Re: Cnc PCB drilling machines z axis linear pot

> On Sun Dec 9 20:21:11 2001, JanRwl@a..., <JanRwl@a...> wrote:

<snip>

> > so I have no clue how those machines "tell" how deep to "chuck

up"

> >bits, when they change bits, automatically (that's sumpin to

see!). Wonder

> >how "accurate" (repeatable) that is, and how "indexed"???
> >
> >Anyone reading this know????? Jan Rowland
>

Bill Vance <ccq@x> wrote:

> Not a clue, but not _all_ PCB holes are through holes. Some traces

run only on

> the top side, or down to layer(N).
>
> Bill

The rings may be used to control tool length offset during
chucking, or the machine may make its own measurement.
Sometimes the rings are marked by color or lettering to
indicate size.

All actual drilling is completely through the material. When
"blind" holes are needed they are created by laminating cores
of material that have been drilled with other cores that were
not drilled in the location of interest. The cores with copper
on one or both sides are then sandwiched together with an
insulating layer called prepreg. Holes that are to go all the
way through the board are drilled and plated after lamination.

Blind and buried vias are an expensive process and are most
often used to penetrate only one core so as to connect two
ajacent layers without putting a hole through all layers and
thus using up valuable routing space on other layers. The
alignment of layers during lamination is a difficult and
limits the minimum size of drilled pads.

Cheers,
Steve Stallings