C
CryingDragon
Can you use a black light to expose a precoated positive board?? (blacklights are uv),if not what kind of bulb do i need?
I tried an 75W blacklight once. It didn't work for me, exposing time was 40-50 mins. Now I use a Philips MLR 160W. It's an 'blended light lamp', meaning it has both the discharge tube and incandescent filament. The advantage is that it runs from regular mains supply. The disadvantage is that it can't restart imideate, but have to wait 5 mins of cooling time. Exposure is 10-12 mins.
I agree with Thomas here, the blacklight is not suitable for PCB photoresist. I would use a proper UV bulb. I use the Osram 300 W UV (Ultra-Vitalux) bulb and it works perfectly with anything from 3 to 8 minutes exposure time depending on type of photoresist.
/UrSv
/UrSv
I use a photographic lightbox
since all the boards I make are less than 12x12 inches I am able to use the same lightbox which I view negatives and chromes with.
It makes enormous sense to run a series of tests of exposure times -- I made a test pattern with various trace widths from 10mil to 67 mil, various pads etc to see the results (you need a good magnifier at my age). Overexposure will cause closely spaced 10mil traces to merge! If you want to run traces between the pins of DIPs you really need to test for optimal exposure time.
You can/should use the methodology we used to use making test strips -- that is start with an initial time of 3 minutes, up to 8 minutes with 1 minute intervals. As I use big transparent Avery labels I can use a sheet of cardboard to make the various exposures.
since all the boards I make are less than 12x12 inches I am able to use the same lightbox which I view negatives and chromes with.
It makes enormous sense to run a series of tests of exposure times -- I made a test pattern with various trace widths from 10mil to 67 mil, various pads etc to see the results (you need a good magnifier at my age). Overexposure will cause closely spaced 10mil traces to merge! If you want to run traces between the pins of DIPs you really need to test for optimal exposure time.
You can/should use the methodology we used to use making test strips -- that is start with an initial time of 3 minutes, up to 8 minutes with 1 minute intervals. As I use big transparent Avery labels I can use a sheet of cardboard to make the various exposures.
You might find this link of interest
<a href="http://www.thinktink.com/stack/volumes/voliii/equipmnt/uvlamp/uvlamp.htm">Low-cost UV Exposure Source</a>
Regards
James
<a href="http://www.thinktink.com/stack/volumes/voliii/equipmnt/uvlamp/uvlamp.htm">Low-cost UV Exposure Source</a>
Regards
James
In the past, I put a piece of glass over the board and negative and exposed with a number 2 photoflood at 2' distance. Exposure time was 2 minutes. 222, how odd. I sensitized my own boards so your mileage may vary.
Hello,
The 300 or 500 W UV (Ultra-Vitalux) is the very good lamp.
If you can't find it, you can also use the halogen lamp (reflector)
of 500 W or so, and you can find it almost anywhere at really low
cost.
The sun light is also effective.
Place the piece of the glass over the film and the PCB when
exposuring the photoresist, or use pausklar spray.
Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip
The 300 or 500 W UV (Ultra-Vitalux) is the very good lamp.
If you can't find it, you can also use the halogen lamp (reflector)
of 500 W or so, and you can find it almost anywhere at really low
cost.
The sun light is also effective.
Place the piece of the glass over the film and the PCB when
exposuring the photoresist, or use pausklar spray.
Best regards,
Kristijan Kljucaric
http://web.vip.hr/pcb-design.vip
I use precoated boards, and a GE F15T8-BLB bulb. (black light, flourescent).
I think that an incadescent filiment doesn't produce as much (or the same) UV as a flourescent, and thus is the reason incadescents take forever to expose a board.
Becareful with halogens, some are coated to keep UV in the bulb.
Mosty companies recomend a -BL, not BLB bulb. I'be been using the BLB, and been happy. I paid $20 at a party store for a fixture and bulb. But if you can find a BL bulb, that's the way to go. You may check some pet or garden stores for 'full spectrum' lights.
-Dan
I think that an incadescent filiment doesn't produce as much (or the same) UV as a flourescent, and thus is the reason incadescents take forever to expose a board.
Becareful with halogens, some are coated to keep UV in the bulb.
Mosty companies recomend a -BL, not BLB bulb. I'be been using the BLB, and been happy. I paid $20 at a party store for a fixture and bulb. But if you can find a BL bulb, that's the way to go. You may check some pet or garden stores for 'full spectrum' lights.
-Dan
Differences between BL and BLB
Reason why BL is more recommended that BLB is because their output of usefull UV light is about 10-20% larger than of BLB.
Check out this link - special application fluorescent lamps , it will tell you much more about UV fluo tubes. You are interested in first two, germicidal are a big no-no
- skin cancer etc... though I saw one moron recommending just them on his web site!
When Thomas talked about blacklight, I see that he meant incadescent ones, and they really do have much smaller output of UV light than fluo ones.
I'm just building my UV-light exposure box with three 8W BLB tubes (upgradable to four), and in about a week I hope to have first results (good ones I hope) 🙂
Reason why BL is more recommended that BLB is because their output of usefull UV light is about 10-20% larger than of BLB.
Check out this link - special application fluorescent lamps , it will tell you much more about UV fluo tubes. You are interested in first two, germicidal are a big no-no
- skin cancer etc... though I saw one moron recommending just them on his web site!When Thomas talked about blacklight, I see that he meant incadescent ones, and they really do have much smaller output of UV light than fluo ones.
