JP2004153413A - Surface acoustic wave device and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized surface acoustic wave device with a low profile and high reliability. <P>SOLUTION: A face of a surface acoustic wave element 2 having an interdigital electrode section 4 and an electrode pad 6 or the like on a piezoelectric substrate 3 is opposed and joined with a joining substrate 9 having an electrode land 10, a via-hole 11, and an external terminal 12 so that the surface having the electrode 4 section faces the joining substrate. A film 8 is adhered to the joining substrate 9 in a way of covering the surface acoustic wave element 2, and a sealing reinforcement resin 13 covers the adhered part of the film 8 to the joining substrate 9 and the joining substrate 9 therearound. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a surface acoustic wave device, and more particularly, to a surface acoustic wave device for a chip size package.
[0002]
[Prior art]
2. Description of the Related Art In recent years, as mobile communication devices such as mobile phones and mobile phones have become smaller, lighter, and higher in frequency, small and lightweight surface acoustic wave devices have been frequently used as filters mounted on these mobile communication devices. .
[0003]
In a surface acoustic wave device, since a surface acoustic wave propagating on the surface of a piezoelectric substrate is used, it is necessary to protect a surface portion (functional portion) where the surface acoustic wave propagates from moisture, dust, and the like. Therefore, in the conventional packaging method of the surface acoustic wave device, a structure in which a surface acoustic wave element is mounted on a package made of alumina or the like by wire bonding or flip chip bonding and sealed with a lid material has been mainly used.
[0004]
However, in such a structure, when the surface acoustic wave element is downsized due to the advancement of fine wiring technology, unless the package mounting the surface acoustic wave element is downsized, the surface acoustic wave device is reduced in size and height. There was a problem that it could not be changed.
[0005]
Therefore, a surface acoustic wave device using a chip size package using flip chip bonding, which is currently used in the field of semiconductor components, has been developed.
[0006]
The above-described conventional surface acoustic wave device will be specifically described with reference to FIG. A surface acoustic wave element 52 in which a comb-shaped electrode portion 54 and an electrode pad 56 are formed of a metal such as Al on a piezoelectric substrate 53 is mounted on a bonding substrate 59 having electrode lands 60, via holes 61 and external terminals 62. The surfaces having the portions 54 are opposed to each other and are joined by flip chip bonding. At this time, the surface acoustic wave element 52, the external terminal 62, the via hole 61 connected to the external terminal 62, and the electrode land 60 are electrically connected via the bump 57. Then, in order to protect the surface portion (functional portion) through which the surface acoustic wave including the comb-shaped electrode portion 54 propagates, a plastic film 58 is bonded to the bonding substrate 59 so as to cover the surface acoustic wave element 52. . The surface acoustic wave device 51 is sealed from above the film 58 with the sealing resin 63 in order to enhance the confidentiality.
[0007]
Further, in the structure shown in FIG. 5, a structure is disclosed in which a deformable film such as a plastic film, a conductive film, or a film to which a metal is adhered is adhered, and then sealed with a sealing resin. Reference 1).
[0008]
Further, a structure using a second deformable film in place of the sealing resin in order to enhance confidentiality is disclosed.
[0009]
[Patent Document 1]
JP 2001-176995 A
[Problems to be solved by the invention]
However, in the structure shown in FIG. 5 and the structure disclosed in Patent Literature 1, since the film alone is insufficient in confidentiality, the film is sealed with a sealing resin from above the film. This makes it difficult to reduce the height of the surface acoustic wave device.
[0011]
Further, in the structure using the second deformable film without using the resin, when the adhesion of the deformable film to the substrate is insufficient, there is a problem that the confidentiality cannot be secured.
[0012]
The surface acoustic wave device of the present invention has been made in view of the above problems, and has as its object to solve these problems and to provide a small, low-profile, and highly reliable surface acoustic wave device. .
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a surface acoustic wave device according to the present invention is characterized in that the surface acoustic wave element having a piezoelectric substrate and at least one interdigital electrode formed on one surface of the piezoelectric substrate includes the interdigital electrode. A surface acoustic wave device bonded to one surface of a bonding substrate with the surfaces having the surfaces facing each other, and a film adhered to one surface of the bonding substrate so as to cover the surface acoustic wave element; and It is characterized by having a sealing reinforcing resin provided so as to cover the bonding portion with the bonding substrate and the surrounding bonding substrate.
