Zero Ohm Resistor Jumper

[htho55]

pcb trace as 0 ohm jumper

Hi all,
Does anybody know that the equivalent inductance of 0402 SMD zero ohm resistor jumper ?
Thanks.

 

[FvM]

0402 jumper

I think, the inductance can't be determined without defining the respective return path.

 

[vfone]

0402 zero ohm resisor inductance

Approximately 0.2nH @ 1GHz.

 

[madengr]

resistor jumper

I think, the inductance can't be determined without defining the respective return path.

It's a partial inductance, similar to a piece of wire.

 

[aho911]

0402 resistor inductance

Thanks for all your response.
What is the self-resonant freqeucny (SFR) for general 0402 zero ohm resistor jumper?
Is it still around 0.2nH on 2~5GHz?

 

[sgperzoid]

low inductance resistor 0402

Thanks for all your response.
What is the self-resonant freqeucny (SFR) for general 0402 zero ohm resistor jumper?
Is it still around 0.2nH on 2~5GHz?

You need to check with the specific 0 Ohm 0402 device vendor for the exact specifications. Murata or Johanson devices could have different performance.

Personally, I think the inductance is less than 0.1nH at 1GHz and may rise to 0.3nH at 5GHz. However, the SFR should be beyond 15GHz for this device.

 

[FvM]

zero ohm resistor for inductance

It's a partial inductance, similar to a piece of wire.

Unfortunately, the piece of wire would show different inductances with each different distance to the ground plane.

With 0402 chip, depending on where you define your reference planes, the pads may have a higher inductance than the chip itself. A meaningful analysis and measurement could be like this: Have e. g. a 8 mil trace on a 4 layer board, it has an inductance of about 0.5 nH/mm with a ground plane below. How does the inductance of a connection change, if you cut the trace and place a 0402 Jumper? In this case, the jumper may have virtually zero or even negative inductance, cause the overall inductance is reduced by the rather wide pads and jumper compared to the wire.

P.S.: Another realistic setup is a 20 mils/0.5 mm trace as reference. In this case, the said 0.1 nH are a good estimation for regular wrap around mount of the jumper. The inductance can be assumed effectively zero for a reversed flip-chip mount.

 

[madengr]

It's a partial inductance, similar to a piece of wire.

Unfortunately, the piece of wire would show different inductances with each different distance to the ground plane.

With 0402 chip, depending on where you define your reference planes, the pads may have a higher inductance than the chip itself. A meaningful analysis and measurement could be like this: Have e. g. a 8 mil trace on a 4 layer board, it has an inductance of about 0.5 nH/mm with a ground plane below. How does the inductance of a connection change, if you cut the trace and place a 0402 Jumper? In this case, the jumper may have virtually zero or even negative inductance, cause the overall inductance is reduced by the rather wide pads and jumper compared to the wire.

P.S.: Another realistic setup is a 20 mils/0.5 mm trace as reference. In this case, the said 0.1 nH are a good estimation for regular wrap around mount of the jumper. The inductance can be assumed effectively zero for a reversed flip-chip mount.

I think we are just talking semantics here. As you change the height of the wire then it's impedance changes, so you could infer it's inductance is changes. However if you extract a lumped PI model (series inductor with shunt capacitor on either side) of the wire, then that inductance value should remain fixed, rather the capacitance drops as you move away from the ground plane. The inductance would only change if you got so close to the ground plane to disturb it's magnetic flux. In summary, it's self inductance does not change but it's measured inductance does. At least that's the way I look at it. If someone asks me what the inductance of something is I think of a lumped model.

Take a chip inductor for instance. Some people say it's inductance increases as it approaches the first self resonance. Not really. It's impedance increases due to the inductance resonating with the inter-winding capacitance. The inductance only changes slightly due to skin effect. However you can measure the impedance and calculate a large change in inductance.

 

[FvM]

I agree in so far, that assuming a constant, assembly indenpendant self inductance for a part is a useful approximation in many cases. But it's not exact and needs a reference geometry, if the inductor terminals have a distance, particularly for the very low self inductance of a piece of wire or a straight PCB trace.

If you assume a PCB trace of same width as the jumper (0.5 mm) as reference geometry, than you get around 0.1 nH inductance for a 0402 jumper. That means the trace inductance is increased by this amount, when you cut it and assemble the jumper above the gap. But you can also see, that this increment varies with the distance to a below ground plane. It may be e. g. 0.13 nH with a 4-layer board (.38 mm substrat height) and 0.1 nH with 1.6 mm substrat height.

The other point is, that the jumper could be assembled also to a trace of different width. This changes it's apparent self inductance, e. g. if mounted on a 1 mm trace, it seems to have 0.25 nH inductance. In contrast, when mounted on a 0.2 mm trace, it shows a negative inductance of 0.04 nH.

 

[htho55]

Thanks for all your help.