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Old Dec 07, 2012, 01:34 PM
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Update, and further question

So, I made myself a small UV light box, about 4" square, using 90 3mm UV LEDs. It's powered by a 5S A123 pack. I did a couple of test pieces today using ready-coated photo sensitive board, and a pattern printed onto clear vinyl using my HP inkjet printer. One exposure was 60 seconds, the other was 30 seconds, and both of them developed and etched brilliantly

So then I tried an actual circuit board that I'd designed. I gave it a 60-second exposure, and it seemed to develop okay. But when I started etching, I saw that the tracks were becoming pitted.

I suspect I hadn't developed it properly, but there's nothing in the instructions for my "universal" developer to tell me how long I should leave the piece in it. What I did each time was swish it about until all the brown crud had washed off the surface, leaving the tracks showing up nice and clear. I didn't time it, but it didn't take more than about a minute. My question is, am I supposed to leave it in the developer a little longer so that it "fixes" the etch-resist, or am I maybe leaving it too long so that the etch-resist is getting eroded by the developer chemical?
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Old Dec 08, 2012, 01:51 AM
supreme being of leisure
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the red staedtler lumocolor has always worked great for me but i etch in a peroxide/ hydrochloric acid mix that's much quicker. a clean board is important but anything that leaves visible scratches is bad, that goes for toner as well. best way to clean the bare board IMO is with one of those melamine foam magic sponge eraser things.
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Old Dec 08, 2012, 06:17 AM
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First off, I hope you people aren't trying to reinvent a $20 product? That would necessitate therapy.

The "tracks" referred to are known as "circuit lans" and the point made about scouring the surface with a Brillo pad is very true. But make sure you choose no particular direction, scour in a circular motion like when you wax your car, or your resist pen will only be effective drawn in the same direction as your scouring lines. Also keep fingerprints off the copper surface, that will guarantee failure. The worst pen you could acquire will likely come with a Radio Shack style hobby kit. For touch-ups, a good cheap solution had been brush-on White Out. Don't think they make that now.
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Old Dec 08, 2012, 01:38 PM
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Thanks for the advice about the pens. Scouring, washing, and drying the board before drawing the circuit (what does "LAN" stand for in this context?) solved my problem. I've made some successful boards since my original post.

My light box cost me 9, if that's what you're referring to XtalHunt And, if so, where do you get one for $20? All I can find in the UK is boxes costing from about 100 -- and that's from Maplin, our equivalent (I think) of RadioShack

Anyway, I'm sold on the photo method, partly because I don't have a laser printer to do the transfer method. So my only question is about the photo developer -- what is the correct time for immersion in the developer, and does too long or too short in the developer have adverse affects? I ask because my first two trials turned out great, but my effort with a real circuit was a disaster ... the photo-resist was porous after developing, so some of my copper traces were pitted, and others dissolved completely in the etchant.
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Old Dec 10, 2012, 12:16 PM
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http://www.electricstuff.co.uk/pcbs.html

is a very good read.

Tracing paper is a very good tip, Far better than clear film (which scratches easily)

Exposure I use 2 x 15W "Energy saving bulbs" for 3mins.
at approx 6" distance.
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Old Dec 10, 2012, 01:33 PM
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Very interesting reading, Reflex1 Although my developer is Disodium Metasilicate, as recommended in the article, it seems that that's where my problem lies, though my symptoms were more like the over-development the writer says can happen when using Sodium Hydroxide.

Anyway, I'll try again when I've got time, in a couple of days. Thank you.
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Old Dec 10, 2012, 04:38 PM
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I use this to Develop
http://uk.rs-online.com/web/p/proces...icals/3636517/

It works well
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Old Dec 13, 2012, 06:13 AM
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anyone remember the thread from a few years back about hacking an ink-jet to print directly on the PCB material with a suitable ink resist?
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Old Dec 13, 2012, 01:50 PM
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Almost there ...

I've done some more trials, and I'm beginning to get something that'll work, though it's not as good as my first test piece yet (beginner's luck, I suppose).

