Electronics > Beginners
Is oxide on surface of RF conductor problem?
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fonograph:
Lead,tin,copper... they all oxidize,the oxide is insulator.At RF frequencies,skin depth might be only 1 micron deep.Now,ofcourse,if have 4 GHz signal with 1 micron skin depth,and 1 micron thick conductor gets oxidized 1 micron deep,thats obviously a problem.

What if same scenario happens but the conductor is 10 micron thick,so when its oxidized 1 micron deep,we are left with 9 microns of unoxidized conductor.Becose the skin depth is only 1 micron,in this case,the oxidation should not cause any problems becose the RF signal will just travel deeper inside,under the oxidized surface layer and no extra resistivity will be measured,right?

My question is,can the surface oxidation/corrosion by countered by making thicker conductors that still allow enough thickness compared to skin depth such that there is always enough unaffected conductor to conduct RF signals even despite surface oxidation?

Or is oxidation big problem no matter how thick conductor is,any surface oxidation or corrosion is bad,in some way,to the RF signal?
DC1MC:
Well, it is really simple, the oxide is reducing the actual cross section of the conductor, it's like someone shaved a bit of the metal, for low freqs doesn't matter too much, until the oxidation goes really deep, for hi freqs it really does, since it produces a lot of side effects, not only reducing the cross section of the conductor, but the oxide itself has a different dielectric characteristic compared to the air and this it's going to change impedances and tunning.
So up to few hundred megs, the normal surface oxidation is no (significant) problem, afterwards it starts to matter.

 Cheers,
 DC1MC
DC1MC:
There is no resistivity on hi freqs, just impedance :), if you have your metal so thin that the normal surface oxide will matter, than is too thin. For hi freqs, usually the bigest problem is not the DC resistance but change of the impedance and q factor of the circuits, not to mention the resonance frequency. this why there a attempts to protect the conduits. Of course as you've mentioned the thicker the metal, the less influence has the oxidation, but for many applications this solution is not possible (strip antennas and friends). Better put a 4 microns layer of gold on it and be done  8).

 Cheers,
 DC1MC
fonograph:
With all due respect,I mean,your da microwave wizard and I am noob but...  I think there is resistivity on high frequencies.Sure impedance becomes much more important,that doesnt mean resistance disappears.

You said (wrote) that the surface oxide layer will mess up the impedance becose of its dielectric constant,but is that even really realistic problem under 10 Ghz? At 10 Ghz the wavelenght is 3 cm,if we consider the slow down due to dielectric constant of 2.2 in ptfe pcb,then the wavelenght is 2 cm long,even at 10 micron deep oxidation,thats 0.5% compared to wavelenght.Copper oxide have 18 dielectric constant,in case like this,it wouldnt be problem,would it?

CJay:
My understanding of this is probably simplistic but adding an insulator to the surface of a conductor has the effect of changing the velocity factor, at HF a thin layer of oxide has little to no effect, a mm of PVC will make a measurable difference.

I assume the effect will be linear and as such a layer of insulation (oxide) will have an effect that increases proportionally with frequency (as well as other effects coming into play) so by the time we're in the cm bands oxidation will have a significant effect?

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