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Old 9th Dec 2016, 10:07 pm   #1
Oldcodger
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Default Lightboxes

Or to give them their Sunday title- UV exposure boxes.
Warning to anyone new to using/making these, the UV LIGHT is harmful to eyes.
I've had it with iron methods- ye old iron ( not the soldering one) is about to go into orbit.
Mooching around on the net, I've found that the tubes & starters can be had from RS or Mega electronics, with RS being slightly dearer, but with no order limit and possibly free delivery ( or possibly being able to collect from local depot- anyone done this as a private party ?)
And data on the required ballast is available from the RS Data sheet for the tubes, or even picking up a cheap 12" fitting .
So can I ask anyone who's got /made a light box for some help , using the tube as an 8W/12inc type ---
1) Using two tubes , optimum distance between tube centres ( from end to end), and maximum width ?
2) optimum distance between board and tubes to give a reasonable time for exposure ,but with reasonable timing tolerance.
3) Given the optimum distances in 1&2 - a suggested range for a timer .
4) Anyone suggest how to wire two tubes in series and any advantages/disadvantages of this


Mods- I'll put the parts numbers in here for any one interested , and refer to this post in where to get ( if that is OK)
RS = 1X 556-250, COST £19.44, but I'd suggest that P&P is free , and collection from local depot seems possible
Mega 2X170011+2X172016 - cost would be £18.72, but Mega have a min order of £30
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Old 9th Dec 2016, 10:57 pm   #2
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Default Re: Lightboxes

I assume this is for PCB production.

Is the UV light actually harmful? I seem to remember RS claming it wasn't (although you might get some discomfort if you look at the tubes for a long enough time). Unlike the short wavelenght UV tubes used for erasing EPROMs.

I have never seen a UV eraser unit without an interlock switch. But equally I have never seen a PCB exposure unit with one. Maybe they have them now, but when I was using commerical ones they didn't.
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Old 9th Dec 2016, 11:32 pm   #3
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Default Re: Lightboxes

I think that nowadays, those who have a laser printer tend to use the ‘iron-on’ technique using scrap glossy magazine paper and seem to get acceptable results. But I’m set in my ways and for maybe 30 years or so, have used a home-made UV exposure box with a built-in timer and 4 x 8 Watt tubes. Nowadays, ultra-bright UV LEDs make it possible to make a UV exposure unit for under £15.00 with no faffing around with tubes, ballasts or mains electricity. There's an excellent design for such a home-brew UV exposure unity using 99 UV LEDs here:

http://www.hobbyelectronics.net/con_...sure-unit.html

For anyone who may wish to consider making their own UV box using fluorescent tubes, there’s a well made video at the link below on how to make an excellent box from a Maplin insect killer at this link. The video also explains about UV light wavelengths:

https://www.youtube.com/watch?v=REnWbrRgZOQ

I thought £15.00 from Maplin was too good to be true - unfortunately the UK insect killer has been discontinued, as have the tubes:

http://www.maplin.co.uk/p/20w-high-p...t-killer-n98gr

http://www.maplin.co.uk/p/10w-uv-rep...-killers-n47ja

However, there's a firm that sells liquidated discontinued stock, and they have the Maplin remaindered stock of the insect killer for £21.50 post free. You couldn't but the tubes for that!:

http://www.cqout.com/item.asp?id=186...FUefGwodbeAG9A

That makes an excellent light box at a fraction of the cost of very basic commercial ones.

I long since gave up buying pre-sensitised UV PCB boards, both on the grounds of cost, and of ending up with lots of useless off-cuts. I usually use PRP positive photo-resist UV aerosol spray lacquer for making PCBs. Not cheap at £15.00 a can, though it goes quite a long way:

http://www.maplin.co.uk/p/positive-photo-resist-n17kh

I came across an alternative method of pcb production, so I thought I’d give it a go. The video at the link below shows how it’s used, but basically, it’s a UV sensitised film from which a protective film is first removed, then the film is applied to the PCB laminate and passed through a document laminator two or three times to ensure that the film adheres to the PCB. Then a protective film is removed and the artwork acetate placed on the laminate to be exposed in the UV box in the normal manner. This method has the benefit of not having to spray lacquer on the board in a dust-free area (no such thing really in a home environment), and waiting 24 hours or so for the lacquer to dry and harden off. (I put my sprayed boards in a desk drawer overnight).

