Power amplifier module

A power amplifier module includes a substrate, a power amplifier having a first surface on which an electrode is defined and a second surface opposite the first surface, the first surface faces a principal surface of the substrate, a surface acoustic wave duplexer having a first surface on which an electrode is defined and a second surface opposite the first surface, the first surface faces the principal surface of the substrate, a heat dissipation unit defined on another principal surface of the substrate, a heat dissipation path that connects a connecting portion between the power amplifier and the principal surface to the heat dissipation unit, an insulating resin that covers the power amplifier and the surface acoustic wave duplexer, a conductive shield that covers the insulating resin, and a first conductive unit defined on the second surface of the surface acoustic wave duplexer and electrically connected to the conductive shield.

BACKGROUND

Technical Field

The present disclosure relates to a power amplifier module.

In a radio communication device such as a cellular phone, a power amplifier (PA) is used to amplify power of a radio frequency (RF) signal to be transmitted to a base station. In the radio communication device, furthermore, a duplexer is used to separate a reception signal from a base station and a transmission signal to the base station to share an antenna between transmission and reception. Examples of the duplexer include a surface acoustic wave (SAW) duplexer (for example, Patent Document 1).

In recent years, with increased compactness of radio communication devices, power amplifier modules in which a power amplifier and a duplexer are packaged as a single product have attracted attention (for example, Patent Document 2). Furthermore, face-down mounting is known as a mounting method for making a module compact (for example, Patent Document 3).Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014-120966Patent Document 2: Japanese Unexamined Patent Application Publication No. 2005-311230Patent Document 3: Japanese Unexamined Patent Application Publication No. 2007-266539

BRIEF SUMMARY

In a power amplifier module, heat from a heat-producing component such as a power amplifier needs to be dissipated. For example, in a semiconductor device disclosed in Patent Document 3, an emitter electrode of a power amplifier mounted face-down on a front surface of a package substrate is connected to a thermal via formed in the package substrate, resulting in heat of the power amplifier being dissipated from a rear surface of the package substrate. In this manner, it is possible to dissipate the heat of the face-down mounted power amplifier from the rear surface of the package substrate through the thermal via.

However, as disclosed in, for example, Patent Document 1, a SAW duplexer has a cavity that is an operating space of an interdigital electrode unit serving as a heating element. In a case where the SAW duplexer is mounted face-down, it is difficult to dissipate heat through a thermal via since the cavity exists between the interdigital electrode unit and the package substrate.

The present disclosure has been made in view of the circumstances described above, and the present disclosure improves the heat dissipation capability of a power amplifier module including a power amplifier and a SAW duplexer.

A power amplifier module according to an aspect of the present disclosure includes a substrate having first and second principal surfaces, a power amplifier having a first surface on which an electrode is defined and a second surface opposite the first surface, the power amplifier being mounted so that the first surface faces the first principal surface of the substrate, a surface acoustic wave duplexer having a first surface on which an electrode is defined and a second surface opposite the first surface, the surface acoustic wave duplexer being mounted so that the first surface faces the first principal surface of the substrate, a heat dissipation unit defined on the second principal surface of the substrate, a heat dissipation path that connects at least part of a connecting portion between the power amplifier and the first principal surface to the heat dissipation unit, an insulating resin that covers the power amplifier and the surface acoustic wave duplexer, a conductive shield that covers a surface of the insulating resin, and a first conductive unit defined on the second surface of the surface acoustic wave duplexer and electrically connected to the conductive shield.

According to the present disclosure, the heat dissipation capability of a power amplifier module including a power amplifier and a SAW duplexer can be improved.

DETAILED DESCRIPTION

An embodiment of the present disclosure will be described hereinafter with reference to the drawings.FIG. 1is a diagram illustrating a configuration of a power amplifier module10A according to an embodiment of the present disclosure.

As illustrated inFIG. 1, the power amplifier module10A includes a power amplifier30and a SAW duplexer40, which are mounted face-down on a package substrate20. The power amplifier30and the SAW duplexer40are covered with an insulating resin50. The insulating resin50is formed of an epoxy resin, for example. A surface of the insulating resin50is covered with a conductive shield60. The conductive shield60is formed of a metal such as gold, silver, copper, or aluminum, for example.

