Homebrew PCBs

having a positive etching problem
I'm using precoated boards, using double pcb masks to 
expose boards, sandwiching 2 laser printouts on top of 
each other. tried single, but did same thing.

exposure 3 1/2 minutes at 11 inches from uv lamp. developer
step looks sharp, but it may be too thin.
tried 3 minutes with single transparancy but looks the same.

on etching they look porous on most of
the traces. doing 3 circuits at once on one board.

typical exposure setup routine,/board / mask / glass cover
i'm using .040 to .060 traces.

tinit .. made up 2 different batches of this stuff and it
didn't do a thing. mixed it with a digital thermometer too!
ain't nuttin goin right. ha ha. figure worst case I can 
drill the boards then flow some solder over the porous sections
then clean out the drill thru's.


using bubbler in etchant ferric cloride
getting agrivated at the junk they sell now days..

Think I may pickup one of those silk screen kits see what it does.
jim
nc4fl

On Thu, 17 Jul 2008 21:04:06 -0000, you wrote:

>having a positive etching problem
>I'm using precoated boards, using double pcb masks to 
>expose boards, sandwiching 2 laser printouts on top of 
>each other. tried single, but did same thing.

Did one single transparency on a laser printer.
>
>exposure 3 1/2 minutes at 11 inches from uv lamp. developer
>step looks sharp, but it may be too thin.
>tried 3 minutes with single transparancy but looks the same.
>

You can't tell when developed.  

>on etching they look porous on most of
>the traces. doing 3 circuits at once on one board.

You overexposed.

Use the most dense setting on your laser printer.

It'll have holes.  Idea is to get the exposure to the point where the
holes are not all the way through, but the clear traces are.

Suggest test exposures with about 15 to 30 second steps up to about 3
minutes.

>
>typical exposure setup routine,/board / mask / glass cover
>i'm using .040 to .060 traces.
>

You should be able to get 0.016 traces or better.


>tinit .. made up 2 different batches of this stuff and it
>didn't do a thing. mixed it with a digital thermometer too!
>ain't nuttin goin right. ha ha. figure worst case I can 
>drill the boards then flow some solder over the porous sections
>then clean out the drill thru's.
>

I use the MG chemicals stuff, pre mixed, works fine.



>
>using bubbler in etchant ferric cloride
>getting agrivated at the junk they sell now days..

You can make your own, but it takes a bit of minor effort.

>
>Think I may pickup one of those silk screen kits see what it does.

Toner transfer works fine, but with different results.  You need to
dump more money in at the start, but the boards are cheaper.

Harvey


>jim
>nc4fl