I'm just building my UV-light exposure box with three 8W BLB tubes (upgradable to four), and in about a week I hope to have first results (good ones I hope) 🙂
Yup, the 8W fluo tubes are the ones you need, and if you get the fittings from a trade electrical wholesaler, you can buy them very cheaply, and just replace the tubes themselves. Just look for undermount worksurface lights, or some bathroom mirror lights.
BTW, a mate of mine once used a 1200W HMI (discharge lamp, used in big theatre lanterns and moving lights) to expose a pcb, he said it took about 15 seconds to get a good exposure, when exposed directly to the lamp.
I don't recommend this, as you can get severe eye burns with just a few seconds exposure...
BTW, a mate of mine once used a 1200W HMI (discharge lamp, used in big theatre lanterns and moving lights) to expose a pcb, he said it took about 15 seconds to get a good exposure, when exposed directly to the lamp.
I don't recommend this, as you can get severe eye burns with just a few seconds exposure...
I just use a pair of basic 8W flourescent tubes and get exposure times in the 4 minute range. No problem with 10 mil traces.
Don't use glass in your lightbox--use plexiglass. Normal glass soaks up too much of the UV.
Don't use glass in your lightbox--use plexiglass. Normal glass soaks up too much of the UV.
Why use anything at all between the tubes and the pcb? Plexiglass absorbs UV as well, that's why it goes cloudy and brittle after a few years in the sun.
Of course, nothing is even better. ^_^ Unless I sandwich the board-film stack though the results aren't great, so plexiglass works for me. With larger feature sizes maybe this is not necessary.
Ah, yes, I see what you mean, to hold the transparency on the board to stop light leaking underneath...
Have you tried a spray adhesive, like photomount?
Have you tried a spray adhesive, like photomount?
Good news
Blacklight fluo tubes DO work just fine!
Today I've made my first test pcb-s with UV tubes and they look very good.
Setup is:
- UV box - three 8 watt BLB tubes spaced 4.5 cm apart, aluminium foil reflectors underneath, 8 cm distance to glass plate 3 mm thick. Tubes are some Chinese ultracheap ones.
- PCB artwork - made with laser printer on tracing paper (if tracing paper is what germans call "paus", semitransparent waxy looking paper used for technical drawings), traces - 12 mil going between IC pads with 12 mil clearances. Size 25 x 20 mm.
- PCB's - precoated ones, don't know the brand, they seem to be pre-cut from some larger board, come wrapped in some toilet paper 🙂 probably the worst crap you could find.
- Developer - I guess it's NaOH, it just says 7 gramms for 1 l of solution.
- Etchant - FeCl.
First try wasn't good, I stacked two layers of artwork because print wasn't perfect (some small cracks and pinpoint holes) and decided on 5 minute exposure. Board was underdeveloped.
Second try - one layer of artwork and 7 minute exposure. it developed perfectly. Etching took longer time than usually. I was afraid that there was still some small amount of coating left but it seems that just my FeCl was no longer in good condition.
Traces look perfect. Under 10X magnifier you can see that edges are not that perfect, but artwork isn't too.
I don't have a digital camera, and if I can find some I'll post some pics.
So, CryingDragon... Just go for it
Blacklight fluo tubes DO work just fine!
Today I've made my first test pcb-s with UV tubes and they look very good.
Setup is:
- UV box - three 8 watt BLB tubes spaced 4.5 cm apart, aluminium foil reflectors underneath, 8 cm distance to glass plate 3 mm thick. Tubes are some Chinese ultracheap ones.
- PCB artwork - made with laser printer on tracing paper (if tracing paper is what germans call "paus", semitransparent waxy looking paper used for technical drawings), traces - 12 mil going between IC pads with 12 mil clearances. Size 25 x 20 mm.
- PCB's - precoated ones, don't know the brand, they seem to be pre-cut from some larger board, come wrapped in some toilet paper 🙂 probably the worst crap you could find.
- Developer - I guess it's NaOH, it just says 7 gramms for 1 l of solution.
- Etchant - FeCl.
First try wasn't good, I stacked two layers of artwork because print wasn't perfect (some small cracks and pinpoint holes) and decided on 5 minute exposure. Board was underdeveloped.
Second try - one layer of artwork and 7 minute exposure. it developed perfectly. Etching took longer time than usually. I was afraid that there was still some small amount of coating left but it seems that just my FeCl was no longer in good condition.
Traces look perfect. Under 10X magnifier you can see that edges are not that perfect, but artwork isn't too.
I don't have a digital camera, and if I can find some I'll post some pics.
So, CryingDragon... Just go for it
7 grams/litre is too potent
at least for the boards I get from the Far East -- something like 3% will give you enough time to inspect the board for "done-ness" Above 5% and it cooks in seconds taking all the resist off..
at least for the boards I get from the Far East -- something like 3% will give you enough time to inspect the board for "done-ness" Above 5% and it cooks in seconds taking all the resist off..
For me it worked just fine. I was developing them for over a minute, and spent at least half minute after all exposed coating seemed to be eaten, even gently rubbed with soft sponge, and had no problems.
But as I said, I have no idea is it really NaOH or something else.
But as I said, I have no idea is it really NaOH or something else.
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