The package substrate20has a top surface21(a first principal surface) and a bottom surface22(a second principal surface). Wiring patterns23ato23eare defined on the top surface21of the package substrate20. Further, electrodes24ato24care defined on the bottom surface22of the package substrate20. In addition, the package substrate20has thermal vias25aand25bextending therethrough from the top surface21to the bottom surface22. The thermal vias25aand25b(heat dissipation paths) electrically connect the wiring pattern23band the electrode24bto each other. The electrode24bis a ground electrode to which a ground potential is applied, and also serves as a heat dissipation unit. The package substrate20also has ground wiring26defined therein. The ground wiring26is connected to the electrode24bthrough, for example, the thermal vias25aand25b.

The power amplifier30is a component that amplifies an RF signal to be transmitted to a base station, and includes a transistor for power amplification, for example. The power amplifier30has a surface33(a first surface) on which electrodes31ato31care defined, and a surface32(a second surface) opposite the surface33. The power amplifier30is mounted face-down on the top surface21of the package substrate20via bumps34ato34cconnected to the electrodes31ato31c. For example, the electrode31bis connected to an emitter of a transistor constituting the power amplifier30, and is electrically connected to the electrode24bvia the bump34b, the wiring pattern23b, and the thermal vias25aand25b. Thus, heat produced at the emitter, which is a portion of the power amplifier30from which heat is generated, is transferred to the electrode24band is then dissipated thereby.

A metal layer35is defined on the surface32of the power amplifier30, which is positioned closer to the conductive shield. The metal layer35is formed of a metal such as gold, silver, copper, aluminum, or titanium, for example. The metal layer35has a wire36(a conductive path) defined thereon. The wire36is cut on the conductive shield60side, and has cut portions37aand37bconnected to the conductive shield60. That is, the metal layer35and the wire36form a conductive unit (a second conductive unit) electrically connected to the conductive shield60. The wire36is formed of a metal such as gold, silver, copper, or aluminum, for example. Since the metal layer35is defined on the surface33of the power amplifier30, heat produced by the power amplifier30is also dissipated via the metal layer35. Since the metal layer35is connected to the conductive shield60via the wire36, the heat dissipation effect can be further enhanced.

Further, for example, on side surfaces of the package substrate20, the conductive shield60is connected to the ground wiring26. Accordingly, the potential of the metal layer35of the power amplifier30is fixed to a ground level. This makes it possible to stabilize the operation of the power amplifier30.

The SAW duplexer40is a component that separates a reception signal from a base station and a transmission signal to the base station. The SAW duplexer40has a surface43(a first surface) on which electrodes41aand41bare defined, and a surface42(a second surface) opposite the surface43. The SAW duplexer40is mounted face-down on the top surface21of the package substrate20via bumps44aand44bconnected to the electrodes41aand41b. The SAW duplexer40has an interdigital electrode unit45. The SAW duplexer40further has a cavity46that is an operating space of the interdigital electrode unit45.

A metal layer47(a first conductive unit) is defined on the surface43of the SAW duplexer40, which is positioned closer to the conductive shield. The metal layer47is formed of a metal such as gold, silver, copper, aluminum, or titanium, for example. The metal layer47has a wire48(a conductive path) defined thereon. The wire48is cut on the conductive shield60side, and has cut portions49aand49bconnected to the conductive shield60. That is, the metal layer47and the wire48form a conductive unit (a first conductive unit) electrically connected to the conductive shield60. The wire48is formed of a metal such as gold, silver, copper, or aluminum, for example. Since the metal layer47is defined on the surface43of the SAW duplexer40, heat produced by the SAW duplexer40is dissipated via the metal layer47. Since the metal layer47is connected to the conductive shield60via the wire48, the heat dissipation effect can be further enhanced.

