Need help on PCB photo resist development process

Hi,

This was the first time I tried Photo Resist process for etching a PCB. I printed out the schematic on OHP Transparency thru Inkjet printer and placed it over the pre-coated photoresist FR1 PCB with the Ink directly in contact with the board and exposed for with normal white tubelight for about 9min.

After that I disolved the developer crystal (Sodium Meta Silicate) in luke warm water and submerged the exposed board in it for around 1min. During the time it was in the developer I was continuously making the developer flow over it. I noticed that the (PCB) unexposed part started to convert to shiny copperish color, instead of changing the color to green / blue, also exposed part started to come out like skin of a boiled patato. Finally after 1min I gave up and wash it in running water and that took off the remaing resist material and it got converter to shiny copper clad.

Can some one help me out why the board didn't developed?
1. Is it because I over / under exposed it?
2. developer was a concentrated solution, I should have diluted it?
3. Is it because I used tubelight and not a proper UV light?

Thanks,
Kunal

you can search photo resist in this forum for more results

there are two types of photo resists coated boards available positive and negative acting

make sure your dark area in your artwork is dark enough to block all light passing through it
make sure the contact with the pcb and artwork is not having any small gap (puting a small weight on the glass will do it )
after expose you can see a image og the copper clad before you develop it ( i am not using uv tube but i thing 10 min in normal tube will be ok if the distance is about 2")

Hi Rajudb,

Thanks for this info. I think Silicate developers are Positive type.

Is it normal that poto-resist material over PCB comes out like a skin and doesn't get disolved in the solution? I'll try it agin and let you know the result.

Thanks,
Kunal

The concentration and temperature of the developer are important to getting repeatable results. Try warming the solution a little, not too much! You can gently wipe the board with some paper towel in the developer also (wear gloves!).

The UV from a proper tube will be much higher than standard tube. You should cut some small squares of board and expose them for different times and record the results.

Unexposed (positive) resist should not change colour during develop. The exposed resist should wash off in the developer - should disappear completely or look like weak tea dissolving before disappearing. The potato skin you describe is usually called orange peel and is the result of under exposure. Although white fluourescent lamps contain UV, different lamps give different results.
Follow Rob B advice and try experimenting with exposure develop using test mask.

Also... remember that the board is still sensitive to light until it is completely developed. If possible, work in low light conditions until the board is fully developed.

Brian.

bro,

i guess its easier to use photoresist method by printing your lay-out using a photo paper in a LASER PRINTER. that's the suggested method and i even tried it too..

photoresist using photo paper?,

i am now using dry film photoresist