Create a footprint for RF PCB antennas with "ENIG only"

ahhh … maybe this again is “special”, depends on 3D viewer settings: pls compare

the difference is the setting “Use bare copper color for unplated copper”:

what the hell is “plating” anyways? I haven’t defined such stuff as “unplated areas” if that makes sense.

‘Clearly understanding’ this stuff is fairly quick and easy; it amounts to little more than Googling related interests such as, “what is ENIG on PCB” and asking the PCB fab-house questions. Then, playing with Kicad and trying different thing to see what they do…

With the knowledge gained, you’ll be able to apply it to using Kicad’s tools and settings to get what you ‘will’ want. But, until you have the knowledge, you won’t know what you will want.

Nothing to be ‘sorry’ about - Your questions are good but perhaps better suited to be asked at PCB design sites. Kicad is a tool for implementing design knowledge, not a ‘how to design’ resource.

You see from your work that Mask’s, Layer-stuff, etc, is all available and wonder/ask what to do and how to do it… So, your effort and Googling will pay-off…

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sure, RTFM, will do! =) np. thank you so much for your help!

beside RTFM, I’ll

a) just have the pcb manufactured to check physically - which is the ultimate test;) I do know what I want … I think … seeing/measuring is believing

b) the KiCad 3D viewer is fantastic! for design. but with the RF antenna specifically, I actually want to feed openEMS to simulate.

and I just finally figured out how to transport the RF antenna including vias and ground planes in a clean way!

tried various things, but fcad_pcb finally worked:

traces included, clean cylinders for vias, proper 3d meshes, all ground planes (2 here), everything script driven. python. awesome!

now comes openEMS … finally;) I want to compute some dBi’s … maybe render a movie … will see. then of course optimize/tune my antenna. anyways. tomorrow;)

It’s best to think of ENIG (or other copper finishes) as a post-processing step. This is not strictly true, but it’s close. This can be and usually is specified separately from the Gerber files, i.e. the Gerber’s don’t know what ENIG, HASL, etc. are. There’s no rule that the color you see in the PCB CAD file corresponds to any finish. This is not a flaw in the software, more in how the PCB process has evolved over the decades. Maybe newer file formats like ODB++ or similar specify this, but this is newish territory.

So, if you specify ENIG finish, or any other finish, it will cover any exposed copper that is not covered with soldermask. There are a few exceptions, like if you want hard gold plated connector fingers or something like that. No personal experience about how to make that happen, though.

BTW, you should be aware that ENIG is a thin flash of gold over a much thicker (but still thin) layer of nickel, and nickel has high RF losses due to both low conductivity and especially the fact that it is magnetic. How much it will affect your antennas, I do not know. For some RF circuits, I know that immersion silver is used.

Here’s a quick intro: Anything more and you will need to do some additional research because I am not an expert.

Hope this helps,


Oh, thank you so much, love you;) This article seems spot on! and also is readable for an amateur like me.

I will study that in detail.

FWIW, as above I was also hinted at “first know what you want”: yeah, that’s part of my problem;) I am a software guy that for reasons became interested in creating an own device. I do have some basic hardware understanding, looong ago I even etched PCBs in my parent’s bathroom … well, I also lack any manufacturing, any RF experience …

I want to get as close as possible and cost-feasible to a perfect electrical conductor for RF <1GHz at a specific manufacturer I’ve chosen.

the piece I do understand is, in general, some materials are better than others for that, changing materials within a trace/antenna is always bad (reflections / impedance changes), and I assume say 200MHz-1GHz waves already mostly transit at material surfaces (skin effect).

anyways, maybe. I will study the article you linked in detail tomorrow! thanks again,



fwiw, I don’t fully/really trust it, but here is what ChatGPT has to say:

FWIW, to conclude this post, and maybe of use for others, I’ve RTFM, here is the conclusion;)

Actually, there is a fantastic FAQ by @eelik that explains how solder masks work in KiCad:

The crucial piece I was missing is right at the top:

In KiCad (and other EDA) the graphical layer which represents solder mask is negative. Where there is graphics in this layer, the physical solder mask isn’t applied and there will be a hole in the solder mask.

Negative! Right. And this is specific to the mask layers, and only those.

Then, the article linked by @JohnSG clarified other confusions of mine, including this basic one:

A PCB surface finish is a thin layer applied to the exposed copper surfaces (exposed traces, pads, ground plains and holes) of a printed circuit board.

All exposed elements. Right. And “exposed” is controlled by solder mask layers (but that cannot control holes/vias, those are always exposed without special manufacturing)

Electroless Nickel Immersion Gold (ENIG) is a popular PCB surface finish that consists of two layers: an electroless nickel layer and a thin layer of immersion gold.


