Homebrew PCBs

Simao Cardoso wrote:
>  
> 
> 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?

I have no desmear removal step. Never had an inner layer electrical 
problem yet. I think because professionals use 100k+ RPM drill speeds 
there is much more probability of epoxy smear. My home made manual drill 
press runs at 15k RPM max.
98% sulfuric is an excellent  epoxy etch. In hot H2SO4 for few hours 
your can remove all epoxy and just have nothing but bare copper traces.

> 
> 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.