At 12:45 PM 9/24/98 -0400, Bob Walker wrote:
...
>And I can also generate different drill files that
>can either include all hole styles, only plated holes or only non-plated
>holes which I thought would help my board fabricator out by not having to
>separate out the plated from the non-plated hole coordinates in the drill
>file. But when I called him to see if he could make better use of 2 drill
>files (plated and non-plated), he said he only wants the 1 file that
>contains both the plated and non-plated hole locations. Wouldn't it be
>better to have the 2 files?
...
The fabricator, most likely, would then merge these two files into one. A
drill file, typically, is a series of locations for holes, divided up into
sections assigned by tool number. While some files prefix hole assignments
to tool numbers, fabricators already adjust specified hole sizes, which are
usually finished sizes, to factor for plating thickness and the available
drill sizes, and they might even combine holes where the sizes are close to
each other and within the allowable tolerance.
So they already have to go over your tool list. As long as your information
indicates whether or not the hole is plated, they can adjust accordingly.
Theoretically, one could drill the holes to be plated, plate and etch, and
then drill the unplated holes. But I don't think most fabricators work that
way. It might depend on *how many* unplated holes there are; they
apparently prefer to protect holes from plating than to drill them after
plating. That post-plating drill process could leave exposed copper if any
of the unplated holes have pads. So one might want to drill after
electroless and before tin/lead plating. Again, I think fabricators would
be leery of this. Electroless copper is very, very thin and susceptible to
damage, I think.
One could drill after plating tin-lead and then plate some more tin/lead.
This requires, however, two complete additional steps: an extra drilling
step and an extra plating step. So, unless there are a lot of holes, it is
easy to see why fabricators normally drill all the holes in one step. But
it might be practical without the extra plating if all the non-plated holes
had no pads. Or the customer was willing to accept some corrosion on those
pads (which, presumably, have no electrical function). And there were
enough of these holes to make it worthwhile adding another trip to the
drilling machine.
I have designed one set of boards which required post-electroless drilling.
Protecting the holes from plating would have been impractical; not only
were there 98 of them on the board, but plugs could not be used because of
the hole locations (as ears on a larger plated hole). It works, but there
were numerous technical problems. The boards are still in production after
about eight years. The unplated holes are used to break the plating on
either side of a larger hole, splitting the hole into two halves, which
then can be connected together with a banana jack. A cheap cross-point
switch, with the banana jacks making a visual display of the switch
pattern.... My client tried to patent it (naming me as the inventor, it was
indeed my idea), but it turned out someone had patented something similar
to it forty or so years ago, and it was not considered sufficiently
original. Hmmph. :-)
[log in to unmask]
Abdulrahman Lomax
P.O. Box 423
Sonoma, CA 95476
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