One important difference with the film technique is that the artwork for the mask must be a negative – not positive. This is easily accomplished in MS ‘PAINT’ by selecting the artwork image, right clicking on it and in the drop down menu, clicking on ‘invert colour’ then saving, and printing the acetate. In the video, the text refers to printing the artwork onto ‘vegetal paper’ which is just another term for tracing paper. Personally, for artwork I use ‘micro-porous film’ from Crafty Computer Paper and based on a ‘Big Clive’ video, I’ve managed to fool my Epson ink jet printer into printing onto acetate, which ordinarily, Epsons won’t do in a quality that comes close to what’s needed for PCB production. I now get completely opaque high quality images.

Here’s the photo-sensitive film technique process:

https://www.youtube.com/watch?v=2hQfGtSFe_0

Another video here:

https://www.youtube.com/watch?annota...&v=cRCFGZxmob0

The film that’s used costs a little over a fiver post free for a roll 30cms wide x 5M long - way cheaper than UV lacquer and should enable more consistent results to be obtained. To comply with forum rules, I won’t give the e-bay link but a search for '30cm x 5M Photosensitive Dry Film For PCB Circuit Production Photoresist Sheets' should find it. The sodium carbonate (AKA ‘soda ash’, ‘isinglass’), developer is cheap enough too, at £5.49 per KG on eBay and only a few grams are needed for each board.

I’ve just designed the artwork for a PCB that I wish to produce and have hedged my bets – I’ve created both a positive and a negative mask, so if the negative film method doesn’t come up to expectations, I’ll revert to UV spray. I’ve had one attempt at getting the negative UV film onto the board, but there were a few tiny bubbles even with three passes through the laminator, so I’ll strip the film off with acetone and try it again taking more care to exclude the tiny bubbles.

If I've got anything worthwhile to add, I'll give an update.

Hope that's of interest.
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Old 9th Dec 2016, 11:36 pm   #4
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Default Re: Lightboxes

Some time ago I was looking at building my own lightbox using UV LEDs, but decided that they weren't quite ready for the job. (And also, there was the problem that I would need some way to make a PCB for the LEDs in the lightbox .....) I ended up buying a ready-made unit with six traditional 8W tubes, an electronic ballast and timer from The Usual Place. This just needed the Schuko plug cutting off and a BS1363 plug fitting (the "deathdaptor" supplied with the unit did not provide an earth connection).

LED technology has only continued to get better and cheaper since then, so an LED-based solution might be a more viable proposition by the time you are reading this .....
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Old 9th Dec 2016, 11:38 pm   #5
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Default Re: Lightboxes

Tony-It's for PCB production at home.
I could make a home brew one that didn't have an interlock. But, I'm more interested in finding from those that have commercial ones the data I've asked for. Just lost out on a bid for a very cheap box, so I think I'll have to just make my own. But, I need the measurements- so I'd appreciate any members with a working box getting out the tape measure and posting.
For those posting on iron technique- TBH- I've had it with these- either missed bits or nothing. Missed bits- means I've got to remove a lot of ink, without scratching the copper .
SO -ANYONE GET THE TAPE OUT, AND POST DATA.

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Old 10th Dec 2016, 1:28 am   #6
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Default Re: Lightboxes

This is my homemade UV lightbox, getting on for 30 years old now.

Uses 20w tubes in a dual light batten.
Height, top of tube to top edge of box 50mm, so with glass recessed in frame - 58mm.

Box, inside measurements 62cm long and 23cm wide.
Height, didn't measure, but enough to place tube at 50mm height as above

For a timer, I'm using a modified microwave oven control panel (not shown in pics).

Bearing in mind, I use UV imageable ink (TER-20 from Taiyo), my exposure time is around 50 secs (varies depending on how thick the ink is applied).

Terry

I should add, if you are building your own and using glass, make sure the glass is NOT UV restrictive.
A great proportion of glass you buy these days either has a coating or additives in the glass to restrict UV passing through. Not what you want in a UV light box.
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Old 10th Dec 2016, 2:33 pm   #7
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Default Re: Lightboxes

Hi my RS unit has 4 tubes and has an A4 size area available. The timer goes to 20mins.
The only "interlock is a red "processing" neon.

