JP2005129855A - High frequency module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a highly reliable high-frequency module capable of reducing a packaging area and a height by packaging a bare SAW chip on a module substrate together with other electronic components. <P>SOLUTION: Respective electrodes of the bare SAW chip having an excitation electrode, a grounded electrode surrounding the excitation electrode, and input/output electrodes formed on a principal plane, are opposed to electrodes formed on the surface of the module substrate. The grounded electrode and the input/output electrodes of the bare SAW chip are connected with the electrodes on the module substrate with a conductive adhesive so as to form a sealed space on a SAW propagation part of the excitation electrode. In addition, other electronic components are mounted on the surface of the module substrate, and/or a passive circuit is formed on the substrate surface, thereby providing the high-frequency module. At least, the bare SAW chip is hermetically sealed with a thermosetting resin with a flexural modulus of 4-8 GPa at ordinary temperatures and 0.2-0.5 GPa at 220°C and with a glass transfer temperature of 100-150°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency module that can be reduced in size and height and applied to a mobile phone, mobile communication, wireless communication, and the like.

  The mobile phone and wireless LAN markets are expected to grow rapidly, and the number of third-generation mobile phones produced is increasing rapidly. As mobile phone functions advance to the third generation, built-in cameras, TV reception, and other wireless communications (Bluetooth, infrared communications, wireless LAN) are also being used together, and the area occupied by high-frequency circuits decreases year by year. doing. For this reason, mobile phone parts are rapidly becoming smaller and lighter, and it is necessary to meet the demands for reducing the number of parts and reducing power consumption while improving individual performance.

  In order to realize such requirements, integration of chipsets and improvement in performance are advancing, and high frequency modules in which peripheral high frequency components are also integrated have been proposed.

  Among high-frequency components used in mobile communication devices such as mobile phones, in the case of a surface acoustic wave (SAW) filter or the like, the SAW chip prevents foreign matter such as moisture and dust from adhering to the excitation electrode through which the SAW chip propagates. It is necessary to hermetically seal in a hollow state so as not to hinder the propagation of.

(package)
Therefore, conventionally, as shown in FIG. 5, a predetermined bare SAW chip 31 is housed in a package 33 so that the excitation electrode 32 is on the upper surface, and is connected to a wiring layer 35 of the package 33 by a wire 34, and a lid body. A structure in which 36 is joined and hermetically sealed has been proposed (see Patent Document 1). However, if the wire 34 is used for connection, it is necessary to form a high hermetic space with the wire 34, so that there is a limit to reducing the package height.

  In addition, as shown in FIG. 6, so-called face-down bonding is also proposed in which the excitation electrode 32 of the bare SAW chip 31 is disposed on the lower surface and connected to the wiring layer 35 on the surface of the package 33 with solder 37. (See Patent Document 2). Such a structure can achieve a lower profile than that of FIG. 5, but as long as the lid body 36 is used, the thickness of the lid body 36 cannot be eliminated. In addition, when the lid body 36 is used, there is a problem that the cost of the lid body 36 and a high airtight joining process are indispensable, resulting in an increase in cost.

With respect to these package structures, as shown in FIG. 7, without being packaged, the excitation electrodes 32 of the bare SAW chip 31 are arranged on the lower surface and directly mounted on the wiring layers 38 and 38 on the surface of the substrate 37. A surface acoustic wave device has been proposed (see Patent Document 3). According to this structure, the ground electrode 41 is disposed around the excitation electrode 32 and the input / output electrode 40 and is connected to the wiring layer 38 on the surface of the substrate by the solder 42, whereby the excitation electrode connection portion and the input / output electrode connection portion. Is sealed in an airtight space 43 surrounded by the surface of the substrate 37, the bare SAW chip 31 and the ground electrode 41 connecting portion. Furthermore, as shown in FIG. 7, a structure in which a bare SAW chip mounted on the substrate surface is sealed with a sealing resin 39 has been proposed (see Patent Document 4).
JP 2002-118487 A JP 2002-76832 A JP2002-196400 JP 2003-168942 A

