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With a little practice, you can make excellent double-sided PCBs by combining a laser cutter with chemical etching. The basic idea is: the laser cutter blasts away spray painted etch resist, then chemicals eat away the exposed copper. Once the copper is gone, the underlying board can be cut again with the laser to make through-holes. No drilling required! After some setup and practice, you should get reliable boards with 8-mil trace/space and hundreds of holes in about 2 hours. You can even cut internal routing and odd board-shapes!

You'd never want to make a bunch of boards this way, but if you want a same-day prototype of a new design it's perfect. I love this process because I don't have to wait 2 weeks for boards to come back from fab, so I can design aggressively and try new ideas. If you're in a research lab or shop you'll have no trouble finding the materials, but you should also be able to find everything you need at a hardware store and pharmacy.

This Instructable will go step-by-step through the process of making a double-sided board, with special attention paid to using software to generate a good laser path, and some neat tricks to help get good alignment between the top and bottom sides of the board. Drop me a note if you've got feedback or new ideas!

The steps are:

(1) Coat PCB stock with spray paint
(2) Laser cut a spring-form alignment jig
(3) Optimize your board layout for fabrication
(4) Generate vector art for the cutter
(5) Etch away black spray paint with the laser on both sides
(6) Chemically etch away exposed copper
(7) Laser cut through-holes in the exposed board
(8) Tricks and tips for soldering DIY boards

Stuff you'll need:

Access to a laser cutter
FR1 PCB blanks (try www.inventables.com)
Spray paint (McMaster #7719T9)
6"x6" of acrylic between 1/8" and 1/4" thick (3 mm - 6 mm) for making a jig
Drill press or rotary tool with small bit (optional, but helpful for alignment)
Gloves, goggles
Non-metallic dish, measuring device, and tools
Hydrogen peroxide (3%)
Hydrochloric acid (30-37%, also called muratic acid)
Paper towels

You'll also need some access to software:

A PCB design, exported to a format your graphics program can read (I use Eagle exporting to EPS)
A vector graphics program to edit the art in. I used Adobe Illustrator.

A brief note on safety and the environment:

If you have access to a laser cutter you should be familiar with the dangers involved with that. But these instructions also guide you through copper chloride etching, which you may not be familiar with. The chemicals used are dangerous. Hydrochloric acid can burn your skin, blind you, and generates poisonous fumes. The hydrogen peroxide is reactive with lots of stuff, and the heavy metals (copper) are poisonous. Always work outside (or in a chemical fume hood), in gloves and goggles. And make sure you have adult supervision if you're under the age of, say, 40.

Finally don't put your etch waste down the drain - it will poison both people and the environment. Store it safely in a labelled container, and dispose of it properly by contacting a hazardous waste disposal agency in your area.

Prior art:

Lots of people have previously documented parts of this process in some detail. I'm a huge fan of:

https://www.instructables.com/id/Stop-using-Ferric-...

https://www.instructables.com/id/Custom-PCB-Prototy...

https://www.instructables.com/id/Printed-Circuit-Bo...

You should check these out.

Alright. Let's get started!

Step 1: Coat PCB Stock With Spray Paint.

First, you'll need to acquire some PCB blanks. I've found that FR1 (a paper and resin based stock) laser cuts much more reliably (and without noxious fumes) than the conventional fiberglass FR4. This is critical if you want to generate through-holes or board edge routing. You can purchase FR1 copper-clad in both single- and double-sided flavors at http://www.inventables.com.

Next you'll need to coat the stock on both sides with spray paint. I've had good luck with Rustoleum Flat Black (McMaster #7719T9). Go for the thinnest coat you can get that reliably coats the whole board, and error on the side of not enough paint (you can do touch-ups with a Sharpie marker later). Thin paint is important because when you blast the paint off with the laser a thin film of it will resettle. The thinner the paint layer you blast away, the less there is to resettle. Keep the spray nozzle at least 18 inches from the boards to get a light and even coat.

(BTW, I've tried a few other spray coatings - one acrylic based, and one epoxy based - to find something that didn't leave an etch resisting mist. But the flat black seemed to work the best.)

Allow about 15 minutes for the top-side paint to dry before flipping the board. Try to keep the paint on the back-side the same thickness, or else the two sides of the board may etch at different rates.

Spray painting is messy, so either do it outside where nobody will mind the mess, or do it someplace where you won't get caught. I usually do a batch of 10 or so boards at a time and keep them in reserve. Be careful not to scratch the paint when you store them. (But if you do, you can touch it up later.)
 