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Old 10th Dec 2016, 3:47 pm   #8
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Default Re: Lightboxes

Quote:
Originally Posted by TonyDuell View Post
I assume this is for PCB production.

Is the UV light actually harmful?
Some wavelengths are, but not those used for UV light exposure boxes. The UV spectrum ranges from 100nM to 400nM. From 400nM to 780nM is visible light and beyond 780nM is infra red. (Wavelengths below 100nM are X rays). Those which risk harm to eyes or skin are in the range 265 - 275. The wavelengths used to UV light exposure boxes are UVA - in the 315-400nM spectrum, which is the longest UV wavelength - the same spectrum as the tubes used as insect attractants in 'bug zappers'. Not a good idea to stare at them, but anything above 300nM is not harmful.

100 - 200nM called 'vacuum UV is for medical use and in the production of ICs.
200 - 280 nM is 'UVC' and is used for sterilising in laboratories, decontamination of water
280 - 315 nM is UVB Used in pond filters to kill algae, and for light therapy.
315 - 400 nM is UVA, which is the spectrum used in 'bug zappers' often seen in restaurants and the like to attract insects and flies to be zapped. Also, for some barcode readers, and more importantly, for UV light box tubes. The spectrum for light boxes is 350 - 400 NM, 360 being the optimum. The tubes used by Mega and the like tend to be 360 - 365 NM. It's also the spectrum covered by ultra bright UV LEDs, and with 100 flat lens 5mm LEDs at under a tenner including limiting resistors, to make a light box needing no mains, ballast choke or starters, it's easy to see why there are so many such designs on youtube. (Some constructors use the LED strip arrays to cut down on soldering).
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Old 10th Dec 2016, 6:28 pm   #9
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Default Re: Lightboxes

At the intensity emitted by these small tubes, UVA is indeed unlikely to be harmful. However, the eye's natural protective reflexes (blinking, pupil contraction etc.) are not triggered by the invisible radiation, so there is a risk associated with higher-intensity sources. Not very relevant here, but mentioned just in case comments are taken too generally.
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Old 10th Dec 2016, 7:34 pm   #10
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Default Re: Lightboxes

Quote:
Originally Posted by Oldcodger View Post
So can I ask anyone who's got /made a light box for some help , using the tube as an 8W/12inc type ---
1) Using two tubes , optimum distance between tube centres ( from end to end), and maximum width ?
2) optimum distance between board and tubes to give a reasonable time for exposure ,but with reasonable timing tolerance.
3) Given the optimum distances in 1&2 - a suggested range for a timer .
4) Anyone suggest how to wire two tubes in series and any advantages/disadvantages of this
I made the box that I use back in 1985 from an article in Everyday Electronics (Sept 1985). It uses four 12" 8 Watt 365nM tubes. It was made much more complex by including a timer, which needed a relay to switch the 240V AC from the low voltage timer circuit. I've attached a copy of the circuit, and you'll see that most of it is the timing circuit. If I knew then what I know now, I wouldn't have bothered with a timer. The (expensive but basic) boxes sold by Mega, Maplin etc, generally don't have a timer - you just switch it on and use, say, a kitchen timer.

Depending on what product your using for your boards - pre-sensitised boards or self-sprayed UV lacquer, you do a few tests to determine the optimum exposure time, which isn't too critical. You make a test strip, say 10cm long x 2.5cm wide, mark it off at 2.5cm intervals, place it on some artwork, then using a strip of card, reveal and expose an area 2.5cm square at a time with say 1 minute intervals between each. So the first area you reveal and expose will end up having been exposed for 4mins in all, the next for 3 mins, then 2 mins then 1 min. Then you develop the board and see which exposure has given the best results.

To answer the points above, none of those dimensions are in any way critical so there is no 'optimum' distance. I've attached a couple of pics of a Mega exposure box, which has a mechanical timer that can be set for up to 6 minutes. It uses 2 x 12" 8 Watt 365nM tubes, which are about 5cms apart, and are about 2.5cms beneath the glass. The box is lined with shiny thin-gauge dimpled metal to reflect the UV light to give it a good spread within the box. The glass exposure area is 15cms x 22.5 cms (6" x 9"). The exposure area of my own box is about A4 size - larger than any PCB is every likely to be.

