Hi Adam,
If I understand, you mean to ask: "How long
should it take to create the first ppms of a full conductive copper layer inside
the PTH?" (something like that - how long untill the whole hole wall gets the
"good" conductivity of copper).
I cannot relate specifically to Blackhole
since I work with SHADOW, but I think the answer is really not that straight
forward, as Rudy implied.
In general I can tell you that the creation of
this "first conductive layer" does take relativly considerable time
compared to electroless copper. This time depends on many factors, starting with
the conductivity of the direct metallization layer, the diameter of the via, the
Aspect ratio (I did mention the latter two separately in purpose), the actual
current density, the agitaion and more.
If you want to get some approximation of this
time dependency of plating, I would advise you to create an artwork of a mesh
that has diffrent square sizes. You can image and etch this mesh on a regular
double sided board, direct plate it and then copper plate. Examine the board
every few minutes and see how the gaps in the mesh "close". The rate of closing
should give you some idea regarding the time.
Of couse, you must keep in mind that this time
dependency that exists on the outerlayer of a board is different from what you
get inside a via, especially a small and deep via. For vias you may create a
board with differnt hole sizes (many coupons - each containing 4-5 hole
sizes) partially routed out, direct plate and electroplate it. Every few
minutes lift the board out of the plating bath and break off one coupon (your
partial routing should be such that would allow easy breaking off of these
coupons, but not too easy that would break off during agitation). Microsection
the different coupons and get a better knowledge of the time dependency of
copper. It is more difficult and time consuming but a little more accurate (the
actual current density will depend on the specific board layout and it will be
always different from your test board, by definition).
I'll take this opportunity to wish You and all
Technetters a very happy and an even happier and less eventfull
New-Year.
Yehuda Weisz