Zero ohm resistors - Page 1
Forum section: electronics / beginners

author: spanakop
author_rank: Contributor
timestamp: July 27, 2022, 03:19:48 pm
content: Hi all. Newbie question. I've seen mentioned a few times zero ohm resistors on PCB's. This is really confusing me because I can't see the point of it.Can someone explain to me why there is such a thing as zero ohm resistor please? if such a thing is used on a PCB, why not just bridge it with solder or just complete the track on the PCB in the first place.

author: radiolistener
author_rank: Super Contributor
timestamp: July 27, 2022, 03:23:08 pm
content: usually it is used as a jumpers. But sometimes can be used as a low resistance or even as a fuse

author: langwadt
author_rank: Super Contributor
timestamp: July 27, 2022, 03:29:22 pm
content: a resistor can cross other traces, you can't do that with a trackyou might want to enable/disable stuff, you can do that by mounting or not mounting a resistorand a resistor can be machine mounted

author: TimFox
author_rank: Super Contributor
timestamp: July 27, 2022, 03:31:39 pm
content: In a later revision of the circuit, you might want to replace the zero-ohm resistor with a finite-value component in the same package.

author: mag_therm
author_rank: Frequent Contributor
timestamp: July 27, 2022, 03:33:08 pm
content: I etch my own pcbs for surface mount as single sided.Using the 0.25 Watt 1206 resistor kit allows a track to run under a resistor.So far I have not used 0 Ohm to do that, but I would if there is a track with no resistor already in it.

author: wraper
author_rank: Unknown
timestamp: July 27, 2022, 03:42:12 pm
content: Usually they are used to assemble the same PCB in different variants, instead of some other component like ferrite bead which turned out to be not required or for diagnostic purposes. For example circuit may have a lot of stuff connected to the same power rail. Short circuit in this case may be very hard to find due to amount of components connected but adding a bunch of zero ohm resistors allows disconnecting parts of the circuit. This may also be used for R&D purposes, not just repair, it allows measuring current in different parts of the circuit during development and during production zero ohm resistors will be placed. No need to replace them with traces as they are cheap as dirt, and respinning another revision of PCB likely will be more expensive than adding them to every device.

author: tooki
author_rank: Super Contributor
timestamp: July 27, 2022, 05:26:31 pm
content: Quote from: spanakop on July 27, 2022, 03:19:48 pmAlso, if you’re assembling boards using solder paste and a stencil, it’d be hard to apply enough solder to make a solder bridge. A 0 ohm jumper just drops in place, super easy.

author: james_s
author_rank: Super Contributor
timestamp: July 27, 2022, 06:17:54 pm
content: I use zero-ohm resistors as configuration jumpers, the same PCB can be used for multiple different versions of a device. A zero ohm resistor can be installed by the same machine that populates the rest of the components. A solder bridge cannot. Zero ohm resistors are nothing more than jumpers that are designed to be handled by the standard machinery that handles resistors, both through hole and surface mount varieties.

author: mariush
author_rank: Super Contributor
timestamp: July 27, 2022, 06:58:09 pm
content: Jumpers... allows 1 or more traces to go under the resistor...Sometimes you don't want to have holes in the pcb but don't want to pay more for a 4 layer board.Sometimes the pcb place charges ore for vias, or only allows via on bigger area boards...so you can work around these limitations by using such jumpers ...Could also be used to enable or disable parts of a circuit ... for example, imagine a monitor with an optional headphones amplifier that would only be used if you sell the monitor with a HDMI jack (because hdmi carries audio)So you could have the pcb with footprints for the audio amplifier but on the monitor version with just DVI and VGA, you don't populate the amplified part of the pcb and you can use a jumper to tell your display controller chip that the amplifier is not present.

author: wraper
author_rank: Unknown
timestamp: July 27, 2022, 07:09:36 pm
content: Quote from: mariush on July 27, 2022, 06:58:09 pmVias are not replaced by SMD jumpers over a trace on 2 layer boards (by anyone sane), going 0R resistors "instead of 4L" makes even less sense. 2L PCB with no vias make no sense (unless home made and hand soldered). Of course there may be some special cases, but they are so rare and obscure, they are not intended application of 0R resistors.

