PCB Layout Perspective - Is it how you look at it?

When you are laying out a PCB, do you lay it out in eschema from the perspective of looking at if from the top (component side) or from the perspective of looking at the back of the board ?

Let’s assume a single sided board with all the tracks on the back, but components soldered to BOTH sides.

Thanks

Well, when I lay it out in Eeschema (or any schematic capture program) I lay it out in what makes logical sense for the function of the circuit. Very little effort made to make it match any physical layout.

But if you just used the wrong module name and instead meant in laying out in pcbNew… There I lay out the circuit as if looking down from top/front, or component side. This gets a little murky because you actually specify components soldered to both sides… This distinction is much easier with THT only designs with components on one side of the board. There it is very clear the difference between the component side and the solder side. Often the component side would also be called the front or the top, and the solder side would also be called the back or bottom side.

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Yes I would say it may be easy to go wrong if you rely too much on the schematic to guide component placement on the pcb. My best example is that power supply bypass capacitors should usually be as close as possible to the IC supply pins but are typically an afterthought on the schematic.

Why would you use a single sided (copper) board with parts on both sides? Are you going to etch it yourself? For what I see in small quantity builds I am not aware of any price advantage of single sided copper versus two sided. Most often I would put parts on one side only but nothing wrong with parts on both sides if you see advantages to doing so.

This is actually the PCB from a very popular Battery Charger sold on Amazon and ebay

Like SembazuruCDE in eeschema I don’t think about sides, it’s a schematic, not a realisation. In pcbnew I do whatever feels natural. I’ve put components on the back too, a LED display board of mine has the LEDs in front but most of the other discretes on the back. I just have to flip those components when laying out. It’s pretty easy to spot in the 3D view if you forgot to flip any.

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The schematic and the PCB are made with completely different rules in mind.

For a schematic, the main purpose is to be clear and easy to read by humans. Even whether the schematic itself “works” or not is secondary to that. The reason for this is simple to understand: If the schematic is made “correctly” but it’s difficult to read, then it’s also difficult to verify if the connections themselves are correct. When a schematic is drawn in a logical and easy to comprehend way, then errors in the wiring between parts are generally easy to spot.

For a PCB, the rules are completely different.

  • EMC considerations.
  • Layout that minimizes track length, especially for high current tracks.
  • Sometimes a set of tracks must have specific lengths for high speed digital interfaces. (For example DDR memory interfaces).
  • Solve the puzzle of “crossing track on the same layer”.
  • Separation of digital and analog stuff.
  • Placement of heatsinks in convenient and effective places.
  • Placement of connectors in logical places.
  • Placement of electrolytic capacitors where they stay cool.
  • Physical constraints, such as 4 opamps in a single IC. Wires that are bundled in a connector, The size and form of the enclosure, etc.
  • Many, many more…

So the main purpose of the schematic is to make it easy to understand for the people reading it, while the PCB layout has lots of rules that affect the quality of how good the end product works. A bad PCB layout can even cause a circuit to not function at all.

A big of digging in my memory and this forum brings up your older thread:

There too you are making some mental connection between the schematic and the PCB that simply does not exist.
Because the goals of the schematic and the PCB are so vastly different, the only link wetween the schematic and the PCB is the mapping from schematic symbols to footprints, and the netlist.

So stop doing that. There is no correlation between placement of parts on the schematic and the PCB. There is no “backside of the schematic” on which to place wires, etc. So stop pretending there is. The whole concept of thinking along these lines is flawed.

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I am laying out PCB in PCB editor and not schematic editor.
For me it is not important if elements are at top or at bottom. You can easily get used to work with elements at bottom. My decision is typically based on other conditions.
For example in one our product I have two PCBs in paralel connected by long pin-headers + pin sockets and at each PCB elements are toward the second one. So to not need to mirror that connector arrangement at one of PCBs (to minimize chance of bug) I have one of them designed with elements at top and other at bottom.
The other rule can be to look at PCB the same way as user will be looking at it. It helps for example to imagine what is the correct place for regulation elements or LEDs and displays. May be i think that way because I have never used any 3D design software. Since I start to use KiCad I also learned a little of FreeCAD but till now I use it sporadically and only for 3D models of elements.

I believe the answer is “you don’t”.

The schematic is (hopefully) drawn with the “circuit flow” in mind. In a simple circuit this usually means the inputs are on the left of the schematic, proceeding through the circuitry with the outputs on the right.
Often this makes sense on the PCB, however device size, pin placement etc doesn’t make that the case.

It sounds like you might be copying a published design. In which case you will need a copy or some information on the suggested layout.

In any case the layer location of a section of circuitry is never shown in the schematic diagram. If the physical layout of a group of components is important the requirements will be in a note.

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And if you’re using an IC with multiple identical sections (glue logic, dual or quad op-amps, etc.), you’ll probably end up having to swap sections around to get an arrangement that plays nice with the routing desired.

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Why not post your schematic here? Depending upon the type of design, there is a good chance that I and others on this discussion can give you some general pointers regarding how to lay it out.

One thing…as a general rule especially for beginner circuits, a solid ground plane (as solid as possible) on the back side of the board is almost always a good idea. Unless there is a good reason to the contrary, do a double sided board with a solid ground plane.

To keep the ground plane solid, I will often use some sort of jumpers to hop over traces. In an SMT design I will use a 1206 size 0 ohm chip resistor. In thru hole you can use a 1 cm long (for example) wire. This is just an idea and preference. But it is a method which can work well.

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