Printed Circuit Board Holes

Drilling holes in PCB's is not complex: put a drill bit in a drill press, position the drill where you want the hole and pull the lever slowly and gently until the drill passed through. If you don't have a drill press, you can make a PCB drilling machine from a dremel or other high speed rotary tool mounted vertically to a hinged piece of plywood or the like. As long as the hinge is a couple of feet back from the bit, the arc of the drill will not be significant. If you want to get fancy, use two hinged pieces in a parallelogram arrangement. A spring or two can help make the drill easy to lift.

Vias

The industry standard connecting between multiple layers for commercially made PCBs is plated through holes. There are a number of alternatives:

Dwayne Reid of Trinity Electronics Systems Ltd Edmonton, AB, CANADA says:

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.

Tony says:

What you could do is use a PC Board repair kit. They have small, metal, funnel shaped things that are hollow inside, actually like a real funnel:

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\         /
 \       /
  |     |
  |     |

You drop these into your thru holes. Then you take two pointy headed tools, and you press one into the top of the 'funnel' and one into the 'tube' end of the funnel. You expand the bottom of the tube and have a thing that looks like an empty thread spool thru your hole.

      -----------
     \           /
-----|          |---------
     |          |          PC Board
-----|          |-----------
     /           \
      -----------

We used them in the USAF to repair boards that a via or pad disintegrated due to heat.

Alan King says:

Don't forget you have another option, that may be viable since you described it as a lot of address/data lines. Old useless chips (or maybe even the blank test ones some places sell for soldering practice) make good via makers if you have a bit of flexibility in layout and can align your holes. Put them on .1" centers, bend the leads straight out from the chip so they'll be easier to cut, and solder in. Solder both sides and cut off the rest of the leads and chip. Is a heck of a lot faster than placing single wires by hand. Can use header etc what ever you have on hand, I just usually have junk chips. 50 is a bit much, but if you can lay it out so you have 2 rows of 20 and use an old 40 pin chip it can be managed..

Other methods and thier limitations:

• Conductive inks can be painted into the holes and do work, but are delicate, unreliable, and can not be solder through.
• Carbon processes use a micro etch step which involves covering the pcb with a plastic sheet, drilling, squeeze in ink, then vacuum and oven cure.
• Conductive polymer is a simple procedure, but the chemical is volatile and has a very short shelf life so it must be replenished often.

Also:

• Layers has tips for finding how many layers you need, and what to put on each layer

See also:

• http://retromaster.wordpress.com/pcb-making/ Brilliant system for making PCBs including vias made from short lengths of copper wire pressed to form them into the holes and connect to the traces at the top and bottom.+
• http://www.lpkfusa.com/Store/ProductDetail.asp?ProductID=147 Very expensive ($475 as of 2010/05/13)
• http://voodooengineering.com/index.php/pcbprocess/plating Making actual copper plated through holes. Uses just the chemicals and anode from the kit at:
  http://www.caswellplating.com/kits/copper.htm the crystals are $60, the brighteners are $12 combined and the annode is about $26, so just under $100.
• http://www.thinktink.com/frstpage.htm
  http://www.thinktink.com/stack/volumes/voli/store/catalog.htm They have an interesting conductive ink
• http://www.ping.be/~ping0751/pcbzone.htm
• http://www.jlc.net/~preid/pcbpro/indexpcb.htm

Comments:

• Your local fabric store carries "sequin pins". These are small (0.018" diam by 1/2" long) pins with small heads. $3 or so for about 400. Drill a 0.022-0.024" hole, push the pin thru, and solder in place. Cut off the sharp end, and you've got a FAST, CHEAP, and EASY feedthru.+

Questions:

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