[0014]
Preferably, the film comprises a liquid crystal polymer.
[0015]
It is also preferable that the film has a multilayer structure in which a metal layer or a ceramic layer is sandwiched between resin layers.
[0016]
In particular, the water vapor permeability coefficient of the film is preferably 6.9 × 10 ⁻¹¹ [g · m / m ² · S] or less.
[0017]
It is preferable that the bonding substrate has an external terminal, an electrode land, and a via hole connecting the external terminal and the electrode land.
[0018]
Further, the method for manufacturing a surface acoustic wave device according to the present invention includes a step of manufacturing a plurality of surface acoustic wave elements each having a piezoelectric substrate and at least one comb-shaped electrode portion formed on one surface of the piezoelectric substrate; Forming a bump on the surface acoustic wave element, preparing an aggregate substrate of a bonding substrate having an external terminal, an electrode land, and a via hole connecting the external terminal and the electrode land; A step of bonding the element to the collective substrate with the surface having the comb-shaped electrode portion facing each other via a bump, covering each of the plurality of surface acoustic wave elements with a film, and applying heat or pressure to the film. A step of bonding to the bonding substrate by at least one of the steps, a step of covering the bonding portion of the film, and a bonding substrate therearound with a sealing reinforcing resin; Characterized by a step of cutting out the individual surface acoustic wave device.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(Embodiment) FIG. 1 is a sectional view showing an embodiment of a surface acoustic wave device according to the present invention, FIG. 2 is a plan view of a surface acoustic wave device according to an embodiment of the present invention, and FIG. FIG. 4 is a plan view of a surface acoustic wave device mounted on a collective substrate (joined substrate) according to an embodiment of the present invention.
[0020]
As shown in FIG. 1, the surface acoustic wave device 1 of the present invention includes a surface acoustic wave element 2, a bonding substrate 9, a film 8, and a sealing reinforcing resin 13. The surface acoustic wave element 2 includes a piezoelectric substrate 3, a comb-shaped electrode portion 4 formed on the piezoelectric substrate 3, a reflector (not shown), and an electrode pad 6. The bonding substrate 9 includes an electrode land 10, a via hole 11, and an external terminal 12. The surface acoustic wave element 2 is bonded to the bonding substrate 9 via the bumps 7 formed on the electrode pads 6 in a state where the surface having the comb-shaped electrode portion 4 faces the film substrate 8. Covered by This film 8 is adhered to a bonding substrate 9. Further, the bonding portion of the film 8 to the bonding substrate 9 and the surrounding bonding substrate 9 are covered with a sealing reinforcing resin 13.
[0021]
The protective film 8 used in the present invention needs to have a high barrier property in order to protect a surface portion (functional portion) through which the surface acoustic wave propagates, particularly from moisture. Therefore, various films were prepared and evaluated. The following evaluations were performed using a surface acoustic wave device having a frequency characteristic of 1.9 GHz, with only the film being different. In the evaluation of characteristics, a good product and a bad product were judged as defective when the insertion loss deteriorated by 0.3 dB or more.
[0022]
First, the correlation between the water vapor transmission coefficient of the protective film 8 and the non-defective product ratio of the surface acoustic wave device was investigated using a single-layer film made of polyimide and a multi-layer film made of polyimide and Al ₂ O ₃ . . At this time, the total thickness of the protective film was set to 100 μm. This is because, when actually used for a surface acoustic wave device, as the protective film becomes thicker, it is necessary to increase the height of the bump. To reduce the height, the lower the height of the bump is, the more preferable it is. This is because it is difficult and expensive to produce the above bumps.
[0023]
In addition, as for the film having a multilayer structure, samples in which the water vapor transmission coefficient of the protective film was changed by preparing Al ₂ O ₃ on polyimide and gradually increasing the thickness of Al ₂ O ₃ were prepared. Was subjected to a reliability test.
[0024]
In the evaluation sample, a protective member is formed around a surface portion (functional portion) of the surface acoustic wave element where the surface acoustic wave propagates, and then the protective member covers the surface portion (functional portion) of the surface acoustic wave and the protective member. The test was performed with a structure in which a protective film was adhered to the piezoelectric substrate, and evaluated by the number of non-defective products after leaving in a wet test tank for 2000 hours.
