The outer copper layers / conductive patterns of printed circuit boards are refered as outer layers (named top and bottom). A printed circuit board has one (single-sided PCB) or two (two-sided or multilayer PCB) outer layers, which can be assembled with SMD- or THT-components.
The thickness of the copper foil (start copper) on the (FR4) material on the outer layers increases by 20 - 25µm through the galvanic procedure of the through-plating process other than on the inner layers.
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