Some photoetching questions - positiv 20

[Nordic]

Just how thick should I apply the spray on photosenitiser?

I made my first board attempt today... followed the instructions on the can....including drying in the oven - was very hard to get an even layer!!! maybe I should apply 2 coats?

I used 1 minute of African sunlight to expose the board.

I think my caustic soda may have been mixed too strong, in places it washed off the traces with the the rest... the traces that stayed looks nice.

Do I keep it in the soda until the non copper parts are totaly clear of the purple stuff or is there a set time?

Not going to etch this board, although parts of it looks very good... will try the acetone now to remove the purple stuff and try again...

[MikeB]

I believe that the African sun is quite strong, but 1 minute ? Consider at least 10. I use 90seconds with a very strong UV-lamp (> 100watts mercury lamp)
And make the caustic soda solution much weaker... This way you have more time to keep the pcb in the soda.

Mike

[Nordic]

Would aqquarium lights work... I have quite a mean 4 tube rig I made when I had time for a planted aquarium.... electronics stole my life.... think its about +-100w with 2 daylight and 2 normal florecent tubes... Will be a heck of an excersise rigging it up, but if it can work consistently, I'm game....

[MikeB]

You need to try, but i doubt that these lamps emit much UV-light.

Mike

[Nordic]

Should I worry If some areas come out darker sprayed than others... i.e. should I aim for a minimal layer or a solid layer of spray?

Your other answers are much aprreciated and noted down

[poobah]

Can't answer your questions regarding thickness. I would presume an even and consistent coating would help.

Here's one old trick, that I thought was silly... until I tried it. Take your spray can, hold and swirl it under running hot water until you can feel that the contents are warm. Don't blow the can up... nothing extreme here!

Warming the liquid helps reduce viscosity and yields a finer spray. It also works against the cooling that take place as you spray.

[Nordic]

Yep yep, I do that with normal spray cans, but read abot guys cooling the pcb and spray, as it apparently works poorly on hot days... I did mine early morning... nie and cold.. but yeah preasure would help....

I was given a very bad copy of positiv 20, called cramilin positiv, it blows chunks, literaly, it blows droplets of whatever the stuff is supended in (well droplets), which disperces the allready sprayed area... and I'm pretty used to spraying with a can... kinda addicted to spraying everything I touch... hold-over from the model plane building phase....

[poobah]

Hmmm,

I won't discourage you... I never got it to work. I started buying pre-coated boards. I thought I just had a bad can of spray also!

[Nordic]

Ok reapplication went a bit better I think, its in the oven now.

Diffirence in method so far...
used acetone to clean pcb as opposed to soap and water, then sanded it lightly till shiny all over with dry 800 grit waterpaper, then buffed with a ball of kitchen towel...

I reccon thats the cleanest I'm ever going to get anything....

[poobah]

I think that will help...

Leave it in the oven until there is no smell.