Printed circuit board, design method thereof and mainboard of terminal product

A mainboard of a terminal product, comprising a basedband or radio frequency core chip, wherein:

• the mainboard of the terminal product is a four-layer printed circuit board comprising surface layers and two inner layers between the surface layers;
• the surface layers comprise a top layer and a bottom layer, the top layer is configured as a primary reference ground layer consisting of a ground copper sheet with a large area, the bottom layer is interconnected with the top layer by through vias, and the inner layers are primary wiring layers where wiring areas are divided by functions;
• a distance between the inner layers is at least twice a distance between each of the surface layers and the inner layers adjacent to the surface layer;
• the wiring area at each of the inner layers corresponds to the ground copper sheet with the large area at a layer adjacent to the inner layer or vertically arranged traveling lines at the layer adjacent to the inner layer;
• and
• a blank area at the inner layers other than the wiring areas is grounded, the top layer is arranged as a keyboard arrangement side of the terminal product, the bottom layer is arranged as a primary device arrangement side of the terminal device, and audio lines are arranged at the inner layer adjacent to the top layer, and correspond to the keyboard arrangement side and avoid a projection of a keyboard pad at the inner layer adjacent to the top layer.