JP2005191740A - Surface acoustic wave device and electronic circuit device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device and an electronic circuit device which are excellent in reliability without connection failure or the like.
A surface acoustic wave element in which an excitation electrode is provided on one main surface of a piezoelectric substrate is disposed on an upper surface of a base body with the one main surface of the piezoelectric substrate facing the surface. . Then, a through hole 9 penetrating between the upper surface and the lower surface of the base 2, a lead electrode 10 that closes the through hole 9 and is electrically connected to the excitation electrode 5, and the lead The surface acoustic wave device includes an insulator 11 that covers the electrode 10 so as to expose a partial region thereof. As a result, when the surface acoustic wave device is mounted on a circuit board or the like, bubbles are not generated in the through-holes 9, and the generation of cracks can be prevented. Can be provided.
[Selection] Figure 1

Description

  A surface acoustic wave device having a so-called face-down structure, in which a surface acoustic wave element provided with an excitation electrode on one main surface of a piezoelectric substrate is provided on an upper surface of a base so that the one main surface of the piezoelectric substrate faces the surface. The present invention also relates to an electronic circuit device in which the circuit board is disposed.

  In recent years, surface acoustic wave filters, which are a type of surface acoustic wave device, have been widely used in the communication field, and in particular, are often used in mobile communication devices. This mobile communication device has evolved into a multi-function device having a function as a digital camera and a radio receiver, and further a function of remotely controlling home appliances. In such a trend, devices used for mobile communication devices tend to increase. However, since the size of mobile communication devices cannot be increased due to market demands, devices used in mobile communication devices are required to be small and low.

  Up to now, a surface acoustic wave filter used for mobile communication devices generally has a so-called chip size package (CSP) structure in which a ceramic substrate is mounted in a face-down structure. Recently, a CSP structure using a resin substrate has been proposed for reasons such as easy manufacture.

An example of a surface acoustic wave device having a CSP structure using such a resin substrate is shown in FIG. Here, 2 is a base of the resin substrate in which the through hole 9 is formed. On the lower surface of the base 2, an extraction electrode 10 in which a via conductor is formed in the through hole 9 is provided. A connection conductor 8 and a solder bump 7 are formed in a portion where the through hole 9 is located on the upper surface of the base 2, and these are the excitation electrode 5 formed on the lower surface of the piezoelectric substrate 3 constituting the surface acoustic wave element and the electric electrode. Connected to the input / output electrode 6 (not connected because of the cross-sectional view schematically shown in the drawing). In this way, the surface acoustic wave device 1 ′ is configured by mounting the surface acoustic wave element on the substrate 2 with the face-down bonding structure. In the figure, reference numeral 11 denotes an insulator (solder resist film) for preventing the lead electrodes 10 from being short-circuited by the solder when the surface acoustic wave device 1 'is mounted on the circuit board described later via the solder. is there.
JP 11-55069 A

  However, as shown in FIG. 6A, solder bumps 13 are formed on the input / output pads 12 of the circuit conductor pattern formed on the circuit board 15, and the solder bumps 13 are shown in FIG. When the surface acoustic wave device 1 ′ is disposed, the connection conductor 8 of the base 2, the solder bump 7, and the via conductor of the lead electrode 10 need to be positioned immediately above the solder bump 13. The formation positions of these conductors on the side are limited.

  Further, as shown in FIG. 6A, when the connection is made between the circuit board 15 and the solder bump 13 in a state where the via conductor formed in the through hole 9 of the surface acoustic wave device 1 ′ has a recess. Then, as shown in FIG. 6B, when the surface acoustic wave device 1 ′ is mounted, the thickness of the solder bump 13 cannot be accurately controlled. This is a problem because the solder of the solder bump 13 flows into the gap 20 and may be short-circuited by being electrically connected to the excitation electrode 5.

  Further, when the solder bumps 13 are connected, bubbles 14 may remain in the via conductor recesses as shown in FIG. 6B. If moisture is contained in the bubbles 14, moisture is vaporized and the bubbles 14 rapidly expand due to heat generated during reflow soldering or heat generated from the surface acoustic wave device itself when high power is applied. Peeling occurs between the piezoelectric substrate 3 and the piezoelectric substrate 3 or a crack is generated in the extraction electrode 10 and the solder bump 13 due to the impact of the rapid expansion of the bubbles 14 (hereinafter this phenomenon is referred to as a popcorn phenomenon). ) Occurs, which leads to poor connection of the input / output pads 12 of the circuit conductor pattern, which in turn reduces the reliability of the surface acoustic wave device and the electronic circuit device using it.

