Joe G Malley@MACDERMID
11/29/99 11:56 AM
Hi Ted,
From my understanding of periodic pulse reverse it works like this:
The additive systems have two components that do most of the work.
Different people give these different names such as wetter, carrier,
brightener, leveler, etc. For simplicity sake there are 2 basic actions
that occur.
The first is a suppression of the plating in certain areas. This is due to
the effect of a long chain organic molecule that will increase the
polarization resistance of the cathode film. This material functions in
the presence of chloride in the bath which seems to aid its adsorption on
the cathode film.. Since the chloride ion has a negative charge it is felt
that the brief anodic (positive) pulses on the cathode allow the suppressor
to be adsorbed more fully. Areas of higher current would favor additional
adsorption.
The second action is due to the anti-suppressor. These materials typically
contain sulfur which will allow this additive to bond with the copper
surface. These materials accelerate the reduction of the copper ions to
copper metal. When the reverse pulse is applied there is some stripping of
the copper which will remove the anti-suppressor. Because of the quick
reverse pulse. the effectiveness of this stripping diminishes as you
progress into the local areas of low current (in the holes for example).
In some of these very low current areas it is possible that no copper has
been stripped and therefore none of the anti-suppressor has been removed.
When you now return to the forward pulse, the anti-suppressor is effective
immediately in these areas and accelerates the reduction of copper ions.
In the other areas where the copper was stripped, it is first necessary to
re-adsorb the anti-suppressor before the acceleration takes place. This
mechanism allows you to increase the plating in the lower current areas -
the holes.
I know that there must be some Electrochemists out there that can explain
this better by describing the Tafel plots and using the Wagner number
calculations. Perhaps they can lend their expertise to this discussion.
I hope my very basic explanation begins to answer your question. I think
that there are other theories out there, some of them close to my
explanation and others a bit different. It would be interesting to hear
from all interested parties.
Joe Malley
Research Manager
MacDermid Inc.
(203) 575-7921 phone
(203) 575-7916 fax
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Ted Stern <[log in to unmask]> on 11/29/99 11:13:59 AM
Please respond to "TechNet E-Mail Forum." <[log in to unmask]>; Please respond
to Ted Stern <[log in to unmask]>
To: [log in to unmask]
cc: (bcc: Joe G Malley/MacDermid/MACDERMID/US)
Subject: Re: [TN] Pulse plating
Dear Ms. Menard:
I was interested in your reply, and specifically your description of
"modified
polarization characteristics" on the board. Being a novice in periodic
reverse pulse
plating theory, I was wondering if you could further elaborate on the
mechanism?
I have been told the copper "stipping" associated with the reverse pulse
has to due
with the disruption of the cuprous diffusion barrier at the surface of the
cathode. Do
you believe this is accurate?
Thanks,
Ted Stern
Stephane Menard wrote:
> Dear Mr. Savard,
>
> I am sorry to say that I do not agree with your short summary on the
> mechanism of pulse periodic reverse technology for copper plating on PCB
and
> especially what you call the 'stripping' phase.
> I do not believe that you want to strip the copper. This would induce
> unsatisfactory roughness of the deposit and probably unappropriate
> metallurgical properties (for the PCB specs).
>
> The very short and very intense reverse pulse is actually designed to
modify
> the polarization characteristics on the boards (basically increasing
> polarization at high current density area). Of course, the chemistry will
> then play a very important role also because she needs to be able to
> 'respond' to the pulse and this, at a quite high frequency
>
> Without going into details, this proposed theory has been demonstrated
and is
> based on electrochemical studies which clearly showed the influence of
such
> pulses on polarization.
>
> One last thing, if it would be based on pure 'stripping' of the copper,
we
> could assume that it would work with any chemistry. Believe me, it is not
....
>
> Sincerely,
> Stephane Menard
> Micropulse Plating Concepts
>
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