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



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