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buzzforb 11th May 2013 07:34 PM

Photoresist etching
I cant seem to get this to work. No matter how long I expose the boards, when put into the positive developer, it just dissolves away. I am using dual 15W daylight flourescents. Any help appreciated.
Is my transparency not dark enough?

Conrad Hoffman 11th May 2013 08:23 PM

FWIW, any photoresist I've used takes a lot to fully expose it, and it takes UV. Commercially they use things like mercury arc lamps. What's great for exposing the stuff is really bad for your skin and eyes. Maybe the lamps from an EPROM eraser would work, or some quartz halogens with no protective cover- blocks the UV. Bright sun perhaps?

buzzforb 11th May 2013 08:38 PM

Gonna try the sun tomorrow.

dmills 11th May 2013 08:50 PM

Yup, UV it must be, visable light just is not energetic enough.

The sun might get there eventually, but for my money proper UV tubes are not that expensive, and will get the job done quick like.

Regards, Dan.

buzzforb 11th May 2013 09:11 PM

PLease give me an example of a proper UV bulb. Seem difficult to find these days.
May try UV LED's. Mouser sells them for $.70/piece at 385nm. Should do the trick nicely and is inexpensive.

EssB 11th May 2013 10:58 PM

Hang on, if all your resist dissolves away in the developer then you've over exposed it. At least that's the way the stuff I use works - exposed parts dissolve away and then get etched away, non exposed parts ... leave copper.
Have you tried doing a test strip ?
FWIW I use 2 mins UV exposure in a fairly 'bright' UV box.

counter culture 12th May 2013 04:13 AM

I have about 100 UV LEDs in a 12*10 inch array. Throw is about 12 inches. Exposure time is ~6 minutes using inkjet transparencies.

surface tension 12th May 2013 05:09 AM

If you are using MG Chemicals presensitized boards (from Fry's) about 30 seconds under bright midday sun with a piece of glass usually works. The image on the transparency film needs to be dark. I take my artwork to the local reprographics shop and print black only on a Canon color laser copier ($2-3 for an 8.5x11) and spot with a black Sharpie to cover any pinholes. Keep trying!

dangus 13th May 2013 12:04 AM

Another vote for doing a test strip. It's the only way to be sure.

With inkjet or laser-printed artwork, I use two layers so it's completely opaque.

I've never used sunlight to expose boards; I started with a photoflood intended for home movies, then used incandescent tanning bulbs, and finally got a pair of fluorescent tubes, probably F15T8/BL.

nigelwright7557 13th May 2013 12:52 AM

I gave up on home grown pcb's and buy in low quantities from China.
I get back very professional looking pcb's at a very low price.
Its usually about 55 for 5 medium sized pcb's.
With 2 week turnaround.

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