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I am new to PCB design and I want to understand to understand how many layers to choose. I just know more layers helps to make the routing easy but I don't understand what is power plane, ground plane etc and how they are related to the traces which are going in the PCB. I have a circuit in mind, it is Double Pulse Test done at 100 VDC and operating current in the setup around 30 A.

What would be a decent choice regarding numbers of layers?

enter image description here

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    \$\begingroup\$ Tell us more about your circuit? Is it an SMPS? High speed communication? RF? \$\endgroup\$
    – winny
    Nov 23, 2023 at 11:31
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    \$\begingroup\$ Generally you want to use as few layers as you can while still meeting other requirements. More layers is more expensive. \$\endgroup\$
    – Hearth
    Nov 23, 2023 at 14:43
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    \$\begingroup\$ A lot depends on your market and cost constraints, how complex your design is, and what your packaging looks like. Most of our power supplies use a minimum of 10 layers, but PWB cost is not a big cost factor in these designs. \$\endgroup\$
    – SteveSh
    Nov 24, 2023 at 19:13
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    \$\begingroup\$ I would start off with 6 2-oz copper layers (because of your current requirements). You then may be able to reduce it to 4 layers after layout and routing. \$\endgroup\$
    – SteveSh
    Nov 24, 2023 at 19:16
  • \$\begingroup\$ @SteveSh what about just 2 layers to start from? \$\endgroup\$
    – Andr7
    Nov 25, 2023 at 19:34

3 Answers 3

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More layers = more cost, in general.

  • 1 layer: only for the limited cases of mass production where saving cents per unit counts, or for home-etched PCBs. Often have to use link wires to join up parts that cross on the board, which you'd normally do on another layer if you had one. Also for some power supplies due to isolation and/or extra thick boards for support of big mechanical components like transformers.

  • 2 layers: the cheapest common format. The bread-and-butter of budget PCB houses.

  • 4 layers: used where 2 layers aren't enough, or you need extra power or ground planes for high speed circuits. Having power/ground planes can also make routing complex boards easier, since power/ground is always close at hand on the inner layer, rather than having to run a track on the surface.

  • 6+ layers: when you have too much that won't fit in the space available on 4 layers.

I would start at 2 layers and only increase the number of layers if you can't route your board in the physical space you have available. Your board house will have design rules (eg no tracks narrower than 0.2mm, spacing between tracks must be more than 0.15mm, minimum hole size 0.2mm) which will constrain how small you can make them, so going to more layers allows you an alternative in case you bump into these limitations. Or find another board house with tighter design rules.

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  • \$\begingroup\$ Thankyou! @user1908704 , should I keep the bottom layer only for High voltage ground? How should I go? \$\endgroup\$
    – Andr7
    Nov 27, 2023 at 10:06
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Most designs need only four layers if you need more for current carrying capacity then increase the thickness and get more than one ounce copper weight when you order the PCB.

Typically only high speed and high density PCB circuits need to have six or more layers.

BGA needs typically six layers.

If you only have one component you probably would not need anything more than four wearers just use a higher copperweight

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Because you are doing Double Pulse Testing the duty cycle is very low. While I think you should use 30A traces, it is not necessary.
You need to make a very small loop from C1,2, Q1,2, R3. Wide traces or large copper areas. L1,2 can have longer leads, but keep wide traces. Do not use thin traces on U2_outb to Q2 Gate.
The VSSB needs to connect to the Source of Q2 and not to R3_bottom.

enter image description here

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  • \$\begingroup\$ Thank you so much @ronsimpson! If I go with 2 layers, how do I decide which components to place where? and which traces to go through where? \$\endgroup\$
    – Andr7
    Nov 25, 2023 at 19:38
  • \$\begingroup\$ Also, if I do the connection you mentioned, what about the drain current measurement through R3? \$\endgroup\$
    – Andr7
    Nov 26, 2023 at 5:09

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