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Who etches photoresist PCBs?

Discussion in 'PCB Layout, Design and Manufacture' started by TTL, Feb 13, 2014.

  1. TTL

    TTL

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    Oct 24, 2013
    I need to have some small single-sided PCBs made from various projects published in magazines. Hence, the photoresist method.

    Alas, I don't have the gear needed, nor any good experience having tried this in the past, so I'm wondering if there are companies around which can do this for me (or someone reading this) for reasonable cost? All I can find online when searching are companies doing prototypes from Eagle, Gerber or similar files.
     
  2. shumifan50

    shumifan50

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    Updating your location will help.
     
  3. TTL

    TTL

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    It doesn't matter to me where it's done.
    I'm in Norway.
     
  4. jpanhalt

    jpanhalt

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    I doubt you will find a company willing to take your magazine design or even your transparency, expose a sensitized PCB, and etch it for a reasonable cost. By "reasonable," I mean a cost that would be less than the cost for submitting a design and having a professional board made. In fact, I suspect the cost for the one-off project might be several times the cost of a professional board.

    If you do not have the equipment for the photoresist method, you might consider the "toner transfer" method using an electric iron. Alternatively, if you can find a local hobbyist he might be willing to do it for you with whatever method he usually uses.

    John
     
  5. shumifan50

    shumifan50

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    The only 'special equipment' you really need is a UV exposure unit. Scan the design from the magazine, clean it up in GIMP or Photoshop and print it on transparency.

    Buy a UV fluorescent tube, mount it in a box(multiples will be better depending on PCB size), put a sheet of glass about 100-150mm above the tube(s) and a cover across the top to protect your eyes.

    OR
    UV Exposure unit on fleabay £50

    The cost of buying the UV unit will most likely be recovered with the first PCB you make. I am not sure how good the LED units are, but fluorescent units are about £89. The rest is patience, especially to determine exposure time.
     
  6. TTL

    TTL

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    Are there UV light bulbs out there which can temporarily be put in a normal table lamp?
    What kind of UV lamp should I look for as there are many which go by the "UV lamp" description from detecting fake banknotes to lamps used to erase EPROMs.
     
  7. jpanhalt

    jpanhalt

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    I don't know what a "normal table lamp" is in Norway. There are certainly table lamps that use standard 15-W fluorescent bulbs in the the USA.

    You have not said which photoresist you are using. Presumably, it is a common version, positive acting resist with a photosensitizer incorporated into the resist. Such resists often just require light of 390 to 405 nm or so.

    Ordinary fluorescent bulbs produce light in that range as do many incandescent bulbs. So-called sunlamps also produce in that range and have standard screw bases. I would not recommend such a lamp, as they produce considerable heat too.

    I us a 15-W fluorescent straight tubular bulb that is labeled "BL," meaning its phosphor emits in the wavelength region already mentioned. There is apparently inconsistency on bulb designations. Some may just be labeled "B" for a similar phosphor. You do not want a "germicidal" lamp or one that emits at a much shorter wavelength, such as 366 nm. The optimal exposure light for the Injectorall plates I use is in the 390 to 405 range. I believe MG Chemicals plates are similar.

    First, read the information that comes with the plates you are planning to use. It will tell you the best exposure wavelengths.

    Second, check out which bulbs are available at your store and write down the full number. For mine, it is something like F15T8BL (http://www.amazon.com/GE-35884-F15T8-Fluorescent-Black/dp/B002CYXIEM). Then confirm that the emission is in the correct range. A white phosphor is probably going to be OK.

    John
     
  8. davenn

    davenn Moderator

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    you cannot use a normal lamp stand to do the UV exposure ... UV is dangerous for the eyes and skin
    you MUST use a closed in box as said by shumifan50 in post #5

    cheers
    Dave
     
  9. jpanhalt

    jpanhalt

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    Nov 12, 2013
    I respectfully disagree with your conclusions about not using an ordinary lamp stand and needing a enclosed light box.

