Photo-etch light source?

I use sunlight to expose all my boards. The only difficulty is waiting for a clear sky, so the exposure is predictable and the edges are sharp.

"daylight" flourescents are easy to get at your local home store -- as are the fixtures to run them -- buddy of mine used just one... but had some problems with fuzzing that I think would have been solved had he used 2 or 3 for a more even light source -- making an exposure box with 2 or 3 lamps -- the ones about 12" long, and a piece of plexi as the exposure surface is pretty easy.

Waiting for a clear sky may take days or even weeks in this part of the world. Even then exposure time is a long shot. So for years I used a 120W high pressure mercury bulb, meant for streetlighting. It not only produced enough UV, it also produced a lot of visible light and even much more heat. So last year I got an obsolete A4 flatbed scanner and an old home solarium - "face browner" - and build a new exposure box. Works like a charm so the old one is for sale now :) The idea of the new exposure box is not new. Look at

The text is Dutch but the pictures are universal.

Exposure time is 2 min. Make sure the traces on the transparency are pitch black. I always stack two of them as one lets through too much UV and makes the etched copper look like a rats dinner.

petrus bitbyter

Stack 2 of them eh? I never thought of that. I used a tanning bulb for exposing the board when I did that stuff. I built an exposing table with a timer that kept the bulb on for 15 minutes. It had the timer built into the table, and a piece of soft wall conduit that supported the lamp so it was 12" from the board surface. Worked great too! Probably would have been more reliable using 2 transparencies.

I have since switched to the photo paper method published by Thomas P. Goote, and I find very reliable and sufficiently accurate for my needs. FYI, I use ammonium persulfate to etch the boards I make. Check out his web page here;

Have fun!

- Tim -

On a sunny day (Sun, 04 Mar 2007 18:14:40 GMT) it happened Usual Suspect wrote in :

Sure, 250W photolamp at 30cm distance for 8 minutes. Except for DownUnder, where these lightbulbs will be illegal soon.

I've successfully exposed MG pre-sensitized PCB's using a 500W halogen work lamp from a hardware store. Halogen lamps put out UV. Can't remember the exposure time. Lamp was 3ft away. D from BC

I don't know about the MG system, but I have used sunlight a number of years ago. It works well, the only problem is that it's variable depending upon cloud cover and the time of year. Experiments are needed to get the exact exposure.

I now use a Philips TUV 20 flouro lamp and it works fine. However, it is a short wavelength UV and the radiation is considered a little hazardous, I just take care to only switch in on when the artwork is all set-up and everything is covered.

Barry

A point source, like these also throw nice, sharp shadows that make clean edges, compared to more extended sources, like fluorescent lamps.

I've used a 100W mercury vapor lamp, up close and personal. Most of the resists are looking for some UV component. A metal-halide fixture will probably also work well, a sodium vapor light probably would not. 175W is probably easier to find than 100W, that just happened to be the lamp I had handy at the time.

A carbon arc would be just dandy, and could offer some old-fashioned electro-mechanics for a bit of variety in your projects.

--
Cats, coffee, chocolate...vices to live by

Yes, but it's very hard to get an accurate exposure with sunlight.

I've heard that greenhouse fluorescent tubes (the kind used for hydroponics) work okay, but I don't have any personal experience with them.

--
   W  "Some people are alive only because it is illegal to kill them."
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I wonder guys, why wouldn't you just use a proper long-wave UV bulb? They are aplenty and dirt cheap... Any T8 BL or BLB works like a charm, doesn't require anything but regular fluorescent ballast to run and produces that very sub-400nm lightwave required for exposure...

Why are you trying anything but a proper tool? Am I missing something?

Just FUI -- that magical MGC lamp is just a 15 Watt T8 BL bulb in a regular fluorescent fixture...

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If you want to stick with photo-resist methods, the simplest approach is to buy a "tanning" lamp. Mine looks like a standard floodlamp, with a dimple in the center. Puts out plenty of UV, way more than direct sunlight (at least here in Michigan!) and it's consistent even on cloudy days.

Now, I should add that it's been a "few" years since I bought this (20 or more) so they may not be so readily available as they once were. Even back then, it was pretty clear that tanning was not such a smart idea. Now, you'd have to be pretty crazy or illiterate to do it... which means only 99% of students and only half of the voting public. ;-) So the market and supply for these may have slacked off a bit.

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

It's a McGyver thing... It's having options of using anything that is easily available. D from BC

i used a Gralab photo timer with a single 200 watt standard incandescent about 3 feet above the bench.

standard safelight was handy also.

i tape the film onto the pc board. then a single sheet of window glass weights the film/pc board flat.

after 25 yrs, no problems.

time to expose ? always went with about 4-5 minutes. it depended on the ants in my pants. critical it is not,

the solvent bath later i found was the real problem with leaving in too long.

i always used photo filmed positives, very precise and failsafe.

their

transparency;

Nothin' could be simpler...

Now, that's a tome of data!

OK. I won't be a "clock watcher".

You mean the chemical for removing the exposed photo-sensitive stuff from the PCB? Don't you just submerge it and brush it and watch when it's all gone (all the exposed part) then take it out? Or am I missing something?

You're talking about the transparency? I hear that output from a printer is good enough. No?

--
Al, the usual

German description for some unknown brand PCB. At least it will give an indication of the relative exposure times when using alternative lightsources. Nitraphot seems to be a tungsten bulb meant for a certain studio colour temperature standard. Not well suited for this stuff.

Joop

Belichtungszeiten:

30W UV-Röhren 60-90s 1000W Halogenl. 45-70s 250W Nitraphot 12-15min 500W Nitraphot 6- 7min bei ca 30cm Abstand

the developer/xylene (or whatever it is) i never made any mechanical brushing or other attempt to force the residue to release any faster than the dissolving rate.

my problem originally was i left the exposed board in way tooooo long and the light fixed resist actually did disssolve eventually, perhaps 20 minutes! way too long

stick with the manufacturers recommends

i always did a second wash in fresh developer to remove any trace residual.

then after it had completely dried/evaporated, it went under some cool then warm water with small amt of detergent (actually any wetting agent will do, the blu stuff used in automatic dishwashers is cheap and easy to find) before it went into the etch bath. that seemed to make the etch time consistent across the entire board.

yes, the transparency may be made with printer, i have used a good 600 dpi laser printer (overkill actually) but 300 or even 150 dpi will do.

vellum is usable, overhead mylar film is better, plain paper is good for crude stuff

my only hazard with that was the 200 watt bulb often melted the toner and screwed up the board. so i switched to using photo exposed negatives/positives. it takes longer, but results are far superior and the physical stability of the film always gives u the same dimensions EVERY TIME. thats assuming u make it a proper size initially! detail and resolution are superior also.

short runs of less than ten units, i usually winged it with the printer though.

incandescent

the

the

is

Time depends on strength of developer, temperature and speed of the resist.

I use sodium hydroxide solution to develop and a brush to speed the process.

Yes.Beware of laser printing onto acetate sheet it can melt the sheet and wreck the printer. I use good quality tracing paper and find it works well with both laser printers and highest density ink jet printers.

Regards sirkituk

Yes. You need to use acetate sheets that are specifically labelled as being suitable for photocopiers or laser printers. They are perfectly safe for this purpose. Ones intended for inkjet ARE NOT safe in lasers. Don't take the salesperson's word for it, check the label on the box yourself.

I've heard others say that too, but haven't tried it myself. Can you recommend any specific brands?

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   W  "Some people are alive only because it is illegal to kill them."
 . | ,. w ,      
  \\|/  \\|/              Perna condita delenda est
---^----^---------------------------------------------------------------