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I am working on a 4-layer PCB where an electric current of 40 A - 12 VDC needs to pass through 2 traces (for 2-3 cm) between two through-hole components, for 1 minute every hour. 200 units of the electronical cards will be produced, thus I am looking for an "industrial" way of handling this current.

Based on PCB trace width calculators (eg. https://www.4pcb.com/trace-width-calculator.html), with a typical external layer of 18 um, in order to keep a rise in temperature below 10 °C, the required width of the traces is 94.7 mm.

  • By increasing the width of the external layers from 18 to 35 um, the width becomes 48.7 mm. The price increase is negligible.
  • By routing the traces on the top and bottom layers, the width becomes 24.4 mm.
  • By routing the traces on both inner layers, the required width reduces a bit (I have not computed it, maybe around 20 mm).

And now I'm stuck ! I do not have enough space to route 20 mm traces, let's say 8-9 mm at best... How can I solve this ?

  • I cannot increase the acceptable temperature rise (I am inside a housing with sensitive components)
  • I could use a 6-layer PCB and route traces on all layers but it will not meet the required width still
  • I could increase the width of the copper layers to 70 um, but I think it is too expensive : with my current EMS, it triples the price of the PCB !
  • I could remove the solder mask on the traces and ask the EMS to add solder paste during assembly but this is not great for production and it would require LOTS of tin
  • I could use copper busbar to be soldered or screwed onto the traces but I was not able to find one off-the-shelf that would suit my needs so I would need to design one myself which is bad.
  • I could ask the EMS to solder a simple wire that can handle 40 A... Is it a good solution for "mass" production ?

I'm thinking the last solution is the least worst... Do you have a better way of handling this ?

Thanks !

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    \$\begingroup\$ Is the "1 minute every hour" guaranteed, so that it has 59 minutes to cool down in between? Maybe you can allow the temperature to rise more than 10°C while the current is flowing. \$\endgroup\$
    – Theodore
    Oct 25, 2021 at 19:03
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    \$\begingroup\$ 200 units is a pretty tiny number, so your wire solution does not sound too bad. Maybe you could eschew the traces and just use jumpers, maybe like these. The advantage of not having traces is the lack of fire if the jumper is knocked off or forgotten. \$\endgroup\$ Oct 25, 2021 at 19:05
  • \$\begingroup\$ We usually just add layers with heavier weight copper - 1 oz or 2 oz being typical. But our applications are not that price sensitive, and the added cost of the PWB is negligible compared to final cost of the board assembly. \$\endgroup\$
    – SteveSh
    Oct 26, 2021 at 0:25

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To begin with, you have to use thicker copper for boards like this. If you are looking for "industrial way" of doing this, heavy copper PCB up to 6oz is usually available from manufacturing houses. Specialized houses can go even higher than that. But it is very expensive for such a small batch of boards.

If that is not enough, one common approach is to leave traces uncovered and solder copper or nickel-copper strips along them, as in example below.

enter image description here

(image by FLIPSKY)

Another common approach is to use bus bars.

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