The circuit board according to the present invention includes a wiring portion and a non-wiring portion, the wiring portion having a metal layer and a resin layer, the non-wiring portion having a resin layer, the resin layer at a frequency 10 GHZ having a relative permittivity of from 2 to 3 at 23° C., and the circuit hoard satisfying a relationship: (A−B)/B≤0.1 wherein A is the maximum value of the thickness in the wiring portion (μm) and B is the minimum value of the thickness in the non-wiring portion (μm).

A board main body includes first and second resin layers contacting each other and including thermoplastic resin, a first signal conductor layer on an upper main surface of the second resin layer, an overlapping region in which the first and second resin layers are present when viewed in an up-down direction, and a non-overlapping region in which the first resin layer is not present and the second resin layer is present when viewed in the up-down direction. The first signal conductor layer includes a first curved portion in which the first signal conductor layer is curved in the up-down direction such that the first signal conductor layer in the first non-overlapping region is above the first signal conductor layer in the overlapping region. The first signal conductor layer is electrically connectable to an element on the board main body in the first non-overlapping region.

A wiring substrate includes a first insulating layer with a first opening, a second insulating layer with a second opening, a high-frequency wiring layer, a first wiring layer, a second wiring layer, and a plurality of conductive pillars. The high-frequency wiring layer including a high-frequency trace is sandwiched between the first insulating layer and the second insulating layer. The first opening and the second opening expose two sides of the high-frequency trace respectively. The high-frequency trace has a smooth surface which is not covered by the first insulating layer and the second insulating layer and has the roughness ranging between 0.1 and 2 μm. The first insulating layer and the second insulating layer are all located between the first wiring layer and the second wiring layer. The conductive pillars are disposed in the second insulating layer and connected to the high-frequency trace.

A method of a circuit signal enhancement of a circuit board comprises the following steps: forming a first substrate body with a first signal transmission circuit layer and a second substrate body with a second signal transmission circuit layer; forming a first signal enhancement circuit layer and a second signal enhancement circuit layer on the first substrate body and the second substrate body; forming a third substrate body with a third signal transmission circuit layer and a fourth substrate body with a fourth signal transmission circuit layer on the carrier; separating the third substrate body and the fourth substrate body from the carrier; combining the first signal transmission circuit layer and the third signal transmission circuit layer through the first signal enhancement circuit layer; and combining the second signal transmission circuit layer and the fourth signal transmission circuit layer through the second signal enhancement circuit layer.

A signal transmission line includes a signal region that includes a signal conductor layer and insulating base material layers, and a first ground region that includes a first ground conductor layer and insulating base material layers and is located above the signal region. The signal region is not fixed to the first ground region in a first section of a base. One or more first spacers are fixed to the signal region and in contact with the first ground region without being fixed thereto, or are in contact with the signal region without being fixed thereto and fixed to the first ground region. The one or more first spacers are in the first section.

Disclosed is a flexible PCB RF cable having a ground pattern that is divided into two ground patterns, which are connected through a connection pattern arranged in an area overlapped with a signal line pattern, and thus cracks are minimized during bending. The disclosed flexible PCB RF cable comprises: a signal line pattern interposed between a first dielectric sheet and a second dielectric sheet; first and second lower ground patterns, which are mesh patterns arranged to be spaced from each other below the first dielectric sheet; a lower connection pattern connected to the first and second lower ground patterns; first and second upper ground patterns, which are mesh patterns arranged to be spaced from each other above the second dielectric sheet; and an upper connection pattern connected to the first and second ground patterns.

The insertion loss of a multilayer substrate and an antenna element is reduced. A multilayer substrate according to an embodiment of the present disclosure includes a multilayer body, a wire conductor, and a first ground electrode. The multilayer body is formed by dielectric layers being layered. The wire conductor is formed in the multilayer body, and a radio frequency signal passes through the wire conductor. The first ground electrode is formed in or on the multilayer body and includes a first surface that faces the wire conductor. The first surface includes a first region and a second region. The surface roughness of the first region is lower than the surface roughness of the second region. The first region overlaps at least part of the wire conductor in plan view in a direction normal to the first ground electrode.

A wiring substrate includes a first insulating layer with a first opening, a second insulating layer with a second opening, a high-frequency wiring layer, a first wiring layer, a second wiring layer, and a plurality of conductive pillars. The high-frequency wiring layer including a high-frequency trace is sandwiched between the first insulating layer and the second insulating layer. The first opening and the second opening expose two sides of the high-frequency trace respectively. The high-frequency trace has a smooth surface which is not covered by the first insulating layer and the second insulating layer and has the roughness ranging between 0.1 and 2 μm. The first insulating layer and the second insulating layer are all located between the first wiring layer and the second wiring layer. The conductive pillars are disposed in the second insulating layer and connected to the high-frequency trace.

A high-frequency circuit includes a first dielectric layer, a circuit layer, a second dielectric layer arranged in this order, the circuit layer includes a transmission line of a high-frequency signal and a ground pattern disposed around the transmission line. An electromagnetic wave shield is disposed in the first dielectric layer and the second dielectric layer around the transmission line. The electromagnetic wave shield includes a first ground electric conductor formed on an inner surface of at least one first hole formed to extend through the first dielectric layer without extending through the ground pattern, and a second ground electric conductor formed on an inner surface of at least one second hole formed to extend through the second dielectric layer without extending through the ground pattern. The first ground electric conductor and the second ground electric conductor are each electrically connected to the ground pattern.

A signal transmission circuit includes a printed circuit board including a surface layer including a signal transmission path that transmits a signal, a signal line through hole that connects the signal transmission path with a signal layer arranged in an inner layer of the printed circuit board, a ground layer of the inner layer of the printed circuit board that forms a return current transmission path for the signal transmission path, and a ground through hole that is connected to the ground layer adjacent to the signal line through hole. A ground pattern including ground areas disposed with a certain distance therebetween and a side ground area connected with at least one end side of the ground areas is disposed at positions of both sides of the signal transmission path. The ground through hole is disposed to connect the ground pattern with the ground layer.