"Z" wire for double sided PCBs

[J-P-G]

Hi,
I soldered together the Noise Toaster

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most of it is working. some of it, like the white noise generator, is not working, so Im troubleshooting it.

I went back through the instructions and diagrams and read the section below, which I didnt remember reading before:

"double sided PCBs have plated through-holes, which are often used to route circuit connections between the top and bottom sides of the board. These top-to-bottom circuit connections are called vias. All pads on the board not used for component leads must be drilled and have a 'Z' wire inserted and soldered. A 'Z' wire is a piece of solid 22 or 24 gauge hookup wire that is inserted through the pad's hole and then bent at a 90-degree angle on the top and bottom sides of the PCB. Trim any excess wire after bending, make sure the ends are not shorting to adjacent pads, and then solder the 'Z' wire top and bottom."

First, why would there be vias that wouldnt be used for component leads on the board? If the board was professionally manufactured, wouldnt all vias be used for component leads?

Next, what is the purpose of the 'Z' wire? It seems like it's supposed to continue the flow of electricity from the top of the board to the bottom or vice versa, but the way it's described in the instructions is confusing. It seems like that the 'Z' wire should be connecting two pads.

Last, since the PCB is professionally manufactured, wouldnt all of the vias already be connected with the top and bottom copper layers?

I searched online for other people talking about 'z' wires but I havent found anything.

 

[Nigel Goodwin]

First, why would there be vias that wouldnt be used for component leads on the board? If the board was professionally manufactured, wouldnt all vias be used for component leads?

Certainly not, why would even imagine such a thing? - if they were all used for components you wouldn't even need vias, you could simply solder top and bottom.

However, if it's a professionally manufactured PCB, then it should have all required vias anyway, the technique of soldering wires through (never heard the term Z wires) if for home made PCB's where you can't plate through the holes.

Easy to check, just use your meter on low ohms to check for continuity through the vias.

 

[rjenkinsgb]

I've never heard of "Z wires" either.

You used to be able to get a thing called "track pins", which were something like shorter and slightly tapered veropins in continuous break-off lengths - you push the pin in one side, it wedges, you break off the rest of the strip and solder both sides.

T1559-01 | PC TRACK PINS 0.84MM | RS

uk.rs-online.com

Without those:
Rest the board on something so it's got a slight space under it, drop offcuts of component leads in the via holes, solder the visible joints then turn the board over and solder all the ends sticking through. Then trim the excess bits.

Vias are a fundamental part of PCB design; the higher component the density of the board, typically the more via holes needed.
They are also used for heat transfer and to electrically bond two or more layers of tracks for higher current capability or impedance control.

eg. This looks to be something like a part of a PC motherboard, probably below one of the large surface mount ICs:

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