Homebrew PCBs

Adam Seychell wrote: 
> 
> 
> Thanks for the interesting link. I've been looking for a good 
> explanation of the various multilayer techniques but never found 
> anything.

Replace the '11' in that url by '12' or start from '01' or click this
for the all thing.
http://www.precisioncircuits.com.au/pdf/cid_booklet.pdf
But there are better docs on the web and youtube videos, manuals from
lpkf bungard and mega have some nice info too. And 'Printed Circuits
Handbook' has almost 100 pages about it, but drawings are not much
explicit.

> My method is similar to "3) Double-Sided Cap Sheet Lamination"
> except I use liquid epoxy with glass cloth instead of pre-preg.

In you method you stack two double sided board leaving glue on the
center. Multilayers are normally stacks around one double sided board.
Adding prepreg and copper sheets around and press, just like making a
blank pcb laminate. I write about a method to print one time only,
following one idea of stacking single sided boards, which i think is
much easier for the homebrew. If the method i described didn't had
fails, since i can get 18panels 20x30cm 0.3mm thick by 32eur with tax
and postage will be a very cheap (and easy on print) method for
producing 1 to 6 layers small boards.


> 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.

There are better desmear than permanganate, since it needs to be
replaced every time. Its used in much plating chemistries because of
oxidizing properties, where the activator bonds only to the resin hole
sidewall because its oxidized, and not to all board avoiding microetch
before plating. But are glycol ethers  desmears to use before
permanganate to make it last longer, and there are additives to make
permanganete regenerate, being Sodium hypochlorite (Bleach) the most
popular. The common setup from what i know is 90�C at pH around 10. A
example for one litre is  Potassium permanganate 60g; Sodium hydroxide
50g; Sodium hypochlorite 10g .
But 90�C is a no way for homebrew i don't want to wait hours until use
it. The room temp version is potassium permanganate and sulphuric acid
which is explosive, maybe few grams on 1 liter water won't explode but
it needs to be fresh all time so it fails on the same, only useful if
you have a multimillion dollar machine with concentration sensors and
precision pumps constantly renewing the thing.

About being MEA and PEG600 is what i think '2-aminoethanol and secondary
alchool ethoxylat (C12 C14)' from one MSDS means. Long shoot? I think
not. But i don't want MEA either, slow heating required and the vapor
makes you talk funny. 

> 
> 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'.


It's not hot, and i really need it! I should explain, i am not fat but
have this big strong warm hands which leave big marks on everything.
Since i am a lazy and don't wish to scrub or use gloves all the time,
your great tank idea answered this problems, i could degrease it on the
titanium holder without touch it. Your tank idea made me search for the
burrs problem (i hated the need to sand the boards when i worked with
them, and the expensive cnc was really against me on burrs matter), it
seems the machines for deburring  use high pressure water jets, i have
one water gun with a 3hp thiphase motor so i should try it.  
And btw do you know a homebrew version of this expensive ScotchBrite
roll brushes? They are used in pcb before lamination and after plating.
http://3m.hillas.com/pc-71200-867-3m-scotch-brite-printed-circuit-cleaning-brush-4-in-x-14-in-x-1-14-in-6s-sfn-1-per-case-custom.aspx


> 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.

What do you say about the Pd/Sn NaCl and vanilla activator i described?
I still didn't find the patent of the chemistry i used or the company
name which makes it. (bungard cuts the manufactor logo from labels on
bottles and sells then with the x-acto marks on the plastic! nice
business hein?!) I have metallic palladium here, should i convert it to
PdCl with aqua regia like in the books, with HCl and H2O2, bubbling air
in HCl for days, or electrolise in HCl?

> 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.

Continual active filtration and eductors are used like/insted the anode
bags for the same reason, removing copper shunks. By jetting filtered
plating solution against the pcb, only clean liquid is in contact with
the pcb. Is not about contamination, or it works or it doesn't work with
the contaminates you put in, no filtration can repair that. The machine
i have used don't have filtration either (but by the price should have
it and also a robotic arm to change pcb between tanks). But one time i
slit some anode bag content in to the tank when replacing anodes and was
a mess, hours of plating until that copper 'sand' disappear.

Is offtopic but see this gigantic machine, maybe the most advanced in
the world, in the video http://www.youtube.com/watch?v=5z8pV1ReuMs on
minute 5, no anode bags! because active filtering! (ok and some very
crazy chemistry - see the darken copper balls?)



> 
> 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.
> 

I would prefer a low concentration of sulphuric acid with EG or
derivates form things like anti freezer or brake fluid but this is still
a long shoot for me. I should keep to the things wrote by who really
knows. Just to get thiourea was a nightmare! To get all this will be
easier going to that Atotech representative at 40km from me.
Other thing, do you think i can mix easy to get NaHCO3 and KOH and heat
to get some K2CO3 in solution (along with Na2CO3), will it work for
vanilla-tin removal?

Another long email and is already really late in this side of the world,
very thanks.