  However, like a high-frequency module, electronic components such as capacitors and other components such as semiconductor elements are solder-mounted together with the bare SAW chip 31 on the surface of one dielectric substrate 37, and the bare SAW chip 31 is shown in FIG. When formed by the mounting structure as shown, the high-frequency module is secondarily mounted on the mother board by solder or the like, and the input / output electrodes that join the bare SAW chip 31 and the high-frequency module substrate 37 when the electronic component is solder-mounted. 40, the solder 42 of the ground electrode 41 connection portion is remelted, and the melted solder 42 moves to the airtight space 43 side as indicated by an arrow. As a result, the airtight destruction of the airtight space 43 in the bare SAW chip 31 is performed. There has been a problem that the connection between the input / output electrode 40 and the ground electrode 41 is short-circuited by solder.

  This phenomenon is caused by the fact that when the solder 42 of the input / output electrode connection portion and the ground electrode connection portion is remelted, the melt expansion pressure acts on the inner side of the bare SAW chip 32, so that the solder 42 flows into the inner side, causing a short circuit or disconnection. It leads to.

  As a countermeasure, the input / output electrode connecting portion and the ground electrode connecting portion are made of a material having a high melting point that does not remelt, or the input / output electrode connecting portion so as not to flow into the airtight space 43 even when melted, It is conceivable to provide a dam material between the ground electrode connection portion, but the manufacturing process can be increased by changing only the solder 42 for mounting the bare SAW chip 32 or adding a different material such as a dam material. There were problems such as incurring an increase in costs.

  Therefore, in view of the above points, an object of the present invention is to provide a high-reliability high-frequency module in which a bare SAW chip is mounted on a module substrate together with other electronic components, and the mounting area can be reduced and the height can be reduced. There is to do.

  The high-frequency module of the present invention is configured such that each electrode of a bare SAW chip having an excitation electrode, a ground electrode surrounding the excitation electrode, and an input / output electrode on the main surface faces the electrode formed on the surface of the module substrate. The ground electrode and input / output electrodes of the bare SAW chip and the electrode on the module substrate side are connected by a conductive adhesive so that a sealed space is formed in the SAW propagation portion of the excitation electrode, A high-frequency module in which other electronic components are mounted on the surface of the module substrate and / or a passive circuit is formed on the surface of the substrate, wherein at least the bare SAW chip has a bending elastic modulus of 4 to 8 GPa at room temperature and 0 at 220 ° C. It is characterized by being hermetically sealed with a thermosetting resin having a glass transition temperature of 100 to 150 ° C. of 2 to 0.5 GPa.

  In the high-frequency module, the other electronic component is at least one selected from the group of semiconductor elements such as surface mount components such as chip capacitors, inductors, resistors, power amplifiers, switches, power control, detection, and power control. It is characterized by being.

  Furthermore, the passive circuit in the high-frequency module includes at least one of a demultiplexing circuit, a multiplexing circuit, a coupler, a balun, and a filter.

  Further, the other electronic component in the high-frequency module is connected to an electrode formed on the surface of the module substrate via solder.

In addition, the linear expansion coefficient of the module substrate is 8 to 18 × 10 ⁻⁶ / ° C. or less at 25 to 400 ° C., and further the linear expansion coefficient is 25 to 80 or less of the glass transition temperature of the thermosetting resin. It is desirable to be × 10 ⁻⁶ / ° C.

  According to the high frequency module of the present invention, when face-down bonding a bare SAW chip to a module substrate, at least the bare SAW chip has a bending elastic modulus of 4 to 8 GPa at room temperature and 0.2 to 0.5 GPa at 220 ° C. In addition, by hermetically sealing with a thermosetting resin having a glass transition temperature of 100 to 150 ° C., even when the high frequency module is secondarily mounted or another electronic component is solder mounted after the bare SAW chip is mounted, Under the temperature conditions at the time of mounting, the rigidity of the sealing resin is low, so even when the solder of the input / output electrode connection part and the ground electrode connection part is remelted, the melt expansion pressure is not limited to the airtight space side, Since it is possible to diffuse to the sealing resin side, it is possible to prevent the solder from flowing to the airtight space side, improve the airtight sealing performance, Fault, it is possible to prevent the occurrence of disconnection.

