On Mon, 6 Dec 1999 15:29:33 -0700, you wrote:

>>> Can anyone tell me how plated-through holes are done on pcb's?
>
>I have used the Multicore 'Coperset' system.  They extrude solder in rods of
>the appropriate diameter and electroplate copper onto those rods.  Then they
>score the copper at intervals somewhat more than 1/16th inches (longer than
>a PCB thickness).  To use the system, you drill the holes EXACTLY the right
>diameter, place the board over an anvil and stick one of the rods into the
>hole.  You break off a section by bending the rod back and forth so that you
>are left with a little cylinder sticking above the board.  A sping-loaded
>punch is used to flatten that cyclinder - when you squash it length-wise, it
>gets fatter and the copper plating 'grips' the inside of the hole.  Think of
>an old fashioned thermos bottle with the lever-type rubber stopper.
>
>Anyways, when you have done all the holes, you flood both sides of each
>loaction with solder, then heat up and remove the solder.  Multicore
>suggests using solder-wick but I get better results with my vacuum
>desoldering system.  Voila!  Plated thru holes!
>
>Downsides: the orignal rods that I got weren't scored at the right distances
>(too short) and the little cylinders didn't grip the holes reliably.  I
>understand that has been fixed.  Also - its expensive and its
>time-consuming.  But it does work.
You can save a lot of money by not buying the kit - only the rod
refils. you can use an automatic pencil to dispense them 
see www.netcomuk.co.uk/~wwl/pcbs.html - scroll down to 'through
plating'