UV exposure times for a PCB

Anyone know a spreadsheet or whatever to give the exposure times for a pre-coated PCB? I've seen figures from 30 seconds to 3 hours quoted. Even the makers of UV boxes for the purpose say to experiment...

Reply to
Dave Plowman (News)
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developed it and worked out the optimum time.

two prints taped together seem to give a better outcome for us

Reply to
Ghostrecon

Thanks. What is the UV source and how far away from the PCB?

Right. I've got a light box with two UV tubes.

I've found I get a better print with the ink jet. Much darker black. But of course it's how it blocks UV that matters.

I've done quite a bit, but never been very happy. A bit too mean to experiment. But your method of experimenting seems good and I'll try it.

I've played with the 'iron on' stuff and it's nowhere as good.

I did a bit of Googling and came across several Utube videos on how to. All of which very different methods. ;-)

Reply to
Dave Plowman (News)

In message , "Dave Plowman (News)" writes

I've used 2 different light boxes, the first was from Maplin, with 2 tubes and the 2nd, that I use now is an A3 sized one of unknown make that I found at an auction, it has a rather heavy lid and gas struts! I think I may still have another unknown one in the garage (junk store) that even has a vacuum pump to make sure the acetate is held firmly against the PCB. So, I do not know the spec on the tubes, but I could open one and check if you really want to know. Distance from the PCB is about 2" with a reflecting surface behind the tubes to give a more even spread of light.

Sounds similar to my 1st Maplin one, which worked well.

I found that the laser produced a darker, sharper image. The 1st one I used was a very old HP LaserJet, when it failed it was a sad day, I'm still trying to find a replacement that is as good. Some of the permanent black marker pens are good for touching up the acetate if you are worried. I hold mine up to the light to check for any holes in the printing.

When I put the acetate against the PCB I do it so that the printed surface is against the PCB, even the thickness of the acetate can cause a slight shadow from the printed track to the PCB, so the closer to the board the better, this does involve reversing the print when printing, shouldn't be a problem..

I printed a grid of lines of varying thickness for the test, it also gave me a chance to see how thin a track I could practically hope to create. Which was useful as one of the first boards I made had 2 X 40 pin chips on it about the size of a postage stamp and I needed to get track between some of the pins. Always try NOT to have to do this!!

I've never tried it, I'm not sure I'd have the dexterity to lay the tracks down. I had "fun" today wiring up some small Lemo connectors, must invest in some new eyes and smaller fingers.

Finding a good developing tank and etching tank is important, I was lucky to come across an RS one in an auction at a good price, makes life a lot easier if you can find a way of heating and agitating both the developer and etchant.

You've got me thinking now, I've not made a board for about a year, I suppose I really should find some thing to build.

Reply to
Bill

Similar to mine. One of the Utube videos showed a UV reflector spot - I'd guess based on a 150W tungsten - about 12" away from the work with a quoted exposure time of 60 seconds.

I've only got a cheap Samsung mono which is ideal for just running off cheap print stuff.

I'm odd ;-) in that I now work from the component side. So component layout diagrams and PCB legend are the same. That means the print for making a PCB is correct. Of course I'd flip it if sending it anywhere, as that is the convention.

Ah. I don't yet require that accuracy.

There is one method where you laser print to special paper (some say magazine glossy paper will work too) then iron that on to the clean copper.

Got very good with those. On my radio mics they're the connector for the personal mic, and some talent is pretty good at ripping it out. Bit of a knife edge getting the cable clamp so it will pull out of the connector rather than breaking the cable itself...

That part is fine. I have a heated bubble one.

If I were doing it every day I suppose I'd get good at it. But it's so infrequent, I'm trying to get advice to short circuit the experimenting.

Reply to
Dave Plowman (News)

Spent some time experimenting, and 5 minutes came out best with my box. I'm very pleased with the result. Should have done all this years ago. But always in too much of a rush.

Reply to
Dave Plowman (News)

In message , "Dave Plowman (News)" writes

Glad you are pleased with it, when I was most active making PCBs at home I would run them off for almost everything I was building, a lot more robust and neater than Vero board :-)

Reply to
Bill

For the definitive solution I think you should ask our rodders.

*whisper* i'm taking the piss.
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Reply to
brass monkey

As a matter of interest, I looked at the exposure boxes Maplin sell. One of the questions was 'do you give exposure times' and the answer was no. For a box costing well over 100 quid. I do realise the transparencies will vary - but it does seem strange.

Other thing is, will partially used etchant store? It's quite expensive to throw away. Any old plastic bottle do?

Reply to
Dave Plowman (News)

It kept fine in my day. It was left in the etching machine for months on end. The concentration needed increasing when etching time got too slow (loads of dissolved copper). 1 min in this heated etcher and the job was a good'un.

Reply to
brass monkey

Snag is my etching tank is open topped, and I'm not sure I'd like to leave it filled, in case it got knocked over. So it would make more sense for me to store it in a sealed container.

Reply to
Dave Plowman (News)

Photographic chemical bottles are ideal - got any professional photo- developer studios nearby - empties should cost nowt?

Reply to
Tim Watts

If it might get knocked over, bung it in a pop bottle, you'll NEVER get any stains out. Awful stuff. IIRC it also etches aluminium and brass.

Reply to
brass monkey

snipped-for-privacy@davenoise.co.uk...

Ferric chloride will also take chrome plating off sink drains and attack stainless...

Cheers Adam

Reply to
Adam Aglionby

In message , "Dave Plowman (News)" writes

From Maplin I wouldn't expect anything less. They don't seem very technical. Do your research elsewhere first.

I've kept mine in the bubble tank for more years than I like to think about, I've just topped it up occasionally . So any plastic or glass container should be fine.

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Reply to
Bill

With UV tubes in a commercial exposure unit an inch or so away I've used 1.5 - 2 minutes in the very dim and distant past but that was with one board supplier and they do vary.

Some of the UK suppliers of photo resist FR4 used to sell an exposure guide - a graduated acetate with dots and a few calibration markings that you expose for a set time and then develope (and maybe etch?) and then you read off the optimum exposure time.

These days I'll either use wirewrap or a prototyping board or let a sweat shop in China make near perfect PCB's for me with a solder mask silkscreen and plated through holes. Value your time at more than a few pence per hour and it's cheaper for the Chinese to do it.

There is at least one company in the UK that will produce one off prototype PCB's for free (yes free), even double sided ones. No silk screen or solder mask or plated through holes.

Be buggered if I can remember their name though!

Reply to
The Other Mike

I'll still use Vero for a one off - but this time I wanted a few. I could have had them pro made - but it's a hobby I enjoy doing. When it goes well, of course.

Reply to
Dave Plowman (News)

There is at least one company in the UK that will produce one off prototype PCB's for free (yes free), even double sided ones. No silk screen or solder mask or plated through holes.

Be buggered if I can remember their name though!

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've no connection to them. Used them a couple of times, but would rather get a finished board - even for a prototype.

Reply to
Grumps

They supply these to anyone - or just approved customers?

Reply to
Dave Plowman (News)

I'm not sure. I've only ever obtained them through the company I work for, and we've never bought PCBs from them. The last time I used them (for the freebie) I put 6 identical circuits on a panel (which I'd have to later cut out myself) but they only supplied one. Having no solder mask is a bitch when you're used to having a finished PCB. It reminds me of when I used to make my own. At least Spirit drill the holes for you, and make a better job of it than me and my B&D.

Reply to
Grumps

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