Nickel, in its pure form, is magnetic. However, in the context of ENIG (Electroless Nickel Immersion Gold) as a PCB surface finish, the nickel layer used is typically a specific type of nickel known as electroless nickel, which is non-magnetic. The reason it’s non-magnetic is that it lacks the ferromagnetic properties found in pure nickel.

So, while pure nickel is magnetic, the electroless nickel used in the ENIG process, particularly when combined with the gold immersion, does not exhibit significant magnetic properties. This makes ENIG suitable for RF applications and PCB antenna traces where non-magnetic materials are preferred.

Source: ChatGPT

It may be that the losses in ENIG are low enough for the purpose, but if you want the lowest loss, immersion silver will be lower. I am not an RF expert, but I’ve had to make some stuff work over the years. Also, I know enough about looking stuff up.

EDITED: corrected link below

Here is some real info on losses due to ENIG:

The upshot: at 1 GHz, the losses in a microstrip are small, even negligible. For a CPWG (coplanar waveguide), they start to get worse. The linked article even has a physics-based explanation, which has to do with the location of fields. In microstrip, they are mostly trapped between two copper surfaces, and the ENIG plating is on the “outside” of the structure. In CPWG, more of the field intersects the ENIG coating and the losses get worse.

You don’t have microstrip or coplanar waveguide. If you understand the explanation above, it might make you at least look at the dimensions and shape of your antenna and consider that its entire point of existence is to radiate energy to the outside. I’m not an expert, but it suggests to me that the helical antenna you propose will have a lot of ENIG surface intersecting with fields, worsening the losses. It could be simulated, but this will be difficult due to the discrepancy between the wavelength of interest and the thickness of the nickel layer.

The explanation given by ChatGPT about nickel is woefully incomplete. It’s permeability decreases with phosphorus content. You can search for real references about this. If I put a small rare earth magnet on a string, it is attracted to the ENIG layer of several blank PCBs I have lying around, in spite of the fact that it is only microns thick and area on 1 cm^2 or so.

ChatCPT sounds like an engineer who worked one year and spent the next decade or two on the marketing team. They only know some buzzwords and and remember enough engineering-speak to string them together in a grammatically correct manner, but talk with confidence like they are experts.



Thanks again for your comments, and for the new link / article! I need to study that.

Rgd ChatGPT: yeah, I absolutely agree! it can be dangerous to take it “as is”. for me it’s just a different search engine / another opinion. But one must be aware that ChatGPT is quick at “hallucinations”:wink:

Rgd waveguides and such: luckily, I’m only interested in 200MHz to 1GHz. I don’t have to deal with microwaves, and I don’t want to now (in this project) deal with crazy/“interesting” wave propagation modes like skywaves <30MHz.

Rgd antenna, sure, easy: I want an isotropic radiator with 20dB gain, low cost and small size. That was a joke;)

The device I want to create is a handheld device for outdoor use:

  • I can’t have a Lambda/2 dipole or even a Lambda/4 vertical at 200MHz in a handheld device due to size
  • it’s for outdoor use, so I’d be worried about immersion silver as silver is prone to tarnish and can oxidize over time
  • I think my manufacturer doesn’t support immersion silver anyways (at least in the prototyping service they offer)

Doesn’t matter, I highly appreciate your comments and new article! Will read in detail.

It occurs to me that CrapGPT needs to start doing citations. :wink:


I’m also not an expert even less so;)

My assumptions (which might be wrong of course) would have been slightly different … for sub-GHz, non-waveguide/microstrip at least:

  • the electromagnetic waves within the PCB antenna travel at the surface (skin effect) - thus, within the ENIG - rather than in between the 2 layers of a waveguide/microstrip - thus, within the Cu

  • the electromagnetic waves from the PCB antenna, traveling within the ENIG surface, will “peel off” from there into space. thus, there is no material transition

Anyways, I am aware I am in deep water / on thin ice as an amateur.

By coincidence, via some other post/discussion I started here on the KiCad forums rgd SMA connectors, I got into contact with a RF expert working full-time in RF who very kindly hinted he might give me some tips rgd questions once he finds time.

I have to say: I pretty much start to love this forum and the KiCad community. lot’s of knowledgable, nice and helpful people! =)

hahaha - made my day=)

yeah, this.

it’s an interesting tech, but I’ve seen it blubbering hallucinations which it clearly made up from the contents of my own question as that alone was detailed enough for it to associate/hallucinate.

what’s really a bit annoying to me though is the fact that it currently always starts to apologize and what if you nail it down pointing out errors or contradictions. I know that it doesn’t really understands anything. Nothing to apologize:)

Sounds like ENIG is the best choice for you, then. Your frequency is not too high, and your concern about corrosion of silver is real.

