Senior Member
In the UK - PCB Draughting Film A4, 5 Sheets - Farnell 141331 £4.27Originally Posted by The_Doctor
Has a very finely pitted matt finish to aid holding toner and inkjet ink.
Pricey but the Polyester film has a melting point of 260C
I have had 3 tracks between the pads of a 1206 resistor using a laser
printer and this film.
Print a mirror image and then place the toner side against your UV sensitive
board.
Rgds,
Robin
Senior Member
Thankyou, I'll avoid that stuff then. I suspect it wouldn't have passed my soldering iron test anyway.
Robin, that stuff looks like the same stuff Maplin had, theirs was A5 though.
Jem, thanks, that's really useful info. I think that 100 sheets might be in the 'group buy' scale of things, if it's going to be £50 minimum spend. I could do it but 100 sheets is more than I need, I'd sell some on if I did it to get some money back. Can't find it though, that site has a shop site that doesn't have anything like what's described on the page that links directly to it.
I checked http://rswww.com as well, their order code 286-6773 is for a film that has a more complex procedure for use but is priced well enough to consider trying it. I can't understand the data sheet though, it seems to be describing more than one thing, and doesn't seem to be describing what I need, it seems to be to do with vinyl label making.
Last edited by The_Doctor; 10-14-2007 at 08:57.
Senior Member
Doc
Send me a PM with your Address to save me time hunting through my old stuff to find it again
I'll send you a few sheets of the Folex I have here and you can give it a try.
Jem
Senior Member
Thankyou, pm on its way.
In case anyone's wondering how the hell I used to do this as it looks like I'm starting on something that might be familiar to most who make boards, bear in mind I couldn't afford a laser printer before.
This is what I used to do:
Inkjet rendering to fine paper, enlarged four or even eight times.
Carry it two miles to a trade screen printer who'd use a phto-reduction tool to print it to acetate.
Pay a fiver or so and carry it back and do the UV exposure.
The accuracy was good, but the tedium was terrible, and as a decent laser printer can now be bought used for not much more than I'd spend per board design I wanted to make, it's better to do it all here now. Besides, the trade screen printer vanished, building and all.
Last edited by The_Doctor; 10-14-2007 at 08:54.
Senior Member
FYI have just found out that Rapid do 10 sheets for £4.80
Laser Star Film 39-0774
http://www.rapidonline.com/
Senior Member
Jem sent me some Folex sheets. That's a better buy, if it's not much more than 50 pence a sheet. It's 90 microns thick as opposed to only 75 too, so I'm contemplating buying the full 100 sheet box. It's the same stuff Maplin sold me years ago, but the chemistry is better. Either that or it ages so that older sheets will warp and yellow slightly when being passed through the fuser. The Folex sheet doesn't do this. Toner adhesion is better during fusing too. Broad tracks and especially large fills are thinner than fine tracks, but there doesn't seem to be much I can do about that.
I looked into this enhancer stuff too, not got any yet but nothing special is needed, I found more than enough screen printers posting online to discover that it's a gloss acrylic clear spray paint. Krylon Crystal Clear is one brand, but in the UK I'll have to search by actual material, not brand name. Artists suppliers sell it as charcoal fixative, but I think I might find it cheaper in a hardware shop. Doesn't matter what the solvent is much, Folex and other polyester films can withstand prolonged contact with acetone.
I also think a second non-printing pass through the fuser first might help. Wouldn't want to do that afterwards though, not with acrylic.
If anyone ever figured out a way to put a sheet through a laser printer for a second print with VERY accurate placement for the second pass, please let me know. I've given up quickly on efforts to make that work, but there might be a way I haven't considered.
Last edited by The_Doctor; 10-18-2007 at 16:21.
Senior Member
I have done several PCBs using the toner transfer method. I can get tracks down to 12 mils fairly reliably, and there is no development step to do. I use an HP laserjet 4 which can be found for $50 used surplus.
process is similar to this:
http://myweb.cableone.net/wheedal/pcb.htm
Senior Member
Needs a special film to bind the toner surface against etchant, and a laminator or other means of applying heat and pressure. I read up on the system often, but I'd rather take my chances with pre-sensitized boards, it's possible to get them at a good price, and exposure/developing isn't that tough to do. If it didn't have a significant edge over toner transfer, it wouldn't be the dominant method.
I meant to do my test etch today but I've been too busy. Did find some clear acetate laquer though, in an artists supply shop as I hoped. 150 ml for less money than the hardware shop wanted for the 100 ml can that was their only offering, so that's good. Stuff works too, it really does blacken the traces and bulk fills adequately. I'll try it on paper too, as well as the polyester Folex sheets. Could work, it will make paper more translucent, and help it to keep long term stability.
Last edited by The_Doctor; 10-19-2007 at 11:53.
Senior Member
First test. Only two errors, none unrecoverable. Got to get the exposure time raised to compensate for UV absorbtion in the film, and increase the linewidth of the corner markings so they survive etching, but everything else went as planned. That lightbox can correctly expose a board 4" by 12" in 5 minutes, so I don't think I need to spend another penny on that task, I won't be developing boards bigger than that on my own, if at all.
To keep this from being too unrelated to lasers, this is version 2 of my laser power meter gain stage. 5VDC goes in the end with 2 pads, the end with 3 pads has a TEC painted black and glued on a big heatsink, commoned to ground with the 5V supply and the output, which scales accurately from 0V (adjustable zero point) to over 20 volts, to measure up to 20 watts on a single range, ideal for connecting to any voltmeter for displaying the value.
The circuit is tested and works well, but version 1 had grounding problems associated with an LED panel meter's wildly changing supply current. These might be avoided with a plastic box, but I'll try again to do it in metal if it will all fit the one I want to use. (very small). There will be two BNC sockets on it, one for sensor input, one for gain stage output to connect to a different meter or a datalogger.
I'll post a full detail on parts including the PCB artwork in 600 DPI bitmap and a schematic eventually, this is just a pointer of one of the ways this work of mine is going. The circuit and parts detail will be all public domain, anyone can use it so long as they don't sell it, or anything built from it.
I intend to make a few ready to use, for sale. I'm after raising money to buy a small mill to do CNC work, to make all this easier than it is now. No prices yet though, too early to know.
Senior Member
Hey just a suggestion for you.
On your pads for through hole components change the pads to have holes in the center. It makes it much easier to drill when there is a center hole to line up the bit, kind of a pilot hole. Other than that they look great. It is hard to beat the presensitized transparency method for good quality low run home made boards prototype boards.
Prices are pretty reasonable for professional boards now days so when you have things working pro boards are a no brainer..
When the going gets weird, the weird turn pro.
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