Meet the Starting Lineup

I've been working on these for a little while now and I have to say the effort has been worth it!

Homebrew Electronics - Toner Transfer Method

It's been awhile since I've been able to work on anything not related to school. On the plus side, I took some great classes in both electronics and in aircraft design during the fall. Now that I'm on break I had some time to get a little work done.

I've had a lot of people ask me how I build my boards. They're always surprised when I tell them that I build them in my small apartment. The Toner Transfer Method requires no special equipment and can be done on a modest budget. I've not yet estimated the cost per square inch of a homebrew circuit board, but I suspect that it is on the range of a few pennies. Compare that to $5 or more per square inch at a professional PCB shop. Of course, the trade off is that my boards don't look quite as nice as the pro boards, but they get the job done.

Some assumptions that I'll make are that you can design a board in a CAD program, and that you'll be making a one-sided board. This means that the copper traces (the circuits) that make the connections will be on one side of the board only.

Step 1.

Etching Mask Exported to PDF

The first step is designing the board. If you've never done this before, I'd recommend using Fritzing, it has a pleasant graphical interface and even assists you checking connections on a breadboard. It is still in beta, and has a few minor glitches. At the moment, I'm using Eagle, but if Fritzing matures and fixes the bugs I don't like, I'll be switching to Fritzing permanently.

Eagle is also available for at no cost for educational/personal use. The main limitation is that you will have to fit your PCB within a size restriction. For me, this is minor, because my boards will fit within this limit. Since this tutorial is about manufacturing PCBs, I won't explain how to use Fritzing or Eagle, but there are some excellent resources on the web for these tools.

Once you have designed your board, I'd recommend exporting it to a PDF file rather than printing it directly from Eagle or Fritzing. This allows you to quick access to your file in case you need to print multiple copies (you probably will!). For one-sided boards, your print out will be reversed. TIP: I usually add a little bit of text or a logo to my board so that I can determine proper orientation of my masks at a glance.

Eagle: Before we export, you'll want to turn off any layers that won't exist on the bottom layer of the board. I use Bottom, Pads, and Dimensions. For one-sided boards, DO NOT select "Mirror" for your print out. This is confusing, and is the reason I put text on my boards. When viewed on paper/screen, you need the text in your etch mask to appear mirrored. This is handled automatically be Eagle. You'll want to print the file and save to PDF. One very frustrating thing about Eagle is that it is very difficult to produce properly sized print-outs. This may be a good reason to use Fritzing! For Eagle, try playing with the settings. I zoom in on my board until it fills the screen without cropping. In the print menu, I set Alignment to "Top-Left", Area to "Full", and page limit to "2". For some reason, the combination of top-left, full, and 2 page limit makes it work for me. This is the reason I recommend exporting to a PDF file; once you get the size right, you have a saved copy. In the worst-case scenario, you can also use Adobe's scale function to adjust the print size until it is just right.

Fritzing: Fritzing does a good job of exporting PDF's. It generates all different kinds. For a one-sided board, you'll want to find the version that represents the mirrored copper bottom etch. Note that a bug in Fritzing generates some line artifacts in the image. This can be fixed and will be discussed later.

When printing, be sure to select "Actual Size" and not "Fit". 

Failure to do so will mean your components won't fit!

Draft Print.

When printing in Adobe Reader/Acrobat, it is very important to ensure that you select "Actual Size" and not "Fit". Failure to make the proper selection will lead to an improperly sized board. For now, just print to regular paper. Our goal is to ensure that the board has the proper size and that the components will fit. Hopefully your board is sized to nice round numbers so you can easily measure it! If, after printing, your board isn't the right size, either fix something in Eagle (if that's what you're using) or use Adobe's Custom Scale to make adjustments until you get it just right.

Placement Model.

This is a trick I learned just today. After you confirm your board's size, cutout the board outline and attach to a piece of styrofoam. Insert components into the foam. This checks that the footprints are the correct size, and gives you a great place to keep your components for easy access while soldering.

