0 ohm resistor (zero-ohm resistor/zero-ohm link) 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. Just because of the resistance value, it has the same error accuracy index as the conventional chip resistor. The two points in the circuit board design cannot be connected by printed circuits. They are often connected by jumpers on the front. This is often seen in ordinary boards. In order to make automatic placement machines and automatic plug-in machines work normally, 0 ohm resistors are used instead of jumpers.

How much current can a 0 ohm resistor pass? I'm sure every hardware engineer has looked into this question. And there is a related question, that is, how big is the resistance value of 0 ohm resistor?

These two questions are very simple and the answer should be very clear, but the Internet users have given different answers. Some say 0 ohm resistor is 50mΩ, others say it is actually only 20mΩ; some say it can only pass 1A current, and others say it can pass 1.5A ......

So, how big is it in the end? Here, we look at it step by step.

Ⅰ 0 ohm resistor resistance value size

In response to these two questions, I specifically looked up the standard of the resistor. According to the EN60115-2 resistor standard document, the resistance value of 0 ohm resistor is 0Ω, but there will be deviations. 0Ω maximum resistance deviation has three options, respectively 10mΩ, 20mΩ and 50mΩ.

In other words, 0 ohm resistor deviation can be allowed to have a variety of deviations, which mainly depends on resistor manufacturers.

0Ω resistor specification

I downloaded the specifications of several major brands, such as Rohm, Kokuyo, and Guangjie's common 0 ohm resistor to check, and found that they are labeled 0 ohm resistor, and the maximum resistance value is 50mΩ.

From this we can conclude that the common 0 ohm resistor’s maximum resistance value does not exceed 50mΩ.

Ⅱ Overcurrent capability of 0 ohm resistors

There is also a view on the Internet that the current of 0 ohm resistor is calculated according to the power. Resistance is calculated according to 50mΩ. In this case, the resistance power of 0805 is generally 1/8W, and the calculated rated current should be 1.58A. However, I checked the specifications and found that the major brands of Roma, Yageo, and Guangjie are all 2A, which is somewhat different from the calculation.

The rated current of ordinary 0 ohm resistors from three major manufacturers, Rohm, Kokuyo, and K Laser, is as follows.

Ordinary 0Ω resistor rated current

As you can see from the above chart, the rated current of the three major manufacturers' 0 ohm resistors still differs slightly. I suggest that you choose the minimum value based on the various brands, so that no matter what brand, it will not exceed the specification design.

The table of rated currents after the synthesis is as follows.

Minimum current of 0Ω resistor

As we can see, the current of conventional resistors are not very large. According to the minimum value of the integrated selection, the largest is only 2A. What should you do if you find that you need to use a 3A or 4A 0 ohm resistor when designing the circuit? In fact, it is very simple, you can use two 0 ohm resistors in parallel on the line.

You may find it strange, why some packages have become larger, but the overcurrent has not increased? For example, 0805 and 1206 are 2A, here should be rated current although not increased, but the instantaneous current should be able to pass a larger. If you open the resistor specification of Kokusai, you will find that it writes two parameters, one is the rated current, and the other is the maximum current. The rated current is both 2A, but the maximum current is 5A for 0805 and 10A for 1206.

YAGEO Resistor specification

Note: Jumper is 0 ohm resistor (that's how the standard document is written, as shown in the picture below).

Resistor standard

Ⅲ Special high current rated 0 ohm resistor

If it is a larger current, the resistance is also optional. However, these resistors are unconventional. For example, this Rohm’s ultra-low resistance resistor has a maximum resistance of 0.5mΩ, which is 100 times smaller, and the rated current has reached 20A+, but the price is more expensive, costing several cents. You can buy several ordinary resistors for a penny.

ROHM jumper chip resistor

Ⅳ Design PCB board with 0 ohm resistor

Many hardware beginners are confused when they see 0Ω resistors used on PCB boards. They often ask: Since there is nothing in this thing, why use it?

In fact, 0Ω resistors can be very useful. If you use it well, you can greatly facilitate the design and debugging of PCB boards. Here, we will briefly explain the role of 0Ω resistors.

For example, the boss asks you to design a single panel out of cost considerations. The installation and wiring of the components can only be done on one side. The most troublesome thing for you is that some wires can't go through. They must be connected across the wires. Use jumper wires to make two holes? If in the development, this method is still possible. But one day your design becomes a product, which requires mass production. It is more troublesome to toss up a jumper than to place a resistor. At this time, 0 ohm resistor can help you a lot! According to your space, you can choose resistors of 0805, 0603 or 0402.

1. Front and rear isolation during debugging

If your design is new and you are not sure about the functions of many parts of the PCB and the performance that can be achieved, you will face a thrilling debugging when you take the board back. An important principle of debugging is to limit the problem to the minimum. Therefore, the isolation between multiple circuits is very important.

When debugging circuit A, you don't want the work of circuit B to affect your debugging, then the best way is to disconnect the connection between them, and 0 ohm resistor is the best way to isolate!

2. For testing current

If you want to test the current of a certain path, one way is to measure the voltage across a resistor on the path with a voltmeter (make sure that the internal resistance of the voltmeter does not affect the accuracy of the measurement), and the current of this path can be calculated by Ohm's law.

Another way is to directly string the ammeter on the circuit, so you can place a 0 ohm resistor on the circuit, measure the current with the ammeter ends instead of the resistor, and when the measurement is complete, you can install the resistor.

3. Bring flexibility to your own debugging

0 ohm resistor Can be reserved for a variety of possibilities. According to the actual needs of the optional installation of different resistors, it can replace the jumper, to avoid the jumper drilling. Installation takes up a relatively large space, and the jumper will also cause high-frequency interference.

For example, the PCB board is designed with a low-pass filter. If you find that you don't need it in the end or you don't have time to debug the low-pass filter when you start debugging, but you must let the signal flow through, you can use a 0Ω resistor to replace the resistor/inductor in the original design without installing a capacitor. When the matching circuit parameters are uncertain, replace it with a 0Ω resistor. In actual debugging, determine the parameters and then replace them with specific numerical components.

4. Single-point connection of analog ground and digital ground for signal integrity

Some people say that 0Ω resistance is the same as nothing, why not connect it directly? Imagine if you don't have this 0Ω resistor in the circuit schematic, you may ignore this single-point connection principle when doing PCB layout, and the CAD software will be connected randomly, and it will not reach your original intention of single-point connection.

Of course, magnetic beads can also be used for single-point connection, but my personal point of view is that if the location of the connection point is selected, magnetic beads have no advantage except that they are more expensive than resistors. In actual operation, you can use smaller packaged 0Ω resistors, such as 0402 and 0201. When soldering, you can directly use a soldering iron to lap the two ends together, so that the resistors are also saved.

5. Increase the difficulty of being reverse engineered

If you put multiple 0 ohm resistors with different colors, different packages, and no resistance marks on the circuit, it will not affect the working performance of the circuit, but it can make people who copy your board crazy instantly.

The PCB board supports different configurations. Some versions may have some circuits that are not installed. You can use it to isolate the circuit parts that are not installed. For example, the iPhone has a WiFi version and a WiFi+3G version, which is actually a design.