Homebrew UV PCBs - an alternative method.

[Yorkie]

I think that nowadays, those who have a laser printer tend to use the ‘iron-on’ technique using scrap golly 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. For anyone who may wish to consider making their own UV box, 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:

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-power...ller-n98gr

http://www.maplin.co.uk/p/10w-uv-replace...lers-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 buy the tubes for that!

http://www.cqout.com/item.asp?id=18665504&gclid=CMKvpqSOqswCFUefGwodbeAG9A

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 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 must be a negative – not positive. This is easily accomplished in MS ‘PAINT’ by selecting the 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 which Joe put me onto, 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?annotation_id=annotation_2190592885&feature=iv&src_vid=Vj_cdBZO1Tk&v=cRCFGZxmob0

This is the film that’s used, (30cms x 5M for a little over a fiver sounds good to me):

http://www.ebay.co.uk/itm/30cm-x-5M-Phot...Sw9N1VyG7s

The sodium carbonate (AKA ‘soda ash’, ‘isinglass’), developer is cheap enough too, at £5.49 per KG and only a few grams are needed for each board:

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

I’m just waiting for the film to arrive on a slow boat from China and when I’ve given it a go, I’ll update the thread.

I'm content with the quality of the PCBs I make, (see below for a couple of recent ones), but on the face of things,  using the film looks like a bit less hassle than UV spray lacquer.

Hope that’s of interest to someone.

[Joe]

You've missed a hole, David:—

   

— Joe

[zx80nut]

...I've lost count on the number of times I've drilled a PCB, sat down to start soldering only to discover I've missed a hole...


I print on two acetates (laser) and put them together - really makes a huge difference to the blackness of the lines and helps stop thin tracks from getting over-exposed. I do use "proper" developer from Mega Electronics that has always served me well - not too expensive, very quick and seems to handle over-developing with no side-effects.

   

Grant

[Radio Fixer]

Very interesting David. One day I'll find a project that I have to do a PCB for and give it a go. Lot of effort for just one of something though.

thanks Gary

[Yorkie]

Thanks for reading the thread guys, and for your comments.

Re the undrilled hole Joe, that was well spotted! I'd have discovered it when I tinned the board, as I always do, but I guess an error rate of less than 1% isn't too bad for an old buffer!

Producing opaque masks does present a bit of a challenge and I don’t think any laser printer, whether for commercial or domestic use, or any type of laser film produces a 100% opaque mask, which is why some hobbyists seem to use 90gsm tracing paper rather than acetate film, and others go for the ‘iron on’ technique. But as you Grant says, you can get away with taping two or sometimes three images together. For many years before home printers became the norm, I used to get acetates done at copy shops and tape them together. Then I had an HP inkjet printer which had an acetate setting and made first class masks. When that gave up the ghost I replaced in with an Epson, assuming that it would print onto acetate, but like others, I discovered that no Epson printers will print onto acetate, which is where ‘Big Clive’ came on the scene and he discovered how to fool the printer. Using his tips in his youtube video,  I’ve have rigged the settings on my Epson printer to print properly onto acetate, and the images are totally opaque when printed onto 'micro porous film'. When printed in reverse so that the ink side can be placed next to the board, the etched PCBs when viewed through a microscope have much cleaner edges.

The developer sold by Mega is simply sodium metasilicate pentahydrate. They sell a 500g plastic bottle of crystals for £11.90, which is double the price that sodium metasilicate pentahydrate can be bought for:

http://www.ebay.co.uk/itm/1kg-Sodium-met...20c0693084

1KG £12.99 post free

The instructions on the Mega bottle are far too broad. They say ‘500g makes 10 – 20 Litres’, so that’s 50g to 1 – 2 Litres. I find that if I use only 1 Litre it’s much too concentrated and risks stripping the board completely, so I start with it weak and add crystals till it becomes effective. I find it lasts for about three months. If you're reading this Grant, I'd be interested to know what proportions of water:developer you use.

