UV lightbox cheap equivalents?

A

alband

Senior Member
Hi,

I've just got a quick question regarding making PCB's using the photoresist board, UV developing, then etch method.

I'm trying to set myself up to make them at home as cheap as possible.

All the UV boxes I've seen are pretty costly so I was wondering if just a UV light strip would do? Is UV particularly dangerous and at what power?
Could I just use one of these:
http://www.rapidonline.com/Electrical-Power/PA-Audio-Video/Lighting/Lamp-with-built-in-blacklight-UV-projector/79509/kw/UV
Just the replacement in this one connected to mains (or if the unit has a transformer low voltage DC would obviously be preferable)
http://cgi.ebay.co.uk/ULTRA-VIOLET-UV-FLUORESCENT-TUBE-LIGHT-BOX-450mm-15W_W0QQitemZ380123127182QQcmdZViewItemQQptZUK_ConElec_LightingLEDsStrobes_RL?hash=item380123127182&_trksid=p3286.c0.m14&_trkparms=72:1683|66:2|65:12|39:1|240:1318|301:1|293:1|294:50

I don't know much about UV light bulbs and tubes :)rolleyes:). Would a simple UV bulb work (like the ones designed to replace real bulbs)? Do fluorescent tubes work with DC? If so what is the lowest voltages they can take?
 
B

BeanieBots

Moderator
Can't comment much on the UV side of things except that is IS dangerous (at certain wavelengths) and I doubt the "black light" domestic 'replacement' type bulbs would work. Commercial UV boxes for PCB use include an interlock which prevents you from being exposed to any UV.

On the fluorescent tube side of things.
You CANNOT run a tube on DC for more than a few minutes without causing it severe damage. Also, it requires several kV to start one. To add to the fun, they are a 'negative resistance'. That is, the voltage across them goes DOWN as the current INCREASES. That makes the control a bit more fun than simply applying a voltage across them!

On a mains driven tube, the 'control' is normally done with little more than a large inductor in series with the AC voltage.
It's not too hard to make an inverter to run off 12v DC but care must be taken to eliminate any net DC or the end(s) will blacken very quickly.
 
K

kevrus

New Member
I made an MDF box to house my 4x15w UV tubes...they are the ones used in insect killers, they look like 'normal white' tubes when off as apposed to the 'black' UV tubes which are the wrong wavelength.

A good idea for a cheap enclosure would be an unwanted 'scanner' (wish I thought of that before I made my box!!).

I saw one somewhere on the net that used UV LEDs moving back and forth as per normal scanner operation. I recall that it took 10 to 15 minutes for full exposure though, whereas fluorescent lamps would be much quicker...mine takes approx 90secs which incidentally uses a picaxe and 2x16 LCD for control.

Considering the cost of commercial units, its worth making your own. You can run two tubes from a single choke....i.e. a 30w balast for two 15w tubes, but willvstill require two starters, albeit 110v rated.
 
A

alband

Senior Member
Thanks for the info BB.

It sounds like using 230VAC to power the tube from rapid would be best.

There doesn't seem much point in converting 12VDC into 230VAC when it is sitting there in the plug. So...
If I mounted (carefully with everything switched off unplugged etc...) the tube from rapid in the lid of a sturdy shoe-box,
all wiring inside the box,
everything insulated,
only a single mains power lead coming out the lid,
only turn it on when the box is closed,
and taking all normal precautions;
this would be safe. :)

Ah kevrus, just got you reply. That sounds like just the kind of thing. I'll ask around if anyone has an old scanner as that would definitely make a good enclosure. I only ever make small circuits so could I get away with only that replacement tube from rapid?
Also, can you explain your last sentence; I have no experience with tubes and how they work so, for instance, what is a choke? Thanks though :D It seems that you too thought :eek: when you saw the prices out there.
 
hippy

hippy

Ex-Staff (retired)
There are many examples of homemade UV lightboxes on Google, Instructables, Make and similar sites. Take the best ideas from those and here and adjust to fit your cirumstances.
 
