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ESL57 strip down EHT issue
ESL57 strip down EHT issue
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Old 1st May 2020, 01:04 AM   #21
stokessd is offline stokessd  United States
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I use pre-sensitized circuit boards for making my own. Here's my instructions that I wrote decades ago and is tacked onto the end of each board manual that I wrote. I just don't have much appetite to make boards for people anymore. So I'm putting my designs on OSH Park.

Sheldon

Board Etching Tips


The artwork is printed onto transparency film from a laser printer, print it three times. Cut out two of the prints with about a quarter inch of clear space around the circuit board image. Then carefully tape these two copies to the uncut one after carefully aligning the traces of the overlay to the uncut sheet's traces. When finished, there should be three perfectly stacked copies. This increases the contrast of the final image. When a transparency is printed with a laser printer, there are usually holes in the black printed parts. And the blacks aren't all that black when it is held up to the light. Overlaying makes the blacks much more black, and gets rid of the holes. Now the artwork is ready to use. For double sided boards, the two sheets of artwork can be taped securely together on three sides after carefully aligning the traces on each side. this forms an envelope which the circuit board gets slid into. It's helpful to tape the board in place inside the envelope with a single piece of tape. This will prevent the board from shifting when it is flipped over to expose the second side.
This method uses GC positive sensitized boards and developer. The FR-4 fiberglass 1 Oz. grade board works very well (they can be gotten local electronics stores). The board emulsion is sensitive to UV light, A good source of UV to expose the board is a GE sunlamp. The sunlamp is hung so the bottom of the bulb is about 12" above the board. The exposure time is 9 minutes. With a yellow incandescent bug light-bulb on, pull the protective coating off the board and carefully align the artwork on top of the board. Then cover the artwork with a piece of glass to hold the artwork against the board (just like making a contact print in photography). Then turn the sun lamp on for 9 min. If a sunlamp is unavailable, the sun at noontime (on a clear day) can be used exposing the board for about 20 minutes.
The exposed board gets dumped into the developer which has been mixed up beforehand. The developer says to use a 1:9 concentration of developer to water, but a 1:5 mix can be used, which works faster and can yield slightly better results. However the timing is more tricky, so it is not recommended for the first time. Submerge the board into the developer (A photography developer tray works very well), and rock the solution back and forth over the board. The exposed parts with start to dissolve. The emulsion is green and it will wash away exposing the copper underneath. This is the tricky part. The board must be removed when all the emulsion is off the exposed areas. If the board is removed too soon, the emulsion won't be completely dissolved off the exposed areas and it won't etch, if the board is in the developer too long all the emulsion dissolves and all that is left is a bare board. With the 1:9 solution this time window is about a minute, with a 1:5 solution it's about 20 seconds. The board is removed from the developer and washed off with room temperature water, then scrape at a an exposed area and see of there is any emulsion left there. if there is, place the board back in the developer for a few seconds. Repeat this as necessary until the exposed areas clear. With a little practice, it's pretty obvious when it's time to pull the board out. Do all the developing using the yellow bug light. When the board is done, wash it off and let it dry. Be careful of the emulsion, it's easily scratched, especially when fresh from the developer.
Next, drop the board into an etching solution. Ferric Chloride is available from the same electronic outlets where the GC boards and developer are purchased or from Radio Shack. Ferric Chloride is a nasty smelling, iodine looking, serious staining stuff. Pour out the developer from the tray, wash it out and add the etchant. Then put the board into the etchant and rock gently back and forth for about a half hour or so, until all the exposed areas are clear. Then remove the board and wash it clean. The emulsion can then be removed with acetone or alcohol.
Then all the holes need to be drilled in the board. A Dremel moto tool works well for drilling the small holes, a small drill press would also work.
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Old 1st May 2020, 01:54 AM   #22
stokessd is offline stokessd  United States
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LOL, I just read my instructions again. "they can be gotten local electronics stores" what's that? grandpa
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Old 1st May 2020, 03:00 AM   #23
mhenschel is offline mhenschel  Canada
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That rings a faint and distant bell from the last time I made boards... for my Leach preamp and head amp circa 1980.

After that I found a guy to translate my artwork into "hard copy". But even that is ancient history.

Now I guess I have to figure out some newfangled software and find a service. [sigh]
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Old 1st May 2020, 04:23 PM   #24
stokessd is offline stokessd  United States
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KICAD sucks compared to expensive commercial software, but I find it pretty usable once I got used to it (the cursor handling is satanic, and the ******** responses from the developer don't hold water in my opinion). If you do your design in KiCAD you can get them easily fabricated at a variety of places. I have been using OSH Park with good success.

Sheldon
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Old 1st May 2020, 04:39 PM   #25
mhenschel is offline mhenschel  Canada
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Thanks. Appreciate the advice. M
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