  Embodiments of a bare SAW chip mounting and sealing structure and a high-frequency module according to the present invention will be described below. FIG. 1A is a schematic cross-sectional view of a mounting structure in which a bare SAW chip is face-down bonded to a module substrate surface. FIG. 1B is a plan view showing a conductor pattern on the surface of the bare SAW chip. FIG. 1C is a plan view showing a conductor pattern on the module substrate side on which the bare SAW chip of FIG. 1B is mounted.

  As shown in FIG. 1, a bare SAW chip 1 constituting a surface acoustic wave filter includes, for example, a lithium tantalate single crystal, a lanthanum-gallium-niobium single crystal, and a lithium tetraborate single crystal having a langasite type crystal structure. A plurality of resonator electrodes 4 as excitation electrodes are connected to, for example, a ladder-type circuit on the surface of the substrate 2 made of a piezoelectric single crystal such as an input / output electrode 7A at one end of the excitation electrode. Further, a ground electrode 9A is formed around the excitation electrode 4 and the input / output electrode 7A.

  A semiconductive or insulating protective film such as silicon or silicon oxide is formed on the surface of these electrodes as necessary.

  On the other hand, on the surface of the module substrate 8, an input / output electrode 7B made of a conductor such as silver, copper, or gold is opposite to the input / output electrode 7A of the bare SAW chip 1, and a portion opposite to the ground electrode 9A. A ground electrode 9B is deposited on the surface.

  The bare SAW chip 1 is placed on the surface of the module substrate 8 and is electrically connected by a conductive adhesive 3 such as solder or conductive resin.

  According to such a connection structure, the portion where the excitation electrode 4 is formed is sealed in the space 5 formed by the conductive adhesive 3 of the bare SAW chip 1, the module substrate 8, and the ground electrode 9 connection portion. According to such a structure, the bare SAW chip 1 can be sealed without taking up a large volume, and the height can be reduced.

  FIG. 2 is an example of a block circuit diagram of a front end module of a cellular phone. This block diagram assumes a CDMA terminal composed of a US cellular band and a PCS band. European GSM, DCS terminal, 2.4 GHz Bluetooth, W-LAN and other front ends may be used.

  The transmission filter, reception filter, and duplexer in this block diagram can be formed by a bare SAW filter. These components constitute a high frequency module with a bare SAW filter mounting structure as shown in FIG.

  FIG. 3 is a plan view of a front end module on which the block circuit of FIG. 2 is mounted, and FIG. 4 is a schematic sectional view taken along line xx of FIG.

  In such a high-frequency module, a transmission filter, a reception filter, and a duplexer are formed by the bare SAW chip 1 and are mounted on the surface of the module substrate 18 by the mounting structure shown in FIG.

  Further, surface mount components such as a chip capacitor 13 and a chip inductor 14 are solder mounted on the surface of the module substrate 18. Further, a semiconductor chip (power amplifier IC) 11 is mounted on the surface of the module substrate 18 by wires 12. In some cases, a high-frequency circuit pattern 10 such as a matching circuit pattern is also deposited on the surface or inside of the module substrate 18 with a conductive material. Further, a thermal via 15 for radiating heat generated from the semiconductor element 11 is formed inside the module substrate, and a coupler 16 and the like are also built therein. Furthermore, a capacitor, an inductor, a matching circuit, and the like are incorporated as necessary.

  The bare SAW chip 1, the semiconductor chip 11, and the surface mount components 13 and 14 are all sealed with a sealing resin 6. The high-frequency module according to the present invention is incorporated into a small portable electronic device such as a portable telephone with such a structure.