As to etchant, as I've mentioned before, I find sodium persulphate is a much cleaner alternative to ferric chloride, and I’m surprised that so many on internet videos soldier on with ferric chloride. Sodium persulphate just turns light blue in use, and can be re-used. The only snag is that it’s more effective at 40 – 45 degrees C. That’s fine when first mixed as you can use hot water, but if stored for re-use it needs heating up, for which I use an aquarium heater, though they’re thermostatic and shut off at about 30C. When I get round to it I’ll dismantle the heater and bridge the bimetal strip.  The etchant still works if not heated – just takes a bit longer.

http://www.ebay.co.uk/itm/1kg-Sodium-Per...Sw9N1Vm8bZ

£13.99 post free for 1 kG

Primarily, I started the thread to mention the UV film technique, which is new to me and obviates both pre-sensitised or self-sprayed UV lacquer, so seems quite promising, but I'll reserve judgement on that.

The other thing is the UV light-box for about £20 by 're-purposing' a Maplin two tube fly killer. Exactly on the right UV spectrum for PCBs, more powerful than the little Mega box which is an unbelievable £149.

As you say Gary, unless you're going to make lots of PCBs, it's a non-runner, but the laser printer/iron on technique is a zero cost option as you just use glossy paper torn from magazines as a print medium, so for anyone who has a laser printer, that cuts out a lot of faff. I got into making PCBs with UV back in the early 80s as most of what I've done over the years has been home-brew projects such as simple test gear, receivers, and gadgets, which I still do. I don't find making PCBs for my projects a chore, or I wouldn't do it! The only commodity that's scarce is time, which I seem to have less and less of, and as the years pass, I become only too aware that I'm approaching my appointed time with the grim reaper, as we all are, but not for some time yet I hope.    Meanwhile, I'll carry on enjoying life, as indeed I do!

[Joe]

I've got a laser printer but have never had much luck with old magazine pages. Instead I use Poundland's glossy ink-jet photo paper.

— Joe

[Yorkie]

For anyone unfamiliar with the laser print/iron-on technique, the video at the link below is quite good, until it gets to the drilling stage at 13mins, which is just dire.

https://www.youtube.com/watch?v=imQTCW1yWkg

For anyone who has a laser printer, there's no doubt that it cuts out a lot of the processes called for by UV.

As to drilling, I have a Minicraft drill and stand, and a home-brew drill speed controller.

I have a chum who has one of the ones at the link below and is highly chuffed with it.  Made in China but from a UK supplier, £49.99 post free. Variable speed in three ranges up to 8,500RPM:

http://www.ebay.co.uk/itm/PCB-Art-Jewler...1698846631

[ed731pdh]

Laser print onto WHSmith 63gsm tracing paper, twice, sandwich together and under the exposure box for 45 seconds. OK for single sided boards but if you are doing double sided stuff the acetate method is better suited as the acetate tends to be more hole alignment accurate.

[davegsm82]

Interesting thread, I'll have to give this a shot once I get my artwork finished.

I have a couple of boards I need to roll off, one for a freezer thermostat and one for my pocket geiger counter project which is currently on veroboard despite using 0.05" pitch IC's.

I have an RS exposure box which was junked at my previous employer, I picked it up and fixed it but have not had a chance to use it since.

Dave.

[Mike Watterson]

Some combinations of tracing or grease proof paper and laser printer:
1) Clean & degrease PCB
2) Preheat board under grill
3) Iron on the laser print out
4) Allow to cool and soak off the backing.
5) Etch

If needing 5 or more, then order from China via ebay!

An budget insectcutor from Aldi/Lidl/Maplin (occasionally) can be a cheap UV source. I've not made PCBS at home since 1982, (UV then, nail varnish in 1970s!) but sent files to PCB makers.
In 2008 I used a computer controlled mill in work to make double sided down to 0.5mm pitch on 0.8mm thick PCBs. It was used to drill too. Step one was to fit a 1cm thick plastic sheet and mill it all over to have a level bed. I used thin double sided tape and a pair of pins in holes drilled in PCB by mill for holding PCB and registration.
A PCB mill isn't that expensive. Note that a laser X-Y plotter won't cut copper, but could be used to expose UV coated board. They are cheaper than a PCB mill.
I was tempted to try a permanent ink on my A3 plotter, but I have no enthusuism for etching. I use adaptor PCBs (cheap on ebay) for SMT ICs to DIL for stripboard.