Why are 0 Ohm resistances connected in a PCB?

[facetheash]

Why are 0 Ohm resistances connected in a PCB?
Example UARTs have 0 ohm resistances as interface between two ICs.... Why is that so?

 

[OLIVE2222]

They are used as jumper to made cheap single side PCB. The are available in reel which ease automated production. They can also replace a real resistance for various design buiding on the same PCB.

 

[facetheash]

They are used as jumper to made cheap single side PCB. The are available in reel which ease automated production. They can also replace a real resistance for various design buiding on the same PCB.

I'm not clear........... what do you really refer here as jumper.... particularly on a PCB

 

[OLIVE2222]

I am not very clear too.
I mean it's cheaper to produce single side PCBs with many 0 Ohm R (acting as top layer tracks) compare to double side PCBs without 0 Ohm R.
Be aware that single side PCB can be made with punched FR2 to be compare with drilled FR4. hope it's more clear now.

 

[shrtrnd]

I've worked a lot of old Hewlett Packard test and measurement instruments.
The practical effect of the zero ohm resistors, which are heavily used in old HP gear,
are as fuses to protect the circuit on the next board, from a circuit problem on another
board.
Somebody may offer you a more technically significant explanation of why HP designed
their circuits this way, but as somebody who spent the last 42 years working their
gear, that's the practical effect of having them between boards in a circuit.

 

[KX36]

AFAIK, it's mainly as OLIVE2222 has said. Circuits may need jumpers for various reasons, adding or leaving out a 0R resistor at the time of manufacturing is a way of doing this so that a circuit could act in different ways depending on the presence or absense of a jumper without having to change any of the copper on the board. zero-ohm link resistors are the surface-mount equivalent of using a wire as a jumper, the only reason they're the shape of a resistor is to make it easy for a pick-and-place machine to assemble them.