Fluorescent light for photo-resist

[patroclus]

Hello, I want to start making photo-resist PCB, and I thinking of using NaOH for developer, and wonder if I could use a 8W fluorescent tube for exposure. I know UV light is the best, but I have some fluorescent 8W tubes, that are cheaper, and I heard some people say that it works fine, but it takes 10 minutes or so, instead of a few minutes using UV.
Any experiences?

 

[justDIY]

manuf of my boards recommends a min of 10 min with a 15w bulb, and that's for a small surface area... I generally use two 15w bulbs at 10min, but i raise the bulbs up a bit, so their light is better distributed.

i think your 8w bulb would be too small, but of course, you could just give it more time, or do an exposure test ... get a piece of cardboard and some test artwork (various lines, and various sized pads), and expose a new section of board every 5 min, run the test for 30 or 60 min ... then pick which result looks best.

 

[patroclus]

are you talking about UV or standar fluorescent lights?
I was talking about fluorecents. I can use two 8 W tubes in put together

 

[Oznog]

Std flourescent has such a low content of effective wavelengths it would take a pretty long time. Hard to say how long too. Just get blacklight tubes, they're not too expensive.

Me, I lament the loss of readily accessible blacklight-white tubes. These don't have the purple filter on its glass (the "blacklight-blue" tube) and put out a much more visible light which makes it easier to observe the setup and is probably a bit more intense. They still make them but they're just not in the hardware stores anymore.

 

[patroclus]

I can get blacklight tubes too. In the store they told me they have std flourescent, and backlight fluorescent. Should I get the blacklight ones? I think those are more or less the same as UV lights?

 

[jbeng]

Me, I lament the loss of readily accessible blacklight-white tubes... They still make them but they're just not in the hardware stores anymore.

Here's a link to a place you can get them for $5US each plus shipping.
**broken link removed**

I use two of these tubes at a distance of 4 inches, an exposure time of 90 seconds, through a 1/4 inch thick sheet of plate glass as a contact frame.

Also, links to a couple of threads where we have discussed this subject previously...
https://www.electro-tech-online.com/threads/pci-card-blank.9965/
https://www.electro-tech-online.com/threads/10296/
JB

 

[RadioRon]

I have a left-over item that may be useful and I'll give it away to whoever wants to cover the shipping. Its one of these gadgets for drying fingernail polish that you can see in the typical Ebay ad like this one.
**broken link removed**

The one I have is missing its line cord plug, which got cut off some time ago leaving only about 6 inches of wire sticking out but it would be easy to attach a new cord to this. It worked OK before losing its plug and the ultraviolet bulbs included are new. The bulbs are qty3 of OSRAM DULUX S G23 which are specifically built to generate UVA rays. Each bulb is 9 Watts and there are three sockets in the box so you get a total of 36 watts.

This seems like a good little light box for exposing UV sensitized pcb boards. I live in Canada, and am willing to ship whatever method is cheapest (probably just Canada Post / USPS). Anyone want it for nothing?

 

[justDIY]

do the "blacklight" or near-uv bulbs really work with these boards, I was under the impression they needed "real" uv bulbs, that is, the mercury vapor fluorescents, with no coating at all.


General Electric F15T8/BL bulbs (white when off, pinkish when on) are $1.99 at the local discount store ... right now I'm using GE F15T8/Daylight Deluxe bulbs, also $1.99 from the same source.

 

[jbeng]

Years ago (15+) when I first started using the photo method for producing PCB's, I used photosensitizer marketed by GC Electronics. The F15T8/BL tubes are the ones they specified to use and I've never used any other bulbs. GC had pre-coated boards and spray-on sensitizer back then but stopped selling the spray-on stuff after a while. I don't even know if you can still get pre-coated boards from them any more. These days I use boards I get from Circuit Specialists. Here's a link: **broken link removed**
I use standard sodium hydroxide developer with these boards then etch with ferric chloride. I'm always very satisfied with the results.
JB

 

[justDIY]

well then ... I'll have to go grab a few more of those bl tubes while they're cheap, and do an exposure test

big problem I'm having right now is my printer refusing to lay the toner down real heavy ... even with the density set to 5 (max), there's lots of pin-holes in the traces and pads. maybe it's a problem with the transparency itself, not the printer

 

[Oznog]

do the "blacklight" or near-uv bulbs really work with these boards, I was under the impression they needed "real" uv bulbs, that is, the mercury vapor fluorescents, with no coating at all.

