Dear Parrish,

Probably photos would be far more helpful. I had a similar experience even
without any bubbles. Your post dimensions are important but separation of
clear areas on the mask should also be considered.

Among many causes one may be that your openings are starving.  When the mask
design is not uniform or is not periodic, or if unintentional wide openings
are present, large clear areas sink the electric field lines in the
electro-plating solution.  If you have clear fields around your intended
area, they may steal the e-field.  (That's what people call "thief mask"
which is sometimes used intentionally to equalize e-field on the wafer).  If
you have such large clear areas I would coat those first.

Second cause would be the large separation between posts. This is opposite
of the previous case but the result is same.  This is also logical because
if there is too much dark area between the open areas, too much field
accumulates at the edges of your openings.  In this case I would put dummy
openings between the posts.

Other cause may be the already low e-field or hard-seeding in the solution.
In my experience this kind of hard seeding causes edges to rise rapidly.
And once they rise, they keep going on because electric field lines are
denser there.  According to my experience I would increase the pulsed
plating peak x5 to x10 times and  wait to seed every point, and then lower
the current density to a better value.

If you still have rising edges, I would segment the post openings to smaller
patches if the device design allows.

After-plating solution would be reflowing the electroplated posts with RTP
to make it fill the center itself (if you allow rounder shape for the posts)

And lastly, what is your wetting layer ? What kind of cleaning do you do
prior to plating ?

Good luck,

Oray Orkun Cellek


On Fri, May 8, 2009 at 7:31 PM,  wrote:

> I am trying to electroplate gold posts that are 50-100 microns wide using a
> KMPR
> mold that is about 60-70 microns thick.  Using TG-25 electroplating
> solution I
> have tried to electroplate at various current densities (1-10 mA/cm2) and
> have
> tried DC, pulsed, and reverse pulsed plating.  I consistently get the same
> results; “crown shaped” pins where very little gold is plated in the center
> of
> the KMPR hole and the plating on the sides of the holes is much higher.
>
> I have tried to ultrasonicate the chip in water before performing the
> plating to
> remove any air bubbles that remain in the KMPR holes.  This seems to
> improve the
> quality of the plating (the plating looks more yellow in color), but the
> pins
> are still hollow. Perhaps I am not removing all the air from the holes?
>
> Anyone run into this problem?  Any suggestions for a solution??
>
> Thank you,
> Parrish