  The present invention has been proposed to solve the above-described problems, and an object of the present invention is to provide a versatile surface acoustic wave device having a large degree of freedom in the formation position of the conductor of the surface acoustic wave device. Another object of the present invention is to provide a highly reliable surface acoustic wave device and electronic circuit device that can prevent the flow of solder as much as possible and that are free from problems such as poor connection.

  In order to solve the above-described problems, a surface acoustic wave device according to the present invention includes: 1) a surface acoustic wave element in which an excitation electrode is provided on one main surface of a piezoelectric substrate on an upper surface of a substrate; On the other hand, it is a surface acoustic wave device that is arranged with the main surfaces facing each other, and is formed on the lower surface of the base body and the through hole that penetrates the upper surface and the lower surface of the base body. A conductor pattern electrically connected to the excitation electrode and an insulator covering the conductor pattern so as to expose a partial region thereof are provided.

  2) In the surface acoustic wave device according to 1) above, a concave portion is formed by the conductor pattern in the through hole, and the concave portion is filled with the insulator.

  In the electronic circuit device of the present invention, 3) the surface acoustic wave device according to 1) or 2) is provided on a circuit board via a connection conductor connected to the partial region of the conductor pattern. It is characterized by.

  4) In the electronic circuit device according to 3), the connection conductor includes a connection pad and solder formed on the connection pad, and the insulator is connected to the connection pad and the conductor pattern. It is characterized by being sandwiched between.

  According to the surface acoustic wave device of the above 1) and the electronic circuit device of the above 3), the through hole penetrating the upper surface and the lower surface of the base, and the excitation formed on the lower surface of the base while closing the through hole. Since a conductor pattern electrically connected to the electrode and an insulator covering the conductor pattern so as to expose a part of the conductor pattern are provided, depending on a predetermined position of the conductor formed on the circuit board A mode in which a partial region (exposed region) of the conductor pattern connected to the conductor is covered with an insulator can be appropriately set. Thereby, a versatile surface acoustic wave device and an electronic circuit device having a large degree of freedom in the position of the conductor connected to the circuit board can be provided.

  Further, according to the surface acoustic wave device of 2) and the electronic circuit device of 3), the concave portion is formed by the conductor pattern in the through hole, and the concave portion is filled with the insulator. When the surface acoustic wave device is disposed on the substrate, the connecting conductor such as molten solder does not flow into the concave portion, so that bubbles are generated in the concave portion when joining with the molten conductor such as solder. There is nothing. Thereby, the popcorn phenomenon can be completely eliminated, and damage to the surface acoustic wave device, the extraction electrode, and the joint can be prevented as much as possible. Further, since no bubbles are generated in the recess, it is possible to prevent the conductor in the recess from being oxidized and corroded. Furthermore, when moving the surface acoustic wave device, foreign matter such as dust and dirt does not enter the concave portion. As described above, there is no contact failure due to foreign matter when mounted on a circuit board, and no corrosion due to dust, dirt, etc. occurs. Thus, a highly reliable surface acoustic wave device and electronic circuit device can be provided.

  Further, according to the electronic circuit device of 4), it is possible to prevent the molten solder on the circuit board side from flowing out, and to prevent a short circuit between conductors to be insulated. Further, it is possible to prevent the insulator from peeling as much as possible. Thereby, it is possible to prevent moisture and air from entering between the circuit board and the insulator as much as possible, to eliminate the occurrence of oxidative corrosion and popcorn phenomenon, and to provide a highly reliable electronic circuit device.

  Hereinafter, embodiments of a surface acoustic wave device according to the present invention will be described in detail with reference to the drawings schematically showing the embodiments. In addition, in drawing demonstrated below, the same code | symbol shall be attached | subjected to the same member and the same part.

  FIG. 1 is a sectional view of a surface acoustic wave device 1 according to the present invention. 2 (a) and 2 (b) are cross-sectional views for explaining how the surface acoustic wave device 1 is mounted on the circuit board 15 to constitute an electronic circuit device. As shown in FIG. 1, the surface acoustic wave device 1 includes a laminated structure of an Al—Cu alloy, an Al—Cu—Mg alloy and Ti having an IDT (Inter Digital Transducer) electrode on one main surface of the piezoelectric substrate 3. The excitation electrode 5 made of a material such as a laminated structure of an Al—Cu alloy and Ti and the same material as the excitation electrode 5 connected thereto, or Al, Au, An input / output electrode 6 made of a material such as Ag, Cu, Ni, Cr, Mg or an alloy containing these materials as a main component is formed, and a solder bump 7 made of a material such as lead-free solder. And bonded to a substrate 2 such as an inorganic material substrate made of ceramics such as a resin substrate, alumina, LTCC (low temperature fired ceramics), etc. The substrate 2 has a through hole 9 and a via conductor having a recess formed therein. The lead electrode 10 is formed as a conductor pattern including an insulator 11. An insulator 11 such as a solder resist film is formed so as to fill the recess of the via conductor in the through hole 9, and is insulated at a position away from the through hole 9. A connection pad 16 is formed in which the lead electrode 10 is not covered with the body 11. Further, the surface acoustic wave element and the substrate 2 are joined by the solder bumps 7, and further, the protective cover 4 which is a sealing resin is used. The surface acoustic wave device of the present invention is completed by hermetically sealing the periphery of the surface acoustic wave element.

