A surface acoustic wave device includes a piezoelectric substrate, an interdigital transducer (IDT) electrode on the substrate, a cover over the substrate and IDT electrode, and hollow spaces between the IDT electrode and the cover. The hollow spaces are defined by partition supports between the substrate and the cover. The partition supports include a first and second partition supports extending in a first direction without contacting each other. The first and second partition supports each include first and second ends along the first direction. The first and second direction perpendicular to the first direction. The first end of the first partition support is closer to an outer periphery of the substrate than is the second end, and the first end of the second partition support is farther away from the outer periphery than is the second end.

A multiplexer includes a common connection terminal on a first surface of a substrate and to be connected to an antenna element, and transmission-side and reception-side elastic wave filters of Band25 and Band66 mounted on a second surface of the substrate opposite the first surface, that are connected to the common connection terminal, and that have pass bands different from each other. The transmission-side elastic wave filter of Band66 is located nearest on the substrate to the common connection terminal among the elastic wave filters.

A wafer-level chip-scale package includes a polymeric body having a conductive via passing through the polymeric body and a piezoelectric substrate directly bonded to an upper end of the conductive via. The wafer-level chip-scale package further includes a cavity defined between a portion of the polymeric body and the piezoelectric substrate and a metal seal ring disposed in the body and having an upper end bonded to the piezoelectric substrate, the metal seal ring passing only partially through the body.

An elastic wave device includes a mount board, a transmit filter, a receive filter, and a sealing resin layer. The transmit filter includes a first piezoelectric substrate, and is joined to the mount board by first bumps. The receive filter includes a second piezoelectric substrate, and is joined to the mount board by second bumps. The sealing resin layer is provided on the mount board. The height of each first bump is H1; the joint area, on the first piezoelectric substrate side, of each first bump is A1; and the joint area, on the mount board side, of each first bump is B1; the height of each second bump is H2; the joint area, on the second piezoelectric substrate side, of each second bump is A2; and the joint area, on the mount board side, of each second bump is B2. The first bumps and the second bumps satisfy at least one of: A1>A2 and B1>B2; and H1<H2.

A multiplexer (1) includes a plurality of filters connected to a common terminal (110). The multiplexer (1) includes: a low-frequency filter (11L) that is formed of at least one surface acoustic wave resonator arranged between the common terminal (110) and the input/output terminal (120) and has a first pass band; a high-frequency filter (12H) that is connected between the common terminal (110) and the input/output terminal (130) and has a second pass band located at a higher frequency than the first pass band; and a capacitor (C.sub.B1) that is serially arranged in a connection path between the common terminal (110) and the low-frequency filter (11L). The Q value of the capacitor (C.sub.B1) in the second pass band is higher than the Q value in the second pass band of a capacitance obtained by treating the at least one surface acoustic wave resonator of the low-frequency filter (11L) as a capacitance.

An electronic component device includes first and second mount boards, and first, second, and third electronic components. The first electronic component includes a first major surface and a second major surface, and is disposed on the first mount board. The first major surface is positioned closer to the first mount board than the second major surface. The second electronic component includes a third major surface and a fourth major surface, and is disposed on the second mount board. The third major surface is positioned closer to the second mount board than the fourth major surface. The third electronic component includes a fifth major surface and a sixth major surface, and is disposed on the second mount board. The fifth major surface is positioned closer to the second mount board than the sixth major surface. The second major surface directly contacts the fourth and sixth major surfaces, or indirectly contacts the fourth and sixth major surfaces with a bonding layer interposed therebetween.

A multiplexer includes filters and a common terminal connected to an antenna element by a connection path, a first inductance element being connected between the connection path and a reference terminal. A terminal closer to the antenna element among an input terminal and an output terminal of one filter among the filters is connected to a parallel resonator and is connected to the common terminal with a second inductance element interposed therebetween. A terminal closer to the antenna element among an input terminal and an output terminal of each of other filters other than the one filter among the filters is connected to the common terminal and a series resonator.

An acoustic wave device includes a first acoustic wave element including a first substrate having piezoelectricity at least in a portion thereof, a first functional electrode provided on a first surface of the first substrate, and a first wiring conductor electrically connected to the first functional electrode. The first acoustic wave element further includes a relay electrode on the first surface of the first substrate and electrically connected to a second wiring conductor, and a ground electrode on the first surface of the first substrate and electrically connected to the first functional electrode. The ground electrode is between at least one of the first functional electrode and the first wiring conductor, and the relay electrode, and is electrically insulated from the relay electrode.

In a multiplexer, input or output terminals of four acoustic wave filters are connected to, among a plurality of terminals provided on piezoelectric substrates, antenna terminals connected to an antenna connection terminal; the four acoustic wave filters include a first acoustic wave filter and a second acoustic wave filter that is located at a farther position from the antenna connection terminal than a position of the first acoustic wave filter in a plan view of a substrate; and among the plurality of terminals, the terminals located at the closest position to the antenna connection terminal in the plan view of the substrate are connected to the second acoustic wave filter as the antenna terminals.

A multiplexer includes: a first terminal; a second terminal; a third terminal; a first filter connected between the first and second terminals, including a first capacitor, a first inductor, and one or more first acoustic wave resonators, and having a first passband; a second filter connected between the first and third terminals, including a second capacitor, a second inductor, and one or more second acoustic wave resonators, and having a second passband higher than the first passband; a substrate having a surface on which at least one first acoustic wave resonator of the one or more first acoustic wave resonators and at least one second acoustic wave resonator of the one or more second acoustic wave resonators are located; and a metal structure located on the surface and located between the at least one first acoustic wave resonator and the at least one second acoustic wave resonator.