    1) An ordinary lamp stand will work, as stated in my reply above. I use an ordinary fuorescent lamp stand for 15-W bulbs. My lamps happen to be type BL, as that was what Injectorall recommended a decade or more ago when I set it up, but ordinary daylight fluorescent bulbs will work. You can also use ordinary incandescent lamp stand. Such lamps produce adequate light in the range needed. In fact, in years past, high quality spectrophotometers used ordinary incandescent lamps to cover the range from visible to 350 nm. Remember, though, that your exposure times needs to be adjusted to the lamp you are using. The biggest disadvantage to incandescent lamps is the heat produced. To reiterate, ordinary fluorescent light bulbs will work. They are not used in art gallarys because of the amount of near UVA they produce. Note: Although typical positive resists (e.g., Novolak resins modified with a diazodinapthoquinone photosensitizer) absorb strongly at shorter wavelength than recommended here, longer wavelengths work just fine. I am not recommending use of so-called BLB bulbs that are designed to emit mostly near 366 nm. Industrial users may use shorter wavelengths of light for exposure to get better resolution.

    2) Yes, UV can be dangerous to tissues. Oxygen can also be dangerous. Both are necessary for human life. All light, including the visible and infrared, can be dangerous. Just don't glue your eyeballs to the light bulbs.

    3) With regard to mandating an enclosed box, TTL's question was clearly related to using low-intensity ordinary table lamps. If you put an ordinary reading lamp in a box to protect one from the light, where do you suggest the reader sit? ;)
    One situation where you might want to use an enclosure is to eliminate ambient stray light. Sunlight and ordinary fluorescent lamps can be quite intense compared to what is needed for exposure of these PCB boards. I do my set-ups and exposures in a darkened room to minimize that variable. I don't sit in the room and stare at the exposure table during exposure. I also leave bright lights off until after development. After development of the image, further exposure to ambient light is not an issue.

    Unfortunately, it can be difficult to find the emission spectra for various types of lamp bulbs. Moreover, many sources mention that labeling is not entirely consistent; although, there seems to be greater standardization today than there was just 10 to 15 years ago. Wikipedia has a nicely animated illustration of current nomenclature and color temperature: http://en.wikipedia.org/wiki/Color_temperature

    MG Chemicals, a major supplier of pre-sensitized, positive-resist boards, is currently recommending a standard "daylight" fluorescent bulb (D-65 probably) for exposure of its positive resist plates. Interestingly, the above Wikipedia article shows that bulb produces less of the shorter wavelength UV than an LCD monitor. Surely, that bulb is not dangerous when used responsibly in an ordinary light fixture.

    Regards, John
     
  10. chopnhack

    chopnhack

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    Over a decade ago Radio Shack, an electronics provider in the states used to sell a PCB etching kit with copper clad plate and a resist pen. I had used that to make a few circuits. They come out well, the only bad part was disposing of the fluid. The gentleman in this video shows the more modern method (photoresist) without using a specialized bulb.

     
    Supercap2F likes this.
  11. davenn

    davenn Moderator

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    Sep 5, 2009
  12. jpanhalt

    jpanhalt

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    Dave,

    It appears you have neither not read what I wrote nor understood it. It seems you think that ordinary incandescent and fluorescent lamps in a home are dangerous.

    So, go ahead and use candles, if you prefer. Oops, they produce CO2 and carbon soot, so forget about that.

    I see no reason to prolong this dialog.

    Regards, John
     
  13. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I am sure you and Dave were arguing at cross purposes and I think we can all agree that
    1. Using specialist UV bulbs in a normal light fitting is a bad idea
    2. Using normal fluorescents (or any other "normal" bulb) is obviously not bad in the same way
    3. Whatever you use, you will need to experiment to get the timing right (and that normal bulbs will typically result in longer -- perhaps much longer -- exposure times)
     
  14. davenn

    davenn Moderator

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    Yup, Steve, exactly :)

    Dave
     
  15. TTL

    TTL

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    Oct 24, 2013
    I'm the OP.
    All this stuff seems very complex and time consuming, which is why I've been trying to find someone who can develop/etch my PCBs. But perhaps with a press n' peel/toner transfer method it might not be too complicated to do myself after all.
     
