Thermal wax printers OK for PCB photo resist transparencies?

[Chris Wilson]

My ol HP 4000n black and white laser printer packed up recently, not that
it gave very dense black images on transparencies for photoresist printing
for PCB etching. I went to a fairy local large printer refurb
place yesterday and they ran my pdf ile through a few different laser
black and white printers and the results were less than stunning. The
senior technician there reckoned a thermal wax printer would be more
appropriate and has set one up for me to try today. he says the
results on my transparency film were much better than even a high end
laser achieved.

has anyone any experience of using a thermal wax printer for
transparencies for photo resist board?

[Fred27]

Forget transparencies - you want to print the wax as etch resist straight to the PCB!

Sent from my Nexus 6 using Tapatalk

[Kean]

If he is talking about a Tek/Xerox Phaser type printer then the paper path isn't going to handle PCB material.
Maybe the *really* thin stuff - i.e. 5 mil = 0.127mm, which I think is about the same as 100gsm paper.
Like this https://pcbfx.com/main_site/pages/products/flex_pc_board.html

The quality of a Phaser is very good - but I suspect they may be a bit expensive to run.  Never tried one for PCB exposure.
Not sure how hot the Phasers get during printing - but you can get higher temperature transparencies for laser printers if necessary.

[bw2341]

There's the thermal transfer printer where a full-width thermal printhead selectively melts ink off a full-area ribbon onto the paper. I don't think this is what the technician is recommending since thermal transfer is usually used for high-speed, easy-maintenance label printing in narrower widths (4-inches). There's the related dye-sublimation technology which thermally transfers dye to its own dedicated paper. Its selling point is continuous tone printing for photos.

I think your technician is recommending solid ink printer technology. Waxy ink blocks are melted and the printhead deposits it on the page. It's compatible with a wide range range of media and the ink is very opaque. However, it might be a bad choice for a low usage application. The printer has to keep the ink melted for on-demand printing. If you only print a few pages once in a while, you'll cook the inks in the tanks so much that they'll go bad. Ask your technician how many pages a month are needed to keep the inks fresh. Ask if you can disable the color part of printer as you won't be using color printing at all for photoresist masks.

[Kean]

There's the thermal transfer printer where a full-width thermal printhead selectively melts ink off a full-area ribbon onto the paper. I don't think this is what the technician is recommending since thermal transfer is usually used for high-speed, easy-maintenance label printing in narrower widths (4-inches).

Yeah, these would be something like the Zebra label printers used in warehouses.  I deal with them regularly in my IT consulting role.  The commonly available (& thus cheap) ones are 203 DPI (8 dots per mm) so really not suitable for PCB use.  There are higher spec ones that do 400 DPI or 600 DPI which might be OK - but they're designed for printing on rolls of labels, not transparencies.  They have an optical sensor for detecting the gaps between labels, which you'd have to defeat.  Pretty sure this isn't what the OP's technician had in mind.

I think your technician is recommending solid ink printer technology. Waxy ink blocks are melted and the printhead deposits it on the page. It's compatible with a wide range range of media and the ink is very opaque. However, it might be a bad choice for a low usage application. The printer has to keep the ink melted for on-demand printing. If you only print a few pages once in a while, you'll cook the inks in the tanks so much that they'll go bad. Ask your technician how many pages a month are needed to keep the inks fresh. Ask if you can disable the color part of printer as you won't be using color printing at all for photoresist masks.

And this is the Tek/Xerox Phaser style printer I mentioned above.  I agree that solid ink printer isn't ideal for occasional use, so you'd want to be using it for day to day printing as well, and it will hurt your power bill a bit due to the high idle power consumption.  I don't think it will "cook" the inks, but it will waste them if you power it down fully.  A list of advantage & disadvantages to keep in mind with these types of printers are summarised on https://en.wikipedia.org/wiki/Solid_ink

[bw2341]

The repair horror stories I've read point to the color quality going bad after months of cooking the ink. This worst-case scenario happens when the printer is timer started every day but very rarely used. Flushing out the bad ink can be a bit of an ordeal and might require a service technician. I suppose the ink won't go bad if the printer is cold started only when needed, but the cost per page will be higher due to waste.

[CJay]

I'm self sufficient in Xerox ink for a while yet, shame we've no Xerox printers left on site.

Those Zebra printers, an idea occurs to me that the waste part of the thermal ink roll could be pressed into use as transparency, if there was a way to print fine graphics then it'd leave a roll of transparency with the negative of the image on it...

Generally find turning off all the image 'enhancement' on laser printers gives a better result, the dithering on even the enterprise grade one here makes it completely unsuited for PCB transparencies, I've tried.

I have to admit I've not tried the wax printers though, I'd be interested to know how they perform.

As for timers and ink cooking, they're designed to be left switched on 24x7 which reduces the issues with clogged ink I believe but does reduce the service life of the printer and lead to more regular maintenance/cleaning.

[SeanB]

Got a Phasor340 in the garage ( and a lifetime supply of black colourstix as well) and would not recommend it as a PCB coat, even though the wax will be a near perfect resist. The issue is the silicone oil that is used as a release agent on the drum, which will also coat the paper and the board, and which is also a near perfect resist as well. As well the wax prints are very easy to smear, and tended to do that just from handling.

Would recommend an older HP laserjet though, and a non genuine T shirt transfer toner cartridge, as these do print a very nice black.

Funny enough took the CF280 cartridge in to have it refilled, as it has been running with the "toner very low" warning on it for the last 2 weeks. 4600 pages printed though, while the OEM cartridge ( with the same average density of print as well) barely makes 2000 pages before fading, and shows low at 1500 pages. funny that, the refill is better all round, better black, better life and better price. Just had to buy 12 for the 1 year warranty period, so had plenty of refill blanks after that.

[Chris Wilson]

I wasn't intending trying to put the wax image straight on the PCB, just wanted to get an image on acetate sheet or the tracing type paper that is dense. the LaserJet 4000 has been a great printer for normal duties but the images for PCB photoresist were semi transparent so it was always a
juggling act getting enough UV to expose where needed without semi exposing the tracks.

Anyway, i went over the tech demonstrated a Xerox and as soon as i saw the results I knwe I'd be taking it home. TOTALLY dense black, even held by a light bulb no light gets through, and detail was spot on. Running costs are pretty academic as I will only use it for the odd PCB and the odd photo, (which it reproduces in very vibrant colours with a photo like sheen). The way i see it is photoresist is also costly, so if I bugger a few photo resist boards it's not only time consuming and frustrating, but hits the wallet. The guy did warn me occasional use was not very cost efficient, for the reasons others have stated above, but hey, if my PCB's are better and I don't waste as much other material, maybe it'll balance out!

Happy so far, if I hit snags I'll post `em up here, thanks everyone.

[Fred27]

I was only joking about putting the PCB through the printer. The wax would be great in theory but that would be one bitch of a paper jam to clear. I know laser printers have been converted to print onto PCBs with limited success.