JP3677409B2 - Surface acoustic wave device and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a surface acoustic wave device mainly used in a radio communication circuit such as a mobile communication device, and more particularly to a surface acoustic wave device that can be downsized and packaged by a wafer process. The present invention relates to a wave device and a manufacturing method thereof.
[0002]
[Prior art]
In recent years, many surface acoustic wave devices have been used as elements such as filters, delay lines, and transmitters of electronic devices that use radio waves. In particular, surface acoustic wave filters that are small and lightweight and have high steep cut-off performance as filters have come to be widely used as RF-stage and IF-stage filters of mobile terminal devices in the field of mobile communication.
[0003]
As mobile terminal devices are becoming smaller and lighter, the number of built-in circuits has increased due to the multi-band technology that supports multiple communication systems, and the electronic components used are small components that can be surface-mounted to improve their mounting density. Is strongly demanded. A surface acoustic wave filter which is a key part of a portable terminal device is also required to have a small surface acoustic wave filter which can be surface-mounted with low loss and a cutoff characteristic outside the passband.
[0004]
Conventionally, the surface acoustic wave filter has been put to practical use in the ceramic package type rather than the can package type. Among these, the ceramic package type can be surface-mounted and can be downsized compared to the can package type. Has come to be widely used.
[0005]
In the first generation ceramic package type surface acoustic wave filter, the surface acoustic wave element bonded and fixed in the package and the internal electrode of the package are electrically connected by wire bonding. As a result, the surface acoustic wave filter has an occupied area 5 to 6 times that of the built-in surface acoustic wave element.
[0006]
In order to solve this problem and reduce the size, a second-generation ceramic package type surface acoustic wave filter, in which a surface acoustic wave element is face-down bonded inside the package, as shown in FIG. 6, has been put into practical use. Yes.
[0007]
This surface acoustic wave filter J is mainly composed of a substrate 51 made of a piezoelectric single crystal on which an excitation electrode 2 is formed, and a ceramic package containing the substrate 51. The ceramic package includes a base 53 and a frame. 54, a lid 55, an internal electrode 56, an external electrode 57, and the like. In the surface acoustic wave element, the excitation electrode 52 and the external electrode 57 of the package are electrically connected through the pad 58 and the bump 59.
[0008]
Since the surface acoustic wave filter J does not use wire bonding, the surface acoustic wave filter J can be reduced in size by about a half compared with the first generation ceramic package type surface acoustic wave filter.
[0009]
[Problems to be solved by the invention]
However, in the second generation face-down mounting type ceramic package type surface acoustic wave filter, the size of the package is about three times that of the built-in surface acoustic wave element, and is not sufficiently miniaturized. There's a problem.
[0010]
In addition, the conventional method for mounting on a package has a drawback that it lacks mass productivity because it is assembled using individual packages after the device chip is cut from the wafer.
[0011]
Therefore, the present invention has been made to cope with such a problem, and is an extremely miniaturized surface-mountable elastic surface whose surface area is substantially equal to that of a built-in surface acoustic wave device. It is an object of the present invention to provide a surface acoustic wave device such as a wave filter and a vibrator, and a manufacturing method that can be packaged in a wafer state and has excellent mass productivity.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, a surface acoustic wave device according to the present invention forms an excitation electrode covered with a protective cover bonded via a low-melting glass on a piezoelectric substrate and an input / output pad connected to the excitation electrode. The columnar electrodes are erected on each input / output pad by electrolytic plating, and at least the outer periphery of the columnar electrode is surrounded by an insulator, and the upper end of the columnar electrode is used as an input / output terminal for an electric signal. It is characterized by that.
[0013]
In particular, the protective cover is conductive and is disposed on the input / output pad via an insulating member.
[0014]
The surface acoustic wave device manufacturing method of the present invention includes a step of forming a protective cover on a cover forming substrate, and a step of forming an excitation electrode and an input / output pad connected to the excitation electrode on the piezoelectric substrate. A step of adhering the protective cover to the piezoelectric substrate through a low melting point glass so as to cover the excitation electrode with the protective cover, a step of removing the cover forming substrate, and electrolytic plating of the columnar electrode on the input / output pad And a step of surrounding at least the outer periphery of the columnar electrode with an insulator and using the upper end of the columnar electrode as an input / output terminal.
