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I'm designing my first PCB (2-sided) and can't quite understand. I'm going to be soldering the through-hole components myself such as the resistors. Typically, I put a leg through the hole, heat them, and let the solder flow.

Now the way I have it, the 5 V and signal traces would be on the top, go through a resistor, and then the resistor would connect to GND. I've seen a lot of recommendations for ground/Vcc planes.

But if I use a through hole resistor and solder it from underneath the board where I have a ground plane, would I be shorting one side? When soldering the hole, do I actually need to ensure it doesn't reach the top layer? Or are there gaps between the planes/holes?

For example, do I actually have to solder one leg of the resistor on the top, and the ground side from the bottom?

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  • \$\begingroup\$ The whole hole is coated in copper, so do not short the back side of the hole to another net. Typically design software will prevent you from doing this anyway. \$\endgroup\$ Jan 26, 2023 at 1:45
  • \$\begingroup\$ @user1850479 thanks! im using EasyEDA. each hole is only connected either to a ground on bottom, or to a signal on top. I was worried that when soldering a resistor i could only solder it to the top or bottom of the pad. when i do a ground plane i didnt necessarily see how it connected to the pad so thats what worried me \$\endgroup\$
    – D P
    Jan 26, 2023 at 1:50
  • \$\begingroup\$ The plane should be covered with solder mask and a gap around the through hole to prevent shorting. Software typically does this automatically when you put a through hole over a plane that is on a different net. \$\endgroup\$ Jan 26, 2023 at 2:09
  • \$\begingroup\$ @user1850479 thanks so much! perfect description! \$\endgroup\$
    – D P
    Jan 26, 2023 at 2:23
  • \$\begingroup\$ Yes, there are gaps between the plane and the holes to avoid shorting. \$\endgroup\$
    – user57037
    Jan 26, 2023 at 2:39

3 Answers 3

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The “planes” are that by name, but in reality they are complex polygon fills that connect to the pads that have the same net. So, if you place a GND plane on, say, the bottom side of the board, it will only connect to GND pads and nothing else. The pads are always connected top-to-bottom since the holes are metallized. The pads that are on any other net will have an isolation gap around them and won’t be connected to the plane. It also will “flow” around and be isolated from any traces that may be on the same layer and aren’t on the same net as the polygon fill.

In many CAD programs the fills have to be regenerated as the components and traces are moved/changed. That’s mainly because the data structures needed for real-time polygon fill updates are more cumbersome to design. Modern CPUs are more than capable of keeping those fills updated as you modify the rest of the layout, just that it’s way more work to make it work :)

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  • \$\begingroup\$ If I may add: pads/holes that are to be connected with the GND plane need to be done so through "thermal relief", a couple of traces (4 typically, like a cross) across the isolation gap. Otherwise the GND plane will absorb all heat from the soldering process and make hand soldering in particular a real pain. \$\endgroup\$
    – Lundin
    Jan 27, 2023 at 7:20
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The PCB CAD program should place pads isolated from the ground plane for any component leads or vias that do not connect to the ground plane, so you can solder the leads on the bottom.

If the board is made by a commercial shop, all through holes will be plated so the top and bottom pads for a component lead will be connected. (For a home-brew board the holes will not be plated, so no connection.)

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You create a multilayer pad and it's automatically manufactured with a plated through hole, and the software will only allow you to connect the pad to one net.

If you want something else (like two pads on either side with an unplated hole between) it's possible, even in EasyEDA, but you have to jump through some hoops and it will "look wrong" so there's always the risk it might get fixed for you.

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