K

kevrus

New Member
The 'choke' is what BB described as a 'large inductor'. It is sometimes called a ballast, and is a wound inductor that is used to provide a high voltage spike to strike the tube and then restrict the current flow to the tube heaters when the lamp has struck. I actually used electronic high frequency ballasts in my light box, but thats because I had access to them.
 
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J

jaka

Member
Home made light box

I made one for about £20. Wooden box about 20" x 6" - 12" bedside fitting with insect tube fitted and a timer/relay using a 08M. Coat the inside with white paint or baking foil.

Good for boards up to 4" x 8". About 10 mins exposure seems to work ok. Sandwich board between two pieces of very clean glass.

Cover box before with a piece of board before switching on. To be safe I press the start button (in my garage) the go inside and wait 12 mins.

Be prepared to make a few mistakes at fist.

Bigest problem is getting rid of the chemicals.

jaka
 
A

alband

Senior Member
I've just looked up a few insect killer tubes on eBay and they all seem to be of the "blacklight" variety. Will they work?
Also, does anyone happen to have this light box because if the tubes in it are smaller than 13" then I'll use those.
 
N

nbw

Senior Member
Have you considered a bank of UV LEDs? You can get a little variation in the wavelengths produced, you may find some with an acceptable lambda, good mcd output, and a wide-ish beam?
 
B

BeanieBots

Moderator
I think we've concluded that 'black light' tubes WON'T work.
Can't comment on the others.

Do you know how to drive a tube?
You can't just hook it up to a voltage. It won't start until there are several kilo-volts across it. Once it starts, the impedance drops and the voltage across it drops as the current increases.
I mentioned this earlier but I don't think you took it on board.

To make it work, as an absolute minimum you also need a ballast and a starter.
(as an aside, PICAXEs don't like working anywhere near a flourescent tube).
Be warned!
 
A

alband

Senior Member
I did think about that actually, it makes sense doesn't it, as a low cost solution. I'm not sure though if they would be powerful enough. :confused:
 
A

alband

Senior Member
Sorry BB, we replied at the same time. My confusion was that Flykillers seem to work but that after searching eBay for Flykillers they all were Blacklights which apparently don't work. Also, there are some UVA LED's on rapid that are also blacklight which adds to my confusion.

LED's certainly look like a good option, if they do work. That instructables you found, Chigley, clearly surgests they do work and for under 10 minuites which is nice, but I still get the feeling that if 2X 8W UV tubes are needed then surely 84 LED wouldn't be equevalent :confused:

Despite this, these look like the right type?

On the tubes side of things:

To get a UV tube working I would need: a tube, a holder that has the electronics to turn mains into "tube" and a choke.
The problem is I can find any of these holders, I've look on the oh-so-helpful B&Q website and can't find any but I doubt this means they wouldn't have any if I went in with some tubes.

@ Andrew: are these the ones you mean? What holders did you use?
 
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HowieD231

New Member
I have made many homebrew PC boards using presensitized copper and just about any strong light source will work, even sunlight. The secret to getting reasonable quality boards is even, consistant light. The best light source is also the one that is dangerous to your eyes, unfortunately I found out the hard way. The most common source are the bulbs used in germicidel lamps for sterilizing air and water. This type of bulb will generate enough UV at the correct wavelength that it allows you to move the board a far enough distance away for even illumination. Plan on using up allot of material at first until you find the correct exposure time for your setup. Don't look at the light !
 
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alband

Senior Member
That's exactly it! except they are out of stock.

I assume this would do instead (once I knew what to call it i found some)?

It would also make sense to get the bulbs from rapid as that is where I will get all the etching stuff etc. but I need to check if they'll fit first.
:)
 
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manuka

Senior Member
I've mentioned this before, but "old sol" itself can indeed be very handy for simple needs. Naturally a UV box is MUCH more convenient, but ~30 years back I recall ~1 minute of NZ wintery bright sunlight was sufficient for some skinflint PCBs I was supervising.
 