[0025]
Here, the water vapor transmission coefficient used for evaluation of the characteristics is determined by how much weight (g) of water vapor permeates with a protective film having a thickness of 1 m per unit time (S) and unit area (m ² ). Is a coefficient [g · m / m ² · S]. The water vapor transmission coefficient indicates the amount of water vapor permeated per unit thickness and is a value that is not related to the film thickness. The smaller the coefficient, the greater the effect as a barrier against water vapor.
[0026]
The results of the evaluation test are as follows: (1) Polyimide (100 μm): 2.3 × 10 ⁻⁸ [g · m / m ² · S] = 1/100 (1 good sample per 100 evaluation samples (2) Polyimide (99.5 μm) + Al ₂ O ₃ (0.5 μm): 9.7 × 10 ⁻¹⁰ [g · m / m ² · S] = 9/100 (3) polyimide (99 μm) + Al ₂ O ₃ (1 μm): 6.9 × 10 ⁻¹¹ [g · m / m ² · S] = 91/100, (4) polyimide (95 μm) + Al ₂ O ₃ ( 5 μm): 3.5 × 10 ⁻¹¹ [g · m / m ² · S] = 99/100, (5) Polyimide (90 μm) + Al ₂ O ₃ (10 μm): 1.2 × 10 ⁻¹¹ [g · m m / m ² · S] = 99/100, (6) polyimide (80 μm) + Al ₂ O ₃ (20 μm): 8.8 × 10 ⁻¹² [g · m / m ² · S] = 100/100, (7) Polyimide (75 μm) + Al ₂ O ₃ (25 μm): 5.0 × 10 ⁻¹² [ g · m / m ² · S] = 100/100, (8) polyimide (50 μm) + copper foil (25 μm) + Al ₂ O ₃ (25 μm): 5.0 × 10 ⁻¹³ [g · m / m ^2. S] = 100/100.
[0027]
From the above results, it can be seen that as the thickness of Al ₂ O ₃ is increased and the water vapor transmission coefficient of the protective film is reduced, the characteristics are less likely to deteriorate. In particular, when the water vapor transmission coefficient is 6.9 × 10 ⁻¹¹ [g · m / m ² · S], it can be seen that 90% or more can maintain the good quality standard only by the barrier property of the protective film. Furthermore, it is understood that, when the value is 3.5 × 10 ⁻¹¹ [g · m / m ² · S] or less, 99% or more can maintain the standard with good characteristics only by the barrier property of the protective film. In this case, a polyimide film was used as the resin layer. However, the present invention is not limited to this. Any film having heat resistance such as polyethylene naphthalate may be used.
[0028]
The above results are obtained for a single-layer film made of polyimide and a multilayer film made of polyimide and Al ₂ O _{3. The} single-layer film has a water vapor transmission coefficient of 6.9 × 10 ^{−. As} a material having a density of ¹¹ [g · m / m ² · S] or less, there is a liquid crystal polymer. The water vapor transmission coefficient of the liquid crystal polymer is 3.0 × 10 ⁻¹¹ [g · m / m ² · S], the characteristic yield is 100/100, and if a protective film made of the liquid crystal polymer is used, a single layer is obtained. Even high reliability can be obtained.
[0029]
In a film having a multilayer structure, a metal layer such as a copper foil may be formed between resin layers in order to reduce the water vapor transmission coefficient and impart a shielding effect to the film. However, the adhesion between the resin layer and the metal layer is basically weak, and a short circuit may occur when the film having the metal layer comes into contact with a bump or the like. In addition to these problems, the process of forming the multilayer structure is complicated, so that it is preferable to use, as the protective film 8, a liquid crystal polymer that can obtain a high barrier property with one layer.
[0030]
The method for manufacturing the surface acoustic wave device 1 according to the present invention is as follows.
[0031]
First, a resist pattern (not shown) having a desired opening pattern is formed by using a photolithography technique in which a resist is applied on the piezoelectric substrate 3 and then exposed using a mask.