  As described above, the surface acoustic wave device 1 has the surface acoustic wave element in which the excitation electrode 5 is provided on the one main surface of the piezoelectric substrate 3 on the upper surface of the base 2 and the one main surface of the piezoelectric substrate 3 is opposed to the surface. It is arranged in a state. Then, a through-hole 9 penetrating between the upper surface and the lower surface of the base 2, a lead-out electrode 10 that closes the through-hole 9 and is electrically connected to the excitation electrode 5, and this lead-out An insulator 11 is provided to cover the electrode 10 so as to expose a partial region (region of the connection pad 16). As the material of the piezoelectric substrate 3, various piezoelectric materials such as a lithium tetraborate single crystal and a langasite single crystal can be applied in addition to the above-described materials.

  Here, the base 2 is easy to manufacture, is lightweight, and can be easily cut even by a cutting method other than dicing. In addition, when a resin substrate is used, there are advantages such as easy processing and low cost. The base 2 made of this resin substrate will be described in detail. The substrate 2 is preferably made of a plastic substrate such as a high heat-resistant BT resin (resin mainly composed of bismaleimide triazine), a polyimide resin, an epoxy resin, or a glass epoxy resin. This is because these resin materials are preferable from the viewpoints of good heat resistance and water resistance, low cost and economical.

  The through holes 9 provided in the base 2 are formed by first etching a thin electrode (for example, about 5 μm) on one side of a resin substrate in which metal films are formed on both main surfaces of the base 2 to reflect at the time of laser irradiation. Then, the laser absorptance is improved and then a through hole 9 having a diameter of about 0.1 mm is formed by using a carbon dioxide laser, for example. Next, after applying a catalyst such as palladium to the substrate, electroless plating is performed in a strong alkaline aqueous solution using, for example, formalin as a reducing agent. And the conductor formed in both surfaces of the base | substrate 2 will be in electrical continuity through the electroless copper plating conductor film formed in the inner wall face of the through-hole 9. FIG. In this way, the base body 2 subjected to electroless copper plating is disposed as an object to be plated on the cathode side in a plating bath made of, for example, copper sulfate, pyrophosphoric acid, and the like, and a copper plate is disposed on the anode side. Is applied to deposit the copper on the surface of the substrate 2 on which the electroless copper plating is applied to form a film of electrolytic copper plating. Thereby, the extraction electrode 10 which electrically conducts both surfaces of the base 2 is formed. Next, an insulator 11 such as a solder resist film is formed in order to close the concave portion of the via conductor formed in the through hole 9. As a method for forming the insulator 11, for example, a paste solder resist is printed by screen printing or the like and then dried.

  The surface acoustic wave device includes an excitation electrode 5 for exciting surface acoustic waves on the surface of a piezoelectric substrate 3 made of a piezoelectric single crystal such as a lithium tantalate single crystal, a lithium niobate single crystal, or a lithium tetraborate single crystal. And an input / output electrode 6 connected to the. Here, an annular electrode may be formed so as to surround the excitation electrode 5 as shown in the figure. When this annular electrode is formed, the excitation electrode is formed when the substrate 2 and the surface acoustic wave element are joined. 5 can be hermetically sealed, and the reliability can be further improved. The excitation electrode 5 and the input / output electrode 6 used a thin film formation method such as a sputtering method, a vapor deposition method or a CVD (Chemical Vapor Deposition) method, a reduction projection exposure machine (stepper), and an RIE (Reactive Ion Etching) apparatus. It is formed by photolithography.

  After that, the surface acoustic wave element and the substrate 2 are joined by the solder bump 7, and thermosetting resin (epoxy, silicone, phenol, polyimide, polyurethane, etc.), thermoplastic resin (polyphenylene sulfide, etc.) The surface acoustic wave device 1 of the present invention is completed by hermetically sealing the surface of the surface acoustic wave element with the protective cover 4 made of a sealing resin made of a material such as ultraviolet curable resin or low-melting glass. .