Component Test Fit in Foam

TIP: You might notice that there are a pair of unoccupied holes near the tactile button switch (the blue button) in the lower left side. I reclaimed a bunch of tactile buttons from an old VCR several years ago and just found them. These buttons were a 2-hole model whereas I was planning on using a 4 hole model. It fits fine in the footprint, except that it is shifted a little. No big deal. It is always wise to check that reclaimed parts still work. The first switch I tested actually didn't work. I can't remember what was wrong with the VCR other than the owner (my dad) said it wasn't working. There is a good chance that the stuck switch was the culprit. More interestingly, in the last two weeks, I've fixed two devices that were "broken" and discarded. Turns out, all that was wrong with them were switches and after addressing the problem, both devices (a blender and a faux-fireplace heater) are working properly. Fixing the switches cost me about 5 cents and an hour of time each. Moral of the story: You can save yourself some cash with broken appliances by checking for simple fixes before you discard them. With this in mind, I recently acquired a broken Blu-ray player. I have no idea what's wrong with it... my dad's repeated response was a very irritated "IT DOESN'T WORK". So hopefully all that's wrong is a faulty switch.

Masking

Now that we have our drawing completed, sized, and ready to go, we are ready to print. But first, a word on paper. Many of the tutorials for the Toner Transfer Method recommend using photo paper. This works but it is difficult to sense when you are done ironing the toner to the board. It also takes an agonizingly long time for the paper to dissolve in water. Therefore, I recommend using an unlikely alternative.

The glossy paper from magazines is perfect for our toner transfer. I happened to scavenge a Harper's and found two different types of paper inside. One is like newspaper; do not use this; it will not transfer the toner. The thin glossy paper used for most of the articles is perfect. It is thin, so you can actually see that the toner has adhered to the board after ironing. The paper also dissolves nearly instantly once immersed in water.

There is only one problem. The paper is not strong enough to run through a printer. It tends to get stuck and jams the printer. So we need to tape the magazine paper to a piece of printer paper. If you have heavy paper such as construction paper, even better. If your printout board doesn't land in the center of the paper, I'd recommend printing one copy of the board on the carrier paper. Then when you tape the magazine paper, you know exactly where to put it. Tape all edges to prevent jams.





Printer Selection.

I use a Samsung SCX-3405W that I found for about $75 online. It included the toner, which is good because a replacement toner cartridge is about $80. The only requirements are that you use a black laser jet printer. I've been told that color printers, even when printing in black and white, do not work properly. I've also been told that some of the newer Epson or Brother printers do not work properly. I am only passing on second hand information and have not confirmed this. If shopping for a printer, bring some photo paper and see if they would print out some sample pages for you. You can try to transfer the toner and see what works best. A cheaper alternative would be to see if FedEx/Kinkos or your local library has a black only laser printer. I doubt they would allow you to print to magazine paper, but the photo paper works. It's just more time consuming. If using a commercial printer, it would be wise to print out multiple copies on a single page. I'd recommend getting at least 10 copies of your board because there is a learning curve.

Heat Transfer.

Use a napkin so that you can hold the board. It gets HOT!

The napkin also keep the tape from melting onto the iron.

Transferring the toner is a bit of an art and takes some practice. Fortunately, if you mess up, you can strip the toner with acetone and start over. All you need to transfer the toner is a cheap iron. Be sure to drain out the water so that it doesn't ruin your print. Set the iron to it's highest setting and let it warm up. Align the transfer sheet to your board and tape along two edges. Some people recommend preheating the board, but I find this to be unnecessary. I'd recommend using a couple of napkins to hold the board while your heating it... it gets hot! After your iron is hot, run it over the board... AVOID THE TAPE for now! The tape could ruin your iron and will likely leave a messy residue on your board. Check the un-taped edges of the board; the transfer should stick on it's own so you can remove the tape. I iron one-half of the board at a time, holding the other half of the board with a folded up napkin so I don't get burned. Then I rotate the board 90-degrees and continue the cycle until the board has been ironed several times. Keep the iron moving so you don't burn the toner. Allow the board to cool and check to see if all the toner has adhered to the board. This can be tricky to do. Try to lift up the edges of the paper. Another trick is to take a bead of water and smear it across the paper. The paper will warp slightly allowing you to find toner that didn't adhere. Once you are satisfied, submerge the board in lukewarm water and let sit for about a minute. Slowly peel the paper, you don't want to move too quickly or risk pulling up some of the toner.

