Etching with Photoemulsion

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adaminc

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Hello all!

I was sitting watching tv, and a show about how they build things came on, one of the processes they showed was how they silk screen clothing. It got me to thinking, has anyone tried this process for applying an acid resist to pcb?

I am going to try something similar this weekend, however I will modify the process. I am going to put the photoemulsion directly on the pcb, let it dry, then expose it using a inkjet transparency as my artwork, and hopefully it wont wash away in the piranha solution.

If all goes to plan, and I think it will, I will let you guys know. I will probably also document the process as much as possible and post it on my website (which I am also making this weekend).
 
adaminc said:
Hello all!

I was sitting watching tv, and a show about how they build things came on, one of the processes they showed was how they silk screen clothing. It got me to thinking, has anyone tried this process for applying an acid resist to pcb?
Click to expand...
It has been a standard process for many years.

If you want to play with it go ahead. But if you just want a process that works the positive and negative photoresist works well as does the toner transfer.

I have tried the regular silkscreen method but not the slant you are attempting.
To get good results you need an even coating/layer of your photoemulsion.

Have fun.
 
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Yeah, I've done the Photolitography methods in College, and the Toner Transfer Methods back in high school. But I just wanted to try this method, simply because its something new, and it could possibly become a good cheap method. I already have a jig setup for applying a thin coating of emulsion to 1/16" FR4 board with a squeegee. It's essentially the same as the litography method, except instead of a laminate, i'm using the emulsion.

At first I am going to just buy a emulsion kit from the local art store (only $10), if it works well, I will probably start making my own potassium dichromate based photoemulsion if I can get a good supply of potassium dichromate. Or I could buy a 4L jug from the same store for $52.
 
We have talked about making boards a lot in the past.

If you are doing it to save money there is already an inexpensive system in place.

I use toner transfer paper from PulsarProFx.com. Mouser and DigiKey also sell it. They also have a green foil that can be laminated over the toner that helps stabilize the toner during etching. It is an optional step. I do .01 inch lines without it but like using .012 in because they hold up better if rework is needed. You can run 2 traces between dip IC pads without problem. Good system.

It is very easy to use. The image is not limited by the paper but by the image your printer can produce. That is about as good as it gets.

Single sided boards are very easy to make. I spray the top side white with crylon fusion paint and do a 2nd toner transfer for the silkscreen layer. They look nice.

These days I only do toner transfer with a laminator.
 
I guess in the long run, buying a laser printer, and this toner transfer system will be cheaper.

I have a question about their system. If you only want to do 1 small board, you run the whole sheet through the laser printer, then use an iron instead of a laminator to apply it to the PCB, that way you are saving the rest of the sheet? or do you cut that section out of the sheet and run it through the laminator?
 

To do any size board.
1. Print artwork or outline of artwork on regular paper to determine where the printer is going to print the image.
2. Cut transfer paper that is large enough to cover the area to be printed.
3. Tape the transfer paper to the regular paper so that it covers the image. Tape on the top edge only.
4. Run the assembly from above through the printer. The result will be the artwork image on the transfer paper.
5. Remove the transfer paper from the regular paper and tape it to the PCB.
6. Run through laminator a few times
7 Soak in water for about a minute.
8. Etch.

You can add green foil between steps 7 and 8. This is a quick and dirty version but it gives you the idea.
 
You don't even need any special proprietary paper for the toner transfer process, I've used magazine paper and had perfect results every time. I just rip a section from an old magazine, print the art work on it, iron it to a polished piece of copper clad board, leave it to soak in cold water for ten miniutes, remove the paper and etch as usual. The photo resist method is better for finer derailed designs but for ordinary through hole desings nothing is more cost effective than toner transfer with magazine paper.
 

Magazine paper works but as you said it does not provide fine detail. With the special paper you get better results. A while back I did some testing. As a rule what the laser printer printed was what ended up on the board. The paper is coated with a starch that sticks to the toner when dry and becomes as slick as snot when wet. The paper falls off the copper in about a minute.

I feel that it is better for people new to the process to start with the good paper. There is a much better chance of success.

If you remove the paper from the water as soon as it releases there is enough starch left on it to use it again. The trick is getting it to dry flat. AT 1.7 cents per square inch it is not worth the effort. $15/(10 sheets * 8 * 11)

A pack of 10 sheets is $15US from mouser.. The last time I checked Digikey had it too.
 
You have a point but it depends on one's budget and access to suppliers. I still think 10 seets for $15 is too expensive considering I can get magazine paper for free.

