The present disclosure discloses a multilayer circuit board comprising a plurality of metal layers, a blind via and/or a buried via, the multilayer circuit board is capable of transmitting signal between the different metal layers. The blind via has a pad on a non-opening side of the blind via. An upper or lower layer metal layer on the non-opening side of the blind via adjacent to the blind via has a first hole which is located in a position corresponding to the pad on the non-opening side of the blind via in a depth direction of the blind via; and/or an upper and/or lower layer adjacent to the buried via has a second hole which is located in a position corresponding to the pad of an upper and/or lower orifice of the buried via in a depth direction of the buried via.

A high-frequency circuit includes a first electric conductor layer, a first dielectric layer, a circuit layer, a second dielectric layer, a second electric conductor layer arranged in this order, and the circuit layer includes a ground pattern and a transmission line of a high-frequency signal. An electromagnetic wave shield is disposed around the transmission line. The electromagnetic wave shield includes a ground electric conductor on inner surfaces of a plurality of holes extending through the first dielectric layer, the ground pattern, the second dielectric layer, the first electric conductor layer, and the second electric conductor layer. The plurality of holes are a plurality of elongated holes provided at an interval in a direction in which the transmission line is surrounded. In each of the plurality of elongated holes, a longitudinal dimension in the direction in which the transmission line is surrounded is larger than a width dimension.

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 printed circuit board includes: a first layer including a first ground including a first opening, wherein a first ground wire is within the first opening; a second layer disposed in a direction from the first layer and including a second ground including a second opening, wherein the second opening at least partially overlaps with the first opening and wherein a second ground wire is within the second opening; a third layer between the first layer and the second layer and including a third opening, wherein the third opening at least partially overlaps with the first opening and wherein a first via pad is within the third opening; and a fourth layer between the second layer and the third layer and including a fourth opening, wherein the fourth opening at least partially overlaps with the third opening and wherein a second via pad is within the fourth opening.

In a transmission line, a thickness of a second section is smaller than that of a first section and of a third section. A center of the second section is above a center of the first section and a center of the third section in a laminated body up-down direction. A distance between a second signal conductor layer and a neutral plane of the second section is shorter than a distance between a first signal conductor layer and a neutral plane of the second section and a distance between a third signal conductor layer and a neutral plane of the second section in the laminated body up-down direction. A length of the second signal conductor layer between first and second interlayer connection conductors is equal to or less than about ½ of a wavelength of a high-frequency signal transmitted by the transmission line.

A transmission line board includes an insulating substrate including a first principal surface, first and second signal lines, first and second signal electrodes, which are provided at the insulating substrate. The first signal electrode is connected to the first signal line, and is connected by capacitive coupling to a different circuit board. The second signal electrode is connected to the second signal line, and is connected to the different circuit board via a conductive binder. The first signal line is provided to transmit a signal in a first frequency band, and the second signal line is provided to transmit a signal in a second frequency band lower than the first frequency band.

A circuit structure includes a circuit board, microstrips, a stripline, and vias. The circuit board includes conductive levels. A first and second transceiving circuits are disposed on a first conductive level. A first microstrip is disposed on the first conductive level, and configured to couple a first pin of the first transceiving circuit to a second pin of the second transceiving circuit. A second and third microstrips are disposed on the first conductive level, and coupled to a third pin of the first transceiving circuit and a fourth pin of the second transceiving circuit, respectively. The stripline is disposed on a second conductive level. A first and second vias cross the first and second levels, and couple the second and third microstrips to the stripline. The first and third pins are an inner and outer pins of a front line of a BGA of the first transceiving circuit, respectively.

A flexible circuit board includes liquid crystal polymer (LCP) layers and metal layers including circuit routes. Each of the LCP layers includes via structures. The metal layers and the LCP layers are alternatively stacked to form a multi-layer structure. Adjacent metal layers are electrically connected through the via structures. Some via structures of different LCP layers are substantially aligned with one another to form a stack of via structures. Each of the via structures includes openings filled with conductive material. The size of the opening fulfils the following equation: Vb≥cos(Bh/Vh)*Vt/k*2, where Vb is a diameter of a smaller aperture, Vt is a diameter of a bigger aperture, Vh is a combined thickness of a LCP layer and a metal layer, Bh is a thickness of a LCP layer and k is a tensile modulus.

A transmission line includes connecting portion connected to the outside and a main body connected to the connecting portion. The connecting portion includes a terminal electrode connected to an external electrode, a signal conductor, and a ground conductor. The main body includes the signal conductor and the ground conductor. The connecting portion includes a first region including the terminal electrode, a second region adjacent to the first region along a signal transmission path, and a third region located between the second region and the main body. Impedance matching at the at least one of the connecting portions is achieved by the first region, the second region, and the third region.

A circuit board is disclosed, including a circuit board body and at least one via apparatus provided on the circuit board body. The via apparatus includes a via (101) formed on the circuit board body, a via pad (201) surrounding the via and separately provided from the via, and an electrical conductor (301) electrically connecting the via pad (201) with the via (101).