View source for Printedcircuitboard:ThruHole:RD:20140830

Copy paste de l'email qu'il m'a envoyé.


Hi,

As you may have noticed by the boards I have left, I've replicated the process
I had at home almost exactly. The problem was the kitchen scale; it was completely
unreliable and this screwed up the ratio of the solution.

I have since made a second batch that looks and works exactly as intended.
At the bottom are my calculations of the proportions, adjusted for NH3 we had.

As per the boards themselves, it's written on the boards in abbreviated form,
but eventually I came to the following rules:

  * *don't* scrub the board to remove hypophosphite remains from top/bottom.
    Think of this: we want these remains to be well plated over inside holes,
    so how much does it matter if they remain on top/bottom? Does not seem to
    be a big problem in practice as well. Scrubbing however may screw up the
    fragile layer at the very edge of the hole.

  * Use a squeegee to remove extraneous solution from the board. Surprisingly
    this almost never removes solution from holes.

  * Drill quality doesn't seem to differ much or affect result much. Your
    40000rpm machine and my 18000rpm crappy CNC produce nearly identical holes.

Despite everything, the holes aren't completely plated as I want them to be.
I haven't had any time to try to determine chloride ion concentration or
add the gelatime... (indeed, I missed my flight even as such)

Original recipe
---------------

 * take 80ml of water
 * dissolve 15g of CuSO4
 * while mixing add 11g of Ca(H2PO2)2
 * filter the residue and wash it with 20ml of water
 * add 16-25ml of 25% NH4OH

For 13% NH3
-----------

5g = 40ml of NH3 in wt

start with 60ml of water

Deconstruction
--------------

(assuming 20ml of NH4OH)

 * 120ml of water
 * 15g of CuSO4·5H2O = 0.060 mol = 0.50M
 * 11g of Ca(H2PO2)2 = 0.065 mol = 0.53M (in excess!)
 * 5g  of NH3        = 0.295 mol = 2.45M

Reaction: Ca^2+ + SO4^2- -> CaSO4


-- 
Peter Zotov