Laser Printed Transparency Enhancement for PCB Photoresist - Page 1
Forum section: electronics / general

author: jpanhalt
author_rank: Super Contributor
timestamp: February 03, 2017, 09:01:05 pm
content: In a another thread, I mentioned a method I had been using to enhance the color density of LaserJet transparencies used for masking photoresists. See here:https://www.eevblog.com/forum/beginners/good-printer-for-transparencies-for-uv-pcb/msg1107747/#msg1107747The crux of my comment was that the method worked well with HP LaserJet toner, but not with Brother and probably many other toners.I needed some quick PCB's, so I played a little with the Brother laser transparencies:Printer = Brother HL-2270DWPrinter settings: HQ1200 ; Advanced>Other Print Options>Improve Print Output>select Improve Toner FixingTransparency: 3M CG3300DryErase marker: Expo Low Odor black (Walmart and many others)Program: Eagle 7.2.0The problem with Brother's toner (and probably other low-temperature fusers too) appears to be that the toner is soft relative to HP's LaserJets. Microscopically HP's toner appears as relatively small dots; Brother's appears more blotchy like fine ink splatters. The process of going over the transparency liberally and then wiping the dried marker off left scratches and removed some of the original toner. On redoing it, I became suspicious that most of the damage happened while trying to paint the DryErase marker on the image. Also, according to the MSDS's, it appears that the different formulations all contain a relatively high boiling solvent like 2-propoxyethanol (aka a glycol ether, "Cellosolve", see:https://en.wikipedia.org/wiki/Glycol_ethers) or a similar solvent, diacetone alcohol.So, here is what I did:1) Removed ink cartridge from the maker and squeezed out the ink.*2) Used a small, round camel hair brush to paint a thin layer of the ink onto the printed transparency.3) Use a hot air gun (low temp space heater) to thoroughly dry the solvent before wiping the excess off with a soft tissue. Glycol ethers have a characteristic odor, and I heated until the odor was effectively gone.4) (optional) I added a very small amount of isopropyl alcohol to the ink to get a thinner layer. The thinner layer is easier to remove, but putting less ink on the brush also works. A brush wetted with alcohol was all that was needed for 2 mL of ink. Too much diluent will ruin the ink for this purpose.Attached photos:Brother PCB 020317 #2: Image with view box (fluorescent bulbs) back light showing difference between treated and untreated areas. Unfortunately, my camera had a tough time focusing because of the inherent flicker of the lamps.Brother PCB 020317 #3: Magnified image with an Adonstar cameraAfter thorough drying, I found the Brother toner just as durable as the HP toner. In fact, you can polish the image until no more black marker ink is removed without damaging it.John*That procedure can be really messy or clean. Wear gloves and do not do it over carpet or good flooring, just in case. I used a tubing or pipe cutter to make a deep score about 1/2" from the read end of the marker. Then a sharp razor blade finished removing the endcap. The ink is absorbed onto a cylindrical substrate which has a smooth outer sleeve ("tampon"). I put the whole thing into a plastic sleeve (I have 2" flat sleeving that I heat seal, a small ziplock freezer bag would probably work. I suggest freezer bags as the plastic is a littler heavier gauge. I then used a pair of wide nose vise grips (3" wide, #8R) to squeeze the ink from the tampon from the outside of the bag. Remove the tampon with tweezers, and your are set. Individual markers are less than $1 each, so I just used the bag of ink and did not try to transfer it to a storage bottle.

author: KL27x
author_rank: Super Contributor
timestamp: February 04, 2017, 12:09:06 am
content: Im curious what makes you think the Brother toner is "low temp."I have Brother printer that takes TN330 cartridge. The toner doesn't melt/transfer unless you use super high heat. Some reviewers complained it dimmed their light when the fuser turned on. Your printer takes TN420.... MSDS shows different ingredients between these toners... and also for HP. if TN420, indeed, melts at lower temp than HP/standard toner, maybe it's easier to transfer than normal toner? (Using HP now, for transfer... maybe there's better/eaiser? I shoot it with hot air gun when going thru the laminator.)

author: AlfBaz
author_rank: Super Contributor
timestamp: February 04, 2017, 01:01:20 am
content: Jpanhalt, not to take away from your technique but I've mentioned thisbefore. By far the easiest method of getting 100% opacity with the ability to get down to 4/4mil track spacing is inkjet, sprinkle transparency with talcum powder shortly after it comes out of the printer. When dry wipe away excess talc

author: jpanhalt
author_rank: Super Contributor
timestamp: February 04, 2017, 11:29:54 am
content: @AlfBazI haven't tried talc. That is a good idea. Might do it today. Originally, I was biased by thinking that the particles needed to be in a matrix that would wet the toner on polyester film. I considered Nigrosin, but that was too expensive retail. So, I ordered some "compatible" dry toner today and was planning to try that with a little surfactant and water. The toner should get here today.It has been awhile since I did a homemade board. The current boards are just because I can't wait for overseas shipping.John

author: technotronix
author_rank: Regular Contributor
timestamp: February 20, 2017, 11:59:23 am
content: Inkjet is the best option for you. Great @AlfBaz.

author: jpanhalt
author_rank: Super Contributor
timestamp: February 20, 2017, 12:14:56 pm
content: @technotronixI too prefer inkjet. The transparency doesn't have to be black. You could probably print with just yellow; however, when I had an inkjet, I just let it print in color including black.The method I mentioned in starting this thread is for those who only have laser printers. That was my situation, as my inkjet dried up long ago. When I have time, I don't believe it is cost effective today to make DIY PCB's. However, I resurrected this method and modified it for the Brother printer, because I did not have time for the two to three week TAT of commercial boards from Asia.John