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Direct to PCB InkJet Resist Printing


by Volkan Sahin and Stefan Trethan

This page details the modification and use of Epson^ InkJet printers with MISPRO Inks^ (#MISPRO42-SET-MK) to feed and directly print resist patterns to copper clad printed circuit board stock, ready for etching.
You can skip to the section showing the results you can get using the modified printer, if you like

Once you can feed the PCB through the printer for etch resist, you can then feed it back through the printer for solder mask (yes! Several people report that it works quite well!) and for a component "silk-screen".

Toner transfer is probably easier to set up for and may be as fast, but direct ink is more precise, allows solder mask and component printing in the appropriate color, and most importantly, MUCH finer traces and spaces! And if you admit that a laminator is required for TT, given the prices for old C84 printers^ and the Durabright / MISPRO Ink, direct to PCB InkJet printing is cheaper.

The secret (discovered by Volkan) is that certain pigment based inks can be cured with heat to form a very strong resist. The Epson InkJet printer use pizeo electric actuators in the print head (rather than the thermal method used by other brands) which allows for a wider range of ink types to be squirted out. The "Durabright" inks include a pigment rather than dye. The solid base in pigment inks apparently provides a resistant cover that will actually stand up to the echant after it is melted onto the board. For more, see: http://inkcityusa.com/epson_durabrite_inks.htm

This guide was written by Stefan Trethan and edited with comments added from Volkan Sahin (Volkan not Volan, Voltan, Votan, etc...) who first developed and shared this method on the Homebrew PCB Yahoo Group^. A new group InkJet PCB Construction^ has been formed for more specific discussion.

Printer Modifications:

Process

C84 by Stefen Trethan

Here is a nice shot of the final modified C84 ready to print. The guides are mocked up in this photo, but have been completed as planned.

Details here

C87 by epineh^

. Check out the traces Russell is getting! That is a TSSOP chip!

C88 by wnnelson

I modded a C88 without hacking the frame. I made new bushings for the drive shaft which lowered it by .100". {ed: the new bushings were turned on a lathe to match the shape of the originals on the outside, and then an off center hole was drilled in the inside to hold the shaft in the lower position } I trimmed off {ed: turned down on a lathe} the outfeed rollers to give a flat carrier path and moved the paper sensor to the front. This allows a carrier with no cutout notch for the timing. {ed: because the edge of the tray now triggers the sensor} I put a smaller gear on the end of the drive shaft for the vacuum pump because there was no room for the original gear. {matching a gear like this can be quite difficult. If anyone knows the source of this gear, please share it} This causes the pump to run slower but does not seem to affect the operation. I hope this will help with the clogging problem as the cleaning station has not been modified. I added a little tubing to the pressure rollers to give it a little extra pressure as the carrier is too far away for the regular roller. So far it is working great.

CX4200 by Volkan Sahin

This is Volkan's modifed CX4200 as it prints a PCB. Details for modifying this printer are in the works.

Volkan has also produced a custom flatbed inkjet direct PCB resist printer of his own design, using the heads from an Epson Inkjet.

R220 by Bora Dikman (probably also applies to R280)

Process:

PCB Preparation

Sand the PCB with 600 or 1000 grit paper so that he surface appears scratched everywhere. You may also use a abrasive plastic pad sold for cleaning copper pipes before soldering.

Then wipe with acetone, twice, the first pass should take away the copper dust. The PCB must be grease free now and stay that way.

Bora Dikmen says: "...before printing, you should bath the PCB about 1-2 minutes in acid (H-Cl + H2-O2) to become purple-brown in color. This creates a soft surface and ink will be printed very smoothly as if it is printed onto a paper. Otherwise, ink is populated on some areas, waved in color and not evenly distributed on the PCB."

John Mardock says "... tried the MIS yellow (MP-4-Y) we have been using with the heated board with good results. I made a series of 5 boards using this yellow from 75C to 105C all with about the same success. The boards are heated in the oven for several minutes to stabilize the temp and then removed and positioned in the printer. I am sure there is heat loss during the process. The great news is this board heating does handle the puddling effect that has been such a pain. The dry time for the ink is just about instantaneous on the heated boards as you might imagine. Seemed the higher the heat the better the coating of the ink. ... The other interesting aspect was one of better resist with less ink being deposited on the board."

Printing

Check out this great video showing how to use a modified C87 to print and etch a PCB.


READY


LOADED

To print you must insert the carrier manually into the printer. Turn the printer on, and wait until it has completed it's dance. Now feed the edge of the carrier into the printer so that it just protrudes a few mm from the traction/pressure rollers. Make sure it is straight so it will not run against an edge when the printer feeds. Now print the artwork on your carrier to find the right position (stick some tape or adhesive backed plastic foil on it or you may end up with permanent marking of the carrier). You can use low resolution for this print since you only need to know where it will end up. If you use the fastest draft setting watch out, the printer virtually shoots it through.

Now place the PCB over this position and stick it down with tape along the edges or using double sided tape underneath. You may delay the acetone cleaning of the PCB until this point if you prefer. Again feed the carrier and print the artwork.

Printer Settings

When printing a purely black test pattern I found the transparency setting does not use any ink from the black cart at all. The other settings use ink in varying amounts, the most ink is used for matte paper and the least for glossy or durabright setting. You need Photo or Best Photo resolution. The "fast" setting, which prints in both directions of travel, produces better results for me. No edge smoothing needed.

Curing


START


ALMOST


CURED

This is a key step. The PCB and ink must be heated at a specific temperature to cure it and keep it from coming off in the etchant. To do this, a stove or heat gun will not allow the required temperature control. Something more precise must be used: Basically an old electric hot plate with a aluminum plate on top and a temperature meter attached. It turns out that around 446F / 230C is the sweet spot. keep that for several minutes (at least 3 i'd say for now but more research needed). This incidentally is exactly the point where the copper will start to go from just minimal yellowish oxidation to a purple one (This is probably what Volkan is using to judge the temperature). It is well away from damaging the PCB.

If you are much below or above this temperature the ink will not resist so well. Round about 225C the ink starts to change somehow and can no longer be cleaned off with acetone.

Etching

I suspected Ferric chloride is less aggressive to the [MSPRO] ink than CuCl, so i set up a test. I cut a test PCB in half after curing to get identical samples, and put one in CuCl and one in ferric chloride. If anything the ferric chloride showed more aggressive under-etching. In the samples below, the lines above 3 mills are fine; below 3 they are unreliable.

scc_11067 says: "[using Durabright inks] ... I switched to ferric chloride and get really good results. I am currently using durabrite yellow with really good etch's Could use durabrite magenta, but the ink bunches up on the board if not dried instantly.  The persulfates just lift the ink off the board."

See also:

Questions:

Comments:

file: /techref/pcb/etch/directinkjetresist.htm, 22KB, , updated: 2008/11/7 09:37, local time: 2008/12/3 16:25,
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