In a message dated 12/27/01 9:25:39 PM Eastern Standard Time,
[log in to unmask] writes:
<< What are the typically hole wall initiation times in a commercial process,
such as BLACKHOLE ? >>
Adam -
You have the right concepts for the "knit rate" of acid copper plating over
direct metallization. Basically, there are two major factors.
1) The amount and activity of the carbon deposit on the hole wall
2) The condition of the acid copper brightner system to "bury" the carbon
deposit and slow down the propagation of the acid copper coverage of the
carbon deposit.
The carbon deposition factors depend on many things - the conditioning of the
hole wall to make "water hating" epoxy want to wet with aqueous carbon black
emulsion, the carbon particle size (smaller adheres better), and the
percentage of the deposited carbon kept on the hole wall through steps of
drying, microetching the carbon off the copper surface, dry film developing,
and finally pre-electroplate cleaning and microetching.
All acid copper baths have film formers to act as leveling agents to overcome
rough deposition and achieve throw into the holes of the board. These film
forming agents slow down the propagation of copper plating, so some acid
coppers are more favorable to direct metallizaton than others. In addition,
impurities like wetting agents in developer antifoams or the wetter in
pre-electroplate cleaners can also retard propagaiton of copper plating over
carbon. So even if a copper bath has a very compatible brightner, the
condition of the working bath may retard knitting of copper in carbon direct
metallization holes. I have never seen a good knit rate from a green acid
copper bath ( and I can just guess the poor performance of the same copper
plated barrels in solder shock testing).
Adam, if you wish, I can send you (off line) a reprint of a MacDermid paper
on copper plating propagation as measured by either the copper grid in hull
cell described by Yehuda Weisz, or a MacDermid propagation test vehicle sort
of like this:
__ __ __ __
__! !__! !__! !__! !__
where the horizontal lines are offset dogbones of copper circuitry on the
opposite sides of a double side board, and the vertical lines are the plated
through holes in susscession propagated and plated copper over carbon direct
metallizaton.
Let's just say that usually, we see many holes plated in 30 minutes, so that
the knit time of a single good BlackHole deposit is a minute or so.
Let me know (off line) if you want a copy of the controls paper.
Dennis Fritz
MacDermid, Inc
Waterbury CT..
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