Thru hole vs surface mount R's at ~100MHz.

^^^^^^^^^^^^^^^^^^^^ A good sign that you should question your conclusions.

Just sayin'.

Reply to
JW
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Fuzzy thinking, as usual.

Given 0603, 0805, 1206 resistors, how should the capacitance trend?

John

Reply to
John Larkin

Then one of you should present some measurements of your own. Like, for instance, you.

I described the setup, the parts, and posted the numbers. Are you suggesting that I read the instrument display wrong?

Again, you appeal to authority and measure nothing yourself. Which, again, means you allow emotion to crush your ability to reason. How tedious.

Can you tell us why the values are close to one another? Your mentor Gibberish clearly can't.

John

Reply to
John Larkin

[...]

Perhaps the separation scales along with the area of the contacts on the resistor body. So the area:separation ratio remains roughly constant?

Another theory would be that your meter reponds to leakage through the

1M resistance.

[...]

--

John Devereux
Reply to
John Devereux

doesn't

" Given 0603, 0805, 1206 resistors, how should the capacitance trend?"

I'd guess approximately constant. ('course I have John's numbers to help guide my thinking.) C ~ Area/distance. I remeber way back in college we made these electrostatic measurements of a scaled up thru hole resistor, plotted the field lines and then one could draw in the equi-potential surfaces. You then treated each little 'square' as a capacitor and added up all the C's in parallel and series. Numbers for the capacitance were some fraction of a pF IIRC.

George H.

>
Reply to
George Herold

Right. Standard surfmount resistors are usually manufactured on 20 mil alumina, so capacitance goes as the width/length ratio, which is nearly the same for 0603, 0805, and 1206 resistors. Interestingly, the thermal resistance follows the same math, so all sizes have about the same power dissipation capability, given big pads.

That is possible. The AADE meter is an LC oscillator and frequency counter, so the frequency may depend a little on the resistance. I'll check that a couple of ways: by changing the resistance value on the AADE, and by checking the resistors on a seriously good Boonton C-meter.

A rough calculation of the capacitance of the alumina between the end caps of a 1206 resistor is in the ballpark of 0.1 pF, so maybe my measurements are high, or maybe the resistance element adds some C. As I noted, I'm groveling at my measurement resolution with the AADE.

Somebody with time on their hands (hint, hint) and a little ingenuity (sorry, Bill) could measure these capacitances for themselves at trivial expense.

John

Reply to
John Larkin

Right. All three have the same thickness, 20 mil alumina.

John

Reply to
John Larkin

OK, guys, you should be able to measure the parasitic capacitance of a

1M surface-mount or axial resistor, in a couple of minutes, using a piece of equipment that most of you have.

Do that and tell us what you get.

Bill, give it a shot!

John

Reply to
John Larkin

The lighting wasn't very good. The solder joint was fine.

I didn't solder the resistors for the capacitance measurements, as I noted.

Why don't you repeat the measurements?

John

Reply to
John Larkin

They won't let a janitor play with their test equipment.

--
For the last time:  I am not a mad scientist, I'm just a very ticked off
scientist!!!
Reply to
Michael A. Terrell

Well a complete failure here. I've got a SRS 720 LCR meter. 1 Meg ohm, 1/4 watt metal film axial resistor. C+R

freq C R

100kHz 7pF 1000k ohm 10kHz 23nF 1000k ohm and worse at lower frequencies

1 meg carbon comp gave the same crazy capacitance.

George H.

Reply to
George Herold

Hi, George,

That's not equipment that most people have!

But I think I've been seeing the same thing, namely that C varies with frequency. It makes sense: at low frequencies, the serpentine resistor pattern is relatively low impedance, so it participates in forming the capacitor. At high frequencies, the ceramic alone is much lower impedance than the resistance element, so the ceramic dominates.

But did you really mean 23 NANOfarads? That's extreme.

I hacked a fixture and remeasured some resistors on my Boonton 72B C-meter, which does proper 3-terminal measurements with a phase-sensitive detector at 1 MHz.

1M 0805 0.10 pF 820K 0805 0.12 pF 330K 0805 0.24 pF 100K 0805 0.28 pF

A 1M 1/4w carbon film measures about 1.2 pF, depending some on now I position it. 4.7M measures 1.0. 100K is 1.2.

This is cool: nobody seems to be able to figure out the shunt capacitance of a resistor!

John

Reply to
John Larkin

Sorry, Johnny, but your wimpy attempts at testing my electronics knowledge are... wimpy, at best.

Do you actually think that I do not know what takes place when two terminations are moved closer to each other? Do you actually think that I would fail to account for the decreasing size of the aforementioned device elements? And just as a hint for you, Johnny, the term "account for" connotes math, so you lose... again... on your capacity to "assess" others, as if a dope like you should ever be doing any such thing.

I could argue that since you feel that your numbers are correct, that it is you that has a failed understanding. Either of the physics, or the math, or both. Tee hee hee.

This from a dope that doesn't even understand the concept of vapor phase cleaning mechanisms.

Yeah, Johnny... you're really on-the-ball.

Bwuahahahahahaha!

Reply to
TheGlimmerMan

Actually, we all know that you don't.

Do you actually think that

You are 100% math impaired. Account for that!

And just as a hint for you, Johnny, the term "account

I never said the numbers were correct. I said that they were what the AADE meter reported.

John

Reply to
John Larkin

If it's your fudge, it's dark and stinky.

John

Reply to
John Larkin

" But did you really mean 23 NANOfarads? That's extreme."

Yes! and at 1kHz it was worse... but how is this thing measuring a pF at 1kHz?

With out the 'fancy' LCR meter, I could try and make a capacitance bridge. I've never done that before.

George H.

Reply to
George Herold

You should see someone about your multiple personality disorder.

Better yet, just go jump off a tall bridge. Preferrably landing dead onto a garbage scow.

Your baseless contention alone proves that I know more than you do about the subject.

Reply to
TheGlimmerMan

or

John, I haven't read any of this drivel.

In my opinion it's just better not to reply.

George H.

Reply to
George Herold

Don't get much more retarded than that.

That is EXACTLY what I said you did.

I said that you did it wrong. And you did, dumbass.

Reply to
TheGlimmerMan

Well, herald your stupidity elsewhere.

Reply to
GooseMan

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