But, why not just have soldermask over the copper? It will also affect the antenna due to the extra capacitance, but how much depends on the dimensions of the copper vs. the solder mask thickness. It will also protect the copper to a large extent.


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Yeah, after reading your article (which I am still digesting, it’s pretty dense, lots of new aspects for me), I came to the conclusion:

for Sub-GHz, the insertion loss regardless of these materials is tiny, likely practically irrelevant

for microwaves, completely different story, and immersion silver seems really good

what’s also interesting is the “skin depth” depending on freq … actually I don’t know how thick the nickel+gold finish is at my manuf. … typical seems 0.5 - 2um … and the article claims skin depth of 2.95um at 0.5GHz, which means it could be right within the Nickel, or slightly into the Copper

But, why not just have soldermask over the copper?

That’s a very good point.

Triggered by this, I tried to figure out how it actually would look like, and recognized that I simply don’t know enough about the details. I should probably get over it, just simulate, test & measure, and hope for the best;)

Anyways, now that I spent the time drawing, let me post my naive pictures for how my zig-zag helical planar antenna looks like physically.

Given the following data/definitions

the option you hint at (if I understood right):

and the option I had in mind:

I simply don’t know if above pics are correct, and even if so, I don’t know which one would be “better”, or if it matters at all at sub-GHz … so I basically know nothing to make an informed choice at this point :wink:

I reluctantly post this - look at the screenshot I posted re JLCPCB (above) - they tell user what to do with the VIA (read the Quality Standard text). My point (and please forgive me) is that the info/questions/etc may have been answered and if you hunt further, you may find all the answers you want. As I also mentioned, you need to check with the company making the PCB as they may have different rqmts. Some want to add value by doing some of the stuff…

I leave it here…

np! thanks for all your hints and insisting I should RTFM;) fwiw, I’ve found a 1h video that explains it all:

here is a 15min excerpt

of course my drawings above had bugs. I was missing the magic of “electroless copper deposition” which fills vias with copper. fwiw, here is the corrected drawing:

I will go with Option B since it provides a “constant stackup” throughout the antenna as it switches sides.

They are already risking lawsuits for scraping copyrighted content.

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I recently finished a project it was only 50mm by 50mm and I wanted ENIG for no other reason than “its my gold and I want to see it !” and the way I did it was to create a zone out of a section of trace or the entire trace and make that zone a ‘mask layer’ this was easy just followed the flow it was very intuitive. Here’s a screen shot in PCB Editor which shows that everything in purple is masked and will be gold ignore the blue its on the back !

Then I sent of my files to JLCPCB to be made and what came back was great and the via’s where uncovered. The boards looked exactly like the 3D rendering so that was great :partying_face: here’s a pic of the front.

and just for completeness here is the back.

So my first experience with JLCPCB and ‘ENIG’ went well for me and I hope you have a great result as well :smiley:

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oh, nice! thanks for posting your design=) what’s the device doing?


  • do you have a camera image of the final PCB as you received it from JLPCB?
  • plus, ideally, a screenshot of the KiCad PCB view of your device with the corresponding solder mask layer selected … at least surrounding the SMA?

that would allow me to learn about the correlation between features as designed, colors in the KiCad views (both PCB and 3D), and the final product.

e.g. looking at only the pictures you posted, I’m not sure what’s exactly going on. eg I guess you are using “black” as PCB color, not standard “green”?

did you change any KiCad color settings?

fwiw, here are some screenshots of my current design (I don’t have a real PCB yet):

did you ever use “edge plating”? I don’t need that for my device (I think), but I’d be interested in learning … things like in this PCB:

OT, but I’ve read your blog, and " 20%LOAF" made my day! =) maybe I will try your flowchart, might help.

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The Board is a very low distortion Sine Wave generator (1Khz in my case). The bulb stabilised bit is reference to the use of an incandescent light bulb in the negative feedback. HP (Hewlett Packard) very first instrument was a low distortion sine generator based in this oscillator and Dr Hewlett did a lot of work on this too. Here are a couple of pics of the real board and I must apologise for the quality I rushed ! :crazy_face:

and the back

yes my choice of ‘solder mask’ was black and I’m not sure if I changed the background from default but no major changes where made. Here is a screen grab of the PCB showing the front copper (red) and I have reduced the opacity of the tracks so you can see the masks I put on the tracks to keep the gold. Finally I have no experience with getting the edges of the board coated.

I hope this is useful or interesting ! :smiley:

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