Laser cutting for DIY PCB

[KamalS]

I am interested in knowing how many of you have experimented with a laser cutter for DIY PCB?

Would love to hear what kind of experiences you have had.

This method does away with worrying about a laminiator and laser printer but in this case too, just like toner and paper's critcal for toner transfer, the choice of spray is extremely imporant!

For those who have good experiences using a laser cutter, could you share the details of the spray used?

From what I have read, bad choice of a spray can generate the following issues in the least:

- melts with the laser and cools over the traces which were just engraved, ruins everything

- is very difficult to remove using acetone or thinner (even after etching) in order to solder on the traces; requires to be scrubbed off (potentially damaging very thin traces)

- evaporates but leaves behind a film/residue on the board that is resistant to etching (some can be removed with alcohol/acetone)
This last issue has been well documented on this picture set:

http://groups.yahoo.com/group/Homebrew_PCBs/photos/album/540603270/pic/551305033/view?picmode

What vers5d did first was spray the copper clad with some Rustoleum paint: something like **broken link removed** .
The picture "Before etching" is what he got *after* using the laser cutter to "cut away" that spray on resist from places that needs to be etched later.
(This is the reverse process of toner transfer/plot. Pretty timeconsuming I believe. Perhaps making a pattern like that used in isolation milling would require less time?)

Then he wiped the right hand portion of the PCB with some acetone, thus clearing away the spray residue.

After this he proceeded to etch the board to get "After etching"
"After cleaned" is what he got after scrubbing the board after it was etched

I agree with his observation "With the right resist and some adjustment for the laser's dot size. It should work nicely."

I am interested in taking this further and would entertain exchange from others who are interested likewise.

 

[Orson Cart]

Laser cutters (CO2) aren't used on copper due to the high reflectivity as it melts... Regards, Orson Cart.

 

[FvM]

Your link is for yahoo members only. Please provide open links at edaboard.

Technically, the post misses any clarity. I understand that it's talking about a technique of structuring an etch resist with a laser. Besides the question if it applies as a reasonable suggestion for anyone, references to a description of this technique should be given.

 

[KamalS]

The idea of using a laser cutter for DIY PCB is to spray some kind of an etch resist - like an automotive primer - onto the copper clad.

Then, using the laser cutter, remove/expose the portions that you would like to get etched using the etchant.

The end result, what remains would be a much finer quality etch resist than what you get using toner transfer.

However, selecting a good spray is all important as discussed in my original post.

 

[marce]

Direct Laser Imaging, I believe, not cutting ?

 

[jpanhalt]

I have been a member of that group for a long time and was familiar with the would'a, could'a, should'a aspect of this approach; although, I never tried it myself.

First, note that the example was posted more than 4 years ago. There seems to be a problem with the next step to get it to work.

If you do want to try that, you may consider using the laser to expose a positive (or negative) resist, then develop the image and etch in the usual way. That avoids using a high powered laser, reflections (as mentioned above), and melting/resolidification.

If you do want to remove the resist, I would suggest an approach like is used with PCB milling. That is, you only photomill the isolations, not large open areas. A resist that would be vaporized quickly without appreciable melting would probably be best. I would consider something like a clear acrylic -- like a thin layer of cured super glue, nitrocellulose, or plasticote.

Frankly, I think the direct print to PCB approaches have more appeal for the amateur, but still many problems. It quickly becomes a project just to make PCB boards, not to make electronics.

John

 

[KamalS]

Direct Laser Imaging, I believe, not cutting ?

Only cutting, not DLI.

If you do want to try that, you may consider using the laser to expose a positive (or negative) resist, then develop the image and etch in the usual way. That avoids using a high powered laser, reflections (as mentioned above), and melting/resolidification.

Nice idea. I am not sure whether using the photo resist used for UV exposure would be a good bet.

Also, working in a dark room with a laser cutter would be difficult as these machines are in a techshop.

If you do want to remove the resist, I would suggest an approach like is used with PCB milling. That is, you only photomill the isolations, not large open areas. A resist that would be vaporized quickly without appreciable melting would probably be best. I would consider something like a clear acrylic -- like a thin layer of cured super glue, nitrocellulose, or plasticote.

This is really a great idea! Any links to general stores that carries these "resists" would be very helpful.

 

[jpanhalt]

For Plasticote, try any auto parts store. Solvent-based model airplane dope (if you can get it in SoCal) may also work. There are two classic versions, nitrate and butyrate. The nitrate is "tauntening" and is basically a nitrocellulose. I think you will have better luck finding these finishes in automotive and hobby stores rather than in big box home centers. It is the pigments in paints that I think would be a problem. Krylon is another brand of clear finish to look for. I vaguely recall seeing it in a home center.

As for working in the dark with photoresists, that is not necessary. They are generally quite safe with dim incandescent light. I would avoid bright sunlight and white fluorescent lights. The commercial products contain a photosensitizer that makes them work with light in the near UV and violet (about 400 nm) region.

John

Edit: I occurred to me that the typical photoresists might burn off cleanly with your laser. For example, if you started with a positive resist board, you could burn away those areas of the resist that you want to etch. After etching, the remaining resist could be easily removed with 0.5M NaOH or other strong base. That way, you would avoid having to use organic solvents to remove a lacquer or paint. You would not have to worry about light, since both exposed and unexposed resist would be resistant to acidic etching solutions. (I am assuming as a hobbyist, you use an acidic etch.)