  As shown in FIGS. 2A and 2B, when the surface acoustic wave device 1 is mounted on the circuit board 15, the surface acoustic wave device 1 insulates the extraction electrode 10 on the circuit board 15. An electronic circuit device is configured by being arranged via a connection conductor connected to the exposed partial region (connection pad 16) that is not covered with the body 11. Here, the connection conductor has an input / output pad 12 and a solder bump 13 which are connection pads, and the insulator 11 is sandwiched between the input / output pad 12 and the lead electrode 10, so that the solder bump 13 The flow of the molten solder is suppressed by the insulator 11, so that the solder does not enter the through hole 9, and bubbles that cause the popcorn phenomenon are not generated.

  As described above, according to the surface acoustic wave device and the electronic circuit device of the present invention, the through hole 9 penetrating between the upper surface and the lower surface of the base 2 and the through hole 9 are closed and formed on the lower surface of the base 2. Since the lead electrode 10 which is a conductor pattern electrically connected to the electrode 5 and the insulator 11 covering the lead electrode 10 so as to expose a part of the lead electrode 10 are provided, the lead electrode 10 is formed on the circuit board 15. Depending on the position of the conductor, a mode in which the insulator 11 covers a partial region (exposed region) of the extraction electrode 10 connected to the conductor can be appropriately set. Thereby, a versatile surface acoustic wave device and an electronic circuit device having a large degree of freedom in the position of the conductor connected to the circuit board 15 can be provided.

  The through-hole 9 is closed with the extraction electrode 10 in a state where a recess is formed in the through-hole 9, and this recess is filled with an insulator 11, so that the surface acoustic wave device 1 is provided on the circuit board 15. When the is disposed, the connecting conductor such as molten solder does not flow into the recess. As a result, when joining with a conductor to be melted such as solder, no bubbles are generated in the recess, and the popcorn phenomenon can be completely eliminated, and the surface acoustic wave device 1, the extraction electrode and the joint are damaged. It can be prevented as much as possible. Further, since no bubbles are generated in the recess, it is possible to prevent the conductor in the recess from being oxidized and corroded. Further, when the surface acoustic wave device 1 is moved, foreign matters such as dust and dirt do not enter the concave portion. As described above, there is no contact failure due to foreign matter when mounted on the circuit board 15, and no corrosion due to dust or dirt occurs. Accordingly, a highly reliable surface acoustic wave device and electronic circuit device can be provided.

  Further, according to the electronic circuit device of the present invention, it is possible to prevent the molten solder on the circuit board 15 side from flowing out, and to prevent a short circuit between conductors to be insulated. Further, it is possible to prevent the insulator 11 from peeling off as much as possible. As a result, it is possible to prevent moisture and air from entering between the circuit board 15 and the insulator 11 as much as possible, to eliminate the occurrence of oxidation corrosion and popcorn phenomenon, and to provide a highly reliable electronic circuit device.

  Next, an embodiment of the present invention will be described with reference to the drawings. The surface acoustic wave device shown in FIG. 1 has an AlT (99 mass%)-Cu (1 mass%) IDT electrode pattern on a piezoelectric substrate 3 which is a 38.7 ° Y-cut X direction propagation lithium tantalate single crystal substrate. An output electrode pattern and a wiring pattern for electrically connecting them were formed. In forming these patterns, after forming a thin film by a sputtering method, photolithography was performed using a stepper, an RIE apparatus, or the like to obtain an electrode pattern of a predetermined excitation electrode 5.

  Here, first, a lithium tantalate wafer as a substrate material was ultrasonically cleaned with an organic solvent such as acetone or IPA (isopropyl alcohol) to clean organic components. Next, the substrate was sufficiently dried by a clean oven, and then an electrode was formed.

  In forming this electrode, a sputtering apparatus was used to form an Al—Cu film having the above-described composition, and then a photoresist was spin-coated to a thickness of about 0.5 μm, and a desired electrode pattern was patterned by a stepper. At the same time, the input / output electrodes were patterned.

  Next, an unnecessary portion of resist was melted with an alkaline developer by a developing device to expose a desired electrode pattern, and then the electrode was etched by an RIE device to obtain an electrode pattern of a desired excitation electrode 5.

Thereafter, a protective film was produced. That is, a silicon oxide (SiO ₂ ) film is formed by a sputtering apparatus, and then a resist pattern is formed by photolithography, and an input / output electrode window opening part and an annular electrode part are etched by an RIE apparatus or the like, and a protective film pattern Formed.

  Next, the piezoelectric substrate was diced along dicing lines and divided into chips to obtain a surface acoustic wave device.

