What is the appropriate resistance of a ZERO-OHM resistor?

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buenos

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Hi

I have recently noticed that on my board on one of the power-link zero ohm resistors I got 12mV voltage drop. It is a memory VTT power rail that goes through this 0402/0R resistor. It provides debug isolation for design bringup. The current might be 2-3A (unknown), so it leads to 4-6mR. I have measured it with a normal multimeter which is not very accurate, and it says 0.1 ohm.
So what should I expect? I though it should be as good as 0.1mR or less.
 

Typically the resistance measurements of a multimeter will read .1 or .01 depending on its accuracy. as far as whats appropriate? it depends on your application, and what loss you can deal with ( obviously there is no such thing as 0 ohms, even superconductive material has some resistance). chances are the resistive routing on your board the 0 ohm resistor is attached to, and the solder joints are going to be more resistive then a 0 ohm resistor(which is essentially a block of conductive metal). If this is really important for you you could fork out some money and grab a more expensive more accurate multimeter.

 

The issue is not the multimeter nor the fact that R>0, but how much is too much for a component like this. I thought 4-100mR is too much, and 0.1mR would not be too much. Is it a quality issue?
 

Bourns zero ohm 0402 resistor is specified as <50m ohms. If you are seeing 12mV drop with 2-3A then that is pretty good. If you don't want a significant voltage drop don't use such a small resistor. 0603 would be <10m ohms from Bourns for example. Another alternative is "solder jumpers" where you use pads which are shorted with solder then required i.e. with no component.

Keith.
 

Unless the manufacturer says specifically what resistance is expected, I wouldn't make any assumptions. Most manufacturers will at least give a current rating for the jumpers. 2-3A sounds like a great deal for a 0402 size jumper, you may want to change to 0603.
 

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