JP2000196400A - Mounting structure for surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the mounting structure of a surface acoustic wave device by which micro-chip surface acoustic wave filter is obtained without impairing attenuating characteristic by forming a ground electrode for enclosing exciting electrodes at the lower surface side or the outer peripheral part of a piezoelectric substrate and mounting them on a circuit substrate in the mounting structure of the surface acoustic wave device consisting of the piezoelectric substrate where the exciting electrodes are formed. SOLUTION: Plural interdigital resonator electrodes being the exciting electrode are connected to a ladder circuit on the substrate 2, the connecting electrode, an input/output electrode 3a and the ground electrode 3b are formed and, besides, a semi-conductive or insulated protecting film 4 such as silicone or silicon oxide is formed on it so that the chip surface acoustic wave filter is constituted. In the filter 1 constituted in this way, the ground electrode 3b enclosing the resonator electrodes is formed at the lower surface side or the outer peripheral part of the piezoelectric substrate 2 and mounted on the circuit board 6. The distance (h) between the surface of the circuit board 6 and that of the resonator electrodes is set to be larger than the wave length of the surface acoustic wave.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure of a surface acoustic wave device used for a mobile communication device such as a cellular phone on a circuit board, and more particularly to the mounting of an ultimately miniaturized surface acoustic wave device. Regarding the structure.

[0002]

2. Description of the Related Art Currently, surface acoustic wave filters used in mobile communication devices have extremely low mounting area, low weight, and low height in order to reduce the size of portable telephone terminals. Is desired.

As shown in FIGS. 7A to 7C, in a conventional surface acoustic wave filter 101, a substrate 102 mainly made of a piezoelectric single crystal on which excitation electrodes are formed, and the substrate 102 are sealed and mounted. It consists of a ceramic package 108.

A substrate 102 has a comb-shaped surface acoustic wave resonator electrode (excitation electrode) 103 made of aluminum, an aluminum-copper alloy, or the like, input / output electrodes 113a and 113b, and a ground electrode (not shown). Are formed on the same surface.

The excitation electrode 103 has a protective film 1 on its upper surface.
04 is formed to prevent adhesion and corrosion of dust and the like. The substrate 102 is fixed to the bottom of the ceramic package 108 by a resin 110, and the input / output electrodes 103a and the ground electrode (not shown) on the substrate 102 are connected to the input / output terminal electrodes 113a and 113 of the ceramic package 108.
3b are electrically connected to each other using wires 114.

[0006] A protective film is not formed at a portion where the wire 114 is connected to ensure the stability of the connection. Substrate 10
Since 2 is an elastic body, a space 105 for securing free vibration is required. For this reason, a lid 109 is provided on an upper portion, and a ceramic package 108 and a resin 11 are provided so as to prevent vibration damping due to external moisture.
0 is hermetically sealed.

[0007] In such a surface acoustic wave filter, the electrical connection between the substrate 102 and the ceramic package 108 is made by the wire 114, and the height of the wire is high, which hinders miniaturization. Further, the ceramic package 108 is much larger than the substrate 102,
The size was increased by about 1.5 to 2.1 mm per side, and the bottom area was about three times as large.

Further, since the ground terminal electrode 113b inside the ceramic package 108 shown in FIG. 7A is connected to the back surface of the ceramic package 108 shown in FIG. As shown by a circle in FIG. 8, components were generated, and the attenuation characteristics at the low frequency side of the pass band (hatched portion) and at 4 to 6 GHz were deteriorated.

In the surface acoustic wave filter shown in FIGS. 9A to 9C, an input / output electrode 103a on a substrate 102 and a ground electrode (not shown) are connected to a ceramic package 108 via a metal bump 111. Upper terminal electrodes 113a, 1
13b, the bump 111 and the terminal electrodes 113a, 1
13b to compensate for the low strength of connection with 13b.
2 for reinforcement. In addition, the conductive resin 112 also plays a role of absorbing poor flatness of the bump 111. With the structure described above, the height can be reduced by the height of the loop of the wire.

However, the ceramic package 10
As the bottom area of 8 is reduced, the distance g between the input / output terminal electrodes 113a on the back surface is reduced, and a capacitance is generated between the electrodes. For this reason, as shown by the circles in FIG. 10, the attenuation characteristics on the high frequency side of the pass band (hatched portion) and near 3 GHz were deteriorated. Further, the ceramic package 108 still occupies most of the filter shape, which hinders reduction in size, weight, and height.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a mounting structure of a surface acoustic wave device which can be used as a very small chip surface acoustic wave filter without deteriorating attenuation characteristics.

[0012]

In order to solve the above problems, a surface acoustic wave device according to the present invention is a mounting structure of a surface acoustic wave device comprising a piezoelectric substrate on which excitation electrodes are formed. A ground electrode surrounding the excitation electrode is formed on the side or the outer peripheral portion and mounted on a circuit board.

Here, the ground electrode is a piezoelectric substrate and / or
Alternatively, it may be formed on a circuit board.

Further, the distance between the surface of the circuit board and the surface of the excitation electrode is set to be equal to or longer than the wavelength of the surface acoustic wave.

