Homebrew PCBs

Ron mentioned in a previous post that he was getting uneven etching 
with ferric chloride. When this happens it's usually due to under 
development of the photoresist. I am assuming that dry film resist is 
being used. The best way to develop dry film is with a spray tank set 
up with a 1% sodium carbonate (soda ash)solution. Find out how long 
it takes to "break through" to bare copper and then go about that 
same time again for final developing. For example if the bare copper 
shows up in 1 minute then continue the process for an additional 1 
minute and then you can etch. 

Another good idea is to make up a tray of weak etchant from a couple 
of ounces of ferric chloride in one gallon of water. If a developed 
board is put into this solution for a minute or so the areas that are 
fully developed will turn a dark color and the under developed spots 
will show bright copper. This will amaze you the first time you see 
it because the panel still has some dry film "scum" on the surface 
when the board looked like it was fully developed. If the board has 
scum, just put back in the developer for a bit longer and try again. 
When a uniform dark color appears across the entire surface you will 
be ready for final etching and obtain excellent results.

If developemnt is being done in a tray, try using a very soft 
bristled brush to gently work the solution across the board surface. 
This will help to break through any scum on the board. The bottom 
line is that this scum must be removed or you will never obtain 
uniform etching. Hope this idea helps out.

Tom