Definition of a "single-sided" or "one-layer" printed circuit board in the context of Autodesk Eagle 9.6.2?

Question

I am having trouble understanding the definition of a "single-sided" printed circuit board (PCB). Here are the situations I am confused about.

1. Through hole components on the top layer only and traces on the bottom layer only.

2. Both the through hole components and traces are on top layer only.

3. Traces on both the top layer and the bottom layers and the through hole components only on the top layer.

I have been assuming that only numbers 1 and 2 above are considered "single-sided" because the traces are only on one side of the board. Am I mistaken?

Does the concept of "single-sided" or "double-sided" refer to the placement of the traces only?

In addition, does "single-sided" mean "one-layer"? Are these synonymous terms?

Lastly, could someone explain the distinction between the use of the word "layer" in the above context and in the context of the Eagle software in which there are many "layers" in the PCB layout editor?

Answer 1

In Eagle the word layer refers to Computer Aided Design layers. These can be copper layers but there are also layers for things like silk screen and outline.

Single sided PCBs refer to copper on one side only, components can be placed on both sides. It is common practice to have components on only one side.

Layer when talking about a pcb refers to a copper layer only. A multilayer board will consist of a top layer a bottom layer and a number of internal copper layers.