Circuit module and composite circuit module

A SAW filter includes a piezoelectric substrate, a longitudinal coupling portion disposed on a main surface of the piezoelectric substrate, a support layer and cover layers covering the main surface of the piezoelectric substrate with an air gap on the longitudinal coupling portion, and bumps that are disposed on one of the cover layers and are electrically connected to the longitudinal coupling portion. A mount board is mounted on a motherboard. The SAW filter is mounted on the mount board via the bumps.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to circuit modules and composite circuit modules, and, more particularly, to a circuit module and a composite circuit module provided with a surface acoustic wave filter including a piezoelectric element.

2. Description of the Related Art

Examples of a circuit module in the related art include an electronic component apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2002-299996.FIG. 9is a cross-sectional view of an electronic component apparatus500disclosed in Japanese Unexamined Patent Application Publication No. 2002-299996.

The electronic component apparatus500includes a SAW device502and a base504. The SAW device502includes a piezoelectric monocrystal substrate506and a substantially comb-shaped electrode508. The substantially comb-shaped electrode508is disposed on the piezoelectric monocrystal substrate506. The SAW device502is disposed on the base504via bumps so that the substantially comb-shaped electrode508faces the base504. The electronic component apparatus500having the above-described structure is mounted on, for example, a motherboard when being used.

When the electronic component apparatus500is heated and cooled in a reflowing process, a connection in the electronic component apparatus500may be broken. More specifically, the piezoelectric monocrystal substrate506in the electronic component apparatus500is made of, for example, lithium tantalite. The base504is made of, for example, ceramics such as alumina. A motherboard is made of, for example, glass epoxy. Lithium tantalite, alumina, and glass epoxy have different material properties such as a coefficient of linear expansion and a Young's modulus. Accordingly, when the electronic component apparatus500is heated and cooled in a reflowing process, the SAW device502, the base504, and a motherboard are deformed in different ways. As a result, in the electronic component apparatus500, a connection may be broken. The inventor of the invention described and claimed in the present application discovered via computer simulation that the connection between the SAW device502and the base504is easily broken.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a circuit module and a composite circuit module that prevent a connection therein from being broken or damaged when being heated and cooled.

A circuit module according to a preferred embodiment of the present invention includes a surface acoustic wave filter and a multilayer substrate. The surface acoustic wave filter includes a piezoelectric substrate, a surface acoustic wave element disposed on a main surface of the piezoelectric substrate, a cover layer covering the main surface of the piezoelectric substrate with an air gap on the surface acoustic wave element, and a connection portion that is disposed on the cover layer and is electrically connected to the surface acoustic wave element. The multilayer substrate is a substrate on which the surface acoustic wave filter is mounted via the connection portion and which is mounted on a motherboard.

A composite circuit module according to a preferred embodiment of the present invention includes the circuit module and a motherboard on which the circuit module is mounted.

According to a preferred embodiment of the present invention, it is possible to prevent breaking of or damage to a connection in an apparatus when the apparatus is heated and cooled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A circuit module according to a preferred embodiment of the present invention and a composite circuit module according to a preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

The structure of a circuit module according to a preferred embodiment of the present invention will be described below with reference to the accompanying drawings.FIG. 1is an external perspective view of a circuit module10according to a preferred embodiment of the present invention.FIG. 2is a diagram illustrating the circuit configuration of the circuit module10illustrated inFIG. 1. A height direction of the circuit module10that preferably has a substantially rectangular parallelepiped shape, for example, is defined as a z-axis direction. Lengthwise and widthwise directions of the circuit module10in plan view from the z-axis direction are defined as x-axis and y-axis directions, respectively. An x axis, a y axis, and a z axis are orthogonal to one another.

As illustrated inFIGS. 1 and 2, the circuit module10includes a mount board12, a duplexer14, matching elements16ato16d, and a sealing resin19.

As illustrated inFIG. 1, the mount board12preferably is a substantially rectangular ceramic multilayer substrate obtained by laminating a plurality of insulating layers, and is mounted on, for example, the motherboard of a mobile telephone. A material for the mount board12preferably is, for example, Low Temperature Co-fired Ceramics (LTCC). The mount board12includes a substrate body12aand land electrodes41ato41f,45ato45f, and90ato90i(seeFIG. 2).

