Can Na2PdCl4 be used as a substitute for PdCl2 in electroless copper plating?

[minerva]

TL;DR Summary

I want to do electroless Cu deposition onto a non-conductive material. Reaction doesn't work. Description of the reagents I used, would like some peer-review or help to check this process.

These videos show an electroless Cu deposition process onto a printed circuit board.



I don't care about actually making a PCB, so the other steps such as PCB drilling, photolithography and electroplating thicker Cu aren't relevant. I'm only interested in the steps of electroless Cu deposition.

This doesn't work - a glass slide is cleaned with ethanol and dried, then immersed in the Pd reagent with gentle agitation for 5 minutes, then removed with no rinse and put in the Sn reagent for 5 mintues with gentle agitation.

Then the glass substrate is gently washed with H2O and put into the Cu reagent, for 40 minutes.
There are no gas bubbles and no visible reaction, no copper deposited. I would like any peer-review, experience or advice on what I'm doing wrong.

DI H2O is used for all steps where H2O is needed, not tap water.

I decided to modify this process using a Na2PdCl4 stock solution.
This isn't part of the original process, but I decided to add this step myself and I don't think it should make any difference.

What I actually did for the concentrated Pd stock solution:

Sodium Tetrachloropalladate(II) stock solution.

This is easier to measure and dispense in small portions, easier than measuring out 20mg of PdCl2.

1.0 g of PdCl2 is added to 50ml H2O and 0.659g NaCl, with thorough stirring.
H2O is added to make up to a total volume of 100ml, stirred more, the solution is filtered to remove any insoluble residue (there was essentially none).
This Na2PdCl4 solution provides a water-soluble alternative to PdCl2, which is itself not soluble.
The solution is deep brown but clear, like cola or dark tea in appearance.
10ml of the Na2PdCl4 stock solution is equivalent to 0.1g PdCl2 combined with 0.0659g NaCl in aqueous solution.

Palladium reagent:
The specified original formula for the Pd reagent:

40 ml H2O
20 mg PdCl2
2.25g SnCl2.2H2O
7.75g NaCl
2.5 ml 34% HCl
Topped up to a final volume of 50 ml.

What I actually did for the Pd reagent:

200 ml H2O
10ml Na2PdCl4 stock solution
11.25g SnCl2.2H2O
38.69g NaCl
11.8 ml 36% HCl

Stirred thoroughly, and H2O added to make up 250ml final volume.

I don't think any of these changes are significant - it should be pretty much equivalent?
There is so much NaCl in the formula that the Pd would form the [PdCl4]2- complex when the NaCl is added anyway.

I scaled-up the volume by 5x, I used the Na2PdCl4 stock solution, slightly reduced the HCl volume because my concentrated HCl is 36% not 34%, and I reduced the NaCl by a tiny amount due to the equivalent NaCl in the Na2PdCl4 solution.

The final reagent has a pale yellow colour.
However, the videos show a dark brown, almost black liquid.
But it should have everything in exactly the same concentration?SnCl2 reagent (Pd reducing agent):
The original specified composition of the SnCl2 solution:

182 ml H2O
18ml 34% HCl
4g SnCl2.2H2O

What I actually did for the Sn reagent:

375 ml H2O
42.5 ml 36% HCl
10g SnCl2.2H2O

Thoroughly stirred and made up to a total final volume of 500ml with H2O.

Scaled up to a volume of 500ml. Volume of HCl reduced slightly as I used 36% HCl, not 34%.
This dissolves completely to give a colourless solution, unlike the cloudy solution shown in the original video.

Cu plating reagent:
The original specified formula of the Cu reagent:

150 ml H2O
2.52g CuSO4.5H2O
5.8g Na2EDTA
2g NaOH
4 drops Triton X-100
1.6 ml 37% formaldehyde

EDTA will not dissolve until the NaOH is added.
Top up H2O to a total final volume of 200 ml.

I didn't have any disodium EDTA salt, only acid EDTA so I used the equivalent amount of EDTA combined with two equivalents of extra NaOH.
I think Na2EDTA will be OK to substitute with EDTA combined with an appropriate amount of extra NaOH.
(2g * 2.5) + (0.69g * 2.5 * 2) = 8.45g NaOH.

My formaldehyde is a bit old and had some precipitate of white, insoluble paraformaldehyde in it, so I filtered it before use.
This is commercial aqueous formalin which contains some stabilisers such as methanol.

What I actually did for the Cu reagent:

375 ml H2O
6.3 g CuSO4.5H2O
12.6g EDTA
8.45g NaOH
10 drops Triton X-100
4 ml 38% Formaldehyde
Stirred thoroughly, topped up H2O to 500ml final volume.

Volume scaled up to 500ml.
Forms a clear blue solution with no undissolved material.

 

[Borek]

Have you tried it on other surfaces than glass? Without getting into the details of the concentrations and so on it seems to me like the process requires rough surface that can be to some extent penetrated by the Pd solution so that it can get reduced there. Glass might simply not work because of that.