Count copper layers separately from populated sides
A single-sided PCB has one patterned conductive layer. A double-sided PCB has conductive layers on both sides of its dielectric. These terms describe the bare-board construction; they do not alone specify which side carries components or how those components are soldered.
For a two-layer board, plated through-holes can connect the copper layers. A conventional single-layer board may use nonplated component holes and does not automatically need a hole-plating process. Identify plated and nonplated holes explicitly in the fabrication data.
Compare routing and reference options
Single-layer routing can suit a circuit with modest interconnect demands, but crossings may require jumpers or a different component arrangement. Check the effect on assembly and service before treating a low bare-board cost as the lowest overall cost.
A second copper layer provides more routing choices and may support a more continuous reference region. Its usefulness depends on the actual layout. Routing many traces through a ground pour can interrupt return paths; adding copper does not automatically provide an effective reference plane.
Define materials, finish and mechanical requirements
Choose the laminate, finished thickness, copper and surface finish from the product requirements. FR-4, solder-mask color and lead-free HASL are separate specification items. A color does not establish electrical performance, and a generic material family does not define every thermal property.
Review connector holes, mounting features, current paths and mechanical support. For soldering, evaluate component pitch and coplanarity needs alongside the finish. Include the fabrication drawing, drill definition and outline in the released package instead of relying on a short product-style description.
Move to more layers when the design justifies it
If routing density, return-path control or power distribution becomes difficult, compare a multilayer option before forcing the design into two layers. Assess layout effort, board area, assembly complexity and validation as well as fabrication price.
Inspect the exported layers and drilling against the intended construction. Agree bare-board electrical test and assembly acceptance separately. Prototype findings should feed into a controlled revision; a successful basic continuity check is not proof of the complete product behavior.