  The surface acoustic wave element thus obtained is screen-printed with a solder paste made of lead-free solder, reflowed to form solder bumps, joined to a BT resin substrate, and then surface acoustic wave element with a sealing resin. Then, each surface was diced to obtain the surface acoustic wave device 1.

  Below, the positional relationship between each pattern in which a back electrode pattern made of Cu and a solder resist film made of polybenzoxazole polyimide resin are formed on the substrate 2 which is a resin substrate will be described in detail.

  FIG. 3 shows a plan view of the back side of the resin substrate. FIG. 3A shows the positions of the extraction electrode 10 and the through hole 9. FIG. 3B shows the shape of the insulator 11 which is a solder resist film. FIG. 3 (c) is a diagram showing the superposition of FIGS. 3 (a) and 3 (b), and specifically shows the positional relationship between the positions of the through holes 9 and the connection pads 16 in the present invention. It is.

  As shown in FIG. 3C, an insulator 11 is formed on the through-hole 9 by a screen printing process, and a conductor portion without the insulator 11 is used as a connection pad 16 formed of Cu. In this structure, since the through-hole 9 is completely closed by the insulator 11, when the solder is joined to the circuit board 15 in FIG. 2 with solder, the solder enters the recess of the through-hole 9 to generate bubbles. There is nothing.

  As a comparative example, a back electrode pattern and a solder resist film insulator 11 pattern are shown in FIG. FIG. 4A shows the positions of the extraction electrode 10 and the through hole 9. FIG. 4B shows the shape of the insulator 11. FIG. 4C is a superposition of FIGS. 4A and 4B. As shown in FIG. 4 (c), in the structure of the comparative example, the inside of the recess of the through hole 9 is exposed to the connection pad 16, and when the circuit board 15 shown in FIG. Bubbles sometimes remained.

  Thus, also in the present embodiment, the surface acoustic wave device of the present invention can be a surface acoustic wave device with a lower cost than that using the ceramic substrate of the comparative example by using a resin substrate as the substrate 2. In addition, it was confirmed that the popcorn phenomenon that occurred when mounted on the circuit board 15 shown in FIG. 2 was suppressed. As a result, a surface acoustic wave device and an electronic circuit device excellent in reliability could be obtained.

It is sectional drawing which shows an example of embodiment of the surface acoustic wave apparatus of this invention. (A) is sectional drawing which shows a mode that the surface acoustic wave apparatus shown in FIG. 1 is mounted in a circuit board, (b) is an example of the electronic circuit apparatus which mounted the surface acoustic wave apparatus shown in FIG. 1 in the circuit board. It is sectional drawing shown. (A)-(c) is a top view which shows the mode of the base | substrate back surface side of the surface acoustic wave apparatus of this invention, respectively. (A)-(c) is a top view which shows the mode of the base | substrate back surface side of the surface acoustic wave apparatus of a comparative example, respectively. It is sectional drawing which shows an example of the conventional surface acoustic wave apparatus. (A) is sectional drawing which shows a mode that the surface acoustic wave apparatus shown in FIG. 5 is mounted in a circuit board, (b) is an example of the electronic circuit apparatus which mounted the surface acoustic wave apparatus shown in FIG. 5 in the circuit board. It is sectional drawing shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave apparatus 2 ... Base | substrate 3 ... Piezoelectric substrate 4 ... Protective cover 5 ... Excitation electrode 6 ... Input-output electrode 7, 13 ... Solder bump 8 ... Connecting electrode 9 ... through hole
10 ... Extraction electrode (conductor pattern)
11 ... Insulator
12 ... I / O pad
14 ... Bubble
15 ... Circuit board
16 ... Pad for connection

Claims (4)

A surface acoustic wave device in which a surface acoustic wave element having an excitation electrode provided on one main surface of a piezoelectric substrate is provided on an upper surface of a substrate so that the one main surface of the piezoelectric substrate faces the surface. A through-hole penetrating between the upper surface and the lower surface, a conductor pattern that closes the through-hole and is electrically connected to the excitation electrode formed on the lower surface of the base, and a part of the conductor pattern A surface acoustic wave device comprising: an insulator covering the region so as to expose the region. The surface acoustic wave device according to claim 1, wherein a concave portion is formed in the through hole by the conductor pattern, and the concave portion is filled with the insulator. 3. The electronic circuit device according to claim 1, wherein the surface acoustic wave device according to claim 1 is disposed on a circuit board via a connection conductor connected to the partial region of the conductor pattern. 4. The connection conductor according to claim 3, wherein the connection conductor has a connection pad and solder formed on the connection pad, and the insulator is sandwiched between the connection pad and the conductor pattern. The electronic circuit device described.

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