I was recently engrossed in a popular strategy game, Rise Of Kingdoms. I can’t believe how addictive it is, as I spent hours building a castle and sending troops to war. Besides the heated battles, I managed to pick up some in-game jargon, one of which is ‘zeroed.’
In the game, getting ‘zeroed’ basically means having the wall protecting the castle totally destroyed. With smoke and flames billowing from the castle, getting zeroed in the game is pretty bad news. Thankfully, you don’t get zeroed in PCB design, but the existence of a zero ohm resistor can be quite confusing.
What Is A Zero Ohm Resistor?
A zero ohm resistor is exactly what the term described. It is a single resistor that is manufactured to have zero ohm of resistance when measured. A through-hole resistor with zero ohm is often marked with a single black band, which indicates the value of the resistance.
Meanwhile, a surface mount ceramic resistor will have a single or a multiple number of zeros to represent this zero ohm resistance. You can also imagine zero ohm resistors as jumper wires that are shaped as typical resistors. Measuring a zero ohm resistor with a multimeter will return in a reading that approaches zero ohm.
Why Do You Need Zero Ohm Resistors?
PCB designers who have never encountered zero ohm resistors are often fuelled with questions on the applications and practicality of the component. After all, why the hassle of manufacturing resistors with zero ohm when one could easily use jumper wires on the design?
It’s common that circuits are usually built with jumpers that allow certain subcircuits to be connected flexibly. Often, a circuit is replicated in a few product variations where only selected subcircuits are used. Zero ohm resistors are commonly used to replace jumpers in enabling certain connections on the PCB
If you’re building a PCB with manual placement and soldering, using a jumper wire is probably the best way to establish connections between pads. However, mass production involves a pick-and-place machine, which doesn’t have the capability of unrolling and cutting jumper wires. In such cases, a separate machine is needed for jumper wires.
Using zero ohm resistors reduce the cost of jumper wires insertion.
For mass production, it’s important to keep the cost down. Using an additional machine for jumper wires results in a separate setup and process cost. Therefore, a zero-ohm resistor is the perfect alternative that saves cost and time in assembly.
Single Layer Design
PCB designers are often pressured to keep minimize cost. There’s nothing cheaper than confining a design to a single layer PCB. However, getting the traces to their destination without overlapping is tough when you have quite a number of components on board.
Zero ohm resistors are the perfect remedy to ‘magically’ route a single layer board. Rather than making holes and turning the PCB into a double-layer structure, you can route a trace between the pads of a zero ohm resistor. These resistors are then assembled along with other components during the manufacturing process.
Preventing Reverse Engineering
It’s a bitter truth but there are copycats in the market that will not hesitate to reverse engineer a PCB that’s proven to be a hit. Short of coating the entire PCB with epoxy, zero ohm resistors are a great option to confuse the unethical copycats.
Intentionally placing zero ohm resistors on certain tracks is a good strategy to mislead the perpetrators copying the design. If possible, order zero ohm resistors with no markings to further frustrate their efforts.
Placing zero ohm resistors may prevent illegal reverse engineering.
Design Considerations When Using Zero Ohm Resistors
Using a zero ohm resistor isn’t a complicated process but you’ll need to remember that zero ohm resistors aren’t ideal components. In other words, it has a certain amount of resistance as with other conductive wires and traces.
As there is a tiny amount of resistance in a zero ohm resistor, it can dissipate heat when current passes through. The maximum power rating for the zero ohm resistor is defined by the thermal characteristic of the material and size. You’ll want to ensure that you’ve chosen a zero ohm resistor that can handle the current passing through without burning out.
Whether it’s to protect your design or to fully automate the assembly process, it’s quite easy to add zero ohm resistors if you have a good PCB design software like OrCAD PCB Designer. You’ll be surprised how these tiny components that confused many can result in substantial cost saving. Even more, the whole suite of PCB design and analysis tools from Cadence can augment your design process into excelling at any scenario.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.