[0015]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing a mounting structure of a surface acoustic wave device according to the present invention, and FIG. 2 is a plan view of electrodes of the surface acoustic wave device.

As shown in FIGS. 1 and 2, a surface acoustic wave filter 1 which is a surface acoustic wave device includes, for example, a lithium tantalate single crystal, a lanthanum-gallium-niobium single crystal having a langasite-type crystal structure, for example. A plurality of comb-shaped resonator electrodes 3c, which are excitation electrodes, are connected to, for example, a ladder-type circuit on a substrate 2 made of a piezoelectric single crystal such as lithium tetraborate single crystal. A chip surface acoustic wave filter is formed by forming an input / output electrode 3a and a grounding electrode 3b, and further forming a semiconductive or insulating protective film 4 such as silicon or silicon oxide thereon.

The surface acoustic wave filter 1 constructed as described above is mounted on the circuit board 6 by forming a grounding electrode 3b surrounding the resonator electrode 3c on the lower surface side or the outer peripheral portion of the piezoelectric substrate 2. The distance h between the surface of the circuit board 6 and the surface of the resonator electrode 3c is set to a distance equal to or longer than the wavelength of the surface acoustic wave. In FIG. 1, reference numeral 8 denotes a conductive adhesive made of a conductive resin or the like, and reference numeral 9 denotes a connection pad made of a metal or the like formed on the circuit board 6.

Here, the input / output electrode 3a and the ground electrode 3b
Are formed in the same process, these electrodes have excellent flatness. Further, since the input / output electrodes and the grounding electrode protrude beyond the protective film 4 made of semi-conductive or insulating material, the space 5 for free vibration can be maintained and mounted face-down on the circuit board 6 as it is. It is possible to Further, since the grounding electrode 3b is formed all around the substrate 2, airtightness is also ensured.

Although the ladder type filter has been described in the present invention, the present invention is also applicable to a surface acoustic wave device such as a resonator type or propagation type filter or a duplexer other than a filter as long as it has an excitation electrode. It goes without saying that it can be applied.

[0021]

Next, an embodiment in which a chip surface acoustic wave filter according to the present invention is manufactured will be described.

FIG. 4 shows a manufacturing process of the chip surface acoustic wave filter. In the production, photolithography was performed using a stepper (reduction projection exposure machine) and an RIE (Reactive Ion Etching) apparatus.

(1) Substrate 2 (42 ° Y-cut of lithium tantalate single crystal) was subjected to ultrasonic cleaning using acetone, IPA or the like to remove organic components. Next, after sufficiently drying the substrate with a clean oven, the electrode 3 was formed. The electrode 3 was formed using an Al-Cu (2% by weight) alloy film using a sputtering apparatus. The thickness of the electrode was about 2000 ° (see FIG. 4A).

(2) The resist 7 was spin-coated to a thickness of about 0.5 μm (see FIG. 4B).

(3) Patterning was performed to a desired shape by a stepper, and an unnecessary portion of the resist 7 was dissolved with an alkali developing solution by a developing device to form a desired resist pattern (see FIG. 4C).

(4) Al-Cu electrode 3 by RIE device
Was etched (see FIG. 4D).

(5) The resist 7 was peeled off, and the patterning was completed (see FIG. 4E).

(6) A protective film 4 made of SiO _{2 was formed} to a thickness of 250 ° by a sputtering apparatus (FIG. 4).
(F)).

(7) A resist 7 was applied again on the entire surface of about 3 μm (see FIG. 4G).

(8) The resist 7 on the substrate 2 on which the input / output electrodes 3a and the grounding electrodes 3b are formed is exposed to light and removed (FIG. 4).
(See (h)).

(9) The SiO ₂ protective film 4 of the substrate 2 on which the input / output electrode 3a and the ground electrode 3b are formed is removed by CDE (see FIG. 4 (i)).

(10) An Al electrode was formed by vapor deposition with a thickness of 2 μm so as to be thicker than the protective film 4 (see FIG. 4 (j)).

(11) The electrode 3 on the electrode resist together with the resist 7 was removed by lift-off. (FIG. 4 (k)
See).

(12) The wafer was diced along a dicing line, and the wafer was divided into chips and completed. The chip size was 1.6 × 1.0 mm.

Next, the mounting will be described.

(13) The completed chip surface acoustic wave filter 1 was mounted face down on a circuit board 6 made of glass epoxy (see FIG. 1). For this mounting, a silver filler is applied to the outer periphery of the ground electrode 3b and the input / output electrode portion.
A reactive polyester resin or an epoxy resin containing ９３93% by weight or 81-86% by weight is applied by a screen printing method, temporarily cured at 80 ° C. for about 1 hour, and then cured at 120 ° C. Mounting was performed by curing at ℃ 225 ° C. for 10 to 60 minutes.

According to the mounting structure of the surface acoustic wave filter, the periphery of the substrate 2 is surrounded by the grounding electrode 3b, and airtightness can be secured at the same time. Input / output electrode 3a
And the grounding electrode 3b are formed in the same process, so that they have excellent flatness and extremely high conduction reliability. Further, the height of the space 5 is ensured at 2 μm. This height is substantially equal to the wavelength at the center frequency of the surface acoustic wave filter, and if the height is larger than this, the vibration of the surface acoustic wave will not be hindered.

