Has anyone tried twisting very thin wires(of order 100 microns) and then sandwiching it in between 2 layers of a multilayer PCB? I have a problem of EMI and looks like twisted pair is the only solution as all means of shielding is ineffective due to DC magnetic field near field constrains.

Can experts in PCB comment on this ?

The real problem : Moving pickup coils on top of strong DC magnetic field. These induce heavy noises in a highly complex geometry problem. Of course a normal twisted pair cable would be a temporary solution but it is not robust. Also the use of Via's as twisted pair PCB was ruled out as the movement produces enough jerk to put high stresses on the via's.

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    \$\begingroup\$ Your proposed solution would be extremely expensive, if not impractical. What is the actual problem? \$\endgroup\$ – Matt Young Jan 14 '15 at 21:27
  • \$\begingroup\$ needn't be that expensive in small quantities : conventionally manufacture 2 normal (thin) PCBs, add marine epoxy, fixture to set. But there are almost certainly better solutions... \$\endgroup\$ – Brian Drummond Jan 14 '15 at 21:40
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    \$\begingroup\$ Why is a DC magnetic field affecting your signal at all? \$\endgroup\$ – Dave Tweed Jan 14 '15 at 21:45
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    \$\begingroup\$ A twisted pair jumper cable outside PCB sounds more practical. Even an optical fiber may end up being more practical. That is, without knowing anything else about the O.P.'s design and problems. \$\endgroup\$ – Nick Alexeev Jan 14 '15 at 21:45
  • \$\begingroup\$ Sounds a bit like Multiwire technology, but I don't think they ever did actual twisted pairs. \$\endgroup\$ – Dave Tweed Jan 14 '15 at 21:50

While the whole idea sounds dodgy, I don't see why you need discrete wires to make a twisted pair. Criss-crossing diagonal traces on two adjacent layers, connected at short intervals by plated-through holes will do the same thing. Think of it as a series of X's (when viewed from above), with each segment terminated by a via.

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    \$\begingroup\$ Presumably the OP wants the outer layers to shield the wires. So this same idea with buried vias would work just fine, depending on the signals on the wires. \$\endgroup\$ – Samuel Jan 14 '15 at 23:24
  • \$\begingroup\$ Use of Via's as twisted pair was the first idea but the , the pick up moves at great speed and some experts feel the mechanical stress might break the via's. Also to note in my case the PCB runs as an interconnect over length of 200mm. \$\endgroup\$ – vittal rao Jan 14 '15 at 23:25
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    \$\begingroup\$ Mechanical stress will break the vias? If that's true, the board is flexing under load, and I'd worry about the board delaminating. Use steel stiffeners, and configure them so they provide magnetic shielding along the trace lengths. \$\endgroup\$ – WhatRoughBeast Jan 14 '15 at 23:35
  • \$\begingroup\$ Re: breaking vias, then solder wires through them, or plate 'em thicker. Twisted pair fabbed on a pcb was what I thought. I wondered if you could do better than twisted pair, which is still sensitive to changing fields along the twist axis? \$\endgroup\$ – George Herold Jan 15 '15 at 0:48

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