Dear Mr. Stern,

The concept of polarization is the key to all electrodeposition process.
In the specific case of electrodeposition of copper from an acid base
solution onto PCBs, most additive systems are composed of 2 main components :
- A suppressor, generally high Mw molecule, which has the capability to
strongly adsorb on the surface with the help of the chloride ions and
therefore create a type of 'barrier' which will increase the polarization
('suppressing' the deposition of the copper).
- An anti-suppressor or accelerator, generally a sulfur compound, which will
interact with the cuprous ions (close to the surface) and decrease the
polarization ('accelerating' the deposition of the copper).

With the pulse periodic reverse technology used for this application, we are
using the opposite influence of both components on the polarization.
Specifically, during the reverse pulse, it is proposed that desorption of the
accelerator occurs. However, the magnitude of this phenomenon depends on the
primary current distribution (function of the intensity of the reverse pulse)
meaning that the desorption is 'maximum' at high current density (Surface)
and 'minimum' (ultimately non existant) at low current density (inside the
hole). With this approach, it is then conceivable to obtain a redistribution
of the polarization by selective desorption of the accelerator. Back on the
forward pulse, this modified polarization will dominate until it comes back
to normal (towards the end of the forward pulse) but we then go back to a
reverse pulse in order to repeat the mechanism.

This proposed mechanism is, of course, a simplified version of what is really
happening but I believe it gives an overall good picture of the process.

Regarding the pros and cons of this technology, I think that a lot of people
have described them very accurately and I agree with most of them.

For all those interested in the electrochemical aspect of this technology and
its application to the production environment, do not hesitate to contact me.
I would be happy to converse and discuss with anybody wanting or having
experience with this technique.

Sincerely,
Mr. Stephan Menard
Micropulse Plating Concepts

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