The substrate body12aincludes main surfaces Sa and Sb (seeFIG. 1). The main surface Sa extends in the positive z-axis direction, and the main surface Sb extends in the negative z-axis direction.

The land electrodes41ato41fand45ato45fare used to mount the duplexer14, and are disposed on the main surface Sa (first main surface) of the substrate body12a. The land electrodes90ato90iare used to mount the mount board12on a motherboard, and are disposed on the main surface Sb (second main surface) of the substrate body12a. The land electrode90ais connected to an antenna via a motherboard (not illustrated). The land electrodes90cand90eare connected to a receiving circuit via the motherboard. The land electrode90his connected to a transmission circuit via the motherboard. The land electrodes90b,90d,90f,90g, and90iare connected to the ground via the motherboard.

The duplexer14preferably is a branching circuit that outputs a relatively high-frequency receiving signal received by an antenna (not illustrated) to a receiving circuit (not illustrated) in the circuit module10and to output a relatively low-frequency transmission signal output from a transmission circuit (not illustrated) in the circuit module10to the antenna. The duplexer14is disposed on the main surface Sa of the mount board12as illustrated inFIG. 1, and includes SAW filters32aand32bas illustrated inFIGS. 1 and 2. The frequency of the transmission signal may be higher than that of the receiving signal. The receiving circuit and the transmission circuit may be disposed outside the circuit module10.

The SAW filter32ais disposed between a transmission circuit and an antenna as illustrated inFIG. 2, and has a characteristic with which a relatively low-frequency transmission signal is transmitted from the transmission circuit to the antenna and a relatively high-frequency receiving signal is not transmitted from the antenna to the transmission circuit. The SAW filter32bis disposed between an antenna and a receiving circuit as illustrated inFIG. 2, and has a characteristic with which a relatively high-frequency receiving signal is transmitted from the antenna to the receiving circuit and a relatively low-frequency transmission signal is not transmitted from a transmission circuit to the receiving circuit.

The structure of the SAW filters32aand32bwill be described with reference to the accompanying drawings. Since the SAW filters32aand32bhave substantially the same basic structure, the SAW filter32bwill be described by way of example.FIG. 3is a diagram illustrating the internal structure of the SAW filter32b.FIG. 4is a cross-sectional view of the SAW filter32b.FIG. 5is an exploded view of the SAW filter32b.FIG. 6is a wiring diagram of the SAW filter32b. Referring toFIG. 6, a signal line is represented by a heavy line and a ground line is represented by a thin line. A signal line is a wiring line through which a receiving signal is transmitted. A ground line is a line held at a ground potential.FIG. 7is a cross-sectional view of the circuit module10.

The piezoelectric substrate17preferably is a substantially rectangular plate, and includes a main surface S1(seeFIG. 4). As the piezoelectric substrate17, a lithium tantalate sodium substrate, a lithium tantalate niobate substrate, or a silicon substrate is preferably used, for example. The main surface S1is one of two main surfaces of the piezoelectric substrate17extending in the negative z-axis direction.

As illustrated inFIGS. 3 and 4, on the main surface S1of the piezoelectric substrate17, an element region E is set. The element region E is a region except for corner portions and side portions on the main surface S1.

Each of the connection portions66ato66fis a conductive layer made of Al, Cu, Ni, Au, or Pt on the main surface S1. As illustrated inFIG. 3, the connection portions66a,66c,66d, and66fare individually disposed near four corners of the main surface S1. As illustrated inFIG. 3, the connection portions66band66eare individually disposed near the midpoints of long sides of the main surface S1in the negative and positive y-axis directions.

Each of the longitudinal coupling portions (surface acoustic wave elements)70and74, the shunt traps76and78, and the series traps80and82is a conductive layer made of Al, Cu, Ni, Au, or Pt on the main surface S1, and is disposed in the element region E when viewed in plan from the z-axis direction as illustrated inFIGS. 3 and 5.

As illustrated inFIGS. 3,5, and6, between the connection portions66dand66b, the longitudinal coupling portion70and the series trap80are connected in series. The longitudinal coupling portion70includes facing portions70ato70f. Each of the facing portions70a,70c,70d, and70fis obtained by making the ground line connected to the connection portion66eand a signal line connected to the connection portion66bvia the series trap80face each other in the z-axis direction. Each of the facing portions70band70eis obtained by making a signal line connected to the connection portion66dand the ground line connected to the connection portion66eface each other in the z-axis direction. The facing portions70ato70fare arranged in this order from the negative y-axis direction to the positive y-axis direction.