 

[KamalS]

For Plasticote, try any auto parts store. Solvent-based model airplane dope (if you can get it in SoCal) may also work. There are two classic versions, nitrate and butyrate. The nitrate is "tauntening" and is basically a nitrocellulose. I think you will have better luck finding these finishes in automotive and hobby stores rather than in big box home centers. It is the pigments in paints that I think would be a problem. Krylon is another brand of clear finish to look for. I vaguely recall seeing it in a home center.

Unfortunately, Krylon has been tried and it does leave a very thin layer of paint residue on the copper that will block the etchant solution from working properly.

This issue is documented here : clean up the board

Would you suggest some other brand or type that is not likely to leave residue behind?

What about those acrylic enamel sprays?

As for working in the dark with photoresists, that is not necessary. They are generally quite safe with dim incandescent light. I would avoid bright sunlight and white fluorescent lights. The commercial products contain a photosensitizer that makes them work with light in the near UV and violet (about 400 nm) region.

I occurred to me that the typical photoresists might burn off cleanly with your laser. For example, if you started with a positive resist board, you could burn away those areas of the resist that you want to etch. After etching, the remaining resist could be easily removed with 0.5M NaOH or other strong base. That way, you would avoid having to use organic solvents to remove a lacquer or paint. You would not have to worry about light, since both exposed and unexposed resist would be resistant to acidic etching solutions. (I am assuming as a hobbyist, you use an acidic etch.)

The idea using photoresists is interesting. However, I do not own a laser cutter and the hackerspace where I use one is flooded with fluorescent lights and often UV from weilding.

The space is more of an open warehouse so it would be difficult to cordon off a section around the cutter.

However, I am game for experimentation!

Any suggestions as to where I could get some cheap photoresist to try things out?

 

[jpanhalt]

I am aware of three types/brands of positive acting photoresists. There are probably more, but since the one I use works well, I have never searched very hard for alternatives.

I use Injectorall, which is available from DigiKey (digikey.com). M.G. Chemicals has its branded product, which it sells directly and through Mouser Electronics (mouser.com). Jameco may sell the same product (jameco.com). There used to be a liquid spray you could use for DIY. For your initial experimentation, I would recommend against that. The coating on commercial boards is quite uniform, which should help for laser ablation. A third product by DuPont is more for commercial users. It is sold as a sheet, which must be laminated to the PCB, thus adding additional complexity and chances for problems.

I probably wasn't clear in my afterthought on using a photoresist. It won't matter whether it gets exposed to UV or not. It is not being used because of its photosensitivity, but because the resist lacks pigment (they may contain a clear organic dye) and is probably easily ablated with laser. Whether exposed or not to UV, the photoresists I am describing are removed with strong base. The developer is simply a weaker base or lower concentration of strong base than is used for removing all resist at the end of the process. You can also remove it with acetone, if you prefer.

Whatever you use, try to get something that is crystal clear -- you are using IR, right? I am a little surprised that Krylon left a residue. Clear acrylic enamel might be worth a try, as would clear polyurethane. The problem with enamels and urethanes is removal from the copper areas to which you need to solder after etching. Lacquer and dopes would be removable by solvents like acetone or MEK; cured enamels and polyurethanes would be more resistant to solvents. I would not try shellac as a first experiment. It has some desirable properties, like solubility in alcohol, but it is a natural product, so it may not be too reproducible.

John

 

[KamalS]

I use Injectorall, which is available from DigiKey (digikey.com). M.G. Chemicals has its branded product, which it sells directly and through Mouser Electronics (mouser.com). Jameco may sell the same product (jameco.com). There used to be a liquid spray you could use for DIY. For your initial experimentation, I would recommend against that. The coating on commercial boards is quite uniform, which should help for laser ablation. A third product by DuPont is more for commercial users. It is sold as a sheet, which must be laminated to the PCB, thus adding additional complexity and chances for problems.

The laser I use can cut through 1/16" acrylic like butter and more: I would not worry about issues with ablation due to uneven coating.

The more important question is: how much do these photoresists cost?

I recall the DuPont sheets from 2003: I was considering them due to the bad toner transfers I was getting. I only saw that I could buy in 1k pieces.

I probably wasn't clear in my afterthought on using a photoresist. It won't matter whether it gets exposed to UV or not. It is not being used because of its photosensitivity, but because the resist lacks pigment (they may contain a clear organic dye) and is probably easily ablated with laser. Whether exposed or not to UV, the photoresists I am describing are removed with strong base. The developer is simply a weaker base or lower concentration of strong base than is used for removing all resist at the end of the process. You can also remove it with acetone, if you prefer.

Whatever you use, try to get something that is crystal clear -- you are using IR, right? I am a little surprised that Krylon left a residue. Clear acrylic enamel might be worth a try, as would clear polyurethane. The problem with enamels and urethanes is removal from the copper areas to which you need to solder after etching. Lacquer and dopes would be removable by solvents like acetone or MEK; cured enamels and polyurethanes would be more resistant to solvents.

Synthetic enamels like acrylic would be a good idea: any ideas on a brand to start out with?