A couple of years ago I tried making a couple of PCB's using the light exposure method on positive presensitized pcbs. They came out sorta ok, my main problem is that any place there was a hole for the lead of a component to go through, the very fine copper traces that surround the hole would be missing.
I just tried making another board for the first time in two years, and this time instead of exposing with UV bug zapper bulb (I made a pretty nice custom enclosure), I just used a little desk lamp with a small flourescent bulb. But the light enclosure made it hard to keep it even with the top of the glass, so the light was tilted and part of it was closer to my pcb then the other half. One end of the board was maybe 3/4" away, the other end 1.5" away.
So when I was exposing, after a few minutes I turned the lamp around so it would ultimately expose the board evenly. Well this time, half my board turned out perfect, and the other half turned out the same as from two years ago, where the fine details were gone. I didn't time it perfectly so each side was exposed an identical amount though, one side did get more exposure then the other side.
My question is, is the loss of details from over or under exposing? It would seem to me to be caused by overexposing, since the light makes it so the developer breaks down the coating. If you expose it too much, then there could be more bleed through causing the loss of fine details. And two years ago I was using much more powerful light.
The problem is I don't have much PCB left and it's pretty expensive so I didn't take the time to do any test exposures. If I had taken the time to do this 2 years ago, I would have ultimately had a lot less pcb go to waste.
I bent my transparencys so I had to print new ones (I use 2 or 3 at the same time overlapped to make sure the blacks are very black), and I am ready to try it again. I have enough pcb for two more attempts, then I am out. I am trying to make the board for a pickit2 clone. I am wondering if I should use half of what I got left to try for more test exposures, exposing small pieces to different amounts of light and timing it. If I do that it would leave me with 1 more try for the real board. I was really hoping to get two good pcb's though, I wanted one for myself and one for my brother who was wanting to learn how to get started with programming Microcontrollers.
I just tried making another board for the first time in two years, and this time instead of exposing with UV bug zapper bulb (I made a pretty nice custom enclosure), I just used a little desk lamp with a small flourescent bulb. But the light enclosure made it hard to keep it even with the top of the glass, so the light was tilted and part of it was closer to my pcb then the other half. One end of the board was maybe 3/4" away, the other end 1.5" away.
So when I was exposing, after a few minutes I turned the lamp around so it would ultimately expose the board evenly. Well this time, half my board turned out perfect, and the other half turned out the same as from two years ago, where the fine details were gone. I didn't time it perfectly so each side was exposed an identical amount though, one side did get more exposure then the other side.
My question is, is the loss of details from over or under exposing? It would seem to me to be caused by overexposing, since the light makes it so the developer breaks down the coating. If you expose it too much, then there could be more bleed through causing the loss of fine details. And two years ago I was using much more powerful light.
The problem is I don't have much PCB left and it's pretty expensive so I didn't take the time to do any test exposures. If I had taken the time to do this 2 years ago, I would have ultimately had a lot less pcb go to waste.
I bent my transparencys so I had to print new ones (I use 2 or 3 at the same time overlapped to make sure the blacks are very black), and I am ready to try it again. I have enough pcb for two more attempts, then I am out. I am trying to make the board for a pickit2 clone. I am wondering if I should use half of what I got left to try for more test exposures, exposing small pieces to different amounts of light and timing it. If I do that it would leave me with 1 more try for the real board. I was really hoping to get two good pcb's though, I wanted one for myself and one for my brother who was wanting to learn how to get started with programming Microcontrollers.