EMRFD Message Archive 9340

Message Date From Subject
9340 2013-11-11 17:39:27 Jerry Haigwood Thin Film SMD Resistors

Hi everyone,

    I have a question about thin film SMD resistors.  Are they good for RF use?

Jerry W5JH

"building something without experimenting is just solder practice"

 

9343 2013-11-11 21:38:16 kerrypwr Re: Thin Film SMD Resistors

G'day Jerry.


They certainly are; I and lots of others use them for just that reason in RLBs, calibrati

9344 2013-11-12 10:29:56 Jerry Haigwood Re: Thin Film SMD Resistors

OK, I’ll bite.  How come they would work better upside down?  I checked and it is not April 1!  ;-)

Jerry W5JH

"building something without experimenting is just solder practice"

 

9345 2013-11-12 10:46:24 Richard Hayter Re: Thin Film SMD Resistors
The smoke stays in:)
Sent from my BlackBerry® wireless device

9346 2013-11-12 10:49:31 Dana Myers Re: Thin Film SMD Resistors
9347 2013-11-12 11:20:02 ford@highmarks.co... Re: Thin Film SMD Resistors

Reducing the distance between the substrate and the thin film has just the opposite effect.  Reduce the spacing and capacitance increases, not decreases.

 

The real answer is straight forward…

 

Interdimensional parasitic reactances offset the antigravitational nature of the unobtainium doped bosons as they repel the charges induced by gravitational reactance of the substrate.

 

I’m just sayin…

 

Ford-N0FP

 

 

9348 2013-11-12 11:23:51 William Carver Re: Thin Film SMD Resistors
Those doped bosuns think they have all the answers, don't they? That's
why they migrate through the substrate to Washington DC where they bond
to the dollar-bearing substrate.

W7AAZ

On Tue, 2013-11-12 at 19:19 +0000, ford@highmarks.com wrote:
>
> Reducing the distance between the substrate and the thin film has just
> the opposite effect. Reduce the spacing and capacitance increases,
> not decreases.

> The real answer is straight forward…

> Interdimensional parasitic reactances offset the antigravitational
> nature of the unobtainium doped bosons as they repel the charges
> induced by gravitational reactance of the substrate.
> I’m just sayin…
> Ford-N0FP
9349 2013-11-12 11:27:42 ford@highmarks.co... Re: Thin Film SMD Resistors
Exactly!

And the heat generated by the reaction is the reason smoke rises from the failed dielectric.

Just don't breathe the smoke. It has been known to induce a dependency when the same device is tried in the same topology and a the same reaction results...

Ford-N0FP


-----Original Message-----
9350 2013-11-12 11:30:54 in3otd Re: Thin Film SMD Resistors
Hello,
I too have heard/read about the improved RF performances when mounting SMD resistors upside-down, but a quick test I did some time ago with a 50 ohm SMD R did not show any significant difference up to a few GHz. But the ground plane in that case was quite far away and the setup was far from perfect, which could be the reason for not seeing any difference between the two mounting methods.
BTW, I thought that the improvement when mounting *upside-down* over a ground plane came from the reduced (loop) inductance - more straight path for the current. I suspect the effects are noticeable only at very high frequencies.
Note that some expensive SHF-rated resistors are already designed to be mounted with the resistive film down (e.g. http://www.anaren.com/sites/default/files/R1A100550R0J5C0%20_097_%20Rev%20B.pdf )

Returning to more usual resistors for us, here is a nice page with some data on the stray capacitance for the comm
9351 2013-11-12 11:33:46 Dana Myers Re: Thin Film SMD Resistors
9352 2013-11-12 12:16:02 kerrypwr Re: Thin Film SMD Resistors

Whilst I've enjoyed the replies, Claudio gets the prize; the resistive film is on the marked side and placing the resistor marked-side-down minimises the loop formed by the two end connections and the film.


But the effect, if any, would only matter at extremely high frequencies as Claudio also said.


Thanks for the links, Claudio; all good knowledge.


Here's another SMD mounting "trick"; multi-layer ceramic capacitors are sometimes mounted "edgewise" in microstrip or stripline.


Since this places the layers at right angles to the PCB it reduces parasitic L & C.


To show my mate Jerry that today is not April 1, here is an illustration from a patent application;


http://i41.tinypic.com/126bn61.png


I've seen it described somewhere else too but I can't find the reference at present; it might even have been a MiniCircuits document about MMICs where mounting blocking capacitors this way is said to have the benefit of reduced distortion (I can't remember whether it's harmonic or intermod).


But, whilst interesting, this is high-level lab-class stuff which doesn't really matter to most of us.


Kerry VK2TIL.



9353 2013-11-12 13:11:59 kerrypwr Re: Thin Film SMD Resistors

There is very good information on the capacitor-mounting topic on pages 5 - 7 of Texas Instruments Applicati

9354 2013-11-12 13:20:07 in3otd Re: Thin Film SMD Resistors

Kerry,

I've never seen references to mounting SMD capacitors vertically to reduce distortion (and why orientation should have have an effect on distortion puzzles me) but can certainly be helpful to reduce parasitics effects, as documented also in an ATC application note http://www.atceramics.com/Userfiles/select_cap_wireless.pdf


BTW, since we are talking about fine details of SMD components behavior, it might be interesting to know that a SMD capacitors at high frequencies can be modeled as a sort of transmission line, as the current distributi

9355 2013-11-12 13:51:05 kerrypwr Re: Thin Film SMD Resistors

Yes; it wasn't distortion as such, it's to do with suppressing the parallel-resonances as described in the TI appnote I mentioned.


My memory was a bit hazy but some Googling refreshed it!


Kerry VK2TIL.



9360 2013-11-13 00:43:57 g3wie Re: Thin Film SMD Resistors (*not* April 1)
At 24GHz and above, it makes a difference. This was noticed in the early days of 24GHz when there wasn't the surplus gear to modify.

Look here at an article by G8ACE (c1998) on how to make more mW by paralleling lots of low power FETs available on the surplus market at the time.

http://www.microwaves.dsl.pipex.com/24ghz/24gpa.htm

You'll read about the stability problems with 0805 resistors in the Wilkinson hybrids and how they were overcome by going to 0603. What John told me, but he doesn't say in the article, is that he found a marginal further improvement by mounting them upside down. I believe this is shown if you compare Fig 8 with Fig 9. In Fig 8 you can see the black top surface and the writing on the 0805 resistors; in Fig 9 you can't see the writing