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Capacitance of Double-sided PC Board

I took a piece of double-sided phenolic PC board and put it on the cap meter. For a sheet that is 10.5 in. by 12 in. or 126 sq. in., I get

2074 pf, or 16.46 pF per sq. in., or 2.55 pF per sq. cm.

I didn't have any double sided glass epoxy - I used that up making PC boards decades ago - so I was wondering how that compares to the glass epoxy PC boards. Has anyone ever measured a piece? What did you get?

I've seen RF tx projects where the supports for the components are made from small squares of PCB, having probably less than 2 pF. I've also seen RF low pass filters where the PCB is used for the capacitor to ground (plane) of the pi filter. So does a PCB capacitor have a reasonable Q? I've also seen projects where they recommend using teflon PC boards for low loss at RFs, usually UHF or above.

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Reply to
Watson A.Name - 'Watt Sun'
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Here's a link that'll get you some spec's for FR-4

formatting link

I'll also post an older DOS .exe and its BASIC source code to abse so you can determine the capacitance knowing the dimensions and dielectric constant of the dielectric without having to do any work!^)

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John Fields
Reply to
John Fields

In article , snipped-for-privacy@austininstruments.com mentioned...

Thanks - I think - anti-measling test??? Hokay...

I'll see if it's there. Yep, got both .bas and .exe.

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Reply to
Watson A.Name - 'Watt Sun'

FR-4 varies a bit, but I usually assume 15 pF per square inch (2.3 /sqcm) for standard 0.062 thick stuff. The capacitance TC is remarkable, typically about +950 PPM/K.

John

Reply to
John Larkin

On Sat, 16 Aug 2003 11:10:58 -0700, John Larkin Gave us:

That would be 2.4 sq cm.

Aren't most PCBs these day G10?

We use .032 and .022 designs all the time.

Reply to
DarkMatter 

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That would be...

1" = 2.54cm

1 in² = 1 in * 1 in = 2.54cm * 2.54cm = 6.452cm²

15pF       15pF      2.325pF 
----  =  -------  =  -------
1 in²   6.452cm²      1cm²


Most PCB's these days are FR-4, which is G10 with a fire retardant added
to it.
Reply to
John Fields

Weird. This Dark blather guy follows me around like some crazed Pekingese, biting at my ankles. You'd think that "varies a bit" and "15" would be hints that high-precision metric conversion wasn't called for, and even then you'd think he could get the math right, and maybe even state the engr units properly. And anybody who has bought a PC board in the last 25 years or so would know that everything is now UL flame-retardant. So he insists in taking exception to a lot of what I post, and invariably turns out to be 100% wrong. Some people crave public humiliation, I suppose.

John

Reply to
John Larkin

[snip]

Same here. Everyone, do us all a favor and **please** stop responding to DarkBlather. Put him in your permanent kill file.

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  Jim-T@analog_innovations.com  Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |

            For proper E-mail replies SWAP "-" and "_"
             
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Reply to
Jim Thompson

In article , snipped-for-privacy@highlandSNIPtechTHISnologyPLEASE.com mentioned...

Oh yeah, that er, whatever. I don't see any of his posts anymore since I put in the DMkill filter. It does wonders. Only see 'em when someone quotes his blather.

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goes directly to the trash unless you add NOSPAM in the 
Subject: line with other stuff.  alondra101  hotmail.com
Don't be ripped off by the big book dealers.  Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com  You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
Reply to
Watson A.Name - 'Watt Sun'

On Sat, 16 Aug 2003 15:02:47 -0700, John Larkin Gave us:

You're a retard. This blanket presumption proves it.

We still use G10 everyday without the UL treatment.

For the last 25 years.

You couldn't be any more retarded.

Reply to
DarkMatter

Now that you mention it, he is annoying.

Cheers

Reply to
Martin Riddle

Whatsa matta John, just recovering from your Friday night drunken stupor?

Go back to sleep!

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  Jim-T@analog_innovations.com  Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |

            For proper E-mail replies SWAP "-" and "_"
             
I love to cook with wine.      Sometimes I even put it in the food.
Reply to
Jim Thompson

--- Sure he could. He could be like you, a mean spirited, ignorant little dick with an axe to grind, but he isn't and he's contributed a lot more here than you ever have, (or will...) so what the f*ck's the matter with you anyway? Do you need attention so badly that you're willing to try to destroy the fragile peace that's existed here for a while now just so you'll be noticed? If that's your game then you've already lost. Be advised that you've been noticed. Now go away.

-- John Fields

Reply to
John Fields

If you are still calling out G10 on PCB fab drawings, you are likely actually getting FR-4; it meets all the performance specs of G10, but just uses a flame-supressing additive in the epoxy. Most PCB houses stock FR4, since they often have to make UL boards. Pure (non-bromine) G10 is basicly obsolete in the PCB industry. It is still sometimes used for very thin boards in consumer applications (specifically watches) because it punches a bit better than FR-4.

John

Reply to
John Larkin

On Sun, 17 Aug 2003 00:14:07 GMT, "Martin Riddle" Gave us:

Everything in life must be a riddle to you, f*****ad. Like how to refrain from being a TOP POSTING RETARD in usenet. Bone up on usenet posting practices and protocols, and then MAYBE the shit you spew might not stink so bad that it isn't worth reading.

Reply to
DarkMatter

On Sat, 16 Aug 2003 21:27:28 -0700, John Larkin Gave us:

We use it, unmasked, for HV applications. All the time. I know the difference.

Reply to
DarkMatter

On Sat, 16 Aug 2003 19:55:19 -0700, "John Fields" Gave us:

I'm sorry, dipshit... Did his insults not warrant getting the same thing back in his face? I think that they did.

Take a hike, asswipe.

Reply to
DarkMatter 

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Friday, Saturday, Tuesday...  Who keeps track any more?^)

BTW, that flasher looks like it had a little ethanol behind it, no?
Reply to
John Fields

--- If you've been as annoying as he says you are, (and from what I've read of yours, you are) then you deserve a little slap, which is all he gave you. Aside from your error when doing the English to metric conversion, your question as to whether most PCB's are made with G-10 instead of FR-4 seems to indicate that you didn't know that the use of FR-4 for PCB's is pretty much universal as the glass-epoxy laminate of choice. Now that you've found out, you seem to be saying that you knew it all along and that you people are still using G-10. Perhaps you are, but I suspect if you are it's for structural parts, not PCB's. Check with your PCB vendor(s) to find out what they're _actually_ using and you might be in for a surprise. If you _are_ still using G-10, why?

-- John Fields

Reply to
John Fields

I think FR-4 is G-10 with flame-retardant added, and they are electrically equivalent.

Reply to
Fred Bloggs

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