[0015]
Here, in particular, the protective cover can be efficiently formed by plating and can have a firm structure. In addition, in order to secure the vibration space of the excitation electrode, the protective cover is provided with a recess at least in a region corresponding to, for example, a comb-like electrode constituting the excitation electrode. Further, the recess may be formed in a plurality of regions according to the formation region of the excitation electrode, and may be arranged symmetrically or geometrically.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of a surface acoustic wave device according to the present invention will be described with reference to the drawings.
[0017]
FIG. 1 is a cross-sectional view of a main part schematically showing a surface acoustic wave device S, schematically showing a state cut along a cross-sectional line passing through an excitation electrode and two columnar electrodes. Is not necessarily illustrated accurately.
[0018]
The surface acoustic wave device S includes a comb-tooth-shaped excitation electrode 2 on a piezoelectric substrate 1, a wiring electrode 3 connected to the piezoelectric substrate 1 and including an input / output pad and a ground pad, and a wiring electrode 3 (at least an input / output pad). A plurality of columnar electrodes 5 standing up, a protective cover 4 made of metal or the like covering the excitation electrode 2 to ensure the vibration space G of the excitation electrode 2, and at least the outer periphery of the columnar electrode 5 is an insulator such as a resin And an upper end portion of the columnar electrode 5 as an electric signal input / output terminal. Reference numeral 7 denotes a solder bump, which can be mounted, for example, on an external circuit board (not shown) with the side on which the solder bump 7 is formed facing down.
[0019]
Here, by making the protective cover 4 conductive, it is possible to shield against a disturbance electric wave or the like, and it is possible to stabilize the surface acoustic wave device. However, in this case, the protective cover 4 is disposed on the input / output pad via the insulating member 8. For further stabilization, the protective cover 4 may be connected to the ground potential.
[0020]
Next, a method for manufacturing the surface acoustic wave device S will be described. First, a manufacturing process on the substrate 11 provided with the protective cover 4 will be described with reference to FIG. FIG. 2 is a schematic and partial illustration of a process for producing a protective cover on a substrate necessary for forming one surface acoustic wave element for the sake of simplicity. It is assumed that there are a large number of protective cover formation areas that match the formed excitation electrode areas.
[0021]
As shown in FIG. 2A, an electrode film 40 for plating is formed on a substrate (cover forming substrate) 11 having the same size as the piezoelectric substrate on which the surface acoustic wave element is formed. For the substrate 11, a piezoelectric material, silicon, glass or the like can be used. The electrode film 40 is made of a metal material such as copper, and is formed to a thickness of about 0.2 μm to 1 μm, for example, by sputtering film formation.
[0022]
Next, as shown in FIG. 2B, a plating guide corresponding to the upper portion of the protective cover is formed by photolithography. Here, the thickness of the photoresist 90 is about 50 μm to 100 μm.
[0023]
Next, as shown in FIG. 2C, a region 41 corresponding to the upper side of the protective cover is formed by electrolytic plating of the metal material (for example, copper). For example, copper sulfate 0.5 to 1.0 × 10 ³ mol / m ³ and sulfuric acid 1.5 to 2 × 10 ³ mol / m ³ are used as the electrolysis solution used at this time. Use standard electrodes such as potassium chloride and silver chloride.
[0024]
Next, as shown in FIG. 2D, a plating guide corresponding to the wall portion of the protective cover is formed by photolithography. At this time, the thickness of the photoresist 91 is about 50 μm to 100 μm, and the width of the groove corresponding to the thickness of the wall is about 50 μm to 100 μm.
[0025]
Next, as shown in FIG. 2E, a region 42 corresponding to the wall portion of the protective cover is formed by electrolytic plating of a metal material, and then an insulating member and an adhesive material are formed on the protective cover 42 by screen printing. A low melting point glass which is also 8 is formed to a thickness of about 5 to 10 μm.
