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January 2002

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Subject:
From:
Dougal Stewart <[log in to unmask]>
Reply To:
Dougal Stewart <[log in to unmask]>
Date:
Thu, 31 Jan 2002 15:13:43 -0000
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I don't know whether this is a cynical remark (as if), but none of the
chemistry suppliers have ever promoted pulse plating with copper without
additives. In all the years I have had experience with acid copper pulse
plating (and Exacta led the way) it has been notable that simpler forms of
plating chemistry (ie with carrier and brightener, but NO leveller) worked
best. I have had long discussions with Jack Josefowicz from Tyco on the
subject, and I would suggest that he would be an authority on whether it is
possible.
Dougal Stewart

email:  [log in to unmask]
phone: +44 1896 822204
mob:    +44 7984 629667
----- Original Message -----
From: "Adam Seychell" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, January 30, 2002 8:09 AM
Subject: [TN] pulse plating - without additives


> Hello platers.  I am hoping someone here can share a few words
> of wisdom about reverse pulse plating. I'm having difficulty
> finding detailed information on the subject, as my local university
> library showed to carry almost nothing. It seems  that the
> literature on reverse pulse plating is bound to research papers
> only (which I latter learned can be quite costly and time
> consuming to obtain). What I like to know is a method of plating
> "standard" printed circuit boards in acid copper bath *without*
> the use of additives. Pulse plating without additives has been
> done or so I've been told, however most documents I have
> read only talk about baths containing additives.
>
> Normally, a pure DC in acid copper (200 g/l H2SO4, 20 g/l Cu)
> would produce a rough and grainy deposit, especially when
> thickness' become high ( >35 um). The problem is aggravated by
>  increasing current density. Even at current densities of
> 0.5A/dm2 the deposits still remain unacceptable. This is
> something I have observed through experimentation.
>
> A test panel was plated using reverse pulse technique to see
> what effect it had compared to DC plating at an equivalent
> average current density. Not having a proper pulse plating power
> supply I constructed my own basic one, using standard DC supply
> and an electronic circuit to periodically reverse the output. The
> parameters of the plating were:
>
> forward time = 5 ms
> reverse time = 1.7 ms
> forward & reverse current densities = 3 A/dm2
> average current density = 1.5 A/dm2
>
> The pulse plating deposits were only slightly improved over DC
> plating. A rough and crystalline surface was clearly visible under a
> 40X microscope. This does not sound promising and I am hoping
> this is due to incorrect characteristics of the current pulse. Most
> reverse pulse plating systems tend to use forward/reverse current
> ratios of around 3, forward times of 10~20ms and reverse times
> 1~2ms. Is important for the current reverse pulse to be short and
> high ?
>
> If anyone could guide me to right path I'd be greatly thankful. If
> there is no such thing as additive free copper plating for PC
> fabrication then kindly let me know as this could save me lot of
> time doing what others have already attempted.
>
> regards,
>
> Adam Seychell.
>
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