  16. gorgon

    gorgon

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    Where in Norway are you from? Since I'm from Norway myself I may be of help. I live in Østfold.
     
  17. TTL

    TTL

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    Oct 24, 2013
    Thanks to everybody for all that info!
    Gorgon: reply sent via PM!

    Chopnhack: great video there! Thanks for uploading.
    Makes it look so easy, but I suppose it all takes quite a bit of time consuming experimentation in order to find the right light source, then the correct distance/exposure time and finally the etchant strength/water temperature and etching time before you can just make a board right away.

    About UV lighting:
    I'm a little confused about the light source needed as normal CFL bulbs (as used in the mentioned video) have been suggested here, but then again UV exposure danger has been talked about as well. Surely, "normal" CFL bulbs aren't harmful to they eyes as that defeats their purpose. Or have I misunderstood?
    I'm guessing what's meant is regular CFL bulbs mounted in a common household lamp will work fine for casual hobbyists, but for more professional type of work you'd get a dedicated lightbox with more powerful UV lamps thereby shortening the exposure time, and with the PCB pressed against the glass at the exact same distance to the light source each time you also wouldn't have to measure the distance to get a correct exposure each time either, or worry about uneven exposure from the light source.

    EDIT: come to think of it I do have a UV-eraser box I made years ago. IIRC it has a special fluorescent tube which I suppose is of the dangerous types. Unsuitable for PCB design perhaps?
    The box may be a bit too small as well for many PCBs.

    About printers/toner-transfer methods:
    I've read a bit about the tone-transfer methods and they seem like less of a hassle than UV-lighting (by hassle I mean the initial experimentation to get the distance/exposure timing just right), but I also read about people getting widely differing results depending on the printer/paper or specialized solutions (press 'n peel) used etc. Since I'm about to buy a laser printer myself (the Brother DCP-7065DN multi-function printer is the most likely candidate) I'm also keeping in mind PCB design but just found out that the Brother printers' laser toner melting point is higher than that of other brands (also read here) and therefore unsuitable for this sort of thing! :( That's too bad because I'm looking into Brother printers as they're economical in use, don't use toners that expire by date (I've been told recent Hewlett Packard printers have this) and work great with Mac computers. Designing PCBs (if I need to/decide to to it myself) will only be a small part of what the printer will be used for.
    However, I wonder if replacing the toner with some kind of "compatible" one when used for PCB design would allow Brother printers to be used too?

    Well, at least just about any quality black/white laser printer should do for the photoresist method as far as I know.
     
    Last edited: May 5, 2014
  18. chopnhack

    chopnhack

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    RE: the toner/temps - That is very well researched TTL! I agree with your analysis, the machine you purchase should match your daily needs and not the occasional need. Do you have a local print shop? In the states we have Staples, Office Depot and FedEx office as well as independent print shops that can do a laser print for very little money. A black and white print is typically just pennies.
     
  19. TTL

    TTL

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    Oct 24, 2013
    Great suggestion about using a copier in order to transfer the toner to a PCB.
    I'm sure there's a copy/printshop around here somewhere although I haven't used any.

    What's the easiest way to make a good lightbox without having access to a whole lot of tools/workshop?
    I'm hoping I could just buy some bits and pieces from Ikea or wherever to get a pre-built box, a fluorescent lamp fixture (several lamps are probably an advantage for even lighting) from an electrical shop to mount inside with some screws and a piece of glass (a cheap picture frame) to put on top? (actually I read somewhere that regular glass may be unsuitable for this sort of thing as some glass blocks UV, so plexiglass was recommended instead. Don't know about that as the fluorescent lighting could get pretty hot inside a non-ventilated box).
     
  20. chopnhack

    chopnhack

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    Apr 28, 2014
    Skip the light box altogether! Got a clothes iron?




    I have also read recently somewhere that instead of purchasing Ferric Chloride, you can use muriatic acid - which is far easier and cheaper to obtain. Masons use it as do pool cleaning companies. I take it that pools are not as plentiful in Norway ;-) Another tip I read was to pre treat the copper surface with the acid briefly to give the surface some tooth, neutralize with water and then use the glossy acetate transfer sheet.
     
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