[0026]
Finally, as shown in FIG. 2 (f), the photoresist is removed to complete a cover forming body A provided with a protective cover in which the concave portions 42a are formed symmetrically and geometrically.
[0027]
Next, a process of manufacturing the surface acoustic wave device S using the cover forming body A will be described with reference to FIG. 3 is also schematically shown in the same manner as FIGS.
[0028]
First, as shown in FIG. 3A, the excitation electrode 2 and the first layer 31 of the wiring electrode are formed on the piezoelectric substrate 1. Here, the piezoelectric substrate 1 includes a lithium niobate single crystal substrate, a lithium tantalate single crystal substrate, a quartz crystal substrate, a lithium tetraborate single crystal substrate, a lanthanum-type single crystal lanthanum, gallium, and a group VA element ( A piezoelectric substrate made of any of oxide single crystals containing niobium, tantalum, etc., a piezoelectric substrate such as a PZT substrate, or the like can be used. The first layer 31 of the excitation electrode 2 and the wiring electrode 3 is made of aluminum or aluminum alloy to which copper or the like is added. The excitation electrode 2 is for exciting and receiving surface acoustic waves. In this embodiment, the excitation electrode 2 is a single layer, but it can also be a multilayer electrode for improving the power durability of the electrode. These films are formed by vapor deposition or sputtering and have a thickness of about 0.2 μm to 0.5 μm.
[0029]
Next, as shown in FIG. 3B, the second layer 32 of the wiring electrode 3 is selectively formed by photolithography. As the electrode material of the second layer of the wiring electrode 3, nickel, chromium, titanium or the like and copper are used. The thickness of the second layer 32 of the wiring electrode 3 is about 0.2 μm to 0.5 μm.
[0030]
Next, as shown in FIG. 3C, the above-described cover forming body A is placed in alignment with the excitation electrode 2 on the piezoelectric substrate 1, and is made of low-melting glass in an inert gas atmosphere. Bonding is performed via the insulating member adhesive 8. The bonding temperature of the low melting point glass is 350 ° C. to 450 ° C.
[0031]
Next, as shown in FIG. 3D, a part of the substrate 11 and the plating electrode 41 used for forming the protective cover are removed by polishing, and a plating guide for forming a columnar electrode to be described later by plating. Is formed by photolithography. This polishing is performed in two stages: rough polishing by mechanical polishing using only an abrasive and mechanochemical polishing. The thickness of the photoresist 9 is 200 μm to 400 μm. Moreover, the diameter of the hole for columnar electrodes shall be 50 micrometers-200 micrometers.
[0032]
Next, as shown in FIG. 3E, the columnar electrode 5 is formed by electrolytic plating of copper. The electrolytic solution uses copper sulfate 0.5-1.0 × 10 ³ mol / m ³ and sulfuric acid 1.5-2 × 10 ³ mol / m ^{3. The} reference electrode is a standard electrode of potassium chloride / silver chloride. Is used.
[0033]
Next, as shown in FIG. 3F, the photoresist 9 is removed. Thereafter, a part of the wiring electrode second layer 31 for forming the columnar electrode is removed by etching using the columnar electrode 5 and the protective cover 4 as a mask. For the etching, wet etching or dry etching such as RIE is used.
[0034]
Next, as shown in FIG. 3G, at least the outer periphery of the columnar electrode 5 is covered with an external cover 6 made of resin by a thermosetting resin extrusion molding method. At this time, an upper part of the columnar electrode 5 can be exposed from the resin body by mounting a resin film having a thickness of about 100 μm on the surface of the die that presses the resin from the upper part. The thickness of the outer cover 6 is 200 μm to 400 μm. If there is no problem in strength, the upper surface of the protective cover 4 may be exposed to the outside.
[0035]
Finally, as shown in FIG. 3 (h), cream solder is screen-printed on top of the columnar electrodes and reflowed to form solder bumps 7 and a wafer including a plurality of surface acoustic wave devices S is completed. To do. Each surface acoustic wave device S is obtained by cutting the wafer by dicing or the like. In this way, the elastic surface device S having high reliability and the ultimate size reduction equivalent to the chip size is manufactured by a method that is mass-productive and greatly simplified. can do. The surface acoustic wave device S can be easily mounted on the external circuit board using the upper end portion of the columnar electrode 5 as an input / output terminal.
