Friday, August 28, 2009

Simple DIY PCB Etching

Want to fabricate printed circuit boards (PCB) at home, cheaply, quickly, and easily? So did I.

The tips on these sites worked for me but I have learned more. Read on....
Experimentation and perseverance help. It's ok if you goof up a few times; I did. Hang in there and you'll be a DIY pcb etching guru soon! Find out what works for you, and you're set.

Start with a small, simple circuit and stick to single sided traces! My first circuit was for a 12V/5V dual power supply circuit for another project. It uses only a handful of components.

The design layout fills a 2" square area, using up only a fraction of an already cheap (under $4) PCB blank from the local Radio Shack. In case the etching went poorly, I had enough PCB material to try it a few more times.

PCB Layout and Design
How did I do the printed circuit board layout in the first place? I like to use CadSsoft Eagle which does integrated schematic drawing and PCB layout. I can offer a some tips:
  • Use wirepads (search for wirepad in the Eagle libraries) or pin headers for external interfaces not appearing in the schematic, like the transformer secondary wires, in this case.
  • Use the DRC dialog and Restring tab to change the size of pads; bigger pads are better for manual drilling.
  • Put all traces on the bottom layer so when you print the transfer you can uncheck "mirror"
  • When you print the PCB transfer, hide all the layers you don't want to appear as copper traces, then print with the "black" checkbox option set (see picture to the right)
  • For off-board components like rotary switches, create a custom package in the Eagle library comprised only of wire pads but using the correct schematic symbol.
  • Include dimension lines in the transfer print but make them at least 16 mil.
  • Create fill areas (pour regions) with Eagle, particularly for GND, instead of leaving lots of blank spaces on the PCB.  Saves etchant and time etching. It also saves time laying out the board.
Example of using Eagle Fill Area (Polygon) for GND
    Single Sided Impossible?  Cheat!
    Can't figure out how to fit all the traces on one side?  Cheat!  Use jumper wires  as in the board above and below. Many of the consumer electronics I've taken apart use bus wire.  It's quick to install since there's no insulation to strip.

    Jumper a trace on the "top" of the board with pads.

    • Add two pads where you want your jumpers. 
    • Change their name to match the net you're trying to jumper (e.g., VCC).
    • Draw a trace between these pads on the "top" side of the board (red) to represent the wire
    • Draw traces on the bottom side (blue) to the pads.
    • When you print the PCB (see below) hide the top layer.
    • Drill the holes, and run wire between these two pads
    Magazine Paper Transfer
    Several websites give tips on laser printing on magazine paper and transferring to the printed circuit board. Laser printing (and photocopying) uses melted plastic instead of ink. By applying heat heat, the plastic melts itself to the PCB, then the magazine paper can be soaked in water and rubbed off, leaving the laser print behind as a mask for the etching solution.

    A few companies provide store bought solutions for transferring trace masks to the PCB but those are obviously more expensive than using scrap magazines. I haven't tried them yet.

    Ricci Bitti's website gave the best advice. Printing on magazine paper was no problem and you can easily see the matte laserprint on the material.

    Toner transfer, ready to iron onto the PCB

    Here are some additional tips:

    • Cut down the magazine paper and tape it to scrap laser paper to prevent jams
    • Use the "Wool" (1 below Cotton, 2 below Linen) setting on your iron
    • Use green ScotchBrite pads for cleaning, abrading the PCB
    • Clean the board with acetone (carb/choke cleaner)
    • Apply moderate pressure, and slow circular movement on the iron for about 60 seconds.



    Et voila, after six or more failed attempts, I finally got a good transfer!

    A few of the traces are a little blotchy, but none of the pads are. The fine detail turned out beautifully. Like you can see in the picture, the tiny printing and the crosshairs in the corner drill holes retained their detail.



    I've since found better results when using traces no wider than 32 mil with good results at 24 and 16 mil. Smaller traces are unlikely to work well. You can repair any flaws in the transfer with a fine tip or ultra fine tip Sharpie permanent marker which conveniently resists etchant.

    Etching
    The common chemical of choice for DIY PCB etching is ferric chloride and that's what i use. You can get it from Radio Shackicon. Use suitable disposable gloves to keep the FeCl off your hands. They stain everything yellow. You don't want to look like a Simpsons character. Work in a well ventilated area.

