kurt@think.com (Kurt Thearling) (04/29/91)
I'm trying to get some information about photresist chemicals and was
hoping someone out there might be able to help. Specifically, what
chemicals are available and where can I get them?
First, I will be using this to etch zinc plates for printmaking rather than
coppper coated PC boards, but that shouldn't make much of a difference (at
least as far as the resist is concerned - but I will have to use a
different etchant).
So far I have found a (negative) photo resist made by the Datak Corp (in
Guttenberg, NJ) called ER-71. The electronics store I purchased the PR
from did not carry the Datak brand of PR developer so I bought what they
had, a PR developer from a company called Injecterol (stock no. D1-P). The
PRD bottle listed its ingredients as sodium carbonate solution. Well, I
treated (in a dark, but not completely dark, room) a number of plates with
the resist (varying the amount of PR used) and let them dry. I then
exposed the plates (covered by the image negative) under a photoflood lamp.
But nothing seemed to have happened. Out of the five plates I did, only a
small fraction of one of them seems to have had any of the image
transferred. Does anyone have any idea what went wrong?
I also have been told that the KODAK (now manufactured by the KTI corp)
brand of photo resist chemicals are good (KPR and KPR developer). Does
anyone have any experience with them?
Any information will be greatly appreciated.
kurt
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Kurt Thearling Thinking Machines Corp.
245 First Street
kurt@think.com Cambridge, MA 02142
-----------------------------------------------------------------------cj@hpsad.HP.COM (Chris Johnson) (05/01/91)
>/ hpsad:sci.electronics / kurt@think.com (Kurt Thearling) / 8:53 am Apr 29, 1991 / > >I also have been told that the KODAK (now manufactured by the KTI corp) >brand of photo resist chemicals are good (KPR and KPR developer). Does >anyone have any experience with them? > >Any information will be greatly appreciated. I used to use KPR quite extensively for PC work. It works really well. The basic ides is that it is a plastic which hardens when exposed to ultra-violet light. The developer is just a solvent which dissolves the unexposed (and unhardened) plastic. The developer is essentially trichloroethelyne, that's what we used because we could get it cheap in huge quantities from the university chem. stores. Do not use trichloroethane, it only kinda works and seems to leave a residue. You should probably be careful with these chemicals, they're not real good to breathe and are probably considered toxic waste or something (in other words, use adequate ventilation and dispose of properly). Application of the KPR was best achieved by dipping the boards into the stuff and letting the excess drip off while hanging the board vertically. The stuff is rather thick, so it stays on fairly well. I seem to remember rotating the boards to try to keep the coating from getting too thin on one edge. After application & initial drip drying, we put it in an oven at about 140 F to speed the drying time. It will air dry, but it takes a while and you want it really dry before use. It's probably not a good idea to dry them in your home oven since stuff drips off sometimes and who knows what the residue would do to food, it probably wouldn't be too good. For the UV source for making exposures, we used a "tanning" lamp. Not the new fluorescent tube type, though they would probably work well, but the old incandescent type with the mercury vapor tube in them. Exposure time was on the order of 5 minutes or so, I don't remember, just make sure it's long enough, you can't overexpose. We held the photographic negative (clear where you want resist to remain) in contact with the dried boards with a piece of plate glass (ordinary window kind) in a hinged arrangement, but anything that will hold everything still during exposure is fine. It seems to me that we had to increase exposure when we started using the glass since most glass absorbs some UV. You can do this under normal indoor lighting, sunlight is not too good, especially direct sun (you can use this for exposure though), we usually used "subdued" lighting to lessen the risk of accidentaly hardening the resist before exposure, but you don't really have to be too careful. Developing the exposed boards is accomplished by rinsing them *GENTLY* in the solvent. Be careful, the "hardened" resist will get softened some and can easily be scraped off (this is how you get it off the finished etched boards by the way, solvent & steel wool). We used big glass photo developing trays and just soaked the boards, agitating every so often by moving the boards or sloshing the whole tray (it gets a bit trickier if you're doing both sides since you don't want the side that's down to scrape the bottom). The resist when dry is a slight greenish color, and proper development will be most noticable by the thickness of the remaining resist (it seems to swell up a bit in the solvent & looks a lot thicker than it is when dry). You may have to play around with the time here, I don't remember what we did, just that after some amount of time you looked at it and if it "looked" done, you took it out and dried in in the oven again. After developing, let it dry throrughly. Next, etch with whatever you need to use (assuming it doesn't eat the resist too). For copper PC boards, we used heated (about 150 F) ferric chloride, pumped through spray nozzles. It never seemed to affect the resist, even with the heat and spray pressure. Clean the boards with solvent and steel wool as mentioned above. Steel wool is not necessary, anything that has some abrasive qualities should work as long as the solvent doesn't eat it (something like a tooth brush would be fine, but trichloroethylene likes to melt some plastics). Good luck, -cj cj@hpsad.hp.com