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nickwest

Member
Manuka, remember that down here in the Southern hemisphere we have a much higher UV content in our sunlight, thanks to years of CFCs thinning the ozone layer.

For budget PCB etching, experimentation is probably key. Don't rely on web sources from unknown latitudes, try an exposure at a specific time of day, for a specific period, on a scrap piece of test PCB and gradually increase the exposure time. Also bear in mind that normal window glass blocks a significant amount of UV.

It can work quite reliably if you're methodical about your initial testing.

Unfortunately I don't have specific numbers to quantify the difference between hemispheres, but I can confirm that it's harder to get sunburned at say, 35 degrees North (where I worked in Colorado) as at 35 degrees South (where I work in Canberra). This is the case in both Summer and Winter.
 
M

manuka

Senior Member
Quite true- even at my 41°S latitude (& with additional thanks of course to VERY clear skies),sunshine & UV levels can be very strong "down-under". Many Asian/US/European visitors often wear sunglasses while here in NZ, even in winter. Of course, while in more equatorial Australia, they barely step outside during daylight hours!

The point is that PCB solar exposure (outdoors perhaps),once local UV levels are understood, makes a handy photo resist UV source.
 
L

lanternfish

Senior Member
Have seen a design that utilisises a 'gutted' microwave. Basically the turntable and control panel is retained and tubes fitted above the turntable, interlocked to time and door. Can't remember what magazine I saw it in - Silicon Chip (Australia) or Nuts & Volts (US). WARNING The capacitor inside a microwave can hold its charge for a very long time and is LETHAL
 
C

chigley

Senior Member
Has the LED idea been rejected by most then? As most people seem to be leaning more towards tubes

What are the major benefits to tubes rather than LEDs? I'm interested in making some sort of UV exposure box, but think that the tubes sound too complex for me, whereas I can cope with LEDs just fine!!
 
C

chigley

Senior Member
Andrew Cowan said:
Tubes:
Cheaper
Better + more even coverage (LEDs are very directional)
Brighter (LEDs are slow)

A
Click to expand...
Right OK then thanks. I'll see if I can find another Instructables or similar kind of thing which tells you exactly how to set it up, as I don't think I'd be able to on my own.
 
B

BeanieBots

Moderator
On the other hand,
LEDs are easier to drive.
Don't produce very high electrical noise problems.
Run off low voltage.

If you do not have much electronics experience and wish to build a PICAXE based timer for your UV exposure box, I'd suggest LEDs.
If you are confident about controlling mains and know how to suppress RF & EMI then the tubes would be better.
 
C

chigley

Senior Member
BeanieBots said:
On the other hand,
LEDs are easier to drive.
Don't produce very high electrical noise problems.
Run off low voltage.

If you do not have much electronics experience and wish to build a PICAXE based timer for your UV exposure box, I'd suggest LEDs.
If you are confident about controlling mains and know how to suppress RF & EMI then the tubes would be better.
Click to expand...
I obviously fall into the first category there. Don't want to build it though if it's not going to do its job.
 
C

centrex

Senior Member
I have converted an old scanner into a pcb exposure box.
It uses 40 uv leds mounted as two rows on the origonal light carrier.
It also uses the origonal stepper motor driven by a Picaxe 14M mounted on a small pcb fitted where the origonal controller was mounted. It also has a couple of fet's to turn the uv leds on and off as well as turn the stepper on and off.
The software is just a timing loop to make the carriage move up and down the scanner, it takes about 2 mins to expose the board.

Have a look here, I dont know why the paste put the url on two lines, it wont fit on one, this one was built by a friend in Canberra Aus.

http://www.thebackshed.com/Windmill/FORUM1forum_posts.asp?TID=1516&PN=2

Regards
 
C

chigley

Senior Member
centrex said:
I have converted an old scanner into a pcb exposure box.
It uses 40 uv leds mounted as two rows on the origonal light carrier.
It also uses the origonal stepper motor driven by a Picaxe 14M mounted on a small pcb fitted where the origonal controller was mounted. It also has a couple of fet's to turn the uv leds on and off as well as turn the stepper on and off.
The software is just a timing loop to make the carriage move up and down the scanner, it takes about 2 mins to expose the board.

