Circuit board assembly, manufacturing method, and electronic device
A circuit board assembly, a manufacturing method are provided. The circuit board assembly includes a flexible printed circuit board and a printed circuit board, a pad for disposing a welding piece is provided on the printed circuit board, the flexible printed circuit board includes a main body and a welding part disposed on an inner wall of a through hole of the main body, the through hole includes a recessing part and a connection segment connected to a bottom wall of the recessing part, the recessing part is disposed on a side that is of the connection segment and that is away from the pad, 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 overflows into the recessing part through the connection segment, and welds the welding part to the pad.
1 . 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, a welding part, and a through hole that extends through 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.
2 . The circuit board assembly according to claim 1 , wherein the exposure surface is parallel to a board surface of the flexible printed circuit board; or the exposure surface is obliquely disposed on a board surface of the flexible printed circuit board.
3 . The circuit board assembly according to claim 2 , wherein the through hole is a stepped hole, an end of a larger diameter of the stepped hole forms the recessing part, an end of a smaller diameter of the stepped hole forms the connection segment, and a stepped surface of the stepped hole forms the exposure surface.
4 . The circuit board assembly of claim 1 , wherein the welding piece in a molten state may overflow into the recessing part through the connection segment and the exposure surface; and an overflow height of the welding piece in the recessing part is greater than or equal to half of a recessing depth of the recessing part.
5 . The circuit board assembly according to claim 1 , wherein a minimum radial dimension of the recessing part is greater than or equal to twice an inner diameter of the connection segment.
6 . The circuit board assembly of claim 5 , wherein a distance between a circumferential edge of the recessing part and an edge of the pad is less than or equal to 0.05 mm.
7 . The circuit board assembly of claim 1 , wherein the recessing part has different radial dimensions in a board thickness direction perpendicular to the flexible printed circuit board.
8 . The circuit board assembly according to claim 1 , wherein the recessing part and the connection segment are coaxially disposed.
9 . The circuit board assembly according to claim 1 , wherein the welding part is attached to the inner wall of the through hole.
10 . The circuit board assembly according to claim 9 , wherein two ends of the welding part extend outward in opposite directions along the inner wall of the through hole, and an end of the welding part extends to a board surface of the main body.
11 . The circuit board assembly according to claim 9 , wherein the welding part is a copper welding layer or a copper alloy welding layer.
12 . The circuit board assembly according to claim 1 , wherein the welding piece is solder paste.
13 . 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.
14 . The electronic device according to claim 13 , wherein the exposure surface is parallel to a board surface of the flexible printed circuit board; or the exposure surface is obliquely disposed on a board surface of the flexible printed circuit board.
15 . The electronic device according to claim 14 , wherein the through hole is a stepped hole, an end of a larger diameter of the stepped hole forms the recessing part, an end of a smaller diameter of the stepped hole forms the connection segment, and a stepped surface of the stepped hole forms the exposure surface.
16 . The electronic device of claim 13 , wherein the welding piece in a molten state may overflow into the recessing part through the connection segment and the exposure surface; and an overflow height of the welding piece in the recessing part is greater than or equal to half of a recessing depth of the recessing part.
17 . The electronic device according to claim 13 , wherein a minimum radial dimension of the recessing part is greater than or equal to twice an inner diameter of the connection segment.
18 . The electronic device according to claim 17 , wherein a distance between a circumferential edge of the recessing part and an edge of the pad is less than or equal to 0.05 mm.
19 . The electronic device according to claim 13 , wherein the recessing part has different radial dimensions in a board thickness direction perpendicular to the flexible printed circuit board.