Identification of Top and Bottom Sides of Single-sided Boards

Boards with only one copper layer are considered to be single-sided boards. These boards might have two component layers. Identifying the top and bottom sides of these boards depends on the relative order of the non-copper layer to the copper layer on the non-copper side and the copper layer side.

Non-copper layer side — If the non-copper layer is above the copper layer, the side of the non-copper layer is Top. If the non-copper layer is below the copper layer, the side of the non-copper layer is Bottom.
Copper layer side — The software checks for the existence of one of these layers in this order. Once it finds a layer above or below the copper layer, it determines that the copper layer is Top or Bottom: Solder mask layer, Solderpaste layer, Silkscreen layer, Component layer/s.