  According to the present invention, it is important that the bending elastic modulus of the sealing resin 6 is 4 to 8 GPa at normal temperature and 0.2 to 0.5 GPa at 220 ° C. Since the bending elastic modulus of the sealing resin has the above characteristics, when the high frequency module is connected to the mother board (not shown) by reflow soldering, the solder connection portion is remelted and thermally expanded. Even if a stress is generated toward the periphery, the sealing resin 6 covering most of the solder 3 will buffer this stress, and the solder 3 will be forced between the bare SAW chip 1 and the module substrate 8. Intrusion can be prevented. For this reason, the solder connection portion of the bare SAW chip 1 of the high-frequency module continues to exist at the initial position even after remelting, and does not move to an unnecessary portion, eventually causing a short circuit or airtightness. It wo n’t destroy them.

  On the other hand, if the bending elastic modulus at room temperature of the sealing resin 6 is smaller than 4 GPa, high mechanical strength due to the sealing resin cannot be obtained, and if it is larger than 8 GPa, the load on the wire bonding is increased. It becomes large and causes disconnection. If the bending elastic modulus at 220 ° C. is smaller than 0.2 GPa, it is easy to cause poor connection of wire bonding. If it is larger than 0.5 GPa, stress due to thermal expansion of solder cannot be absorbed and reflow heating is repeated. Each time the melted solder forcibly penetrates into the gap between the semiconductor chip, bare SAW chip, chip component and substrate, or penetrates into the interface between the semiconductor chip and the sealing resin, The airtightness will be destroyed. In particular, the flexural modulus is desirably 5 to 8 GPa at normal temperature and 0.3 to 0.5 GPa at 220 ° C.

  Moreover, as for sealing resin, it is desirable that the glass transition temperature is 100-150 degreeC. This is because the glass transition temperature is in the glassy region at room temperature, so that the mechanical strength of the entire high-frequency module can be sufficiently secured. However, when the glass transition temperature of the sealing resin is less than 100 ° C., the resin itself becomes rubbery or gelled at room temperature, and thus there is a possibility that sufficient mechanical strength cannot be imparted to the high-frequency module. Conversely, when the glass transition temperature exceeds 150 ° C., the hardness of the sealing resin increases, but sufficient toughness cannot be obtained. Therefore, a large number of high-frequency module substrates are divided into product units by dicing or the like during the manufacturing process. In the process, the sealing resin cracks and the product is easily damaged.

  The glass transition point and bending elastic modulus of the sealing resin are controlled by the type and molecular weight of the thermosetting resin, and can also be controlled by adding an inorganic filler to the thermosetting resin. . It should be noted that the thermal conductivity of the sealing resin can be increased by adding an inorganic filler. As a result, heat generated from the semiconductor element or the like can be dissipated to reduce the thermal resistance.

Further, the linear expansion coefficient of the sealing resin at a temperature not higher than the glass transition temperature is preferably 25 to 80 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the substrate is preferably 8 to 15 × 10 ⁻⁶ / ° C. The reason is that the linear expansion coefficient of the sealing resin can be made less than 25 × 10 ⁻⁶ / ° C. by increasing the ratio of the inorganic filler, but in that case, the bending elastic modulus of the sealing resin tends to increase. . Conversely, if the linear expansion coefficient exceeds 80 × 10 ⁻⁶ / ° C., the expansion coefficient difference between the module substrate, the semiconductor chip, and the sealing resin increases, so that the sealing resin is easily peeled off, There is a risk of inducing a short circuit due to solder. Furthermore, if the coefficient of thermal expansion of the module substrate is smaller than 8 × 10 ⁻⁶ / ° C. or exceeds 18 × 10 ⁻⁶ / ° C., the difference in thermal expansion coefficient between the bare SAW chip and the module substrate increases, and the excitation electrode Cracks are likely to occur at the connection between the surrounding ground electrode and the input / output electrodes, leading to a decrease in reliability.

  According to the present invention, at least the bare SAW chip 1 may be sealed with the sealing resin 6 described above. However, as shown in FIG. 3, other capacitors, resistance components, etc. formed on the surface of the module substrate 8 may be used. By collectively sealing the electronic components 13 and 14 and the semiconductor element 11 with the sealing resin 6, the reliability of the hermetic sealing of the connection portion of each component to the module substrate 8 and the bare SAW chip 1 is greatly increased. Can be improved.

