I'm not sure what I'm doing wrong, but it seems that 9/10 times when I try making photo-sensitive PCB's some small tracks near the edge of the board disappear.

This is how I attempt to make a photo-sensitive PCB:

1. Print PCB mask on staples multi-function transparency paper with a brother lazer printer. (URL to paper: http://www.staples.ca/en/Staples-Multipurpose-Transparency-Film/product_954145_2-CA_1_20001)

2. line up two copies of the same mask one on top of the other to create a dark image.

3. Constantly inspect the track alignment by shining a bright light through the transparencies.

4. tape the copies together at corners.

5. turn all lights off and use a dark room with only red ultrabright LED's as light.

6. peel protective layer off PCB and place the artwork upside down so it's the right way after production and toner can touch photo-sensitive material.

7. cover the whole PCB inside a box with an aluminum plate ceiling and use a cfl-compatible blacklight and expose for one hour.

8. I used a 1/4 cup measuring spoon and filled it about 1/2 of the way with sodium hydroxide (mg chemicals positive developer) and mixed that with 5 full spoonfuls (from the same spoon) of hot water.

I then carefully dipped in the board for 1/2 a second at a time and as it was developing the artwork appeared slightly more each time.

Maybe there's something I'm doing wrong here? I did remember once that I had a successful board with the developer substantially more diluted than recommended (1 part developer to 12 parts water?) and waiting forever as the board developed.

My question is can I always get away with substantially diluting the developer and letting a board develop for say 5 minutes in extreme darkness with only red LED's as a light source without a risk of overdevelopment? or is there something better I can do?

 

8. I used a 1/4 cup measuring spoon and filled it about 1/2 of the way with sodium hydroxide (mg chemicals positive developer) and mixed that with 5 full spoonfuls (from the same spoon) of hot water.

That is your mistake. Do not use sodium hydroxide. Instead use a a developer intended for these boards.
e.g. https://www.megauk.com/developers-pre-coated-boards.php

 

I'm not sure what I'm doing wrong, but it seems that 9/10 times when I try making photo-sensitive PCB's some small tracks near the edge of the board disappear.

Pictures would be helpful.

It could be that your light source doesn't expose the outer edges of the board (board size??) as well as it does the interior.

The exterior edges could be more effected during developing. I know that outside traces on boards I etch are over etched. Then I started adding a sacrificial trace for a border.

 

To clarify, this is what I used (see image).

What seemed to work a bit for me is to make the solution more diluted.

 

To clarify, this is what I used (see image).

Is that sodium hydroxide as you said in your post?
The MG website is silent on what it is.

 

it does under its "first aid measures". and now my 2nd attempt sucked because the alignment was off with the pins with the image on board but in the original mask, the image was perfect.. this is going to be a long night.

 

The etchant can get to the traces at the edge of a circuit more easily than traces in the middle of the PCB. This causes the edge traces to etch from both the top and the side. The solution is simple. Put a border around the outside of the board. Then cut what remains of the border off once the board is etched.

 

I never have the problem at the etchant stage. It's the developing stage (removal of proper photo-resist) that I have a problem with. I'm going to buy a professional UV exposure box and see if that helps

 

I never have the problem at the etchant stage. It's the developing stage (removal of proper photo-resist) that I have a problem with.

Same principle. When boards are agitated, outside edges will get different treatment than the interior.

Distance and angle from the light source could also be factors. You haven't indicated whether results on smaller boards are better than with larger boards.

 

I tend to have more problems with bigger boards.

 

How do the small tracks disappear? Are they over exposed or under exposed? I.e. are the tracks etched away or is nothing etched at all near the tracks. Like dl324 said, a picture of the problem would help.

NaOH works fine for me. I use ~2 tea spoons in ~500 ml of water. I also make sure a sheet of glass presses the artwork onto the board. An hour of exposure seems like a long time but I don't know how much UV a cfl-compatible blacklight emits. I bought a used face tanner and expose for about 3 minutes, no box, just put it on 2 stacks of something on either side facing down at about 20 to 30 cm away from the board. Over exposure gives poor results because the artwork is not dense enough. Then I move the board to a different spot a few times during the exposure to get more uniform exposure.

 

It turns out that my problem is solved when I switched the entire exposure process to using a professional UV exposure box instead of my homemade one.