Laser printer transparent paper for PCB making

[madires]

I see more problems with lasers than inkjets  of you look somewhere PCB specific like the HomebrewPCB Google group. And if you've ever spilled toner, you'll know what hell that can be! As with all of us I'm basing my opinions on just what I've observed rather than any scientific testing.

You need to be all thumbs and have a bad day to be able to spill toner all over the place. It's not worse than ink.

Wax printers like many modern Xerox ones are really nice. In theory they could print straight to PCB, but I'm not sure anyone had done it.

The wax printers need a lot of power. And if you dare to switch them off, they'll eat half a stix of all 4 colors when powered on again. I'd prefer a color laser because of that.

[mikeselectricstuff]

I'm told that wax print onto copper clad does work, not sure how well.
I also know someone who was experimenting with printing wax through an epson inkjet head, which they apparently got working pretty well.

[SeanB]

Wax printers like the Phaser series do not work with masking PCB, as they use a thin film of silicone oil on the drum as a transfer medium to hold the image onto the hot drum, and this is transferred to the paper as well, giving it a waterproof coating all over.

Wonder if it would be possible to take the 60 spot print head out of one, and use the step mechanism along with a linear PCB feeder to do a multipass wax deposition, but that would mean ripping the printer apart. That would not need the transfer unit that deposits oil. Probably would be better to get a cheap thermal printer that has a head that can take a wax ribbon and use that as a printer. Those are probably usable pretty much as is.

[radioFlash]

I found the yellow PCB Toner transfer paper from ebay works very well.

[akis]

I use a flatbed UV box that I bought cheap on ebay. It has 6 UV tubes of 9W each. A thick piece of glass (6mm) on the top and a lid with foam to press down on the PCB. One side at a time. After a lot of trial and error and head scratching I finally have figured it out.

1) The UV box must have been on for at least 5 mins prior to exposing anything, and even when turning the board over to do the other side, must keep it on, so the lamps stay warm. Failure to do that means all the timings are off, completely off, one side good, other side bad and so on. This is very important and I bought a lux meter to make sure there is a difference, when warm the lamps are twice the lux output than when cold. Huge difference.

2) To do double sided boards, I print a horizontal and a vertical guide lines on the top left of the board adjacent to the edges, and use those two guide lines to align the board. The reason for only two lines is because the board is not perfectly square. This is very important to note. No matter how it has been cut at home, some sides are better than others (I use a circular tile saw and my cuts are good, but not perfect in terms of absolute squares). I look at the board and choose the two most "straight" sides and mark that corner as "top left". I use this corner to align against the guide lines, if both lines cannot be made perfect, then I choose only one line and make a note which line it is. When I turn the board over, I again align on the same guide line. Using this technique on 110 x 150 mm boards, yields better than 0.5mm accuracy even on the farthest point. I have not yet tried using staples or glue to sandwich the board inside the two transparencies, I cannot see how that will work with exposing one side at a time and having to flip over the whole assembly, and the board inevitably moving.

3) The developer must be at a perfect 23-25C and it takes approx 45 seconds of vigorous splashing to develop. In the winter time the developer must be heated to reach the 24C. a few degrees do make a lot of difference and it is much preferable to spend time getting to the correct temperature than attempting to develop a board which refuses to or over develops. To make sure there is no over development I have 4 very thin crosses on the board - if these disappear it means there has been too much development (or exposure). Typically 45 seconds, max 60 seconds is enough.

4) I have plastic stackable tubs/shoe boxes in which I run all the chemicals, and to heat up a chemical, I put hot or boiling water into one box, and then place the chemical box inside of it (they are stackable). This is the way I do the etching, it takes about one hour, and I re-boil the bottom box water two or three times.

5) My boards are through hole, thinnest traces are usually 0.7mm and gaps are also 0.7mm. I have not attempted better definition.