<p>Lasers are cool, for sure, but you can buy a desktop mechanical milling machine from LPKF that can do much smaller spaces/traces than this example, for under $10K. They also have a pretty incredible line of lasers called the Protolasers that do this directly without any chemical etching required - the laser ablates the metal directly from the CAD data. Search &quot;protolaser&quot; on YouTube, or go to their website at www.lpkfusa.com. It may be beyond most hobby budgets, but they make some really nice stuff for commercial use.</p>
<p>CO2 lasers and copper don't get along too well. The mirrors on a CO2 are copper. Its very reflective at that wavelength.</p>
<p>I was worried about this too, but it turns out not to be a problem for three reasons:</p><p> First, the beam is focused onto the material, so its divergence is quite high. So if the beam actually is reflected its power density falls with the square of the distance. By the time it actually hits anything (like the beam optics housing) its power density is greatly reduced.</p><p>Second, the surface quality of the copper on the PCB is pretty rough. It's actually pretty close to Lambertian (meaning it scatters incident light isotropically in all directions). (You can tell this because when you look into it you don't see a reflected image, like you would with a polished copper mirror.)</p><p>Third, any light that is reflected off the copper just goes back up the beam path - it's not a bad place for it to go.</p><p>So, yeah, they play fine. </p>
<p>Oh ok. if you say so.</p><p>My near 20 years of being a service engineer for CO2's must be pointless.</p><p>And getting the beam back in the resonator isn't a prob? Really? So thats why Trumpf, Bystronic, Mitsubishi, Rofin Sinar, etc waste money installing back reflection isolating mirrors to prevent the beam from re-entering the resonator cavity if the customer cuts SS or alum.</p>
<p>Well, You see that it worked...</p><p>If it didn't, He would tell you...</p>
<p>Whoa there, big fella. I certainly didn't mean to cast judgement on the worth of anyone else's life choices. (Or anyone else's beam-line engineering...)</p><p>All I meant is that (1) I haven't noticed a problem after trying this literally billions (read: a few dozen) times, and (2) there are some pretty simple high-school physics reasons (read: things I made up) that convinced me it probably wouldn't be a problem if I tried it. </p><p>That said, it sounds like you have slightly (read: way gargantuan-ly) more experience with these things than me. So if you've got any (non-hypothetical) stories about people wrecking their cutters, or (potentially hypothetical but still physically plausible) failure modes to avoid, I would be earnestly super-eager to hear about them in detail. (And I suspect everyone else would too, amiright?) </p><p>Obviously even though lasers are cool nobody wants to cause more destruction than intended. So, if this is actually dangerous, what's the deets?</p>
<p>I had the same idea as you and indirectly found this i'ble. I don't have access too a big CO2 laser but eventually get hold of a small 2W engraver. Do you have any figures whether that would be enough to burn the lacquer?</p>
<p>after the etch, but before cutting and drilling, could you do a couple layers of laquer sprayed on, and then etch away just the pads to give yourself a solder mask as well? I assume just lasering off the mask could be relatively quick compared to doing the full traces pre etch</p>
<p>I've tried this, and it kinda sorta works as an insulating mask, but it's not really tough enough to resist solder. (If it's burnable enough for the laser to take it off, it's burnable enough for the iron to take it off...) One related trick for making these circuits a little more robust is just spraying the whole thing with spray-on epoxy lacquer after assembling all the components. (Obviously don't coat any connectors you need.) It looks ugly, but actually makes things pretty waterproof!</p>
<p>I'm working my way through this and have a couple of questions- Have you done this with a board that uses a ground plane, or copper pours? My boards generally have a VCC plane one side and a ground plane on the other. That already isolates traces, but not as elegantly as this method, and requires rastering rather than vectors. It seems like the only way to do it is to output the layers without the planes and then cut gaps in the path by hand in illustrator for the pads that connect to them.</p>
Hmm. I'm not sure that I understand the problem you're concerned about. I've done this on boards with ground planes - as long as your art is correct then Illustrator doesn't really know or care about the connectivity. If you've run into something I'd love to see an example of the problem. Your solution (the manual Illustrator delete...) also seems easy and effective.<br><p><br></p><p><br>But two potential caveats: 1 is that the Illustrator Union step will fill through any traces that are completely surrounded by other edges. So if your ground plane completely surrounds islands of traces you'll need to be careful not to delete those islands, probably by just copying it to a separate layer during that Union step. <br></p><p><br>Caveat 2 is that if all of your traces are adjacent to the ground plane you can add up some gnarly capacitance to ground. This may be desired, but I'd think carefully about whether you really want all of the isolated-away copper to be grounded, or whether you just want to connect a few large pours.</p>
<p>great! thanks!</p>
<p>This is very cool and I'm tempted to give it a go on our laser cutter. It's only 40 watts though so I'm not sure it's powerful enough to cut through the board. What power is the cutter that you used?</p>
<p>Good question! We have two 60-watt tubes, so 120-watts total. But we run them pretty fast cutting through the board. My gut is you could probably get through on 40 watts at reasonable speeds, but you may need to go slow, and maybe make two passes (or a reverse-side pass). </p><p>The etching phase uses very little power. I haven't tried it, but I hear people have removed etch resist with a well-focused diode laser.</p>
