Custom PCB Prototyping Using a Laser Cutter

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Introduction: Custom PCB Prototyping Using a Laser Cutter

I am going to walk you through the process of prototyping a Printed Circuit Board using a laser cutter and supplies from your local Radioshack and hardware store.  This is a process I have perfected after several prototypes I created as part of my thesis, modular//neuroid.

Step 1: Prepare the Board

Remove the bare copper PC Board from the plastic being careful not to get oily fingerprints on it.  Place it on a clean, suitable spraying surface (newspaper or cardboard are great). Using flat black spray paint (I used Krylon brand) coat the copper 3 - 5, allowing time for each coat to dry before applying the next.  If your PC Board is double sided, be sure to repeat this step for the other side.  By the end of this step, your board should look completely black, no bumps or unevenness, and certainly no copper visible at all.

Step 2: Prepare Your File

Most laser cutters use vector files to print. Ours (an Epilog Legend 36 EXT) can print PDF or Adobe Illustrator files.  To build a correct schematic, export the footprint of your components (in this case female mini-USB ports) as vector files from Eagle or Fring.  Import this to Illustrator, and build your own traces.  Keep in mind a few things:

• we want the laser cutter to burn away everything that is NOT a trace, therefore the background is black and our circuit is white
1.5pt lines are the smallest that can be drawn
•  For text, no smaller than 5pt font, and should be placed as a negative inside of a box, otherwise it will get etched away
• If you are making double sided boards, finish your front side and then mirror.  This is the easiest way to keep things lined up with each other.
Be as efficient as possible : cram as many as you can together, it will make cutting boards later easier as well

Step 3: Go Laser Go

Laser your file.  The strength and speed of the print will depend on your specific machine. On ours, medium speed with high power were the best settings.  Also keep in mind the number of coats you used.  The only thing to keep in mind when setting the print : laser bottom to top -  top being the side with air vacuum.  This way the vaporized paint won't re-coat already lasered areas.

Definitely avoid re-lasering a second time over. There's pretty much no way to avoid having to do this if you notice you haven't gotten all the way through the paint, but once you figure out your settings, remember them so as to avoid having to do a twice-over.

Step 4: Clean Up the Board

Now as you can see, the result of the lasering is beautiful, however we are not ready for etching just yet.  There is a very thin layer of paint residue left on the copper that will block the etchant solution from working properly, and will slow that process down a lot.  Here's what to do : Soak one end of a q-tip in  rubbing alcohol (ethyl or isopropyl) and spread it on the exposed copper. Try to keep it off of the black paint, because we want that to stay.  Use the other end of the q-tip to rub away, essentially polishing off the copper, making it shiny and ready for etching.  You can see in the second image, the board on the far right has been cleaned, and is shiny and ready to go.

Step 5: Cut Boards and Etch

It is really your choice to cut the boards first or etch the entire board and then cut it afterwards.  I feel that you need less solution and a require a smaller container if you cut the boards first, and then etch afterwards. With Radioshack's Etchant Solution (Ferric Chloride), you only need to use a little more than enough to cover the boards entirely. Once the boards are submerged you need to "agitate" them for about 20 - 30 minutes.  "Agitate" really just means move around -- I simply lifted and dropped one end of the container every 10 - 20 seconds.  Nothing rough, just a slow wash.  After about 5 - 7 minutes you will begin seeing the orange copper disappear and the yellow color of the fiberglass underneath start to come through.  By the 30 minute mark there should be no more orange copper, only black lines on yellow.  You are done.  As the bottle says, flush the excess solution, and rinse the boards with water in a sink.  The solution will stain, so be careful.  It will also smell of a bizarre and unpleasant musk.  This is normal if you use ferric chloride.

Step 6: Clean and Polish

using a paint remover such as Xylene or paint thinner, bathe or wipe the remaining black paint off of the boards.  It will get a bit dirty (as will your hands) but keep polishing and you will get the boards clean, leaving just your brilliantly designed circuit. Success!

Step 7: Solder and Wire It Up

Here's my USB breakout board (prototype 0.3) ready for testing.

Step 8: Repeat!

That wasn't so bad.  You'll notice that not all of them come out perfectly.  The way the paint dried, the laser settings, all have effects on the final boards. You'll learn, and make it better next time. Eventually the circuit will be perfected, and you can pay a boardhouse to do all this for you!

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    56 Discussions

    You can cut down on the laser time and use up less etchant if your software will allow you to trace the edges of your circuit. That way the laser will remove only the outline of the traces and is much faster since it verctor cuts rather than doing a raster scan of the board. An added bonus is that you can ground the non-trace areas to provide ground plane to your board.