    To speed up pcb etching times, I now use a hot water bath. Put the FeCl in a small disposable tupperware tub. Put water in an electric skillet (I use my reflow skillet). Of course don't use it for food anymore! Put the tub in the water, and heat up the water to somewhat below the "warm" setting.

    Boards usually etch in about 15-30 minutes. Don't let it go too long or it'll etch through the toner. So check it after 15 minutes and ever 5 minutes after that. I no longer use the FeCl-soaked sponge method. Too messy!

    Once your pcb etching is complete, dip the board in water to rinse and neutralize the FeCl then wipe off the toner with acetone (spray carb cleaner) and a paper towel.

    On my first fabricated board (below) the etching worked really well and even the smallest printing came out perfectly. There were a couple of small spots of toner that separated leaving tiny spots on a couple traces that were a little etched.


    Pseudo Silk Screen
    You can do your own "silk screen" printing on the top layer, too. But without real silk screen.  Just use the toner transfer method to transfer printing onto the top of the board to show what components go where.
    • In Eagle, hide all layers except tplace, dimensions, tname, tvalue, and tdocu
    • Use the 'smash' function to enable moving and resizing the labels
    • Add any other text you want (name, copyright, copyleft, whatever)
    • When printing, select print in black and select the mirror image checkbox
    • It's best to drill holes before you silkscreen; it gives you something to align to.
    • Align the printed image to the board and holes.
    • Toner transfer the image onto the blank side of the board.
    Try to do a better job of aligning your "silkscreen" than I...
    Update
    After fabricating many printed circuit boards over the last few years since I first wrote this article, I've been etching more surface mount boards using 16 mil traces with 0805 and 0603 size SMD components, as well as SOIC, SSOP, SOT-223, SOT-23 and 0.6mm QFP packages! Not bad for DIY, eh?

    Here's a couple examples that turned out very nicely. The ability to transfer such fine detail opens up a world of possibilities in board design. I used a Reflow Skillet to populate both boards. I've since started using my Weller station with fine tip along with fine SMD tweezers for the small passives.

    16 mil traces with 0805 SMD components
    16 mil traces with 0603 SMD components.
    Board populated with 0603, TSSOP-8, etc
    Conclusion
    With a little experimentation and perseverance in the face of multiple failures, I was able to reliably etch my own through hole and surface mount printed circuit boards. If you follow these tips, you'll soon be doing the same and a new world of hobby electronics will open itself up to you..

    But hey if you got this far and still don't feel comfortable trying it, then give oshpark.com a try. I highly recommend them and use them all the time. Affordable and outstanding quality.

    Next: Drilling

    7 comments:

    1. There is no need to use dangerous chemicals to etch PCB’s. You can use mono-sodium glutamate (food seasoning) bought from the supermarket. It requires oxygen from the air to work so it can take a few days- a fish tank air pump would help. You could add hydrogen peroxide (sometimes sold as color safe clothing bleach) to hurry the process along.

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    2. I made PCBs with an iron and magazine paper for a while with decent results, but SMT parts were difficult at best. I bought a cheap Scotch brand laminator from Walmart ($27 Cdn) and my transfers are fantastic. No more smudges or missing traces. No mods were necessary to the laminator. Set it for hot and on the thick setting and drop it in. I run ardweeny size boards through 4 or 5 times, and arduino sized boards through 9 or 10 times.

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    3. The Best Solution ( but dangerous - keep away from Kids) is dilute Hydrochloric acid and Hydrogen peroxide. You get 2" X 2" PCB etched in 5 minutes. look for more info for right quantity on Internet. The GAS produced while mixing this solution is a hazardous one.

      ReplyDelete
    4. Gotta say, thumbs down on the Scotch laminator. I tried this the first night and got nothing, zilch, nada for 10 or so tries. They may have turned the heat down in these.

      Got a 1500 watt $25 iron from wally world and got a near perfect transfer first attempt.

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    5. Really nice! Home made PCB is a bit tough in my projects, but you produced with an easiness. Thank you!

      http://www.npeducations.com

      ReplyDelete
    6. Nice work!, I also made an How to about home made PCB's
      http://www.apcc.tk/diy-projects/diy-pcb

      ReplyDelete
    7. This is a really good tutorial. I tweeted it and also shared it on FaceBook. I know that other people will find it helpful.

      The comments are useful as well. Personally, I have never heard of some of the methods people have shared here for etching printed circuit boards, such as the MSG, however I am willing to try it. Anything that reduces the risk of getting a burn or other skin damage is worth a try.

      ReplyDelete