The series trap80preferably is a resonator connected in series between the longitudinal coupling portion70and the connection portion66b. The shunt trap76preferably is a resonator connected in series between the connection portions66dand66a.

Between the connection portions66fand66b, the longitudinal coupling portion74and the series trap82are connected in series. The longitudinal coupling portion74includes facing portions74ato74f. Each of the facing portions74a,74c,74d, and74fis obtained by arranging the ground line connected to the connection portion66eand a signal line connected to the connection portion66bvia the series trap82so as to face each other in the z-axis direction. Each of the facing portions74band74eis obtained by arranging a signal line connected to the connection portion66fand the ground line connected to the connection portion66eso as to face each other in the z-axis direction. The facing portions74ato74fare arranged in this order from the negative y-axis direction to the positive y-axis direction.

The series trap82preferably is a resonator connected in series between the longitudinal coupling portion74and the connection portion66b. The shunt trap78preferably is a resonator connected in series between the connection portions66fand66c.

As illustrated inFIGS. 3 to 5, the support layer18and the cover layers20and22cover the main surface S1of the piezoelectric substrate17with an air gap Sp on the longitudinal coupling portions70and74, the shunt traps76and78, and the series traps80and82.

As illustrated inFIGS. 3 to 5, the support layer18is a substantially rectangular frame surrounding the element region E in plan view from the z-axis direction. More specifically, as illustrated inFIG. 3, the support layer18includes a frame portion18aand protrusion portions18bto18g. The frame portion18apreferably is a substantially rectangular frame along four sides of the main surface S1. The protrusion portions18b,18d,18e, and18gindividually protrude from four corners of the main surface S1toward the inside of the frame portion18a. The protrusion portions18cand18findividually protrude from midpoints of the long sides of the main surface S1in the positive and negative y-axis directions toward the inside of the frame portion18a. As illustrated inFIG. 3, the protrusion portions18bto18goverlap the connection portions66ato66f, respectively in plan view from the z-axis direction. The support layer18protects the SAW filter32bfrom water, and is made of an insulating material (for example, polyimide) that is highly resistant to water. The element region E is a region on the main surface S1in which the support layer18is not located.

As illustrated inFIGS. 4 and 5, the cover layer20extends in the negative z-axis direction with respect to the support layer18and faces the main surface S1. More specifically, the cover layer20preferably has substantially the same rectangular shape as the main surface S1. The cover layer20is laminated on the support layer18in the negative z-axis direction and faces the main surface S1with the air gap Sp therebetween. The cover layer20may be made of an insulating material different from that for the support layer18, and is made of, for example, an epoxy resin.

As illustrated inFIGS. 4 and 5, the cover layer22extends in the negative z-axis direction with respect to the cover layer20. More specifically, the cover layer22has substantially the same rectangular shape as the cover layer20, and entirely overlaps the cover layer20in plan view from the z-axis direction. The cover layer22protects the SAW filter32bfrom water, and is made of an insulating material (for example polyimide) that is highly resistant to water. That is, the cover layer22is made of the same insulating material as the support layer18. The cover layer22is formed after the support layer18has hardened. Accordingly, in a case where the cover layer22is directly laminated on the support layer18, the cover layer22is not brought into full contact with the support layer18. In the SAW filter32b, the cover layer20is therefore disposed between the support layer18and the cover layer22. That is, the cover layer20joins the support layer18and the cover layer22. The cover layers20and22may be made of another material and have different thicknesses. A material for the cover layers20and22may be a flexible material such as a resin or a rigid material such as a monocrystal substrate, for example.

As illustrated inFIGS. 3 to 5, the via-hole conductors V1to V6pass through the support layer18and the cover layers20and22in the z-axis direction. Ends of the via-hole conductors V1to V6in the positive z-axis direction are connected to the connection portions66ato66f, respectively.

The bumps24ato24fare spherical solder bumps arranged on the main surface of the cover layer22in the negative z-axis direction, and are connected to the ends of the via-hole conductors V1to V6in the negative z-axis direction, respectively. As a result, the bumps24ato24fare electrically connected to the longitudinal coupling portions (surface acoustic wave elements)70and74, the shunt traps76and78, and the series traps80and82via the via-hole conductors V1to V6and the connection portions66ato66f.

