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Old 13th September 2013, 11:19 AM   #1
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Default DIY PCB problems

I've never had a problem with making DIY PCBs in the past but this time it's got me confused.

Every time I try to develop the exposed PCB I get an image then it all washes off.

I don't think the developer solution is too strong as I've used the same mix as always.

I thought the negative image might be too translucent so it's now double thick with two prints so that the black is pretty opaque.

If I expose for 10 minutes the image doesn't appear and all the photo resist washes off.

If I expose for 12 minutes the image appears but by the time the unexposed parts of the copper are clean of photo resist the image has started to break up too.

I know you are going to say, "try 11 minutes", but as I've used almost a complete can of photo resist already it's getting expensive.

Is there a clue in the way that the image is always washing off before the photo resist has been completely developed ?

Boards are being washed in meths before respraying in a gloomy environment. The photo resist is evenly covering the board and not too thick.
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Old 13th September 2013, 12:21 PM   #2
AndrewT is offline AndrewT  Scotland
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Is there a "shelf life" for the spray on photoresist?
Is the "light source" working properly?
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regards Andrew T.
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Old 13th September 2013, 12:37 PM   #3
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They are both brand new. UV source is good and strong.
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Old 13th September 2013, 10:20 PM   #4
dangus is offline dangus  Canada
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The answer to exposure time problems is to do a "test strip". Use a small strip of sensitized board, mark divisions on it somehow (scratches, notches), then cover all but one section with an opaque card, and reveal another section every X minutes. Then develop, and see which time(s) work. Google "test strip" and exposure and you'll find a proper explanation. I generally use 5 minute intervals, with the UV source about 2 feet away (two 18" UV tubes).

If you're getting stuff washing away, that suggest either too-strong developer, or insufficient exposure time.

A couple of other things... is the resist completely dry and hard? Did you scrub or sand the oxidation off the copper before wiping it clean and coating it?

Last edited by dangus; 13th September 2013 at 10:24 PM.
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Old 14th September 2013, 08:46 AM   #5
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I'll try a test strip. My tubes are only 6" or sio from the board.

The resist is dry and the board well cleaned.
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Old 14th September 2013, 03:55 PM   #6
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One of the problems that I always get is getting a completely opaque image. I've got two printers, one an Epson RX585 Inkjet and the other a Samsung ML1665 Laser. Both are reasonable printers but, even with the right medium, neither can produce a completely opaque image.

I've taken to printing using both, the laser on OHP transparency and the inkjet on tracing paper. Then I can play with either or lay both one on top of the other.

It seems like one hell of a fad to get one PCB !! :-(
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Old 15th September 2013, 12:14 AM   #7
dangus is offline dangus  Canada
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Oops; I forgot that doing the test strip requires the artwork as well. So, if you're using transparency film and tracing paper, use the same artwork for the test strip. There are transparency films for inkjet printers, and IIRC they produce more uniform blacks than with laser printers. Expensive, but office supply stores may sell them as singles sheets.
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Old 15th September 2013, 03:34 PM   #8
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Well after a bit of experimenting, it looks as though I was under-exposing the boards. The 16min mark seemed best so I'm just trying that with my project board.
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Old 15th September 2013, 04:18 PM   #9
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Finally I've got a photo image that I can etch.
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