RE: gEDA-user: Milling channels in a PCB?

["Andrew Miner" <zminer@xxxxxxx>]

I use to work as a process Engineer at Sheldahl (now Multek) where we made
mostly flexible PCBs.  My CNC drills could hold accurate registration in the
x or y (~1 to 3 mils depending on the machine) but the z (depth) axis has no
real tolerance control. This is because the bits have pointed ends (not flat
so they can enter the FR4 better), you don't know how long the drill bit is,
or how far the bit is mounted into the router's collette (holder).  

When we had to make sure there was a channel of a specified depth, we would
manufacture the circuit on a board of that thickness.  We would then route
those channels all the way through the thickness of the board.  Then we
would route a bare piece of FR4 to match the outline of the regular board
(and make openings for mounting holes or chips that needed clearance on the
bottom side), but leave the FR4 in place where the channel was.  Using
adhesive we would then stick the bare FR4 to the back side of the completed
circuit and that would guarantee the channel has the correct depth.

Hope this helps,
Andrew Miner




-----Original Message-----
From: geda-user-bounces@xxxxxxxxxxxxxx
[mailto:geda-user-bounces@xxxxxxxxxxxxxx] On Behalf Of Stuart Brorson
Sent: Friday, September 22, 2006 9:45 AM
To: geda-user@xxxxxxxxxxxxx
Subject: gEDA-user: Milling channels in a PCB?

Guys --

I have a PCB specification/manufacturing question, and I figure some
of the gurus on this list might have the answer.  I want to create a
PCB with some material (0.030", say) milled off the top of the board
at specific locations.  That is, I want to cut grooves into -- but
not through -- the board.

What is the best way to acheive this (besides buying a milling machine
and doing it myself, that is)?  Specific questions:

*  How do I capture this information so a PCB fab house can use it?
Gerbers only give 2D info, they don't specify anything about where to
mill or route a channel into the PCB.  Or should I define a separate
"mill" layer, and call out the milling depth in the fab drawing?

*  Is it possible to capture this milling info using PCB?  I guess I
can just draw tracks on the "mill" layer . . . . . right?

*  Which PCB houses do this kind of work?

I'd prefer to hear from folks who have actually had this type of job
done, rather than just guesses or hearsay.  OTOH, all suggestions are
welcome.

Cheers and thanks for any info,

Stuart


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