FIG. 3 shows the electrical characteristics of the chip surface acoustic wave filter thus obtained. As shown by the circles in FIGS. 8 and 10, there was no deterioration in the attenuation characteristics, and good attenuation characteristics could be obtained. Further, on the high frequency side of the pass band (hatched portion), an attenuation of 20 dB or more could be obtained, and the attenuation characteristics near the pass band did not deteriorate.

The reason why good damping characteristics were obtained as compared with the conventional example is that the ceramic package is not required, and unnecessary inductance caused by the ceramic package is not generated. Since a wide input / output terminal electrode is not required and only an input / output electrode for conducting connection to the circuit board is required, a facing distance between the input / output electrodes may be wide and a generated capacity may be small.

In the chip surface acoustic wave filter of the present invention, as shown by d in FIG. 2, there is a concern that the characteristics may be deteriorated due to the opposing capacitance between the input / output 3a and the ground electrode 3b. Confirmed that there is no. It is mainly found that the VSWR (standing wave ratio) changes according to the capacitance of this portion, and there is no problem in the attenuation characteristic at all if the VSWR does not change. FIG. 5 is a graph showing the relationship between the input / output opposing distance d and the capacitance C generated there. This shows that when the facing distance d is 20 μm or less, the capacitance that occurs suddenly increases. d is 20 μm
Is about 0.14 pF, the change in VSWR in this case is at most 0.08 pF as shown in FIG.
It turned out to be. Therefore, the facing distance d is 20
It was confirmed that the characteristics were not deteriorated if the thickness was more than μm.

In this embodiment, the circuit board is a glass epoxy board. However, a ceramic board such as glass ceramic or alumina may be used. Although the electrodes were made of an Al--Cu alloy or Al electrodes, Ni
Needless to say, other materials such as Ti and Ti may be used. Although the protective film is made of silicon oxide, another semiconductive or insulating material such as silicon or silicon nitride may be used.

[0042]

According to the mounting structure of the surface acoustic wave device of the present invention, for example, a very small chip surface acoustic wave filter can be realized. In addition, high-frequency attenuation can be secured. This eliminates the need for a package for accommodating a piezoelectric substrate on which excitation electrodes are formed, as in the conventional case.
Light weight and low cost can be achieved.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a mounting structure of a chip surface acoustic wave filter according to the present invention.

FIG. 2 is a plan view schematically showing an electrode structure of the chip surface acoustic wave filter according to the present invention.

FIGS. 3A to 3C are diagrams illustrating electrical characteristics of a chip surface acoustic wave filter according to the present invention.

FIGS. 4A to 4K are cross-sectional views illustrating steps of manufacturing a surface acoustic wave filter according to the present invention.

FIG. 5 is a diagram showing a relationship between a facing distance and a capacitance of the chip surface acoustic wave filter of the present invention.

FIG. 6 is a diagram showing a relationship between a counter capacitance and a VSWR of the chip surface acoustic wave filter of the present invention.

7A and 7B are views for explaining a conventional surface acoustic wave filter, wherein FIG. 7A is a top view in an unsealed state, FIG. 7B is a bottom view, and FIG. 7C is A- of FIG. FIG. 3 is a schematic sectional view taken along line A.

FIGS. 8A to 8C are diagrams illustrating electrical characteristics of a conventional surface acoustic wave filter.

9A and 9B are diagrams illustrating another conventional surface acoustic wave filter, wherein FIG. 9A is a top view in an unsealed state, FIG. 9B is a bottom view, and FIG. 9C is a view of FIG. FIG. 3 is a schematic sectional view taken along line BB.

FIGS. 10A to 10C are diagrams illustrating electrical characteristics of a conventional surface acoustic wave filter.

[Explanation of symbols]

 1: chip surface acoustic wave filter (surface acoustic wave device) 2, 102: substrate 3, 103: excitation electrode 3a: input / output electrode 3b: ground electrode 3c: resonator electrode (excitation electrode) 3d: connection electrode 4, 104 : Protective film 5, 105: space 6: circuit board 7: resist 8: adhesive 9: connection pad 101: conventional surface acoustic wave filter 103a: input / output electrode 108: ceramic package 109: lid 110: resin 111: bump 112 : Conductive resin 113: terminal electrode 113 a: input / output terminal electrode 113 b: ground terminal electrode 114: wire

Claims (2)

[Claims] 1. A mounting structure of a surface acoustic wave device comprising a piezoelectric substrate on which an excitation electrode is formed, wherein a grounding electrode surrounding the excitation electrode is formed on a lower surface side or an outer peripheral portion of the piezoelectric substrate. A mounting structure of a surface acoustic wave device characterized by being mounted on a surface acoustic wave device. 2. The surface acoustic wave device according to claim 1, wherein a distance between a surface of the circuit board and a surface of the excitation electrode is set to be equal to or longer than a wavelength of a surface acoustic wave. Mounting structure.