I print onto tracing paper, [the type schools us] two times, i.e. two seperate prints, using a laserjet printer HP1018 with the plain paper setting, stick double sided tape on the perimeter of one of the images, then use a light box to align the two images, carefully remove the protective film off the double sided tape, one side at a time, preventing the two images from moving out of line is a bit tricky but not impossible, and stick them together, for double sided boards i do this for both side, i.e. 4 prints, then i align the two "double" images and form an envelope, again using double sided tape, i also put a small strip of card along two sides of one of the images like "X" and "Y" in a graph before making the envelope, this is used to make sure the PCB sits in the right place, I leave one side open, then I slide the PCB into the envelope, i have found registration for the two sides to be perfectly adequate, even for complex layouts, I expose each side for 6 minutes, probably too long but the tracing paper isn't totally transparent, and over exposure doesn't seem to affect the end result. I use a home made UV box, 100 5mm 3000 mcd UV leds on a 6" x 8" PCB board that has a sheet of flexible mirror stuck to it, the box has a glass top, the amount of UV the glass prevents from reaching the PCB is negligable, or if this a real concern use clear acrylic sheet 3mm, also works just fine, i keep the PCB and image firmly pressed against the glass with a heavy book, then cover the whole lot with a piece of dark cloth to avoid looking at the UV light, then develop in the normal way, I drill before etching, this way any registration errors can be corrected with a etch resist pen, no problems!!
hope this helps.
David
--- In Homebrew_PCBs@yahoogroups.com, "tda7000" <Tda7000@...> wrote:
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> Recently I had my first try at a UV-exposed board
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> (because I have nightmares from trying to align paper properly for a double-sided board with the laminator, ha ha)
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> I used this photoresist film: http://www.ebay.com/itm/10pcs-Dry-Film-Photoresist-Sheets-for-DIY-PCB-6x8-q-/320735055777 which worked pretty nicely, although it took me a couple of goes to get it on the copper without bubbles!
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> Some UV LEDs on a sheet of protoboard for the exposure lamp, and to test out different spacings etc (Thanks to Chris for the LEDs!) - hopefully I can make a proper exposure box once (if?) I get the other issues sorted.
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> I used my Canon iP2000 inkjet printer and inkjet transparency sheets to make the transparency, unfortunately it did not come out as good as I had hoped, as solid black fills had many quite light parts in them when held up to the light, and when exposed left a speckled pattern on the developed board.
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> I used a solution of Sodium Carbonate (Washing Soda) to do developing.
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> Today I tried with a Laser printer but again, holding the transparency up to the light I see too many light areas. I haven't tried exposing using that printout but I feel it will have a similar problem to the previous one.
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> What does everyone else do to get their printouts opaque enough for the UV process?
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