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PCB Sensitivity to UV exposure?

Discussion in 'Electronic Basics' started by [email protected], Mar 21, 2006.

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  1. Guest

    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 .. ?
  2. No. The UV sensitivity is only during the manufacturing process. Once
    the board is etched, sunlight is not a problem.
  3. Guest

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

    DJ Delorie Guest

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

    That makes sense. Are there other cleaning methods than Etanol or Isopropanol
    that does a significantly better job ..?
  6. Eg when the conductive layer (copper) is exposed to the etch fluid. It will
    harden in such way it become uv-resistent ..?[/QUOTE]


    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.
  7. Guest

    Eg when the conductive layer (copper) is exposed to the etch fluid. It will
    I figured that out, but the science is in the details =)
    I brainstorming on a solution to speed up the process.

  8. What part of what process?
  9. 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).
  10. Guest

    I want a "print pcb" machine ;)
  11. 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.
  12. Guest

    What part of what process?
    For development purposes (one-off). For massproduction there are other means.

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

    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 .. ?
  14. DJ Delorie

    DJ Delorie Guest

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

    Found this excellent guide:

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

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

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

    Good luck.

  17. Guest

    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.
  18. ehsjr

    ehsjr Guest

    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.

  19. DJ Delorie

    DJ Delorie Guest

    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.
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