Printed Circuit Board Holes

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  see

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:

----------
\         /
 \       /
  |     |
  |     |

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..

Markus Zingg says:

^You need a through plating station. I use one with five baths. It's actually not all that complicated, and does also not have to be expensive, but you must be prepared for initial costs of ~$1000 if you have nothing.
...
The advantage of this is that you get very consistent beautiful absolutely repeatable results. The disadvantage is that you have to buy the chemistry.
...
[ed: first you must drill the holes which are to be plated, this is before etching the artwork onto the board. Next, the chemical baths treat the drilled board.]
- The first bath micro etches the FR4 material (and of course also a little the copper but that's a side effect). The purpose of this is to assure that the palladium emulsion which is applied in the fourth bath (see below) can stick to the FR4 making it conductive to the degree needed for the effective plating process. You have to rinse the PCB with water after this step.

- The second bath is a so called pre-dip. It's a sodium chloride solution with additives and the same as the third bath, but there is no palladium emulsion in it. The purpose of this bath is to acclimate the PCB to the following bath and thereby avoiding contamination of the third, bath which is a bit critical and contains the most expensive chemistry (the palladium emulsion). There is therefore NO rinsing after this step.

- The third bath is the one making the holes conductive for the subsequent plating process. It's the same as above, but contains the palladium emulsion. The emulsion is somewhat expensive, but to give you an idea, half a litter costs ~80$, and said half litter will last you for the next ten years with a station of the size of the one I build, so costs are relative. You must rinse the PCB after this step.

- The fourth bath is hardening the palladium. This is having the effect that it sticks better to the FR4, but splitters of from the copper. Also rinse after this step.

- The fifth bath is the effective copper plating. The attached picture^ ... shows the board in this bath. You apply ~2.5 amps per square decimeter of copper material to this bath and run the PCB in there according to the thickness of copper you want to end up with. After this the plating is done. What's left is to thoroughly rinse the PCB, and then of course continue with laminating dryfilm resist, expose and etch the outer layers (or only layers in case of a double sided board).
...
Regarding "keep the holes from being etched off ". That's the point why you have to use dryfilm resist. The resist "tents" the holes (this is called tenting) and thereby protects them from being etched away. That works very reliably. You just must take care to adjust the artwork precisely with the previously plated holes. Once you get the hang of working with dryfilm resist you realize how flexible this method is and you hardly will return to anything else.

[ed: Possible suppliers of the necessary chemicals:

• Markus will be setting up a web site in the future to supply complete systems. Google his name?
• Local boardhouses, some are amazingly friendly and helpful
• Bungard Elektronik in the EU

See also:

• 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.+

  .