MG Chemicals sells pre-sensitized copper-clad PCB blanks for use with their exposure and etch kit. Pretty straightforward "print pattern on transparency; place on PCB; expose to light; wash off exposed portion; etch" process.
The "expose" part of this process consists of using MGC's "daylight" fluorescent lamp.
If it's truly a "daylight" bulb, wouldn't direct sunlight work for this purpose? I presume this bulb is of a particular wavelength. What is it?
Any other ideas to use this process to etch PCBs without their lamp?
"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
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.
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;
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.
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.
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...
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.
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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?
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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.
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.
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?
I live and work in UK I use what I refer to as standard PCB board (purchased from Rapid Electronics) They have a website catalogue you could check for more details
these boards NaOH is the developer The unexposed resist can be removed with alcohol (methylated spirits) but since the heat of a soldering iron strips it as you solder that's not really needed and it does protect the board from oxidation prior to soldering Regards sirkituk