I tried 60-second and 30-second exposures in my light box and got very-poor and not-very-good results. Some of the tracks were etched away in the first one (on the left in the picture) and, although all tracks remained in the second, they were all very pitted.

So then I went back to my printer (HP Photosmart 110) and checked the print settings. I had it set for "best" quality transparency, but then I remembered that with my first test piece I'd used a photo setting. So I printed another transparency using "best" quality photo setting, and the ink seemed much denser. That's what produced the third board with a 20-second exposure, on the right of the picture, which I believe is passable, though by no means perfect.

The article in the link in post #20 doesn't really recommend inkjet printers. But I don't want to go to the expense of a laser if I can make this work.
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Old Dec 13, 2012, 03:14 PM
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It looks like underexposure may be your problem
Try 2- 3mins instead (2x 15W CFL bulbs take me 3mins)
I doubt your getting as much UV from your LEDS .

Also try the Tracing paper it gives a more opaque print

Another Vid.
He shows an 8min exposure time !
http://makeprojects.com/Project/Circ...1#.UMpDOqya98E

Only other thing I can think of
perhaps your printer ink is allowing some UV through
so maybe try another printer ?
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Old Dec 14, 2012, 02:32 AM
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I was thinking my ink may be porous, but I don't have another printer to try. And, if that's the problem, a longer exposure is only going to make things worse, isn't it?

One question I still haven't been able to find a definitive answer to is, what exactly is the UV light doing? Isn't it just "activating" the exposed photo-sensitive etch-resist that's not shielded by the printed pattern, so that it will dissolve in the developer? Mine dissolves almost instantly after a 20-second exposure, so that surely means that no further exposure is needed?

Looks like a b/w laser printer might have to go on my Xmas list!
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Old Dec 14, 2012, 03:44 AM
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You may be right.
I can't answer "what exactly is the UV light doing?"

You can test your Inks though
Just put a thin strip of electric PVC insulating tape across the PCB before Etching the board

If after Etching the copper beneath the tape is ok
then your Ink IS suspect.

I made many small test PCB's around 1cm x 2cm to get it right.
Biggest problem I had, was ensuring the Film was flat to the board
during exposure.

Never tried an Inkjet , I'm using a laser printer
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Old Dec 15, 2012, 01:33 PM
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Some more tests today, following your advice to use a piece of impervious tape -- in fact I used a strip of the protective covering sheet that comes on the pre-sensitised board. The most revealing result is this board that was exposed for 2 minutes; the strip at the left end is where the tape was, and it's still solid after developing, compared with the porous inkjet pattern. So, I need to buy a laser printer

Anyway, I did get a passable board using a 15-second exposure. The pitting was so small that my tinning covered it up, so I'm using it for a circuit. One other thing I've learned today is, it may be better to drill holes before tinning Even though I was using a Dremel drill-press, my 0.8mm drill was knocked off track by a slight thickening of the solder around one of the holes.

By the way, I measured the input watts of my light box, and it's 9W spread over an area about 80x70mm. I don't know how LED output compares with tubes on a per-watt basis, but I suspect the brightness per unit area is greater than two 15W tubes.
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Old Dec 15, 2012, 02:11 PM
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in regards drilling holes. In eagle i change via's and pinheader's to have 0.3 holes and edit outer to suit. So after etching when i drill it centers great. I drill with pcb on hard surface melamine with not to many holes. I tape it to board so i can slide it about. Don't push drill to fast or it damages copper.
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Old Dec 15, 2012, 03:09 PM
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I was going to ask, "is there any brand of laser toner that's better than others for making masks?", but then I saw an article on the internet http://www.piclist.com/techref/pcb/e...otoresists.htm which suggests that laser printers are worse than inkjets

The article also says, "... Laser printers typically do not achieve this, but good results have been obtained with InkJet printers. Different ink colors may have different levels of UV blocking, so black isn't always the best color. MISPro Yellow is best. ..."

So, I'll have to have a go with colour printing before I think about switching to a laser, unless someone can tell me that this article is out of date, and modern lasers can give good heavy coverage.
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