Transfer Mask Inspection.

Some of the toner flaked off of this board. This time it's only

cosmetic; a quick touch-up with a black magic marker saved

the day.

After removing the paper, check the board for paper and tape residue. There can be none left on the bare copper. Check the traces and planes for continuity. It's ok if a few spots are smudged or have flaked off. TIP: Use a sharpie marker to touch up missing toner. I have a fine point (0.5mm) marker to touch up edges and fine traces and a standard sharpie for general purpose touch ups. Sharpie markers are resistant to the etching solution. You could even skip the toner transfer and just use a sharpie marker to mask off a board if you wanted.

If your transfer mask has severe defects, don't panic. You can clean off the board with acetone and a toothbrush. Once complete, give a quick sanding with fine sandpaper. Wash with soapy water and a brush. I dry the board and rinse it with rubbing alcohol to prevent dust or lint from contaminating the board surface.

Etching.

I've been using Ferric Chloride but it's nasty stuff. I'm considering the alternative found at this website in the future: http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc/

Until then I'm still using Ferric Chloride. You can buy a bottle at Radio Shack for less than $10. While you're out shopping, get some good rubber gloves, a large Rubbermaid dishpan, a funnel, and some of those cheap glad food storage containers that are large enough to hold your board. Ferric Chloride will stain anything it touches with a nasty yellow color and (obviously) will dissolve metal.

I use the rubber maid basin as a tote and for storage. If anything leaks, it will be contained in the basin. Put the board in the plastic container and add the etchant solution. Don't use more than you need. You want the board to be submerged, but not so much that you can't see the traces. I've never timed the process but it takes about 10-15 minutes. At first the bare copper turns a pinkish color. Swirl the dish slightly to agitate the solution. This ensures that the board is always in contact with fresh solution and speeds up the process slightly. Occasionally, I tilt the dish so that part of the board emerges from the solution so I can observe the progress. The copper will first be removed from the edges of the board but the traces tend to be the first areas to be finished. Large copper areas will be last. After about 8 minutes, you should be able to see distinct areas where the copper has been removed exposing the substrate. It is very important to keep an eye on your board, especially if you've used marker to touch up the mask. Check to ensure that bits of toner or marker aren't removed during the etching. If you see this happen, remove the board and rinse with water. Dry and touch up the board with a sharpie marker. These spots will be ok as long as you catch the problem early enough.

When you are satisfied that the board has been completely etched, remove from the solution and rinse. I use a plastic fork and rubber gloves to lift the board. For rinsing, I use a second plastic container filled with water. Concentrated Ferric Chloride is hazardous and cannot be poured down a sink or flushed down the toilet. Funnel it into a second plastic or glass bottle and you can reuse it a few times before disposing it properly: http://www.mgchemicals.com/tech-support/ferric_faq/

Drill Holes and Remove Mask:

Dremel Rotary Workstation and a Pin-Vise

Before you remove the mask, drill the holes. I use a Dremel with the Dremel Workstation. It's like a small drill press and works perfectly. Drilling before removing the mask helps to prevent the drill bit from "walking" or wobbling off-target. With the mask on, I very rarely have this issue. Nevertheless, you will on occasion have a hole that won't stay centered. Usually this happens when I start to drill a hole and realize I was off-center. No matter what you do in this instance, the bit will walk back into the hole you started. This can be fixed by using a pin-vise to manually drill the hole. Also use the pin-vise if you need very precisely aligned holes. It takes a bit longer, but the results are worth it.

Once you've drilled all the holes, you can remove the mask with acetone and a toothbrush.









Silkscreen:

This is something that I've just started doing, and I've not seen anyone else do it on homebrewed boards. It takes a little bit of time, but the results are nothing short of professional. Imagine the time you will save later on when you are trying to remember what pin does what!

Remember the toner transfer you just did? The same process works for the silk-screen layer on the top of the board.

This was my first try at creating a silkscreen. Not bad except

for a slight misalignment. Now I include alignment marks

in my silkscreen transfer and it comes out perfect everytime.

