Hi Roger,
I agree with a lot you said, but not all.
(1): The Hull Cell had little to do with plating thickness [remember the Hull
Cell was developed when there were no brighteners at all], but with the
plating current density [controlled by distance to the 40° electrode] a given
plating solution could tolerate before producing 'burned' deposits].
(2): "All they [brighteners] really did was improve the color and physical
appearance of deposits without
improving plating thickness distribution" not so. Just try plating with an
acid bath without brighteners—Sel-Rex's Q-Bath M brighteners revolutionized Cu
plating [I did, see: Engelmaier, W., T. Kessler, and A. Colucci, “Effects of
Agitation by Forced Flow and Air Sparging on Electroplated Copper in Multilayer
Board Plated-Through Holes,” Proc. Electrochemical Soc. Meet., Dallas, TX,
October 1975 & Engelmaier, W., and T. Kessler, “Investigation of Agitation
Effects on Electroplated Copper in Multilayer Board Plated-Through Holes in a
Forced-Flow Plating Cell,” J. Electrochemical Soc., Vol. 125, No. 1, January 1978,
p. 36].
(3): "Reducing overall current density to less than 8 a.s.f. or less (I've
seen it done and so probably have you) does nothing but give the solution
movement in the holes more time to equalize to that on the surface"—of course, the
ultimate 'reduced current density plating is full-built electroless Cu plating
as the Japanese have used for many years.
Werner
**************************************
Get a sneak peek of the all-new AOL at
http://discover.aol.com/memed/aolcom30tour
|