[0036]
4A and 4B and FIGS. 5A and 5B schematically show the state of the excitation electrode portion in the surface acoustic wave device S when a ladder type filter and a dual mode resonator type filter are realized. FIG.
[0037]
4A shows a pattern of the excitation electrode 2 and the wiring electrode (input pad 3a, output pad 3b, and ground pad 3c) on the piezoelectric substrate 1, and FIG. 5A shows the excitation electrode 2 and the wiring electrode (input pad). 3e, patterns of output pads 3m, ground pads 3d, 3f, 3k, 3n, and no connect pads 3g, 3h, 3i, 3j). 4B and 5B are schematic cross-sectional views of the wall surface portion of the protective cover 4.
[0038]
Thus, the mechanical reliability of the protective cover 4 can be greatly improved by arranging the concave portions of the protective cover symmetrically and geometrically only in the portion corresponding to the upper portion of the excitation electrode 2. This is effective for a design with a large electrode area.
[0039]
Further, with the above configuration, by providing a conductive cover between the input and the output, the isolation between the input and the output becomes good, and the attenuation characteristic is improved. In addition, since the input / output terminal and the ground terminal at the upper end of the columnar electrode 5 are symmetric, connection to the circuit board is simplified. In particular, in the case of the double mode resonator type filter shown in FIG. 5, an attenuation pole can be formed near the band by interposing an appropriate capacitance between 3g-3i or 3h-3j. Attenuation amount can be controlled.
[0040]
【Example】
Next, specific examples of the surface acoustic wave filter element to which the present invention is applied will be described.
[0041]
First, as shown in FIG. 3A, an excitation electrode and a wiring electrode first layer were formed on a piezoelectric substrate. A 36 ° Y-cut lithium tantalate substrate having a thickness of 350 microns was used as the piezoelectric substrate, and an aluminum alloy (copper content 1 wt%) was used as the first electrode of the excitation electrode and the wiring electrode. The electrode thickness was 3000 mm. The second layer 32 of the wiring electrode was a nickel / copper two-layer electrode having a thickness of 1000 mm or 2000 mm and selectively formed by photolithography.
[0042]
Next, as shown in FIG. 3C, the protective cover 4 formed on the silicon substrate was bonded with low melting point glass, and then the silicon substrate and the protective cover plating forming metal film 41 were removed using a polishing machine. .
[0043]
Next, as shown in FIGS. 3D and 3E, a guide for forming the columnar electrode by plating was formed of a photoresist, and the columnar electrode was formed by electrolytic plating of copper. The columnar electrode had a diameter of 100 μm and a height of 400 μm.
[0044]
Next, as shown in FIGS. 3F and 3G, after removing the photoresist for the plating guide, sealing was performed by an extrusion method using a thermosetting molding resin. Here, the upper part of the columnar electrode was exposed from the resin layer 6 by mounting a heat-resistant resin film having a thickness of 100 μm on a die for pressing the resin from above. The resin layer thickness was about 400 microns.
[0045]
Next, cream solder was screen-printed on the top of the columnar electrode with a thickness of 10 μm, and then reflowed at 270 ° C. to form solder bumps.
[0046]
Finally, the surface acoustic wave device was separated into one by dicing the substrate to produce a surface acoustic wave device.
[0047]
Since the excitation electrode of the surface acoustic wave device manufactured in this way is protected by a metal protective cover and a sealing resin, it has high reliability and is almost the same as a surface acoustic wave element (1 mm × 1.5 mm). A low profile with the same occupation area and a height of 0.8 mm could be realized.
[0048]
【The invention's effect】
As described above in detail, according to the surface acoustic wave device of the present invention, it is possible to reliably protect the surface acoustic wave element while securing the vibration space of the excitation electrode. Further, it is possible to eliminate the need for a conventional housing such as a package while having input / output terminals. As a result, it is possible to provide a surface acoustic wave device that is highly reliable, can be surface-mounted, and is ultimately reduced in size and is substantially the same size as the surface acoustic wave element.