Back in your CAD program, we need to make the silk screen layer. Fritzing generates a silk screen mask automatically. In eagle you need to turn off all layers, except the silkscreen layers (I use dimension, tPlace, tName, tValues). TIP: before turning off the layers, add some alignment marks. I use very small letter "O's" to mark a few of the hole centers, one or two in each quadrant of the board. It's best to choose holes that you could easily identify later... LED holes are good candidates. The corner pins of an IC are good choices. A middle pin of an IC or header is a bad choice. You can also use ficidual marks, but marking a few existing holes is easier.

Print out the silkscreen so that any text will appear in reverse on the paper. Use the same printing method we used for the mask. If you took my advice and made alignment marks, use pins to punch holes in the paper. Align the paper on the board so that the pins go through the proper holes and tape the paper in place, ensuring that the pins stay aligned and the paper lays flat. Keep the tape away from your silkscreen markings. Remove the pins and iron as before. There won't be enough toner to properly adhere the paper to the board so you'll have to leave the tape on. Use a folded paper napkin to minimize heat transfer into the tape.

When you're done, let the board cool and soak in lukewarm water as before. The paper will probably come off on it's own.

Prep the Board:

Toner removed and ready for tinning or soldering.

For best soldering results, hold off on prepping the board until just before you are actually going to solder parts. The copper needs to be as clean and fresh as possible. Even small amounts of tarnish that accumulate overnight can make soldering difficult.

Once you're ready to solder your board, we are going to clean it, and optionally for best results, tin it (or at least the pads). Clean the board by rubbing it will fine (I use 600-grit) sandpaper ensuring that you remove any remnants of toner and corrosion. The copper should be shiny and new. Scrub with soapy water and a brush. Dry and rinse with rubbing alcohol. It will dry on it's own or you can use a lint free cloth. You don't want any lint or dust on the board at this point.

It's very difficult to solder directly to copper so you'll want to tin your board. In the future, I'll start using tinning solution or this technique: http://stompville.co.uk/?p=85. For now, I have a simple technique, but it requires a little finesse and is probably really bad for my soldering iron's tip. I heat up the iron, then insert the tip into a hole in the PCB, allowing it to heat slightly. I then touch a bit of flux core solder to the pad. It takes a little practice but works nicely. It is best to add the solder at the narrowest point of a pad (the part facing away from the trace). Solder will flow from the narrow part of the pad to the trace, but it won't flow from the trace to the narrow part of the pad. You may have to add solder from multiple angles. When you get the hang of it, solder will flow very easily. We want to use as little as possible, avoid letting it clump up.

This takes a long time, but the results are very much worth the effort. If you follow only one bit of advice in this lengthy tutorial... tin your boards!

Once done, you'll want to open the holes. You did buy that pin vise right? This isn't something you want to do with a drill press. Drill from the solder side of the board. If you drill from the top side of the board, you could peel the copper pad right off the substrate. The same could happen if you don't open the holes and try to push a lead through the hole, so it's best make sure that the holes are still open.

Conclusion:

You should now have a nice-looking homebrew board that is ready to be soldered. I hope that you find these techniques helpful. I've tried very hard to communicate mistakes that I've made in the past so that you don't have to repeat them. I've had good results and hope you do to! - Andrew Ticknor

Resources:
CAD Software: Eagle PCB, Fritzing

Printing:
-Monochrome Laser Printer: Samsung SCX-3405W
-Glossy Magazine Paper

Toner Transfer:
- Scotch Tape
- Iron
- Sharpie Fine Point Marker,
- Sharpie Ultra Fine Point Marker
- Paper Napkins or Hot Mitt\
- Large Head Sewing Pins

Etching:
- Cheaper, reusable and less-toxic Etching Solution or Nasty Ferric Chloride
- Rubber gloves, eye protection
- Rubbermaid Dishpan
- Plastic Containers
- Plastic fork or spoon
- Plastic Funnel

Toner Removal:
- Plastic Containers
- Acetone or nailpolish remover
- Old Toothbrush

Board Prep:
- Dremel Rotary Tool
- Dremel Work Station
- Small Drill Bits (1/16", 1/32", 3/64")
- Pin-vise
- Fine Grit Sandpaper
- Rubbing Alcohol
- Old Toothbrush
- Solder
- Soldering Iron
- Tinning solution or try this link: http://stompville.co.uk/?p=85