Homebrew PCBs

Simao Cardoso wrote:
>  
> 
> Adam Seychell wrote:
>  >
>  > I have no desmear removal step. Never had an inner layer electrical
>  > problem yet.
> 
> Maybe i didn't explain with the right English words. Etchback is used to
> from etch resin sidewalls of holes in order exposing a copper anular
> ring of innerlayers. There are good images on the web to explain this
> but i didn't find any good right know, choose this because is Australian
> and has other useful content
> http://www.precisio ncircuits. com.au/cid/ 011.html 
> <http://www.precisioncircuits.com.au/cid/011.html>
> on bottom 'etch back hole' but not easy understanding
> This is used to improve surface contact between plated copper and
> innerlayers and should be used. For double sided board desmear or good
> cleaning with air compressor or high pressure water on the holes is good
> enough but it surprises me you could do it without even desmear for
> multilayers, but just proves your genius skills again.

Thanks for the interesting link. I've been looking for a good 
explanation of the various multilayer techniques but never found 
anything. My method is similar to "3) Double-Sided Cap Sheet Lamination"
  except I use liquid epoxy with glass cloth instead of pre-preg.
I do not claim desmear is unnecessary, but so far I've found it 
unnecessary in my situation. I am *assuming* because of my slow drill 
speed, that epoxy is less likely to melt and less or no smear over the 
copper annular ring.


> A good easy to use and maintenance free homebrew plating chemistry,
> should not require high temp bath to be always ready to use or
> incompatible consecutive baths for avoid long water rinses and its
> disposal, and bath longer life. I don't like either microetch. So have
> decided for palladium based. Palladium tin colloid with vanilla to
> improve tin stability. The one i have used from bungard from what i know
> now is like this and uses NaCl instead of HCl for Pd/Sn suspension i
> guess to don't attack copper. The next bath is K2CO3 which removes
> vanilla and with it tin and salt leaving only the palladium bonded to
> resin surface. Or at least is what i can understand.
> It uses a mix of MEA and PEG600 (not really sure) for desmear at 60�C
> with slow 3hour heat time. 

I wouldn't expect either of those to even touch epoxy. Epoxy is pretty 
inert. Desmear is normally a hot strong alkaline permanganate solution. 
I forget the exact composition. I found it turns the epoxy surface 
slightly brown, which I suspect is manganese dioxide.

And a 25% NaCl and 1% HCl bath because of the
> incompatibility of the desmear and the activation.

> I would like to make my homebrew version of desmear with a acidic
> version compatible with the activation, i would love to use sulphuric
> acid with EG antifreezer or DOT3/4 brake fluid for desmear but i can't
> be sure it will work and it affects the bath compatibility. But the
> K2CO3 at 40�C bath i don't know any replacement so it still requires a
> water rinse and heat time here before the plating bath.

> Your genius developing tank with nylon brushing fabric answered me
> numerous ideas. Using it with NaOH as a degrease cleaning instead of
> manually scrubbing is a saver way and time saver (no hands on chemicals
> or gloves necessity), followed by one acidic desmear can de-oxidize the
> board also, and be a bit more compatible with the activation.

I use it all the time and it made the developing process a *LOT* easier. 
Just turn on the heater, dip, wait 30 seconds, move up/down 10 strokes, 
and all done.

> My question, can you comment/help/ improve the compatibility between this
> NaOH degrease - H2SO4 desmear - Pd/Sn organic activator - K2CO3 'salt
> remover' - H2SO4/CuSO4 based plating, to minimize water rinses, heat
> time, compatibility (residues from one bath don't affect next one) ? I
> hope to have all this and be doing it in February finally.

Forget heated degrease bath, and desmear. After drilling, I remove the 
drill guide paper off the board (stuck with sticky tape), put on gloves, 
and place board in plastic tray, apply a little alkaline degreaser, 
scrub with 200 grit paper to remove drill burrs, scrub with ScotchBrite, 
then rinse. Its now ready for through hole 'activation'. If your 
activator contains HCl then I'd pre dip in HCl of same concentration 
without a rinse in between. Thats a simple room temp bath with almost 
unlimited shelf life.

> I already suspected that you was able to do pth boards without a cnc (or
> desmear) but is breath taking know that you said it... Congratulations
> i guess... Don't know what to say.

I've learned from previous projects that its sometimes best to attempt 
something in most simplest way first. Then progressively increase 
complexity until it works. I knew about drill smear long before doing 
PTH PCBs, but I omitted this step to see if it worked. I'm sure every 
step, tool and process used by professional PCB manufactures is proven 
to be absolutely necessary for reliable production. Us hobbyists are 
operating on a much smaller scale, and so it quite possible to take 
shortcuts in the process. For example, I found continuous filtration 
unnecessary in the Cu plating tank. The tank is covered 100% of the time 
and only clean PCBs are allowed to enter.


> About drill speed, it's not that fast, and depends on drill diameter, a
> 0.5mm drill is recommended to run at 60.000rpm, 100krpm are for 0.2mm or
> so, but a 2mm should run at 20krpm. But there are under 0.1mm drills and
> above 200krpm spindles (high pressure air bearings). Pcb laminate
> manufacturers say something about 'drill surface speed per minute' but
> my few experiments with a 30-60krpm spindle said faster is not necessary
> better. Maybe is just a recommendable limit speed and not recommended
> speed.


The faster the RPM the faster the feed, which means more holes per 
minute, which means more PCBs per machine, which means less machines per 
factory, which means less $ invested. I'm not sure if there is a lower 
limit. I guess a you could drill a 1 RPM , but it could take days to 
drill one hole.



> Hot sulfuric acid shouldn't etch copper too?
> 

I meant warm ~ 50C, but doesn't seem to attack copper. It was only a 
quick experiment I did some time ago. Its scary stuff to use. Would need 
some thinking to work out a safe way of applying it if you want to go 
down this path. H2SO4 is extremely hygroscopic too, so it won't last 
long in an unsealed tank.