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Old 17th Dec 2016, 6:20 pm   #21
MrBungle
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Default Re: Lightboxes

I got my UV box from eBay about 5 years ago for £7.50 including delivery. Is a standard RS one from the 1990s. Worked fine. Pays to have a look around.

Incidentally though I've only made 2 PCBs with it. Used Eagle, standard laser transparencies, RVFM boards from rapid and cheap developer and etchant. Came out rather good.

I'd rather do SMD boards now for this as I hate drilling holes as I only have a hand held electric drill from machine mart.
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Old 17th Dec 2016, 9:54 pm   #22
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Default Re: Lightboxes

David. G4EBt - fair enough, but the holders /connectors for the tubes only cost 99p/pair and RS sell holders ( but only in packs of 10) @circa £5 so to me £4 is a bit OTT. ( as said, I suspect my contacts in the recycling trade will be called on , as I think that GU10 lamps are of similar design)
Broadgage- many thanks. RS do a choke and once I'd got into their tech data ,I found a diagram , for 8w tubes and that choke. All I've got to do now ( thanks to your info) is to check that the starters with the RS kit are the right ones.
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Old 19th Dec 2016, 2:08 pm   #23
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Default Re: Lightboxes

Sods law- after sourcing the bits and getting info , a few are appearing on e bay around the £20 -30 mark .
Can I ask mods indulgance for help ?
One thing of interest is dry film photosensitive sheet. I assume that this is used with a board that's not treated - just placed on the board with artwork and light treated as a treated board ?
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Old 19th Dec 2016, 5:16 pm   #24
David G4EBT
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Default Re: Lightboxes

PHOTO-RESIST DRY FILM METHOD OF PRODUCING PCBs USING UV EXPOSURE.

The method and processes can be viewed on youtube at this link:

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

The steps are as follows:

There is a clear protective film on either side of the UV film.

• Cut a piece of film to the size of the PCB, and attach a piece of Sellotape to the protective film to peel it off. (Doesn't matter which side you peel off first).

• Place it on the PCB, smooth it out and pass it through a laminator a few times to ensure that it adheres to the PCB with no air bubbles in it.

• Place the artwork on the PCB in the usual manner and expose it in a UV light box. (Note: The artwork must be NEGATIVE – not positive). The exposure time is approx 45 – 60 seconds - maybe more, depending on the light box in use. To create a negative, the method I use is to open the artwork file in MS ‘PAINT’ then use the ‘Select’ option and with the mouse, and select the image. Then right click on the image and a drop-down menu will appear. The bottom option on that menu is ‘invert colour’. Select that option and left click, when it will invert the colour to create the negative. Click on ‘save as’ and rename the image ‘PCB negative’ or whatever.

Developing:

• Peel off the exposed UV film and place the PCB in developer, consisting of a solution of 100 ml of water to 1 – 2 grams of Sodium Carbonate (also known as ‘Soda Ash’), so 1 Litre of water requires 10 – 20 grams of sodium carbonate. (1 KG of sodium carbonate is typically £5.50 post free on e-bay).

• Agitate until the exposed areas of the PCB have dissolved, then rinse in water.

Etch the board with your etchant of choice (in my case, Sodium Persulphate), and when fully etched, remove the resist with meths or acetone.

Photo-resist dry film is much cheaper than using UV lacquer or pre-sensitised boards. I've just ordered a roll 30cms wide x 2M long for £5.79 + £1.49 from a UK drop shipper on ebay. To comply with forum rules I won't give the link but 'Photosensive Film for Printed Circuit Board Development' will find several sources. I made the mistake of buying some direct from China - only a small reel 15cms wide x 1M long. Unfortunately the roll got flattened on its way here, so the film is creased and despite several passes through the laminator, there were tiny creases in the UV layer which could not be eliminated. Nevertheless, I went ahead and developed the board to check the exposure duration and the concentration of developer required, then I etched the board, which came out fine except where the blemishes were. I was only a test run so I scrapped the board. I'm waiting for the new roll from the UK to arrive, which is on a supporting paper tube.

As the film is light sensitive it must be kept in a lightproof container such as a mailing tube.

1 KG of sodium carbonate is typically £5.50 post free on e-bay:

http://www.ebay.co.uk/itm/300980297463

To put into perspective the proportions needed, it's about a teaspoonful to a cup of water.

Do remember of course that the film isn't positive resist - it's negative, so you must invert the colour on your artwork. To illustrate that, I've shown both positive and negative artwork for a PCB I've designed, which I mentioned previously in another post. The first image is negative for use with the dry film technique, so in the first instance, everything black will be etched away, and in the second, everything shown in white will be etched away when used with pre-sensitised positive boards. (Which I don't use anyway - until now, I've used UV spray lacquer).

The film adheres extremely well - far superior in my view to the thin coating on pre-sensitised boards. When the developed and exposed board is place in a container with a small amount of acetone just sufficient to cover the board, the film crinkles up right away and floats off the board.

Hope that helps.

Have fun!
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Old 19th Dec 2016, 11:10 pm   #25
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Default Re: Lightboxes

Many thanks, David - reason I asked is that I spotted the ( possibly ) same source
I've tried spray in the past, with poor results.
Great to find out modern methods- I'm still in the past, but whereas I could draw out a board with a pen, I need pairs of specs to see the board properly ,so PC design is a lot easier .

