Skills of using 0ohm resistor in PCB design

Zero-ohm resistor is also called a jumper resistor. It is a  special-purpose resistor. A 0-ohm resistor does not have a real  resistance value of zero. A 0-ohm resistor is actually a resistor with a  small resistance value.

In the circuit board design, when two points cannot be connected by  circuits. They are often connected by jumpers. This is often seen in  ordinary boards. In order to make the automatic placement machine and  automatic plug-in machine work normally, zero ohm resistor is used to  replace the jumper.

The summary of the functions of zero ohm resistor can include the following:

1. There is no function in the circuit, just for debugging convenience or compatible design on the PCB.

2. Can be used as a jumper to avoid high-frequency interference caused by jumpers (becoming an antenna)

3. When the circuit parameters are uncertain, replace it with 0 ohms. In  actual debugging, determine the parameters and replace them with  specific components.

4. 0 ohm resistor is actually a resistor with a very small resistor  value. When you want to measure the current consumption of a certain  part of the circuit, connect a 0 ohm resistor with an ammeter, so that  it is convenient to measure the current consumption and can be used to  measure large currents.

5. When PCB layout, if it is really not feasible use a line to cross, you can also add a 0 ohm resistor to cross.

6. Under high frequency signals, it acts as an inductor or a capacitor.  (Related to external circuit characteristics) Inductance is mainly used  to solve EMC problems. Such as between ground and ground, power supply  and IC Pin.

7. Single-point grounding (protective grounding, working grounding, and  DC grounding are separated from each other on the equipment, and each  becomes an independent system.)

8. Configure the circuit, engineers do not want jumpers and DIP switches  on products. Sometimes users will change the settings randomly, which  is easy to cause error on PCB. In order to reduce maintenance costs, 0  ohm resistors are used instead of jumpers to be soldered on the board.

9. For circuit protection, it acts as a low-cost fuse. Due to the large  fusing current of the line on the PCB, it is difficult to fuse if a  short-circuit or over-current fault occurs. It may cause bigger  accidents.

Since 0 ohm resistor overload current is relatively small (in fact, 0  ohm resistor also has a certain resistor, but it is very small), the 0  ohm resistor is first fused when overcurrent, thereby disconnecting the  circuit and preventing greater accidents happened. Sometimes small  resistors with a resistor value of a few tenths or a few ohms are used  as fuses. However, this is not recommended, but some manufacturers just  use it in order to save costs.

In mixed circuits such as digital and analog, the two grounds are often  required to be separated and connected at a single point. We can use a 0  ohm resistor to connect the two grounds instead of directly connecting  them together. The advantage of this is that the ground wire is divided  into two networks, which is much more convenient when add large areas of  copper. Incidentally, in such cases, inductors or magnetic beads are  sometimes used for connection.

How much current can a zero-ohm resistor withstand? 

Zero-ohm resistors  are often used in circuit design. Generally, the rated power of the  resistor is selected according to the current. So which package is the  appropriate for 0 ohm?

The actual resistor value of a general 0 ohm resistor is about +-5%  deviation, about 50 milliohms. So based on the rated power, you can  calculate its rated current.

0402 1/16W: 1/16=I*I*0.05 i.e. I=1.118A;

0603 1/8W: 1/8=I*I*0.05 i.e. I=1.58A;

0805 1/4W: 1/4=I*I*0.05 ie I=2.236A;

For each package, how much current the 0 ohm resistor can pass through  is also determined according to the heat dissipation of the resistor on  the PCB board.

The relationship between the current and the voltage across the resistor  under three packages of 0603, 0805, and 1206 are tested below. It can  be seen that the voltage of the three packages begins to rise rapidly  after the current actually exceeds 6A.

This shows that the temperature of the resistor has also increased  sharply, leading to a significant increase in power consumption. The  resistor of 0603 burned when the current increased to 11.5A, the  resistor of 0805 burned when the current increased to 12A, and the  resistor of 1206 was not burned when the current was 12A.