  In the example of FIG. 1, the resonator electrode of the ladder type circuit is used as the excitation electrode in the bare SAW chip 1, but the surface acoustic wave device such as a resonator type or a propagation type filter or a duplexer other than the filter is used. If it has an excitation electrode which needs sealing, it is applied to this invention.

  In the above embodiment, the high-frequency module is a front-end module. However, the high-frequency module includes a surface-mounted component to be solder-mounted and a bare SAW chip, and the surface-mounted component is a sealing resin. Any other semiconductor device may be used as long as it has a structure sealed by.

  The surface mount component is not limited to a chip component or a semiconductor chip, but may be a chip such as an FBAR (Film Bulk Acoustic Resonator), a MEMS switch, or an optical semiconductor element.

  Next, an example in which the high-frequency module according to the present invention is manufactured will be described.

Ceramic in which 10 parts by mass of B in terms of B ₂ O ₃ and 5 parts by mass of Li in terms of LiCO ₃ are added to 100 parts by mass of the main component represented by 0.95 mol MgTiO ₃ -0.05 mol CaTiO ₃ A slurry was prepared using the powder composition, and a green sheet having a thickness of 100 μm was formed by a doctor blade method.

Then, a conductor pattern having a thickness of 20 μm was formed on the surface of the green sheet by screen printing using Ag paste. Further, if necessary, a through hole having a diameter of 200 microns was formed and filled with the above Ag paste to form a through hole conductor. Then, after laminating this green sheet, after removing the binder at 300 ° C. for 4 hours in the atmosphere, firing was performed in the atmosphere at 900 ° C. for 6 hours to obtain a module substrate having a thermal expansion coefficient of 12 × 10 ⁻⁶ / ° C. Produced.

Next, an electrode made of an Al—Cu (2 wt%) alloy was formed on a piezoelectric substrate (42 ° Y cut of lithium tantalate single crystal, thermal expansion coefficient 14 to 16 × 10 ⁻⁶ / ° C.). Thereafter, resist coating, patterning, and peeling were repeated to form excitation electrodes, input / output electrodes, a ground electrode, and a protective film, thereby producing bare SAW chips.

The completed bare SAW chip was mounted face-down on the module substrate according to FIG. For this mounting, high-temperature solder was applied to the ground electrode and the input / output electrodes by screen printing, and mounting was performed by reflow. According to the mounting structure of the bare SAW chip, the periphery of the excitation electrode is surrounded by the ground electrode, and airtightness can be ensured before the resin sealing. Thereafter, the dispenser is soldered to each mounting pattern. After coating, chip parts such as capacitor chips were mounted, and solder was fixed by reflow. Finally, a semiconductor chip was bonded with a silver paste, and then wire bonding was performed using a gold wire.

  By the above method, a high-frequency module mounted with various surface mount components, semiconductor chips, and bare SAW chips was obtained.

  Next, sealing resins A, B, C, D, E, and F having different characteristics in which fused silica was added as a filler to the epoxy resin were prepared. The bending elastic modulus of the sealing resin was measured based on JIS-K-6911, and the glass transition temperature and the linear expansion coefficient were measured based on the dilatometer method.

  Using a metal mask and a squeegee, a glass ceramic substrate having 80 high-frequency module regions formed thereon was coated and collectively sealed by a printing method so as to collectively cover the plurality of module regions 11a with the sealing resin. Furthermore, the sealing resin formed by the printing method was baked and cured. Thereafter, 80 high-frequency module regions were divided using a dicing apparatus, and the high-frequency modules were separated into pieces.

Similarly, as module substrates having different thermal expansion coefficients, commercially available glass ceramic substrates with thermal expansion coefficients of ⁶ , 8.5 × 10 ⁻⁶ / ° C., glass ceramic substrates with 20, 23, 18 × 10 ⁻⁶ / ° C., and A glass fiber-epoxy resin composite module substrate having a thermal expansion coefficient of 19, 20, 23 × 10 ⁻⁶ / ° C. was also used.