[0032]
Next, as shown in FIG. 3 (a), after forming Al, which is an electrode material metal, by a vapor deposition method or the like, the resist pattern is peeled (lifted off) by dipping and rocking in a resist peeling solution, as shown in FIG. On the piezoelectric substrate 3, the comb-shaped electrode portion 4, the reflector 5, the electrode pad 6, the wiring, and the like are formed, and the surface acoustic wave device 2 as shown in FIG. 2 is manufactured.
[0033]
As the piezoelectric substrate, LiTaO ₃ , LiNbO ₃ , quartz, Li ₂ B ₄ O ₇ or the like is used according to target characteristics. Further, as the electrode material, metal materials such as Au, Cu, Ni, Ta, and W can be used in addition to Al.
[0034]
At the same time, a film 8 used to cover the surface acoustic wave element 2 is prepared. As the film 8, a film made of a liquid crystal polymer having a thickness of 44 μm is used. As can be seen from the results of the above evaluation, the liquid crystal polymer has a high water vapor transmission coefficient of 3.0 × 10 ⁻¹¹ [g · m / m ² · S]. It is suitable for protecting the (functional part) from moisture and dust.
[0035]
In this example, a film made of a liquid crystal polymer was used as the film 8, but the present invention is not limited to this, and a film having a multilayer structure such as having a metal layer or a ceramic layer between resin layers is used. Is also good. If the water vapor transmission coefficient is 6.9 × 10 ⁻¹¹ [g · m / m ² · S] or less, the surface portion (functional portion) where the surface acoustic wave propagates by using only the film 8 can be protected from moisture and dust. Can be done.
[0036]
A film having a multilayer structure is prepared by preparing a Si substrate having a polished surface, temporarily bonding a 25 μm-thick polyimide film on the Si substrate, and pasting a 10 μm-thick copper foil formed thereon by rolling, A polyimide film having a thickness of 25 μm is adhered thereon, and heated while applying pressure by a press machine to press-bond the polyimide film and the copper foil. Further, an adhesive layer may be formed thereon by, for example, applying an adhesive layer.
[0037]
Next, a collective substrate 20 to be a bonding substrate 9 later is prepared. An electrode land 10 corresponding to the electrode pad 6 of the surface acoustic wave element 2, an external terminal 12, and a through hole 11 for electrically connecting the electrode land 10 and the external terminal 12 are formed in the collective substrate 20 (bonding substrate 9). Have been.
[0038]
A bump 7 made of Au is formed on the electrode pad 6 of the surface acoustic wave element 2. The height of the bump 7 is set to 20 to 30 μm. In this embodiment, a bump made of Au is used as the bump 7, but the present invention is not limited to this, and a bump made of solder may be used. However, when a bump made of Au-Sn-based or Sn-Ag-based solder is used, it is preferable to form a Ni layer on the electrode pad 6 as an adhesion layer of the bump made of solder.
[0039]
Then, as shown in FIG. 3B, the plurality of surface acoustic wave elements 2 are bonded to the collective substrate 20 by flip chip bonding. The electrode pads 6 of the surface acoustic wave element 2 and the electrode lands 10 of the collective substrate 20 are electrically and mechanically connected via the bumps 7.
[0040]
Subsequently, as shown in FIG. 3C, the surface acoustic wave element 2 joined to the collective substrate 20 (joint substrate 9) is covered with a film 8, and the film 8 is thermocompression-bonded to the collective substrate 20 (joint substrate 9). . At this time, the bonding temperature is 300 ° C., which is a temperature at which the film 8 is easily processed and pyroelectric breakdown due to a temperature change of the piezoelectric substrate does not occur. In this way, it is possible to protect the surface portion (functional portion) where the surface acoustic wave propagates by the film 8 from moisture, dust, and the like, while securing the vibration space of the surface acoustic wave.
[0041]
Then, as shown in FIG. 3D, an epoxy-based resin is applied so as to cover a bonding portion of the film 8 with the collective substrate 20 (joining substrate 9), and is thermally cured to form a sealing reinforcing resin. 13 is formed. At this time, since the film 8 used has a high barrier property, it is not necessary to apply a resin so as to cover the entire film 8.
[0042]
Finally, the surface acoustic wave device is separated into individual chips from the collective substrate 20 by dicing, whereby the surface acoustic wave device 1 shown in FIG. 1 is obtained.
