I've been tinkering on this blinky light project for awhile, almost a year now. I finally got around to etching the all-critical prototype PCB today. Maybe I can finally get this show back on the road. It will be a totem pole of sorts that runs like a solar powered garden light utilizing four independent QLF6 (or Quad LED Flasher v6.0) circuits.
I went the "laserjet-magazine paper toner transfer" route of PCB production. Patrick posted some very cheap places for small-run PCB manufacturing but I don't even know if I need that many yet. I'll get ghetto-fabulous for the first protoboard before potentially tossing my money out the window. Who knows if this thing will fly logistically.
So one of the keys behind this Cheapest of All The Transfer Techniques is using the interior pages of a magazine (not too thick like the magazine covers) that has a shiny look to it. You know, like a magazine, not a newspaper. Keep it as clean and fingerprint-free as you can, before and after you print on it. You can also use ordinary laser printer photopaper. The shiny element on both the magazine and the laser photopaper is a coating that is composed partially of clay. That clay is key to releasing off the paper.
Moving forward, one of the other keys is the laser printer toner. Just like copying machine toner (which also will work for this transfer method), it's composed of very fine plastic particles which are melted onto the paper in the image of your choosing. It doesn't really soak into the paper, but rides on the outside, much like the clay on the above-mentioned paper choices. This is why inkjets printers will not work. Inkjet printers use liquid ink which does nothing for your PCB making goals. The toner is the mask that will keep the etchant away from your traces. Don't cheap out. Turn off the Econo-mode or Toner Saver setting on your printer to maximize your toner to transfer.
The first thing you want to do is obtain your circuit design. This can be done by downloading a picture of the circuit or by designing it yourself with a program such as EAGLE, DipTrace, ExpressPCB, or one of the many others out there. Then you want to print it out on a laser printer (I can't stress this enough) onto your magazine paper. Remember to mirror the printout of the top layer as it will be reversed.
Next you want to prep your clad board, single or double sided. If you're doing double sided, consider how you will line up the top and bottom layers. Lining up the drill holes is critical. Prep the copper cladding with a fine sandpaper or the like until it shines. Then clean off the board with contact cleaner, brake cleaner, or even isopropyl alcohol. The copper needs to be spotless. This is another key.
At this point you will essentially do what a laser printer or copy machine does and you'll melt the image of your PCB design onto your copper board with the paper attached to it. Some people like to use a clothes iron set to its hottest setting with some protective backing paper. Some use laminator machines to varying degrees of success. I use an electric tabletop stove set to medium (high setting burns the paper and toner).
The important things are:
- It must get hot enough (through both sides if using double-clad boards) to melt the toner.
- You must not move the paper while the toner is melted. You will get useless smudged circuit traces.
- Apply pressure to adhere the melted toner to the copper while obeying the above stated condition.
After you feel satisfied it's melted and stuck down, throw the whole thing in cold water while obeying the second above stated bulletpoint. Be very careful not to smudge, it's a real bummer when you do. You can leave it in the water for some time. More is more in this case. The water will let the clay layer on the paper and the paper itself dissolve away and the toner will be left behind. Any residual paper can be rubbed off with your finger or even your fingernail. The toner is quite tough. It will form a protective layer from the etchant and can be cleaned off with acetone.
That's the essence of it.
So onto my pics...
Pics of the top and bottom transfer printouts:
I print out two T's that I use to align the the layers with. I line them up by pointing my bench light at the back of them, lightbox style, and I tape one side together to hold the correct alignment.
Pic of the transfer gizmo I use:
I use a couple flat aluminum blocks that have convenient pin and hole arrangements so I can lock the whole thing together when it's set up just right. It makes flipping the board on the stove easier to do without smearing the toner.
Pics of the boards after heating, cooling, and cleaning (top, bottom):
There are obvious places where the toner smooshed together to create short circuits and places where the toner did not adhere. Just scrape away the toner that makes unwanted connections with a razor blade tip. To fill in gaps, like with the four pin connector on the left of the top layer, you can use a Sharpie marker (black only). Its lacquer-based ink will block the etchant. I use Sharpie Industrial markers. Only acetone will remove that ink. Alcohol can remove ordinary Sharpie ink, for the record.
To conserve etchant (nasty stuff) I use a small baggie to minimize the volume I need. I immerse it in some hot water in the kitchen sink to help it along (heat and oxygen speed things up).
Pic of chemistry in action:
As soon as the required copper was dissolved, out came the board, into some water for a cleaning, and kapowee!...
You can still see the ink printing in the toner. You can also see where I touched up spots with the marker and how well it works.
It still needs to pass the drill test to see if I got everything lined up well enough but it looks ok (not perfect, gah) through the benchlight. Hopefully it will serve its meager purpose as a test fitment unit.
I will post more as things develop.
Nov. 11, 2010:
After drilling, populating, and days of troubleshooting (not to mention making another PCB), I got very frustrated trying to get the circuit to work correctly. After looking at the schematic I realized the PCB circuit will never work correctly if the schematic is screwed up. I have since corrected the mistakes and have the transfers ready to print out but I broke every one of my 0.8mm drill bits fiddling with unfixable PCBs. I'm so broke right now I'm living on a noodle/bread diet. Needless to say there is no room in the budget for replacement bits at the moment. Things will change shortly but this project has come to a halt for the time being.