Thereafter, the sealed high-frequency module was subjected to moisture absorption treatment in an atmosphere at a temperature of 85 ° C. and a humidity of 60% for 168 hours, and then reflow heating (peak temperature: 260 ° C.) was repeated three times. Subsequently, the appearance was checked for cracks, the electrical continuity was checked for shorts, and after dropping in water, the module electrical characteristics were evaluated to confirm the filter airtightness and the power amplifier airtightness. A case where no failure mode such as a short circuit, a crack, or an airtightness was not observed was judged as “◯”, and a case where it was seen was judged as “X”. Further, the occurrence rate (%) of each failure mode is shown in the column of reflow evaluation after moisture absorption treatment in Table 1.

  As can be seen from Table 1, in each example, the occurrence rate of shorts and cracks is 0%, and it is confirmed that no failure mode is observed.

  On the other hand, none of the samples whose bending elastic modulus or thermal expansion coefficient deviates from the scope of the present invention can sufficiently absorb the stress due to the thermal expansion of the solder, and short-circuiting, interfacial delamination and hermeticity degradation are observed. It was.

It is the schematic sectional drawing (a) which shows the mounting form of the bare SAW chip | tip of this invention, the surface pattern (b) of a bare SAW chip, and the surface pattern (c) of a module board | substrate. It is a typical block circuit diagram of the high frequency module of the present invention. It is a schematic plan view which shows an example of the high frequency module of this invention. It is a schematic sectional drawing of the xx line of the high frequency module of FIG. It is a schematic sectional drawing which shows the package of the conventional SAW chip. It is a schematic sectional drawing which shows the package of the other conventional SAW chip | tip. It is a schematic sectional drawing which shows the package of the further another conventional SAW chip.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Bare SAW chip 3 ... Solder 4 ... Excitation electrode 5 ... Airtight space 6 ... Sealing resin 7A, 7B ... Input / output electrode 8 ... Module boards 9A, 9B ... Ground electrode 11 ... Semiconductor chips 13,14 ... Surface mount parts 15 ... Thermal via 16 ... Coupler 18 ... ..High frequency modules

Claims (7)

Each electrode of the bare SAW chip having the excitation electrode, the ground electrode surrounding the excitation electrode, and the input / output electrode formed on the main surface faces the electrode formed on the surface of the module substrate, and the SAW propagation of the excitation electrode The bare SAW chip ground electrode and input / output electrodes and the module substrate side electrode are connected by a conductive adhesive so that a sealed space is formed in the portion, and another surface is provided on the module substrate surface. A high-frequency module in which electronic components are mounted and / or a passive circuit is formed on a substrate surface, and at least the bare SAW chip has a bending elastic modulus of 4 to 8 GPa at room temperature and 0.2 to 0.5 GPa at 220 ° C. A high frequency module characterized by being hermetically sealed with a thermosetting resin having a glass transition temperature of 100 to 150 ° C. The other electronic component is at least one selected from the group of semiconductor elements such as surface mount components such as chip capacitors, inductors, resistors, power amplifiers, switches, power control, detection, power control, etc. The high-frequency module according to claim 1. The high-frequency module according to claim 1 or 2, wherein the passive circuit includes at least one of a demultiplexing circuit, a multiplexing circuit, a coupler, a balun, and a filter. The high frequency module according to any one of claims 1 to 3, wherein the other electronic component is connected to an electrode formed on the surface of the module substrate via solder. 5. The high-frequency module according to claim 1, wherein a linear expansion coefficient of the module substrate is 8 to 18 × 10 ⁻⁶ / ° C. at 25 to 400 ° C. ⁶ . 6. The high-frequency module according to claim 1, wherein the thermosetting resin has a linear expansion coefficient not higher than the glass transition temperature of 25 to 80 × 10 ⁻⁶ / ° C. ⁶ . 7. The high-frequency module according to claim 1, further comprising: an electronic component mounted on the surface of the module substrate and a passive circuit sealed with the sealing resin.

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