    1 reply

    I can get a really nice looking PCB by doing the vector outlines only, and it is WAY faster to prep too. However, if you don't have suitable clearance between pads for SMD components, you're going to have a greatly increased chance of bridging (ESPECIALLY when there are heatsink pads underneath some devices). This wouldn't be as much of a problem if you were using solder mask, but this method of prototyping doesn't involve solder mask.

    Printing a raster image on the laser can end up resulting in jagged edges on the verticals. That can be mitigated by following up the raster etch with an outline cut, which then ensures everything has a crisp transition.

    Avoid jacking up the power too much - it will delaminate the copper (won't etch the copper itself, just cause the adhesive bond underneath it to gas out and separate the copper). Might not seem like a big issue if the spots being heated are areas you want to remove anyway, but this delaminating impacts adjacent material - so that thin trace you DO want may lift away from the PCB (and in fact, may etch away because the etchant gets underneath it).

    Experiment with different paints. Primer versus top coat enamel, versus lacquer, etc. You can have different results between Ferric Chloride (the brown stuff) versus Cupric Chloride (the bright green stuff made from priming Muriatic Acid and Hydrogen Peroxide with Copper). I have some Nalgene bottles with good seals that I use for "shaking it up" with small prototype PCBs - complete etch in < 5 minutes.

    If you botch a laser etch (say because the PCB design wasn't registered proper to your copper and ran off the edge), you can clean the PCB and repaint it to use again later. If you just spray over the botched area, you'll have an uneven thickness of paint and an area which may be more prone to partial etch.

    Note carburetor cleaner also works great for removing paint from the PCB.

    For the best results, make sure your cutting deck is level and the top of the PCB material is at the focal point of the laser.

    How exactly can I draw the trace of everything except the circuit in illustrator?

    I can see a lot of confusion and misinformation in the below comments section. Power is not nearly as critical as the wavelength of the laser you are using. Lasers discriminate. For instance, it doesn't matter how much power you have on a CO2 laser - it just won't cut copper. A UV (355nm) or Green (533) and even near IR (1064nm is common) CAN cut copper. As some have mentioned in the comments below, take a look at the Protolasers from LPKF Laser & Electronics (they have various wavelengths optimized for different substrates and applications). If you search YouTube for Protolaser, you will find several video demonstrations. It's actually quite impressive what they can do.

    Sorry, I don't get the point of all of this. It has been useful when you don't
    need the develop process. The laser cut the traces instead of paint, that would be interesting and time/cost/environment saving.

    1 reply

    Do you realize what type of a laser that would take? A fiber laser that can cut through metal so 30k USD+ The process laid out is for the rest of us mere mortals with a simple $400-5k dollar machine.

    What kind of laser would you recommend, wattage wise?

    Thats brilliant! I can't wait to try to it out. If only I had my own laser cutter... Fortunately a friend has one. Would something like this be suitable for the board http://www.digikey.com/product-detail/en/PC55/PC55-ND/28472 ?

    Are there any specifications for the type of board? I read about one Radioshack board where the copper would separate from the board when it was heated.

    3 replies

    Have a look at gabuleu.blosgpot.com

    I bought a Shapeoko CNC and upgraded it to have a small diode laser. Not so expensive in the end.

    I find that on my 40Watt laser cutter, the copper of a pcb doesnt absorb any noticable amount of the heat from the laser. But any other paint layer above the copper gets 95% destroyed by the laser, just leaving a thin film which is easily removed with a dilute solvent. In the case of brush on paint, i used Metholated Spirits, or for spray paint i used Mineral Turpentine.

    I believe LPKF uses a UV laser, not an IR one. You probably are using a CO2 laser which emits in the infra red (IR).

     Hey is it possible to just cut deeper into the copper and skip the etching step?

    4 replies

    No, Lasers cannot cut into metal (commercial lasers).

    Go to LPKF website and search for ProtoLaser. They do it.

    What about a 150 W radium laser cutter ?

    no, the laser cannot cut through the copper. This is a similar process to etching brass

    even with 150w it is hard as the metal reflects light rather than absorbing it.

    Thanks, friend! Took me 3 tries getting the speed right, I did it going way too fast first off and it didn't make a dent, second time I set it way too slow and I set off a fire alarm. I bought another board I got the right speed and it was so much easier than wrecking a pair of pliers in ammonium persulphate. Thanks a heap

    It sounds odd to me that not only on this build, but on other peoples projects, the reference is made to a laser not being able to cut metal. I had a walkthrough on using our new laser cutter/engraver, and even though we were using wood, the honeycomb base plate was cut in the spots where the test engraving was set progressively deeper. Not being familiar with the process yet, ours will do 500dpi, but I dont know what that translates into for font point. I saw a reference to 1000dpi in the manual, but at this moment I cant recall what it was it was for.

    My concern is that the paint combustion would produce toxic fumes or other containments that could damage me or the very expensive laser cutter filtration system. Did you have to consult the manufacturer of the paint to ensure this wouldn't happen ?