Last edited by Oldcodger; 19th Dec 2016 at 11:17 pm.
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Old 20th Dec 2016, 10:48 am   #26
David G4EBT
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Default Re: Lightboxes

Until I made a light box, I invariably used rub-down transfers and in fact still do for simple one-off boards as it doesn't warrant making a mask and exposing and developing a board using UV.

Prior to UV, I used to tape a photocopy of the artwork (mostly from magazine articles) onto a piece of PCB, drill through all the holes, clean up the board, then use rub-down transfers to complete the design. On occasions, when a project has leant itself to it, I've used white fablon onto which I've traced the design with carbon paper, then cut-out the waste with a modelling knife. I made the PCBs for the P.W. Purbeck 'scope that way, including the EHT board, and also, the R.E.W amateur radio 15 Watt RF P.A.

The first pic below which was for a stabilised 12V PSU for a lather RPM meter which I made using rub-down transfers - too simple to bother with UV. The second one is of the R.E.W P.A which I made by tracing the design onto Fablon and cutting out the waste with a modelling knife, though that was before I had a light box. A light box would make that sort of PCB far simpler.

I only ever used once of these awful Dalo pens one out of curiosity and the result was awful. I'm afraid that in all that I do, I'm towards the OCD end of the spectrum. If anything doesn't look neat, skilful and 'craftsman-like' I find it offensive to the eye and it goes in the bin. I know that the electrons don't care what it looks like if they can get from A to B, but I do!

I'd reiterate that the first challenge with UV is the creation of a high quality acetate mask with a high level of opacity, (if you can see through the artwork, so can UV light), and from my experience, that means an inkjet printer which has a transparency setting in its print options - not all do have.

I hope to have another go with the UV negative film shortly and I'll report back when I do.
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Old 20th Dec 2016, 3:05 pm   #27
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Default Re: Lightboxes

I've found that for precision work using transparencies (smd, vary narrow, close tracks etc) a single UV (405nm) luxeon about 3" above the board works very well and forgives the film lifting (tracks might be slightly bent but not blurred). Lots of small LEDS makes for lots of small shadows if there is any lift.

A vacuum bag used to work well for holding it all together during exposure but after bursting my last one I've also managed by strategically placing nuts and bolts on unused portions of the board to hold the film flat. The best was to get some pieces of 1/4" thick glass samples which work really well to hold it all in place I'm sure they absorb some of the uv but I haven't had any problems. Just remember to deburr the board edges to make sure everything sits nicely.

For double sided boards I usually add some pilot points on the layouts and punch these through with a pin and drill the board with a 1/2mm drill bit in two points and use these to help line the negatives up whils taping them down tight.

D
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Old 20th Dec 2016, 3:33 pm   #28
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Default Re: Lightboxes

Definitely agree with deburring - makes a big difference. I grabbed one of these the other day; really nice: http://uk.rs-online.com/web/p/deburring-tools/1230915/

Quote:
Originally Posted by David G4EBT View Post
I only ever used once of these awful Dalo pens one out of curiosity and the result was awful. I'm afraid that in all that I do, I'm towards the OCD end of the spectrum. If anything doesn't look neat, skilful and 'craftsman-like' I find it offensive to the eye and it goes in the bin. I know that the electrons don't care what it looks like if they can get from A to B, but I do!
The last two boards I did using this method are in something but you can do some gloriously nice looking boards freehand. Trick is to design it on a transparency first 1:1 over a 1/10" grid sheet, PVA the copy to the top of the board, leave it 20 mins, drill all the holes, peel off the clean it up with a tesco value sponge, then draw the rest on the back with a ruler+curve template and the original transparency for reference. Etch it, tin it (powdered solder + flux pen + a 25w iron) If it's a one off, it takes no time at all, looks really good.

Use a Lumocolor pen though, not one of those horrible Dalo things.

I did one with 150 holes in it and it worked nicely.

Drilling was done with an 0.8mm bit and a large DIY hand drill. Didn't break it surprisingly.
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Old 20th Dec 2016, 10:19 pm   #29
Oldcodger
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Default Re: Lightboxes

Likewise on the Dalo pens. I found that a permanant marker ( used with varying degrees of pressure got good results, but nothing like the results on a Xylaphone like keyboard I made. The internals I used a marker free hand, but for the Keyboard, I copied the magazine and traced the breaks in the keys onto the board using carbon paper. That part of the board was then given a coat of two of nail polish, and the breaks marked out with a nail. The keyboard was brilliant. Wife told me that in her magazines, she'd spotted that there was a nail pen ( similar to the stuff in little bottles), but we never found any.
These days for simple circuits, I might be tempted to use a Sharpie pen .
Drilling, I used an old tape recorder motor, with as small a connector as I could use ,powering the motor via a push switch from a DC supply derived from my Weller iron.
David, I'd be interested in results using UV Negative film. I've tried an experiment using your idea of Paint, but with a variation using Express PCB, then Adobe Photoshop elements, and then Microsoft Photodraw 2000 to arrive at a negative image. It looks quite good.
Finally, another idea( I've posted before) might be to use a Teflon sheet designed for cooking. I thought of using it to iron an image( using a laser printer, with a sheet A4 sized, stapled to the Teflon), but hotter the ink got, less it wanted to come off ,and eventually bonded to the sheet. However, this Teflon is not opaque and ( although it might mean longer in exposure) it should work in a lightbox. Beauty is that it won't crinkle or get upset with the heat of a laser ( designed for non fat frying ,) ,and sheet can be used over and over again .

Last edited by Oldcodger; 20th Dec 2016 at 10:38 pm. Reason: finger problems on keys
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