[0049]
In addition, when the area occupied by the excitation electrode and the input / output pad is large, the mechanical reliability can be further improved by dividing the concave portion formed in the protective cover for each excitation electrode formation region.
[0050]
Moreover, it goes without saying that the plurality of recesses formed in the protective cover are effective if they are independent recesses, but the same effect can be obtained even if the recesses are connected so as not to impair the mechanical strength. can get. Thereby, it is possible to provide an excellent surface acoustic wave device that can further improve reliability and can be miniaturized.
[0051]
According to the method of manufacturing a surface acoustic wave device of the present invention, it is possible to perform all the steps by a wafer process, and a wafer comprising a large number of surface acoustic wave devices is cut into individual surface acoustic wave devices by a dicing process. A finished product can be obtained.
[0052]
Therefore, it is possible to realize wafer level packaging, and it is necessary to prepare a package (protective housing) for each surface acoustic wave device as in the past, and individually assemble the surface acoustic elements formed into chips through a dicing process. Therefore, an assembly apparatus such as a die bonder, a wire bonder, and a seam welder having a small processing capacity is not necessary, and the manufacturing process can be greatly simplified and mass-produced.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing a surface acoustic wave device according to the present invention.
FIGS. 2A to 2F are cross-sectional views schematically showing a manufacturing process of a cover forming body.
FIGS. 3A to 3H are cross-sectional views schematically showing manufacturing steps of the surface acoustic wave device according to the present invention.
FIGS. 4A and 4B are diagrams illustrating an embodiment of a ladder-type surface acoustic wave filter element according to the present invention, FIG. 4A is a plan view mainly showing an electrode pattern, and FIG. It is a fragmentary sectional view which shows the mode of a columnar electrode.
FIGS. 5A and 5B are diagrams illustrating an embodiment of a dual-mode resonator type surface acoustic wave filter element according to the present invention. FIG. 5A is a plan view mainly showing a state of an electrode pattern, and FIG. It is a fragmentary sectional view which shows the mode of a protective cover and a columnar electrode.
FIG. 6 is a cross-sectional view schematically showing a conventional surface acoustic wave device.
[Explanation of symbols]
1: Piezoelectric substrate 2: Excitation electrode 3: Wiring electrode (including input / output pads and ground pads)
4: Protective cover 5: Columnar electrode 6: External cover (insulator)
7: Solder bump (insulating material)
8: Low melting point glass 9: Photoresist 11: Cover forming substrate A: Cover forming body G: Vibration space S: Surface acoustic wave device

Claims (4)

Excitation electrodes covered with a protective cover bonded via a low-melting glass on a piezoelectric substrate and input / output pads connected to the excitation electrodes are formed, and columnar electrodes are erected on each input / output pad by electrolytic plating . In addition, the surface acoustic wave device is characterized in that at least an outer peripheral portion of the columnar electrode is surrounded by an insulator, and an upper end portion of the columnar electrode is used as an input / output terminal for an electric signal.   The surface acoustic wave device according to claim 1, wherein the protective cover has conductivity and is disposed on the input / output pad via an insulating member. Forming a protective cover on the cover forming substrate; forming an excitation electrode and an input / output pad connected to the excitation electrode on the piezoelectric substrate; and a protective cover to cover the excitation electrode with the protective cover. Adhering to a piezoelectric substrate through low melting point glass , removing the cover forming substrate, forming a columnar electrode on the input / output pad by electrolytic plating , and at least an outer peripheral portion of the columnar electrode A method of manufacturing a surface acoustic wave device, comprising: enclosing with an insulator and using an upper end portion of the columnar electrode as an input / output terminal. In the step of surrounding at least the outer peripheral portion of the columnar electrode with an insulator made of resin and using the upper end portion of the columnar electrode as an input / output terminal, the die is provided with a resin film on the surface holding the insulator from above. 4. The method of manufacturing a surface acoustic wave device according to claim 3, wherein an upper portion of the columnar electrode is exposed from the insulator by pressing an insulator, and a solder bump is formed on an upper end portion of the columnar electrode.

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