I was wondering if someone can give me advice in routing this PCB.

enter image description here

The PCB contains several triacs driving AC loads and digital end which contains a micro and several digital I/Os. So far, I have decided on the following:

  • Use 18 AWG wire to connect the LIVE via the spade terminals.
  • Use 5oz copper on the top layer to reduce the track width for the high current tracks for triac output to AC load spade terminal.
  • Solder Y caps underneath the board with insulation and hot melt glue.
  • Use 4 layers
  • First layer contains AC tracks on the mains side and DC signal tracks on the digital side.
  • Second layer contains ground layer on the digital side with some signals.
  • Third layer contains digital VCC layer on the digital side with some signals.
  • Fourth layer contains signals on digital and secondary voltage from the transformer.

I have few constraints in the design like the placements of the headers and AC spade terminals cannot be modified plus the board size cannot be changed. I have placed the heatsink/triacs and spade terminals so I can route the signal tracks to the optocouplers and secondary output of the transformer via the middle of the PCB. I am trying to ensure there is a least 2.5mm separation for the AC tracks.

Do anyone see any issues or problems with this layout or have any suggestions?

Regards Paul

  • \$\begingroup\$ I am going to route the AC side on the bottom layer so I can route the digital side on the top layer. \$\endgroup\$
    – Paul
    Commented Oct 13, 2013 at 1:41
  • \$\begingroup\$ How big these currents are? Actually I am not sure you need 4 layers in this PCB. \$\endgroup\$
    – johnfound
    Commented Oct 13, 2013 at 6:15
  • \$\begingroup\$ 15A 230V. The main reason why I chose four layers is to be able to route the optocouplers input/ground and secondary output of the transformer to the digital part of the circuit. \$\endgroup\$
    – Paul
    Commented Oct 13, 2013 at 10:40
  • \$\begingroup\$ The dimension of the board is 240mm x 30mm as an additional information. I have routed the 4 layer board and asked the PCB manufacturer for a quote to see how much it will cost. \$\endgroup\$
    – Paul
    Commented Oct 13, 2013 at 10:42
  • \$\begingroup\$ Related: This excellent reference - TI Analog Engineer’s Pocket Reference - 4th edition provides some useful information on PCB track current/ voltage drop / heat / fusing issues. Especially pages 55-68. \$\endgroup\$
    – Russell McMahon
    Commented May 5, 2016 at 5:31

1 Answer 1


On 15A/230V you need 2mm track width and 2mm of clearances (5Oz/ft2 Cu and 20*C temperature rise).

Although, IMO, using 0.2mm copper PCB is pretty over engineered. The same results can be reached with more careful trace design.

  • \$\begingroup\$ You are probably right. Just by looking at the PCB, I notice I can shift one of my spade terminals and reducing the track length. I could also use both top and bottom layers to route the high current tracks. \$\endgroup\$
    – Paul
    Commented Oct 13, 2013 at 11:10
  • \$\begingroup\$ Reduced it down to two layers. Just finding a way to supply the current. \$\endgroup\$
    – Paul
    Commented Oct 13, 2013 at 11:44
  • \$\begingroup\$ Ok got it down to 2oz of copper and two layers now. This will be a significant drop in cost for the manufactured board. \$\endgroup\$
    – Paul
    Commented Oct 13, 2013 at 12:08
  • \$\begingroup\$ @user468662 Good work. Now it sounds as a reasonable design. :) \$\endgroup\$
    – johnfound
    Commented Oct 13, 2013 at 12:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.