[0043]
【The invention's effect】
As described above, the surface acoustic wave device of the present invention provides a surface acoustic wave element formed by forming a comb-shaped electrode portion, an electrode pad, and the like on a piezoelectric substrate, on a bonding substrate having electrode lands, via holes, and external terminals, After bonding the surfaces having the comb-shaped electrode portions facing each other, the film is bonded to the bonding substrate so as to cover the surface acoustic wave element, and further, the bonding portion of the film to the bonding substrate, and the bonding substrate around the bonding portion. Is covered with a sealing reinforcing resin.
[0044]
With such a structure, the surface portion (functional portion) of the comb-shaped electrode portion, etc., through which the surface acoustic wave propagates, is hermetically sealed while securing the vibration space of the surface acoustic wave. In particular, by using a film made of a liquid crystal polymer or a film having a multilayer structure having a water vapor transmission coefficient of 6.9 × 10 ⁻¹¹ [g · m / m ² · S] or less, the elastic surface can be obtained only by the barrier property of the film. Since the surface portion (functional portion) through which the wave propagates can be protected from moisture and dust, the back surface of the surface acoustic wave element only needs to be covered with a film. Further, by covering only the bonding portion of the film to the bonding substrate and the surrounding bonding substrate with the sealing and reinforcing resin, it is possible to achieve a low profile while securing the adhesion of the film.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an embodiment of a surface acoustic wave device according to the present invention.
FIGS. 2A and 2B are a sectional view and a plan view of a surface acoustic wave device according to an embodiment of the present invention.
FIG. 3 is a diagram illustrating each process of a method for manufacturing a surface acoustic wave device according to an embodiment of the present invention.
FIG. 4 is a plan view of a surface acoustic wave device mounted on a collective board (joined board) according to an embodiment of the present invention.
FIG. 5 is a sectional view of a conventional surface acoustic wave device.
[Explanation of symbols]
1, 51 Surface acoustic wave device 2, 52 Surface acoustic wave element 3, 53 Piezoelectric substrate 4, 54 Comb-shaped electrode part 5 Reflector 6, 56 Electrode pad 7, 57 Bump 8, 58 Film 9, 59 Joint substrate 10, 60 Electrode Land 11, 61 Via hole 12, 62 External terminal 13 Resin for sealing and reinforcement 20 Assembly board 63 Sealing resin

Claims (6)

A surface acoustic wave element having a piezoelectric substrate and at least one comb-shaped electrode portion formed on one surface of the piezoelectric substrate was bonded to one surface of the bonded substrate with the surfaces having the comb-shaped electrode portions facing each other. A surface acoustic wave device,
A film adhered to one surface of the bonding substrate so as to cover the surface acoustic wave element,
A surface acoustic wave device comprising: a sealing reinforcing resin provided so as to cover a bonding portion of the film with the bonding substrate and a bonding substrate around the bonding portion. The surface acoustic wave device according to claim 1, wherein the film is made of a liquid crystal polymer. The surface acoustic wave device according to claim 1, wherein the film has a multilayer structure in which a metal layer or a ceramic layer is sandwiched between resin layers. 4. The surface acoustic wave device according to claim 1, wherein a water vapor transmission coefficient of the film is 6.9 × 10 ⁻¹¹ [g · m / m ² · S] or less. 5. The surface acoustic wave device according to any one of claims 1 to 4, wherein the bonding substrate has an external terminal, an electrode land, and a via hole connecting the external terminal and the electrode land. Manufacturing a plurality of surface acoustic wave devices having a piezoelectric substrate and at least one comb-shaped electrode portion formed on one surface of the piezoelectric substrate,
Forming a bump on the surface acoustic wave element;
An external terminal, an electrode land, and a step of preparing an aggregate substrate of a bonding substrate having a via hole connecting the external terminal and the electrode land,
Bonding the plurality of surface acoustic wave elements to the collective substrate with the surfaces having the comb electrode portions facing each other, via bumps;
A step of covering each of the plurality of surface acoustic wave elements with a film and bonding the film to a bonding substrate by at least one of heat and pressure,
A step of covering the adhesive portion of the film and the surrounding bonding substrate with a sealing reinforcing resin,
Cutting out individual surface acoustic wave devices from the collective substrate by dicing.

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