Archive of the former Yahoo!Groups mailing list: 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