PCB Sensitivity to UV exposure?

I just had a thought.. if pcb's are made by exposeing them to UV light. Followed etch bath. Could sunlight later on compromise the pcb .. ?

Reply to
pbdelete
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No. The UV sensitivity is only during the manufacturing process. Once the board is etched, sunlight is not a problem.

Reply to
DecaturTxCowboy

Eg when the conductive layer (copper) is exposed to the etch fluid. It will harden in such way it become uv-resistent ..?

Reply to
pbdelete

The etch *mask* is UV sensitive. After etching, the remaining mask is cleaned off, leaving just copper. Copper is not UV sensitive.

Reply to
DJ Delorie

That makes sense. Are there other cleaning methods than Etanol or Isopropanol that does a significantly better job ..?

Reply to
pbdelete

No.

The bare copper-clad board is coated with a photosensitive material. A film containing the required copper pattern is placed over the board, then the combination is exposed to UV light. The board is then "developed" to remove the unexposed coating, leaving the desired copper protected by the exposed coating. The board is then etched to remove the unwanted copper, and finally cleaned to remove the remaining photosensitive coating, so you can solder to the copper.

In commercial processing, I think the photosensitive coating is removed over the wanted copper, which is then plated with tin, which will protect that copper during etching.

Copper itself is not light-sensitive.

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Reply to
Peter Bennett

I figured that out, but the science is in the details =) I brainstorming on a solution to speed up the process.

Reply to
pbdelete

What part of what process?

Reply to
DecaturTxCowboy

Not sure what you mean by "significantly better job". What ever method you use, as long as it cleans it off, its suitable. Do you mean is there a faster way?

If doing a small batch by hand, use a minimally abrasive sponge rated for Teflon® cookware. As I recall, the commercial process uses a high pressure solvent wash (but I stand to be corrected on that).

Reply to
DecaturTxCowboy

I want a "print pcb" machine ;)

Reply to
pbdelete

Ummm..let me rephrase that. Are you looking to do one-time PCBs or a batch of just a few, or a production line for PCBs?

The reason I ask it there are so many ways to go about making PCBs and the best way is determined by your volume.

Reply to
DecaturTxCowboy

For development purposes (one-off). For massproduction there are other means.

I want this process in one go: Source file -> Mask -> Exposure

Reply to
pbdelete

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Reply to
DecaturTxCowboy

If I understand it right:

  • Print pattern/mask on a special (glossy) kind of papper. * Ironing it onto a copper pcb at approx ~205 Celsius, 111-134 Newton. * Soak the papper, and rub "it" off. * Put the pcb in the etch bath.

The instructions is a bit unstructured ;)

The procedure still seems a bit messy. I have some other ideas that might push the time significantlty down.

How is the copper film attached to the pcb .. ?

Reply to
pbdelete

Yup. Google for "toner transfer PCB". They even sell special paper for it.

Reply to
DJ Delorie

Found this excellent guide:

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The key is that toner ink will protect the copper from etch fluid?

Reply to
pbdelete

You might want to check out the Homebrew_PCBs discussion group, at

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.

[Or, if you can spend some $, there are CNC (router) machines made specifically to produce prototype pcbs automatically.]

Good luck.

Tom

Reply to
tomg

Laser printer and copier "Toner" (not ink) is mostly plastic, which the acids usually used for etching-away the unwanted portions of the copper can't eat through.

Reply to
tomg

Yes. And if you take the time to absorb and understand the information in the link that Decatur posted, it is even better than the good one you posted.

Let me emphasise some key points in the process:

1) You want the copper on the PC board you will use to be *clean*. I mean *CLEAN* 2) Do *not* rush the ironing. Use the 4 or 5 minutes recommended and keep steady firm pressure while moving the iron to prevent scorching. 3) Soak the bejusus out of the paper and board after ironing - dunk it in a container of hot water and let the thing soak until the paper comes away from the copper without pulling the toner with it. In other words: "DON'T PULL ON THE DAMN PAPER TOO SOON". Ask me how I know. 4) Gently rub the board to get most of the residue paper off. Residue that seems to be embedded in the toner won't hurt as long as the toner paths have crisp edges.

5) This is not so key - but bears mentioning. Etching takes time. It can be sped up by keeping the etching solution warm and by agitating it. But don't look to set speed records. I use a container that I can tilt to expose the board to see how much copper has been removed so that I don't have to stick anything in to the solution to grab the board to inspect it. That keeps the etching solution in the container, rather than getting on a glove or a tool. Once it is out of the container and onto a tool or a glove, it is one short step from staining something. And it *will* stain.

When etching is done, wash the board well with water to remove any etching material. Then remove the toner, drill the holes, and build away.

Ed

Reply to
ehsjr

Last time I etched a board, I attached something to the board that stuck up above the etchant. Thus, I had a handle that I couldn't accidentally put down somewhere. It was a tiny board, I think I just soldered a wire to an empty corner, but I suppose supergluing some toothpicks along the edges would work too.

Reply to
DJ Delorie

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