Further, for example, on the side surfaces of the package substrate20, the conductive shield60is connected to the ground wiring26. Accordingly, the potential of the metal layer47of the SAW duplexer40is fixed to a ground level. This makes it possible to stabilize the operation of the SAW duplexer40. In the SAW duplexer40, in particular, a reception signal from a base station and a transmission signal to the base station may be crossed via the metal layer47. Hence, fixing the metal layer47to a ground level makes it possible to suppress such crossing (cross talk).

Next, a process of manufacturing the power amplifier module10A will be described with reference toFIGS. 2A to 2E.

First, as illustrated inFIG. 2A, the power amplifier30and the SAW duplexer40are mounted face-down on the top surface21of the package substrate20.

Then, as illustrated inFIG. 2B, the wire36is formed on the metal layer35, which is defined on the surface32of the power amplifier30, by wire bonding. Likewise, the wire48is formed on the metal layer47, which is defined on the surface42of the SAW duplexer40, by wire bonding. A plurality of wires36and a plurality of wires48may be formed. The wires36and48may be formed on the metal layers35and47prior to face-down mounting.

The wire36may also be formed so as to be connected to a GND electrode (not illustrated) on the first principal surface of the package substrate20from the metal layer35defined on the surface32of the power amplifier30. The wire48of the SAW duplexer is also formed in a similar way.

Thereafter, as illustrated inFIG. 2C, the power amplifier30and the SAW duplexer40are covered (sealed) by the insulating resin50. The wires36and48are also covered by the insulating resin50.

Subsequently, as illustrated inFIG. 2D, a surface of the insulating resin50is ground with a grinder100to expose the wires36and48. Specifically, a portion of the wire36is cut and the cut portions37aand37bare exposed. Likewise, a portion of the wire48is cut and the cut portions49aand49bare exposed. The wires36and48may be exposed in such a way that the wires36and48are not cut.

Finally, the conductive shield60is formed so as to cover the insulating resin50. Thus, the conductive shield60is connected to the metal layer35via the cut portions37aand37bof the wire36. Further, the conductive shield60is connected to the metal layer47via the cut portions49aand49bof the wire48.

Through the steps described above, the power amplifier module10A illustrated inFIG. 1can be manufactured.

FIG. 3is a diagram illustrating a configuration of a power amplifier module10B, which is an exemplary modification of the power amplifier module10A. The same elements as those of the power amplifier module10A are assigned the same numerals and are not described herein.

The power amplifier module10B includes a conductive unit70and a conductive paste71, instead of the wire36. The conductive unit70(a conductive path) is a columnar metal or a metal pin, for example, and has a bottom surface connected to the metal layer35by using the conductive paste71. Further, a top surface of the conductive unit70is connected to the conductive shield60. The conductive unit70is a metal such as gold, silver, copper, or aluminum, for example. The conductive paste71is, for example, a material or solder made by mixing conductive particles of silver, carbon, or the like into resin.

The power amplifier module10B includes a conductive unit80and a conductive paste81, instead of the wire48. The conductive unit80is columnar, for example, and has a bottom surface connected to the metal layer47by using the conductive paste81. Further, a top surface of the conductive unit80is connected to the conductive shield60. The conductive unit80is a metal such as gold, silver, copper, or aluminum, for example. The conductive paste81is, for example, a material or solder made by mixing conductive particles of silver, carbon, or the like into resin.

In the power amplifier module10B, the use of the conductive units70and80instead of the wires36and48improves the heat dissipation capability of the power amplifier30and the SAW duplexer40. In addition, similarly to the power amplifier module10A, the conductive shield60is connected to the ground wiring26, thus making it possible to stabilize the operation of the power amplifier30and the SAW duplexer40.

FIG. 4is a diagram illustrating a configuration of a power amplifier module10C, which is an exemplary modification of the power amplifier module10A. The same elements as those of the power amplifier module10A are assigned the same numerals and are not described herein.

The power amplifier module10C does not include the wires36and48of the power amplifier module10A. Instead of them, the power amplifier30and the SAW duplexer40have holes90and91defined in upper portions thereof. The holes90and91are formed by, for example, applying a laser to the insulating resin50from above the power amplifier30and the SAW duplexer40. In a state where the holes90and91have been formed, surfaces of the metal layers35and47are exposed. Thereafter, the conductive shield60is formed by sputtering or the like, resulting in the conductive shield60and the metal layers35and47being connected to each other.