Thanks Joe, I'll give it a go an see how it works out!
<p>Nice. I'll have to try this if I can get my laser back online! For people without access to a laser may I recommend my preferred method? </p><p>https://www.instructables.com/id/Toner-transfer-no-soak-high-quality-double-sided/</p>
<p>Where in the EM spectrum is the laser emitted by your cutter? If UV, could it be run in very low power to selectively expose traditional photomask material (like one uses with a stencil and a UV lamp box)? Big advantage here is you can get copper clad boards that already have a professionally applied layer of photomask material and then have the cuter to very accurately &quot;print&quot; the pattern with light and then develop the boards normally for the photomask material. This would eliminate the dual issue of getting an even coating of spraypaint and vaporized paint re-coating exposed copper.</p><p>If the cutters are in the wrong place of the EM spectrum, maybe someone who has access to a DIY CNC machine can replace their CNC head with a scavenged blu-ray laser, experiment, and make an instructable.</p><p>I would to it, but unfortunately I am waiting for either EUC to get passed and/or to finally land a job (preferably the latter). As a result I have negative disposable income for hobbies... Plus the closest hackerspace to me is about 1.5-2 hour drive away in either Baltimore or Philly and I need to save gas money for going to interviews. sLower Delaware sucks for tech things...</p>
<p>Hmm. In general, I like this idea; skipping a step would be awesome.</p><p>That said, the execution might be tough. Our cutter (like many cutters) uses a CO2 laser line at 10.6 microns, so well into the IR. But I'd say it's worth a try putting some sensitized boards into the cutter and seeing if it happens to work, but I no of no reason it should.</p><p>If you have a UV excimer laser cutter you can just cut right through the copper, so you probably wouldn't spend time etching. (It might take some fancy closed-loop logic to keep the underlying substrate intact - that sounds like a fun project, though.)</p><p>Another issue is that the sensitized boards normally require developing (to remove the un-patterned resist) before etching. So that would add a step back in. (And kind of a nasty step at that...)</p><p>As for putting a UV resist developing light on an existing cutter, it's not crazy, but might be hard. Remember that all the paths aren't connected, so the cutter needs to be able to kill the light source when moving from trace to trace. Possible, but not the kind of thing you really want to do to your buddy's laser cutter.</p><p>I have a little DIY CNC I've been playing with (Instructable up soon!) and I've thought about outfitting it with a laser. But it's so easy to just mill copper off the boards that this has so far just seemed like a longer way to get to the same place.</p>
<p>Literally a work of art &ndash; it almost looks like old shields <br>with a current-style &quot;device &ldquo; (that is, the lions and bands of color, swords and <br>all that stuff). Thank you!</p>
<p>Thanks, I'm glad you like it! I actually hadn't thought about that. This board is a small stepper-motor driver designed to be daisy-chained on a two-wire bus - it's shaped like that because it needs to fit in a confined space. But I guess it could be the crest of House Atmega.</p><p>But that reminds me, this etching process also works great for artistic print-making. It's a neat blend of craft and tech to design a pattern digitally, engrave a metal plate with the laser and chemicals, and then print with ink.</p>
<p>hi there,</p><p>Can you inform us about the type of laser cutter you've used? or at least the power to 'drill' through the FR1 material, will this also work with FR2 material like most people use?</p>
<p>Sure. We use a Universal Laser Systems PLS6.150D with two 60 watt tubes, and the 2&quot; HPDFO lens. (This just gives a smaller spot size than the standard 2&quot; lens.) For etching paint we use 10% power, 10% speed, top tube only. For cutting FR1 we use 75% power, 5% speed, both tubes. A ballpark is that it's about like trying to cut through 1.5 mm thick wood.</p><p>My understanding is that FR2 is also a paper/phenolic system and is basically the same as FR1 (but with a slightly lower glass transition temperature). Another common substrate material, FR4 is fiberglass based and is (I hear...) tougher to cut. I've never tried standard thickness (.062&quot;) FR4. However, Digikey has some very thin (.014&quot;) FR4 that I have cut through with no problems after etching off the copper. (Part # PC94-ND). It's pretty neat stuff, but a little flimsy.</p>
<p>I voted for this!</p><p>I just love the ingenious springy clampy neaty (oh yuck)!</p><p>I really like the fact that you ONLY removed cover as required, not removing the useless copper.</p><p>I've always wondered why so many PCB builders remove this copper. It seems so wasteful to waste waste.(oh yuck, again) lol</p>
<p>A very nicely written Instructable, thanks. I'm getting good results with pre-sensitised photo resist boards at the moment, so don't think I'll be risking lasering for now. (I'd worry about reflections from the copper.)</p><p>Whenever I see such nicely made boards I always want to recommend the soldermask I found in this Instructable - https://www.instructables.com/id/Dry-Film-Solder-Mask/</p><p>A CO2 laser also works very well for creating solder stencils from Mylar.</p>
<p>Sorry - just noticed that you already mentioned cutting solder stencils!</p>
<p>I love the laser cut spring jig. Another, &quot;why didn't I think of that?&quot; idea. Thanks</p>
Thanks. It answered all my questions. inspired!
<p>The alignment jig in itself is a great benefit/Instructable. Thank you so much!!</p><p>...and your domain name, belllab.org, is great!</p>
<p>awesome idea!</p>
<p>Well done!!!!</p>

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Bio: MD-PhD student, neuroscientist, cyclist, robot-lover.
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