After adding a few capacitors to the voltage regulator the stepper began to behave and after writing a neat piece of code I was ready for my second attempt at photo-resist exposure. I have to say that it worked very well, I ran the scanner at 1.7cm/minute which was just right. To save PCB I only made a segment of the LED matrix board but it worked very well.
However for the final design I will have to produce 2 double sided boards, so I decided to have another go at etching, this time using double sided PCB. I cut out both acetates and drilled alignment holes in each corner. I used small pieces of wire to hold the acetate in the correct position over the board.
Although the boards did develop very well again, after etching and drilling I discovered a slight alignment issue. Just one of the corner wholes was off by about 1.5mm however this threw the whole design off and meant that all the wholes were in the wrong places. Consequently I have been thinking of a better way to expose the boards ensuring that they are lined up correctly.
Here is my solution to the problem, I have cut two sheets of transparent acrylic roughly 20 x 15 cm. Also I have some strips which are 20 mm wide and of a slightly thicker acrylic. After glueing together I have formed two pieces of acrylic each with a right angled corner on them. This means that they slot together in exactly the same place every time.
I plan to selotape one acetate to one side of acrylic, then line up the other acetate on top with a strip of double sided tape at each end. Then I will place the other acrylic layer on top and the acetate will stick to it in the correct position. Then I can firstly check they are lined up, then insert the PCB and tape the whole thing together. Once I have exposed one side I simply flip the jig over and do the other. Hopefully this should produce a better result.