As illustrated inFIGS. 2 and 7, the bumps24ato24fare connected to the land electrodes45ato45fof the mount board12, respectively, when the SAW filter32bis mounted on the mount board12. More specifically, as illustrated inFIG. 2, the bumps24a,24c, and24eare connected to the land electrodes45a,45c, and45eof the mount board12, respectively, and are connected to the ground via the mount board12and a motherboard. The bump24bis connected to the land electrode45bof the mount board12, and is connected to an antenna via the mount board12and the motherboard. The bumps24dand24fare connected to the land electrodes45dand45fof the mount board12, respectively, and are connected to a receiving circuit via the mount board12and the motherboard. As a result, the SAW filter32bis mounted on the main surface Sa of the mount board12via the bumps24ato24f.

The operation of the SAW filter32bhaving the above-described structure will be described. When a receiving signal is input from the bump24bvia the series trap80, a surface acoustic wave is generated at the facing portions70a,70c,70d, and70f. The surface acoustic wave propagates on the surface of the piezoelectric substrate17. The facing portions70band70econvert the surface acoustic wave generated at the facing portions70a,70c,70d, and70finto a receiving signal. The receiving signal is externally output from the SAW filter32bvia the bump24d.

The receiving signal input from the bump24bis input into the facing portions74a,74c,74d, and74fvia the series trap82and a surface acoustic wave is generated at the facing portions74a,74c,74d, and74f. The surface acoustic wave propagates on the surface of the piezoelectric substrate17. The facing portions74band74econvert the surface acoustic wave generated at the facing portions74a,74c,74d, and74finto a receiving signal. The receiving signal is externally output from the SAW filter32bvia the bump24f. A signal passing through the facing portions70and a signal passing through the facing portions74are 180° out of phase. The bumps24dand24fdefine a balanced receiving terminal.

The circuit module10having the above-described structure is mounted on a motherboard. A composite circuit module200including the circuit module10and a motherboard will be described below with reference to the accompanying drawing.FIG. 8is a diagram illustrating the structure of the composite circuit module200.

A motherboard201includes a substrate body202and land electrodes204. The substrate body202preferably is a substrate made of a resin such as glass epoxy, for example. The land electrodes204are disposed on the surface of the substrate body202in the positive z-axis direction.

The land electrodes90of the mount board12and the land electrodes204of the motherboard201are soldered. As a result, the mount board12is mounted on the motherboard201via the land electrodes90.

As illustrated inFIG. 1, the matching elements16ato16dare chip electronic components that are mounted on the main surface Sa of the mount board12and perform impedance matching between the mount board12and the duplexer14. As illustrated inFIG. 2, the matching elements16a,16b, and16care matching elements connected in series between the land electrodes41a,41c, and45band the land electrodes90i,90h, and90b, respectively. The matching element16dis a matching element connected between a signal line that connects the land electrodes45dand90cand a signal line that connects the land electrodes45fand90e.

The sealing resin19covers the main surface Sa of the mount board12, the duplexer14, and the matching elements16ato16d. As a result, the duplexer14and the matching elements16ato16dare protected. The sealing resin19is, for example, an epoxy resin.

In the circuit module10and the composite circuit module200, the mount board12, the piezoelectric substrate17, the cover layers20and22, and the motherboard201have the following Young's moduli. Table 1 indicates the Young's moduli of the mount board12, the piezoelectric substrate17, the cover layers20and22, and the motherboard201.

Referring to table 1, the Young's modulus of the piezoelectric substrate17is larger than that of the mount board12, the cover layers20and22, and the motherboard201. As materials for the piezoelectric substrate17, the mount board12, the motherboard201, and the cover layers20and22, materials having substantially the same coefficient of linear expansion are used.

The circuit module10having the above-described structure operates as follows. In a case where a transmission signal is transmitted from a radio communication apparatus including the circuit module10, a transmission circuit generates a transmission signal. The transmission signal is transmitted to an antenna via the duplexer14. The SAW filter32ain the duplexer14has a characteristic with which the transmission signal is transmitted between the bumps25cand25dand a receiving signal is not transmitted between the bumps25cand25d. Accordingly, a receiving signal that has been received by the antenna and input into the SAW filter32afrom the bump25dcannot be output from the bump25c. Thus, the entering of a receiving signal into a transmission circuit is prevented from occurring.