author: spanakop
author_rank: Contributor
timestamp: July 28, 2022, 08:27:37 am
content: Cheers guys, makes sense now.

author: MrAl
author_rank: Super Contributor
timestamp: July 28, 2022, 09:44:07 am
content: Quote from: spanakop on July 27, 2022, 03:19:48 pmHi,If you need a jumper over another trace you can use a jumper, but if you are using automatic insertion equipment you will notice that they are good at placing resistors just about anywhere. By using a zero Ohm resistor in place of a wire jumper with added Teflon insulation you can have the automatic insertion equipment install the 'jumpers' so it is much more economical. These resistors will also be insulated by way of the natural body material so no need to add any insulation either. Makes life a lot easier if you intend to use automatic insertion equipment.

author: Infraviolet
author_rank: Super Contributor
timestamp: July 30, 2022, 12:06:36 am
content: Tooki, reply #6, solder mask on PCBs would also fight any attempt to make such a bridge, the solder would likely just ball up and then be washed off when removing flux after soldering.

author: EPAIII
author_rank: Super Contributor
timestamp: July 30, 2022, 08:28:06 am
content: Some boards have pads that are deliberately designed to be used as solder jumpers. They have a narrow, straight line gap, perhaps 0.010" wide that can be easily shorted or opened with a soldering iron. A solder sucker or solder wick is handy for removing the solder. I have used this technique for hand assembled boards.Quote from: Infraviolet on July 30, 2022, 12:06:36 am

author: mariush
author_rank: Super Contributor
timestamp: July 30, 2022, 08:56:28 am
content: A good example of such solderable pads is often found in the 2x16/2x20/2x40 displaysFor example see 3rd picture in :https://newhavendisplay.com/2x16-character-lcd-fstn-display-with-k1z-amber-side-backlight/or click on picture attached , see left side J1, J2 etc

author: rooppoorali
author_rank: Regular Contributor
timestamp: July 30, 2022, 12:23:00 pm
content: Zero ohms resistor is an alternative to jumper wires.

author: tooki
author_rank: Super Contributor
timestamp: July 30, 2022, 01:19:39 pm
content: Quote from: EPAIII on July 30, 2022, 08:28:06 amQuote from: mariush on July 30, 2022, 08:56:28 amWe all know that solder jumpers exist. I didn’t say they don’t. What I said is that it would be very hard, if not altogether impossible, to bridge solderable jumperswith solder paste and a stencil.(I.e. pure reflow soldering.) Solderable jumpers, properly designed, work great for hand soldering. But I’ve never seen one for reflow soldering. The fact that 0 ohm jumpers are routinely used for this purpose (when we all know that companies would do away with it if they could) makes it very unlikely it can be done with just stenciled paste.

author: james_s
author_rank: Super Contributor
timestamp: July 30, 2022, 04:43:59 pm
content: As the saying goes, there's more than one way to skin a cat. The nature of engineering is that there are often multiple perfectly valid ways to accomplish the same thing. Choosing the best solution for a particular set of circumstances is part of the job. Sometimes a solder bridge jumper makes sense, sometimes a zero ohm resistor is a better choice. Sometimes it just comes down to personal preference.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: July 30, 2022, 05:50:10 pm
content: I often see a zero ohm resistor used as a bridge between the PCB ground plane and the shield casing of a USB socket. Is there some LCR reasoning behind this?

author: wraper
author_rank: Unknown
timestamp: July 31, 2022, 03:52:03 pm
content: Quote from: AndyBeez on July 30, 2022, 05:50:10 pmYou only see it because whoever designed it had no clue what they were doing. USB shield connection abuse because "reasons" is a quite common thing. 0R resistor is not that bad actually (worsens high frequency current path). Engineers add capacitors, resistors, inductors or ferrite beads in parallel or series with no idea why whatsoever. Well, it supposedly should help with EMC and fight with ground loops. However it only worsens EMC, adds ESD susceptibility, and does not help with ground loops since there is a GND wire inside the cable anyway.https://www.unit3compliance.co.uk/hdmi-more-like-hdm-why-thoughts-on-cable-shield-grounding/