Have a look here, I dont know why the paste put the url on two lines, it wont fit on one, this one was built by a friend in Canberra Aus.

http://www.thebackshed.com/Windmill/FORUM1forum_posts.asp?TID=1516&PN=2

Regards
Click to expand...
404 error on that link for me?

I think I have an old scanner I can gut somewhere. Do you need to use mains to power the motor which was in there originally, or is it all low voltage DC?

EDIT: You missed a forward slash out of the link. Correct URL is http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1516&PN=2
 
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A

alband

Senior Member
I too am certainly in the same category but would want to make certain I got high enough brightness LED's.

Rapid's only offerings are:
http://www.rapidonline.com/Electronic-Components/Optoelectronics/5mm-LEDs/5mm-Ultraviolet-LED/81695/kw/ultraviolet which I think are blacklight so no good.

http://www.rapidonline.com/Electronic-Components/Optoelectronics/5mm-LEDs/5mm-Ultraviolet-LED/82278/kw/ultraviolet which I doubt will be bright enough.

Maplin only has these: http://www.maplin.co.uk/Module.aspx?ModuleNo=35765 which also don't look bright enough (500mcd)

eBay is pretty useless on UV LED's too.

@ centrex: Where did you get your's from?
 
A

Andrew Cowan

Senior Member
These LEDs on ebay have a wavelength of about 400nm.

link

I bought a set - they don't look particually bright as we can't see UV (Don't look right into them!), but they will energise glow in the dark paint/watches in an instant.

I haven't tried them on PCB.

A
 
E

eclectic

Moderator
Andrew Cowan said:
These LEDs on ebay have a wavelength of about 400nm.

link

I bought a set - they don't look particually bright as we can't see UV (Don't look right into them!), but they will energise glow in the dark paint/watches in an instant.

I haven't tried them on PCB.

A
Click to expand...
Looking at the specs and the delivery times of the ebay LED's

These are more expensive, but closer to home:
The"purple" version

http://www.component-shop.co.uk/

http://www.component-shop.co.uk/html/body_rl50u.html

Perhaps get a couple to test first?

e
 
A

alband

Senior Member
Right, in that case the LED's from maplin look suitable but the P&P from component shops is far better so I might get some of the 10mm purple LED's that have 350mcd. Does mcd only rate the brightness of what humans can see because the purple mcd is uniformly a lot less that the other LED's.
 
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Andrew Cowan

Senior Member
I imagine it is measured by a machine, and manufacturers want their LEDs to be as highly speced as possible. So I think it includes purple and UV.

A
 
A

alband

Senior Member
Yes, good point.

I've actually just found some very similar ones from rapid and since I'm getting the rest of the etching stuff from them, I'll get these ones. How many would I need, I won't be making very big boards 6"x6" would be the max I imagine. 300 be enough?
 
E

eclectic

Moderator
@David and Andrew.

I don't have any photoboard to test.
(I gave it all away in a recent clearout.)

Perhaps one of you could try a small off-cut,
with a simple overlay mask, but try exposing with
an electronic flash?

I'd be interested to know the result.

e
 
C

chigley

Senior Member
alband said:
Yes, good point.

I've actually just found some very similar ones from rapid and since I'm getting the rest of the etching stuff from them, I'll get these ones. How many would I need, I won't be making very big boards 6"x6" would be the max I imagine. 300 be enough?
Click to expand...
Not sure if you've noticed but the UV colour for those LEDs on Rapid is currently out of stock, due in this month.

If the Maplin ones are suitable... why not get them from your nearest store? You can check stock on the website and then just go to the back of the shop with the order codes. That's what I've done in the past. I've always found Maplin quite expensive though.

Also, what other things do you need for etching? In college we use four stages after the exposure:

  • Develop (purple blackcurrant-juice coloured chemical)
  • Bubble etch
  • Resist strip
  • Immerse tin

Are all of these necessary, how expensive are they?
 
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