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I guess these are two very trivial questions, but I couldn't find any conclusive answer.

Below is a part of a PCB I want to create (my first ever), a SOT23 transistor and a 0805 resistor. .

My questions:

  1. Are the red trace lines really on top of the surface, or are they underneath? Meaning, if my soldering wouldn't be so well and I spill a bit over the red traces, would it matter (since they are on top of the PCB) or are they underneath and doesn't matter at all? In case they are on top, I might need to increase the distance between traces and components.
  2. Since pin 5 of the SOT23 is connected to pin 1 of the resistor, can I just put a blob of solder between 1 and 5 (when I put them even closer together) ? Since I'm not sure of above, I will either have one or two paths (which both are ok I guess).

(note: my PCB will have only two copper layers, one F.Cu for signals/VCC and one B.Cu layer that is mostly ground).

enter image description here

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    \$\begingroup\$ I'm not sure what you're asking, but F.Cu is the front copper layer, the only things on top of it are soldermask, solder paste, and silkscreen layers \$\endgroup\$ – Hearth Jun 26 at 12:48
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    \$\begingroup\$ You say you will have only two copper layers, but then list three. What is L.Cu? \$\endgroup\$ – Hearth Jun 26 at 12:49
  • \$\begingroup\$ @Hearth Sorry my mistake, L.Cu is removed \$\endgroup\$ – Michel Keijzers Jun 26 at 12:51
  • \$\begingroup\$ @Hearth but will the soldermask, the solder paste, and silkscreen layers isolate the solder I add on top to solder my components? \$\endgroup\$ – Michel Keijzers Jun 26 at 12:52
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    \$\begingroup\$ What do you mean by isolate? The solder paste certainly won't, because that is the solder you add on top. \$\endgroup\$ – Hearth Jun 26 at 12:53
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Even if you put a bit too much solder on the pad, or spill it, it won't matter. This is because of the solder mask, which is the (typically) green stuff you see on PCBs, although it can differ in colour.

On the pads of your components, you will notice a thin purple border, which indicates the solder mask is not to go there, leaving those copper pads exposed. You seem to have a few layers with similar colours, and I don't use KiCad, but on my package it is just called the solder resist layer.

So yes, the copper layer is just under the surface, as when it is manufactured, there will be a solder mask layer put on top, as well as any silk screen you have on there too.

There is nothing stopping you from putting a blob of solder between the resistor and the SOT23-5 pin, but I would place it close to the pad, and have a short trace connecting them.

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    \$\begingroup\$ F.Mask and B.Mask are the solder resist layers. \$\endgroup\$ – Hearth Jun 26 at 12:54
  • \$\begingroup\$ Thanks for the clear answer! \$\endgroup\$ – Michel Keijzers Jun 26 at 12:56
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    \$\begingroup\$ @MCG I'm using 3 pin transistors (I couldn't find a 23-3 footprint in KiCad), so I will use only 3 legs, that means I can solder the three legs together on one side, I guess that will make it much easier. Than only I have to be careful for the remaining two legs. I couldn't easily found bigger transistors footprints (unless I use through hole). \$\endgroup\$ – Michel Keijzers Jun 26 at 13:06
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    \$\begingroup\$ SOT23-3 and SOT23-5 aren't that difficult to solder, either. A roll of solder wick comes in handy, though, to clean up accidental bridges. \$\endgroup\$ – JRE Jun 26 at 13:19
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    \$\begingroup\$ @JRE indeed, they are not difficult, but there are easier packages to solder by hand. Good tip about the solder wick though. \$\endgroup\$ – MCG Jun 26 at 13:21
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The red is the copper layer as it will be on your board.

There will normally be a coating of solder mask on top of that.

The solder mask will prevent most accidental bridges.

You should in any case have traces for all connections, even if you intend to make a solder blob bridging the two points. KiCad will complain if you don't place a trace for every electrical connection. This is a good thing - it makes sure you really do connect things as they are specified in the schematic diagram. Never turn off the warnings. They might get on your nerves, but they will most certainly save your bacon.

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  • \$\begingroup\$ Thanks for clear answer, and yes, I keep always all warnings on. It is mostly about not having to care much not putting accidentally some solder blob on the traces, so I can keep the traces close to the components. \$\endgroup\$ – Michel Keijzers Jun 26 at 12:57
  • \$\begingroup\$ +1 from me, very important point about making sure you have a trace for every connection! \$\endgroup\$ – MCG Jun 26 at 12:58

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