impedance is 50.4.

We cannot use a stripline because then the part will not flex properly.

We are looking into the x-hatch. This may be the issue.

The pads are directly connected to a mating board by solder reflow but the testing is done before assy.

Pad plate or selective plate means the copper is plated up only around the holes/vias - not on the tracks – so the tracks are consistently .0007 thick.

Regards Steve Kelly

PFC Flexible Circuits Limited

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of JaMi Smith
Sent: Friday, January 24, 2003 3:27 PM
To: TechNet@IPC.ORG
Subject: Re: [TN] FW: HI - SPEED NOISE PROBLEM

Steve,

Just what exactly do you mean by the Subject "HI - SPEED NOISE PROBLEM", and the statement "I have a question about noise levels at high speed on a flex circuit." ?

Just exactly what kind of "noise problems" or "questions" are you talking about: Crosstalk; Interference; Radiation / EMI?

So far it seems that you all you have described is some pretty normal "attenuation" (loss), and possibly an issue of some "resonance" with the length of some of the conductors.

You state that your impedance is "approximately 50 ohms", what does your network analyzer say that it really is.

How good a ground plane do you really have under the traces. Maybe that could be better phrased as asking how large are your openings in your cross-hatched ground plane.

I assume that you do realize that since you are using microstrip (one ground plane)instead of stripline (two ground planes with signal in between) that your are going to "radiate" your signal to some extent no matter what you do, and that your signal is also susceptible to interference from other sources.

Are you using the flex as some form of interconnect?

What are the "pads" for that are selectively plated? Are these some kind of contact for a connector, or are they for mounting parts?

Has Steve Gregory been able to post your pdf, and if so, what is the link.

JaMi Smith

----- Original Message -----

From: [log in to unmask]">Steve kelly

To: [log in to unmask]">[log in to unmask]

Sent: Friday, January 24, 2003 11:07 AM

Subject: [TN] FW: HI - SPEED NOISE PROBLEM

PFC Flexible Circuits Limited

-----Original Message-----
From: Steve Kelly [mailto:[log in to unmask]]
Sent: Friday, January 24, 2003 12:09 PM
To: IPC ([log in to unmask])
Subject: HI - SPEED NOISE PROBLEM

Dear Technetters:

I have a question about noise levels at high speed on a flex circuit. The circuit is:

1) surface microstrip design (.004 tracks on one side – x- hatched ground plane on other)

2) impedance is approx. 50 ohms

3) construction is:   .0005 kapton

                             .0005 adhesive

                             .0007 RA copper )

                             .002 kapton        ) DuPONT AP

                             .0007 RA copper )

                             .0005 adhesive

                             .0005 kapton

4) part is pad plated/selective plated

5) finish is immersion gold over electroless nickel

6) circuit is less than .5 inches long

When we measure the S parameters of the 50 ohm trace, the bandwidth starts dropping at 6 GHZ , peaks at 13 GHZ and then drops – I have a pdf. file which I can send off-line or post it to somewhere?

Any thoughts?

Thanks

Steve Kelly

PFC Flexible Circuits Limited