I can't comment on wiring tubes in series. I've attached a copy of the circuit of the box that I built, and you'll see that it used four small ballast chokes, four starter and four tubes in parallel. You'll also see how much the needless addition of a timer complicated matters.

There are far more critical factors which affect success or failure than the box itself.

I'm my experience, the most critical factor is the creation of a high quality mask.

Going back to the 1980s, prior to home PCs, inkjet printers and film, like most constructors I guess, and no doubt some today, I used to get OHP photocopies of magazine artwork, which are pretty pathetic, then to improve the density of the tracks, I'd tape two or three images above each other. All very hit and miss - even commercial laser printers don't make good high density PCB masks. This makes the exposure time quite critical because too short an exposure will be insufficient to expose the pattern, and too much exposure will make the tracks threadbare where the light shines through the tracks in the artwork.

People will do what works best for them within their limited resources - some say they get along fine using tracing paper in an ink jet printer. I've tried it - no good for me. Others say 'print onto white paper and use 'transaparentizer'. I bought a can - expensive. Yes, it makes the white areas transparent to an extent, but again, it was no use to me. Others say 'print onto white paper and spray it with WD40 to make it transparent'. Another WD40 'snake oil' myth, like 'it cures arthritic knees and frees stuck screws'. Really?

The only successful way I've found of creating a high quality mask on acetate is with an ink jet printer, but it must be a printer which has OHP settings in its software, and not all do. No domestic Epson printers do, and that's well known. A chum pointed me to a 'Big Clive' youtube video on how to fool Epsons into printing properly onto acetate so I've created a 'PCB' setting in my Epson printer options. I also found an excellent product known as 'micro-porous film' from 'Crafty Computer Paper'. Way better than normal OHP film.

Another critical factor in my experience is the pattern of the artwork.

Many people use 'Easy PC' to design artwork - it's free so is appealing. But the reason it's free is that it's primarily intended that you design a PCB then get the firm to make the board for you, using commercial techniques - CNC drilling for example. Hence, the pads tend to be small, the tracks often narrow, and sometimes close together. If a lot of copper needs to be etched off the board, the etching time is longer, and the problem with that, is that the longer the board is in the etchant, the more that any thin tracks and small pads will be 'undercut', then when it comes to tinning tracks and soldering components, the track may lift off the board. Also, with small pads, using a PCB drill even in a precision drill stand using a magnifying lamp and a new drill bit, it's very easy to be a little off centre and wreck the board.

For these reasons, if I'm using someone else's artwork, if I see any small pads or thin tracks, if there is scope, I copy the artwork then make the pads larger and the tracks thicker. The fourth pic below shows the artwork for the April 2003 Radio Bygones Wobbulator, but not as it appeared in the magazine - I thickened the tracks and enlarged the pads. When I'm designing my own boards I try not to use tracks at all. The fifth pic shows a PCB I've just designed for a project I'm currently developing. It could have had titchy pads and thin tracks, but why - when there's no need for it? (I don't use a PCB program - just MS 'PAINT').

For drilling, I use a new HSS 0.8mm bit for each board, then bin the bit. Cheap enough to be disposable, so why wait till the bit skids and wrecks a board?

As to etchant, I pensioned off messy ferric chloride yonks ago in favour of sodium persulphate.

I'm just relating my experiences and what works for me, others will have their own approach, which is fine.

Hope it's helpful.
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Old 10th Dec 2016, 8:22 pm   #11
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Default Re: Lightboxes

Thanks, David, that gives me all the info I need . As I mentioned, in where to get bits, RS tubes are the ones Mega use ,but Mega have an order limit of £30 min, and P&P of £7.5, whereas I can ( hopefully) call in to local RS and pick them up . presuming RS will accept on line debit card.
I'll probably go for the presensitised boards- tried using spray on before ( even abroad, where you didn't need a light box, just a couple of minutes in sun at mid day) ,but I had no success with spray.
I doubt if the glass will be a problem -last time I was looking at a box & got the glass was over 20 years ago.
Timer - I bought a Maplin 555 mono board some time ago for a project and never used it.
Light- I''d err on the cautious side as ( from above , sunlight works well with these boards ) , similar to tanning I'd suggest ,where glasses are needed ,and I remember that local abroad suffered eye problems after a certain age if they didn't wear sunglasses.
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Old 10th Dec 2016, 9:10 pm   #12
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Default Re: Lightboxes

