Homebrew PCBs

Adam Seychell wrote:

> 
> Hi, I've done a number of 4 layers, its very laborious (about 5 hours 
(...)
> * process like an ordinary plated through PCB.

>From your messages describing your PTH chemistry i did not identify a
desmear or etchback bath. Are you using a etchback for multilayers or is
possible to connect tracks in the inner layers without etchback the
holes in a multilayer board? 


One idea to print all the layers at once using thin fr4 in a unmodified
laser or inkjet printer stucks on not having less steps and being
impossible due to etchback. Imagine this, printing all layers in a
20x30cm 0.3mm thick board. All layers in one sheet with registration
holes, plus 2 drill marks on sheet opposite corners to align the print
in a cnc drilling them first and then the registration holes in each
part. Cut and etch the inner layers only and then glue the thing up.
Then procede like one double layer but already printed on out layers. 
It requires negative print outer layers and pattern  plating with
metallic resist so it's nothing easier after all. And fails on that
etchback solutions will remove any useful ink printed on outer layers. 
It made me search for acidic desmear/etchback things. For just resin
smear removal only, concentrated sulfuric acid room temp its said to do
the job, but not etchback. There is also a version of permanganate
desmear with sulfuric acid at room temp instead of caustic soda at 90�C
but is not safe. And EG or PEG with sulfuric acid but slower than with
MEA. 
So what do you use as desmear/etchback?