General Electric F15T8/BL bulbs (white when off, pinkish when on) are $1.99 at the local discount store ... right now I'm using GE F15T8/Daylight Deluxe bulbs, also $1.99 from the same source.

The purple-painted incandescent bulbs are not effective. Any flourescent blacklight tube will be very effective. It takes only a few minutes to completely expose a board.

I prefer the blacklight-white flourescents (white when off, pinkish when on) but really it's just a matter of personal preference.

Non-blacklight flourescents are not effective. Just in case there is any question, effective flourescent blacklight tubes come in black and white types. But none of the white tubes normally used in flourescent fixtures are that blacklight type. It's a specialty item. All purple-colored flourescent tubes are effective blacklights.

 

[patroclus]

So, two 8W blacklight tubes will do ?
As it's my first time, I wonder, when I do the exposure test (using 3 pieces of board, with different exposures, and pick up the best), how do I know it is well exposed, before trowing it to acid??
It would be good to be able to see it without etching it..

 

[jbeng]

General Electric F15T8/BL bulbs (white when off, pinkish when on)

My tubes look white when off, bluish-purple when on. Example: at local grocery stores (around here anyway) they have electric bug-zapper fixtures near the deli section and the meat departments to lure insects away from the food preparation areas. My tubes look just like those tubes when they're on.

... my printer refusing to lay the toner down real heavy ... there's lots of pin-holes ... maybe it's a problem with the transparency itself, not the printer

I found that to be a problem, too. I think it's because the toner is designed to fuse into the fibers of paper and transparency sheets don't have fibers. Some brands have a roughened suface, which works better, but the traces can have "fuzzy" edges because of it. Also, the toner can flake off if the film is flexed too much. Lately, I've tried smooth film thru an HP 1220c inkjet printer. Problem: very slow dry time. Benefits: (a) image is quite opaque with few pinholes, (b) make a mistake? Wash the image off the sheet using water to reuse it.
And as I said earlier, using the F15T8/BL tubes with the boards from Circuit Specialists @ 4 inches distance thru 1/4 inch plate glass, I expose for 90 seconds. Some experimentation may be required for you to optimize your process.
JB

 

[mstechca]

... my printer refusing to lay the toner down real heavy ... there's lots of pin-holes ... maybe it's a problem with the transparency itself, not the printer

I use transparencies designed for inkjet printers, because I own one.
When I print and hold it up near my halogen light, I can see clear spots evenly distributed throughout the PCB design. When I print the same design on top of the printed design, the spots are gone, and the circuit functions much better when the design is passed through the printer more than once.

Also, I recommend using the darkest ink setting, and the setting that allows the printer to spend more time printing.

When I expose my board, I don't do it under 40 minutes. My lamp is about 18 inches away from the board.

 

[zachtheterrible]

Hate to come here and mix you up, but I just use a regular ol' 100W light bulb, 15 minutes exposure time and my circuits come out wonderfully. Might want to just give it a test run before you go off buying UV lights. Probably depends on the photoresist that you are using though :?

 

[patroclus]

I just got two 8W blacklight tubes, and have build some kind of exposure stand. I put the tubes on the bottom, facing up, and 7 cm above there is a transparent 0.5mm crystal. On top of it, it will be the PCB, facing down, with some weigth on it. Do you think this will work?

I just find some problem with this approach:
- No reflector, is it really necesary?
- Maybe 7cm is too close to the blacklight tubes... I really don't know if it will be done in 2 minutes, or 6. But anyway, is it too close?

Thank you

 

[patroclus]

This is how work is at the moment

As I said, there's 8 cm from the tubes to the PCB, that goes on top of a 0.5mm transparent crystal.

Please, give me your opinion!!