Ignoring the fact that this guy is using UV LED strips rather than tubes, and overlooking the fact that he's using a bandsaw and table saw without a push stick, there's a nicely design light box here that might give you a few ideas:

https://www.youtube.com/watch?v=wRdey0U7HZM

Have fun - good luck in your endeavours!
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Old 11th Dec 2016, 9:43 am   #13
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Default Re: Lightboxes

The ubiquitous cheap banknote checking devices house a UVA blacklight tube and control gear of a sort (often just a capacitor). Since quality control seems to be non-existent, large numbers end up as customer returns, which are therefore sometimes available in small quantities as 'spares or repair' for next to nothing.
A possible starting point?
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Old 16th Dec 2016, 8:08 pm   #14
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Default Re: Lightboxes

I have used a 3M UV exposure box since 1985. Its mechanical timer "died" a few months ago and I replaced with a 555 timer running a divide by 100... to give a reasonable delay.
I normally use an exposure time of 70 seconds...... The UV box has X6 tubes spaced at 55mm between CENTRES.. and 420 mm long 8W. Replacement tubes were bought locally from a Commercial Electrical supplier.
I still use pre sensitized pcb material, however CPC have stopped stocking the "budget" boards.
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Old 16th Dec 2016, 8:45 pm   #15
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Default Re: Lightboxes

Thanks Wendy. RS have the tubes ,starters and Ballast used in the box Mega sell ( Mega will only take an order over £30 with high carriage,whereas RS have no limit and there's a branch locally) . I've sourced the tube holders from e bay ,and looking at ideas for starter sockets. I've got an old 555 timer board and bits, so time experiments to come once I've got it made and working. My tubes are 8w but 12inch/30 cm , which fits nicely in an old wooden case I've had knocking around for some time.
Hope mods won't mind ,but HAVE A LOOK AT
https://www.vintage-radio.net/forum/...d.php?t=132258
Maplin are selling off boards cheap .
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Old 16th Dec 2016, 8:52 pm   #16
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Default Re: Lightboxes

Assuming these are the normal 2-contact fluorescent starter things, a google search for 'fluorescent starter holder' gives a large number of suppliers.
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Old 16th Dec 2016, 9:54 pm   #17
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Haven't spotted any at what I'd consider a fair price, compared to what I paid for the tube connectors/holders. RS do them at a decent price, BUT in packs of 10 . Failing all else ,I'll ask my recycling expert to look out for old fittings.
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Old 17th Dec 2016, 1:02 am   #18
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Default Re: Lightboxes

As regards the strictly electrical arrangements, ANY common type of SMALL fluorescent tube may be worked two in series from a single choke.

For two lamps each 12 inch and 8 watt, use a 13 watt choke.
For two lamps each 18 inch and 15 watt, use a 3 foot 30 watt choke.
For two lamps each 24 inch and 18 or 20 watts, use a 4 foot 36/40 watt choke.

Each lamp needs its own starter, and these must be the special ones called series starters, or 110/120 volt starters. There are fairly readily available as many office lights use series pairs of 2 foot lamps.
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Old 17th Dec 2016, 10:09 am   #19
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Default Re: Lightboxes

Quote:
Originally Posted by Oldcodger View Post
Haven't spotted any at what I'd consider a fair price.
Don't know what you consider to be a 'fair price', but these are £3.99 each post free from a UK company:

http://www.ebay.co.uk/itm/Screw-Fit-...YAAOSw-jhUKRkd

Hope that might help a bit.
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Old 17th Dec 2016, 6:02 pm   #20
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David. G4EBT.

Ref the density of Laser printed acetates, I always print two arts either one above the other or side by side, this stops "hopefully" stretched arts. Then cut the acetate and place one on the other, tape with masking tape, ALL 4 SIDES to stop them moving, then a 60/70 second exposure. I have even done very small SMD arts this way, but you MUST be very accurate placing the two together.
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