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
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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.
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...
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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
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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?
Manufacturers of fluorescent light bulbs provide wavelength and light intensity data for their products. If you have the bulb stock number try putting this into google search engine. The retailers of light bulbs sometimes have product info sent to them by manufacturer. Catalogs used by retailers for ordering may have such info. You can always write to the company manufacturer to get product specifications.
There are other applications using bulbs for photo light or chemical reactions. Some types of silk screen processes use exposure bulbs. Diazo-blueprint photo process uses UV light bulbs. E-prom devices use UV to erase content. UV bulbs are used in medical applications for sterilization.
If you get a bulb but need a fixture you can use a screw-in energy saving fluorescent light bulb. In my area these screw-in energy savers cost less than a dollar. I removed the bulb from one of these then replaced it with the fluorescent bulb I wanted to operate. I made sure the wattage ratings for both were nearly the same before I started. The re-wiring should be as short as possible. Be careful and don't forget that fluorescent bulbs run on higher voltage.
btw- I have replaced all incandescent lights in my apartment with the screw-in fluorescent fixtures and have seen a significant savings in electric bill.
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.
BTW- If you ever need to measure light intensity directly, such as lumens/candela etc it is possible to do this with the built-in light meter most 35mm cameras are equipped with. I did this many moons ago so I don't recall the details.
Here is an explanation I just now found in google about the procedure, just in case any one is interested:
Safety reminder: If you use Xylene don't forget that this liquid is as flammable as gasoline. Vapors of xylene from an open container or an evaporating source can crawl invisibly and without detection of it's odor to an ignition point (pilot light, static discharge, electric range etc.)
Xylene should be used in a well-ventilated area nowhere near any flame or possible spark.
Good tip. That should work fine with more modern - even digital - SLR cameras, as long as they have a full manual mode, eg; any Canon or Nikon DLSR. The only problem is that the table in that post is for ASA/ISO 25, which isn't available on many DSLRs. Fortunately, that's easy to correct, by converting it for ISO 100 (2 stops faster), which most DSLRs have, then shifting the shutter speed by 2 stops to compensate:
The problem with this approach (regarding the original photo-etch topic in the subject line) is that it only applies to visible light, whereas photo-resist is sensitive to UV, which is greatly reduced by camera lenses.
So, you can't use this to make any sort of absolute measurement of UV levels, but if you have a source that emits a broad spectrum (like a tanning lamp) such that you can get a reading on the meter, then it would probably be reasonable to assume that everything scales properly. Thus, if you use that same source at a different distance, the camera meter could tell you the *change* in exposure.
Best regards,
Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis
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