Circuit board assembly, manufacturing method, and electronic device

An electronic device, comprising:

• a circuit board assembly comprising a flexible printed circuit board and a printed circuit board, wherein a pad for disposing a welding piece is provided on the printed circuit board;
• the flexible printed circuit board comprises a main body including a flexible dielectric layer and a plurality of metal wires disposed on the flexible dielectric layer, and a welding part, a through hole that is formed in the flexible dielectric layer of the main body and that connects board surfaces of the flexible printed circuit board is provided on the main body, and the welding part is disposed on an inner wall of the through hole;
• the through hole comprises a recessing part and a connection segment that are sequentially connected in a board thickness direction of the flexible printed circuit board, the recessing part is located in the main body and is disposed on a side that is of the connection segment and that is away from the pad, and the connection segment is located in the main body and is connected to a bottom wall of the recessing part;
• and
• an end that is of the connection segment and that is away from the recessing part faces the pad, so that the welding piece welded to the pad overflows into the recessing part through the connection segment, and welds the welding part to the pad;
• wherein the pad is recessed within a bottom portion of a cavity of the printed circuit board, and the welding piece enters a top portion of the cavity to weld the welding part to the pad;
• wherein a side that is of the recessing part and that is away from the connection segment is an open end, and a radial dimension of an open edge of the recessing part is greater than an inner diameter of the connection segment;
• and
• wherein at least a part of an inner wall of the recessing part forms an exposure surface to expose the welding piece, and the exposure surface is disposed on an outer side of a peripheral edge of an end of the connection segment.