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'[OT] FR4 PCB'
1998\10\05@190019 by Peter Schultz

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Hi All,
Quick question,
what is the permittivity (r) of the FR4 PCB material?
Thank You,
PeterS

1998\10\05@211037 by Dave VanHorn

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>Hi All,
>Quick question,
>what is the permittivity (r) of the FR4 PCB material?
>Thank You,
>PeterS

A 50 ohm track on 0.062 material is 108 mils wide, if that helps..  :)

1998\10\05@221947 by Sean Breheny

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At 08:07 PM 10/5/98 -0500, you wrote:
>>Hi All,
>>Quick question,
>>what is the permittivity (r) of the FR4 PCB material?
>>Thank You,
>>PeterS
>
>A 50 ohm track on 0.062 material is 108 mils wide, if that helps..  :)
>

If you could tell me what the velocity factor for that is, I could probably
give him the permittivity.

Sean

+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
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1998\10\05@234530 by steve

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> what is the permittivity (r) of the FR4 PCB material?

I don't suppose "it varies" is the answer you're looking for but it
is quite temperature and manufacturing dependent. For calculations
use a value of 4.5. If you are designing a PCB that requires
impedance controlled tracks, talk to your fab house asap. You can
make life easier for both of you.

Steve.


======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: .....stevebKILLspamspam@spam@tla.co.nz      fax +64 9 820-1929
======================================================

1998\10\05@235834 by Dave VanHorn

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>If you could tell me what the velocity factor for that is, I could
probably
>give him the permittivity.


That I don't know. . Got anything with a stripline stub on it?  The
length will tell you velocity factor, regardless of impedance.  (Talk
about a roundabout way to find something!)

1998\10\06@003443 by Sean Breheny

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Hi All,

At 08:07 PM 10/5/98 -0500, you wrote:
>>Hi All,
>>Quick question,
>>what is the permittivity (r) of the FR4 PCB material?
>>Thank You,
>>PeterS
>
>A 50 ohm track on 0.062 material is 108 mils wide, if that helps..  :)
>

On second thought, I had better try to stay away from my theoretical
calculations <G>, I am getting a value of 18.6 for a permeability of about
1. Somehow, the value of 4.5 given by one of the other piclisters sounds
much more correct. Hmmmm, I must have missed a factor of four.... ;)

In fact, aftet a quick check on Altavista, I see it listed as 4 in one
paper and 4.2 in another place.

What is FR4 made of? Is that the glass/epoxy material? Maybe I could look
it up in my CRC handbook, but it would probably be listed under its
chemical composition, not under any standard eletronics designation
(because the CRC handbook is for chemists and physicists).

Sean


+--------------------------------+
| Sean Breheny                   |
| Amateur Radio Callsign: KA3YXM |
| Electrical Engineering Student |
+--------------------------------+
Save lives, please look at http://www.all.org
Personal page: http://www.people.cornell.edu/pages/shb7
shb7spamKILLspamcornell.edu  Phone(USA): (607) 253-0315 ICQ #: 3329174

1998\10\06@010520 by Norman Gillaspie

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Maybe you can post this to the mailing list. What address should I be using
to post items to the list?

Here is a Java based microstrip calculator.


C:\WINNT\Profiles\Administrator\Desktop\Filter Tune kit\index.htm


Norman Gillaspie

> {Original Message removed}

1998\10\06@011917 by Dave VanHorn

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>What is FR4 made of? Is that the glass/epoxy material? Maybe I could
look
>it up in my CRC handbook, but it would probably be listed under its
>chemical composition, not under any standard eletronics designation
>(because the CRC handbook is for chemists and physicists).
>
>Sean


Glass/epoxy, hopefully no air :)   As someone else said, it could be
rather variable, since the exact ratio of glass to epoxy would change
the aggregate characteristics, and the chemical composition of the
epoxy probably varies from mfg. to mfg..  Another reason the microwave
boys use Teflon?

What'cha makin?

1998\10\06@060211 by Russell McMahon

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NEMA LI-1 gives it as 5.4 @ 1 MHz

All other specs I have give it as 5.5 (MIL, IEC, DIN, BS, UTE)
All at 1 MHz


           Russell



>: Peter Schultz <.....schupetKILLspamspam.....DVP.COM>
>what is the permittivity (r) of the FR4 PCB material?
>Thank You,
>PeterS
>

1998\10\06@125123 by Peter Schultz

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Hi All,
Thank You for everybody who replied. I calculated the average: 4.75.
Just for Your curiosity I am doing a small PCB loop antenna and I wanted to
make a small, around
2 pF capacitor from PCB to tune the antenna and save the price of the
trimmer.
Thanks,
PeterS

1998\10\06@130409 by Norman Gillaspie

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Sounds a little marginal to me. I know someone who is building
GPS recievrs using teflon PCB's and they still each tune each
antenna based upon measured reference patches on each sheet of material.

These low values of capacitance on ordinary material might not
be accurate enough. Why not just use a chip cap you can get them
in .1pf values. A trimmer costs about .40 cents from johanson.

Norman

> {Original Message removed}

1998\10\06@134840 by Peter Schultz

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Hi,
I guess that and that what I will do. Give the manufacturer a special PCB
which contains about hundred different cap size)
let them manufacture from that PCB material what they will use for the
production run, measure which one has the correct
value and modify the layout according to that one. The trimmer very
expensive, the 0.1 pF step caps because they are considered as 1% ones
almost the same price in 1206 size. You can figure out if I can save around
40 cents on a 100000 piece run it will well worth to try it.
Cheers,
PeterS

1998\10\06@144235 by Norman Gillaspie

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What about laser trimmed chip cap. They are supposed to be
cheaper than trimmers and just slghtly more than a chip
cap.

Norman

> {Original Message removed}

1998\10\06@163753 by steve

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> > Just for Your curiosity I am doing a small PCB loop antenna

I would strongly recommend that you talk to your PCB manufacturer.
The permittivity figures are frequency dependant and you are probably
using something higher than 1MHz. Also, if your tracking is on the
surface of the board, only half of the dielectric is FR4. The other
other side of the track has a dielectric of air and soldermask, hence
the difference between stripline and microstrip.

Some fab houses suggest using a different D-code for impedance
controlled tracks so that they can identify them for QA purposes.

If you tell the fab house what you want to do, they can give you the
real figures and advise you on what they can and can't do. Better to
get it from the horses mouth than try to second guess the process.

Steve
======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: EraseMEstevebspam_OUTspamTakeThisOuTtla.co.nz      fax +64 9 820-1929
======================================================

1998\10\07@114715 by cousens

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On some 900 MHz equipment I've seen, they use tuning stubs that
toward the end of the stub are broken by lots of thin lines running
across the width of the stub.
On test just run your soldering iron (to bridge the lines) as far as
necessary,

You could do the same on your cap,
not much good on a 100000 piece run, but for a preproduction run ?


Peter Schultz wrote:
{Quote hidden}

--
Peter Cousens
email: cousensspamspam_OUTher.forthnet.gr  phone: + 3081 380534
snailmail:  Folia, Agia Fotini, Karteros, Heraklion  Crete, Greece.

Is it true? that they have, on the new version of windows
managed to increase the MTBF from 95 to 98 minutes
(Thats why they called it 95)

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