Another solution might be to cover ordinary A4 paper with a water soluble glue such as PVA art glue or wall paper paste. The glue will disolve and leave the toner sticking to the board.
 

We are all free to do as we please.

A lot of people have wasted a bunch of time without good results using the wrong paper. Some have given up. For that reason I feel starting with the Pulsar paper is a good idea.

Given how well this stuff work it is a huge bargain. And there is no need to fall back on expensive sensitised boards for the detailed boards.

If you live in a country where you can not get it then that is another thing.

If one were to attempt to make his own paper I would try using the same starch that Pulsar uses. But at 1.7 cents a square inch I would not bother. Most of the boards I etch use about 25 cents of the paper. Not a problem.

EDIT:
I have linked to this in the past. It is a sample board from Pulsar's site that shows some fine lines.
**broken link removed**
 
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Tat board might demonstrate how good the paper is but it's also a prime example of the bad practice of sticking tracks between IC pins.

I suppose the one good thing about it is, it is honest about its limitations; that 5 mil grid is full of missing lines.
 


I have not found the need to go below .01 and prefer to use .012 traces.

When looking a problems with the process you need to start with the laser printer. The transfer can only be as good a what the printer can do.

Nigel said the same thing about running traces between IC pads. I do little audio or analog but I see no problem with digital. Nnot going between pins would mean extra jumpers or wires between layers.

When I first started soldering these close boards I had a bit of trouble with bridges, experience fixed that.
 
previously ,I print sample on waxed paper using deskjet(inkjet) then iron on white paper the result are not so good and wax are gone. I have no laser printer just wondering what will be the result if I use waxed paper on laser printer. I plan to used it on photo copier(also Idon't have that). Have you try it before ?.

I never try toner transfer on PCB.



hi adaminc,
I got interest too with Photoemulsion.
 
Instead of waxed paper , try the tracing paper with dark xerox print or a laser print (image) at few pennys from outside and then try out the ironing method. However xeroxing from inkjet print reduces the resolution.

3V0 is very correct to use Pulser paper, but this is not of general availability across the world and , if imported, it cost a moon. the method described is nice and in full detail.
 
PVC color on silkscreen!!!

You could do just ordinary print of the silkscreen on the uncoated PCB material. Use PVC based color and higher denisity silk. It works fine especially for smol amount production (say 50 same model PCB-s)
 
I have seen traces on a PC Board near the processor inbetween the BGA's, so I don't have a problem with traces inbetween pads.
 
That's fine as the solder resist prevents bridging but soldering ICs when there are tracks inbetween the pins can be a nighmare.
 
Hero999 said:
That's fine as the solder resist prevents bridging but soldering ICs when there are tracks inbetween the pins can be a nighmare.
Click to expand...

Difficult if you are not careful with the layout but not a nightmare.

Clean copper solders without a protest. If the copper is not clean and you have to futz around to get the solder flowing the chance of a bridge goes up.

I started spraying a thin layer of conformal over the clean copper after etching to keep the copper from oxidizing.

The heat from soldering vaporizes the coating. It may also be that the conformal between traces does not vaporize and acts as a soldermask. I can not swear to this but it sounds good.

Where there is the possibility of bridging I use .015 solder. It allows finer control of how much solder you put on a joint.

If none of that works I use a liquid flux pen.

I use a temp controled soldering station. That may help but my students use 15W Radio Schack irons.
 
Colormaze by Admaze


I've had some success using white Elmer's glue and potassium dichromate emulsion for making silk screens. But, this post is a suggestion regarding the mask.

Use a laser printer to print the foil (or other) pattern onto a VU-Graph transparency sheet. Unfortunately, even though the toner looks pretty dense to the eye (like from an overhead projector), it'sactaully quite transparent.

There is a company called, Admaze that makes a product called, Colormaze which sticks a foil onto the toner by heat (**broken link removed**. I've used the product but, not to make a PCB as I haven't had the photoresist handy. But, it is a lot more opaque than the toner alone.

This product or process may be well known here but...in case...here's the info again. Of course, it can also be used on the mask for making silk screens, too. The foil is extremely thin and gives excellent fine detail (as good as the laser printer can produce).

It's actually fairly inexpensive (about $1 ti $2 a sheet the last time I bought it). It's intended as a "decorative" product so comes in various colors.
 
I've also found that you can do a clean (and very cheap) toner transfer using the backing paper from stickers. I used the backing sheets from CD labels since they're full letter sized and don't jam up my old HP laser printer I got @ Goodwill for $10.

I was using old band advertising slicks (8x10 glossy thin paper) and got really good results, but the slightly waxy but thick sticker backing is the schnitz.

Cheers!
 
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