In the power amplifier module10C, directly connecting the metal layers35and47to the conductive shield60improves the heat dissipation capability of the power amplifier30and the SAW duplexer40. In addition, similarly to the power amplifier module10A, the conductive shield60is connected to the ground wiring26, thus making it possible to stabilize the operation of the power amplifier30and the SAW duplexer40.

FIG. 5is a diagram illustrating a configuration of a power amplifier module10D, which is an exemplary modification of the power amplifier module10A. The same elements as those of the power amplifier module10A are assigned the same numerals and are not described herein.

The power amplifier module10D does not include the wires36and48of the power amplifier module10A. Instead of them, the metal layers35and47have a larger thickness than those of the power amplifier module10A. Further, the top surfaces of the metal layers35and47are directly connected to the conductive shield60.

In the power amplifier module10D, directly connecting the metal layers35and47to the conductive shield60improves the heat dissipation capability of the power amplifier30and the SAW duplexer40. In addition, similarly to the power amplifier module10A, the conductive shield60is connected to the ground wiring26, thus making it possible to stabilize the operation of the power amplifier30and the SAW duplexer40.

The power amplifier modules10A to10D, which are examples of an embodiment of the present disclosure, have been described.

In the power amplifier modules10A to10D, a conductive unit to be electrically connected to the conductive shield60is defined on a surface of the face-down mounted SAW duplexer40, which is positioned closer to the conductive shield60. Accordingly, heat of the SAW duplexer40, which is difficult to dissipate from the package substrate20side due to the influence of the cavity46, can be dissipated from the conductive shield60side.

In the power amplifier module10A, the wire48is provided as a conductive path for connecting the metal layer47to the conductive shield60. The wire48can be easily formed on the metal layer47by wire bonding. Thus, the process of manufacturing the power amplifier module10A can be simplified.

In the power amplifier module10A, furthermore, the insulating resin50is ground to cut a portion of the wire48, resulting in the cut portions49aand49bbeing formed. Then, the cut portions49aand49bare connected to the conductive shield60. As illustrated inFIG. 2D, high-accuracy work is required to expose the wire48without cutting the wire48when the insulating resin50is ground. In the power amplifier module10A, in contrast, there is no need to stop the grinding of the insulating resin50at the portion where the wire48is not cut. Thus, the process of manufacturing the power amplifier module10A can be simplified. In addition, the cut portions49aand49bensure that the wire48can be connected to the conductive shield60.

In the power amplifier modules10A to10D, the conductive shield60is connected to the ground wiring26defined in the package substrate20. This allows the potential of the metal layer47of the SAW duplexer40to be fixed to a ground level and makes it possible to stabilize the operation of the SAW duplexer40.

In the power amplifier modules10A to10D, furthermore, the power amplifier30, whose heat is dissipated from the bottom surface22of the package substrate20through the thermal vias25aand25b, has also defined on a surface thereof, which is positioned closer to the conductive shield60, a conductive unit to be electrically connected to the conductive shield60. This makes it possible to improve the heat dissipation capability of the power amplifier30.

In the power amplifier modules10A to10D, the power amplifier30also has defined on a surface thereof, which is positioned closer to the conductive shield60, a conductive unit to be electrically connected to the conductive shield60. However, the power amplifier30may not have such a conductive unit.

The embodiments described above described above are intended for easy understanding of the present invention, and it is not intended to construe the present invention in a limiting fashion. Changes/improvements can be made to the present invention without departing from the gist of the present invention, and equivalents thereof are also included in the present invention. That is, the embodiments may be appropriately changed in design by those skilled in the art, and such changes also fall within the scope of the present invention so long as the changes include the features of the present invention. For example, the elements included in the embodiments and the arrangement, materials, conditions, shapes, sizes, and the like thereof are not limited to those described in the illustrated examples but can be changed as appropriate. In addition, the elements included in the embodiments can be combined as much as technically possible, and such combined elements also fall within the scope of the present invention so long as the combined elements include the features of the present invention.

REFERENCE SIGNS LIST