In a case where a radio communication apparatus including the circuit module10receives a receiving signal, an antenna receives the receiving signal. The receiving signal passes through the duplexer14and is transmitted to a receiving circuit. The SAW filter32bin the duplexer14has a characteristic with which a receiving signal input from the bump24bis separated into signals of opposite phases and the signals are individually output from the bumps24dand24f. Accordingly, a transmission signal that has been generated by a transmission circuit and input into the SAW filter32bfrom the bump24bcannot be output from the bump24d. A receiving signal that has been received by an antenna and input into the SAW filter32bfrom the bump24bcannot be output from the bumps24dand24f. Thus, the entering of a transmission signal and a receiving signal into a receiving circuit is prevented from occurring.

With the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, it is possible to prevent a connection in the circuit module10from being broken or damaged at the time of heating and cooling in a reflowing process. In the electronic component apparatus500disclosed in Japanese Unexamined Patent Application Publication No. 2002-299996, the piezoelectric monocrystal substrate506is made of, for example, lithium tantalite. The base504is made of, for example, ceramics such as alumina. A motherboard is made of, for example, a glass epoxy resin. Lithium tantalite, alumina, and glass epoxy have different material properties such as a coefficient of linear expansion and a Young's modulus. Accordingly, when the electronic component apparatus500is heated and cooled in a reflowing process, the SAW device502, the base504, and a motherboard are deformed in different ways. As a result, in the electronic component apparatus500, a connection may be broken or damaged. In particular, the connection between the SAW device502and the base504may be broken or damaged.

In the SAW filters32aand32bin the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, the support layer18and the cover layers20and22cover the main surface S1of the piezoelectric substrate17with the air gap Sp on the longitudinal coupling portions (surface acoustic wave elements)70and74, the shunt traps76and78, and the series traps80and82. The bumps24ato24fare disposed on the cover layer22and are electrically connected to the longitudinal coupling portions70and74, the shunt traps76and78, and the series traps80and82. As a result, the SAW filters32aand32bare directly mounted on the mount board12. That is, with the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, the need to dispose the base504made of ceramics such as alumina is eliminated and the profile of the SAW device502is reduced. In the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, there is no connection between the SAW device502and the base504which is easily broken or damaged. As a result, with the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, it is possible to prevent a connection in the circuit module10from being broken or damaged at the time of heating and cooling in a reflowing process.

In the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, the bumps24ato24fare solder bumps. Since the Young's modulus of a solder bump is smaller than that of a gold bump, the solder bump is easily deformed. Accordingly, even in a case where the mount board12and the piezoelectric substrate17are deformed by heating, the bumps24ato24fare more significantly deformed than a gold bump and are therefore hardly broken. As a result, in the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, it is possible to prevent a connection in the circuit module10from being broken. As described previously with reference to table 1, since the cover layers20and22, the mount board12, and the motherboard201have Young's moduli smaller than that of the piezoelectric substrate17, they are more easily deformed than the piezoelectric substrate17. Since a deformation caused by heat or mechanical shock can be absorbed by components other than the piezoelectric substrate17, it is possible to prevent a connection in the circuit module10from being broken or damaged even in a case where the bumps24ato24fare gold bumps.

In the circuit module10and the composite circuit module200according to preferred embodiments of the present invention, the Young's modulus of the piezoelectric substrate17is larger than that of the mount board12, the cover layers20and22, and the motherboard201. Since a stress generated in the circuit module10can be scattered by the cover layers20and22and the mount board12having small Young's moduli, a stress concentration can be significantly reduced and prevented. It is therefore possible to more effectively prevent a connection in the circuit module10from being broken or damaged.

A coefficient of linear expansion may be set for each material with a Young's modulus used in a preferred embodiment of the present invention. By using materials with substantially the same coefficient of linear expansion for the piezoelectric substrate17, the cover layers20and22, the mount board12, and the motherboard201, the differences in expansion and shrinkage among them when they are heated can be reduced. As a result, it is possible to prevent the connection between the piezoelectric substrate17and the mount board12or the connection between the mount board12and the motherboard201from being broken or damaged by a stress concentration.

As described previously, preferred embodiments of the present invention are useful for a circuit module and a composite circuit module, and, in particular, provide an advantage in their suitability to prevent a connection in the circuit module from being broken or damaged at the time of heating in a reflowing process.