Hi All:

I guess I'm very dense today.  Why would you care what the current density is inside
the hole?

Experience demonstrates that the current density varies everywhere inside the plating
tank.  Variables such as board design (copper density and distribution), anode to
cathode separation, rack agitation, fluid agitation, plating current, resistance within
the current distribution network (plating rack, cathode bars, anode bars, rectifier
connections, etc.) all contribute to small local variations of the current density.

We know from experience that the effective current density within the hole is lower
than the surface (external) current density.  Often this is referred to as throwing
power.  A real world practical check: does the barrel of a hole burn before the
surface?  IMO the real trick is to minimize the effects of these variables to maintain
the least variance within and between parts.  In the real world current density is an
number used to predict the average plating rate and the probability that the plated
metal properties will fall into a predictable range.  I believe that everybody in the
fabrication business has their favorite hard to plate design that defies all current
density predictions.

Just had to add my $0.02

Don Vischulis



"Michael D. Doty" wrote:

>      I'm not sure how you would calculate the ASF in the hole. Getting the
>      area is no problem but from there I have no clue. Also how do oyu
>      figure in the effect of the ground shield or circuits or pads.
>
>      In answering the other part of your question the isolated pad has a
>      much higher current density than the pad in the middle of shielding.
>      This can and will cause plating distribution problems if you're not
>      careful. The isolated pad plates at a higher rate and could burn if
>      the ASF is not controlled properly.
>
>      Mike Doty
>      Hadco TCE
>
> ______________________________ Reply Separator _________________________________
> Subject: [TN] ASF info...Super Plater
> Author:  Robert Jordan <[log in to unmask]> at smtplink-hadco
> Date:    10/19/99 7:45 AM
>
> Hello,
> Once again another question drawing in the vast talent and experience of
> Technet. Is there a way to calculate the ASF inside a through hole in a
> printed circuit board during the electroplate copper process? Is that ASF
> different if the pth is in the middle of a ground plane vs. an isolated
> area? If no formula exists please bend my ear with your opinion.
>
> Thanks,
> Bob Jordan

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