JPH11214955A - Surface acoustic wave device - Google Patents

Abstract

(57) [Summary] [Problem] It is possible to shield external electromagnetic waves as much as possible, eliminating the need for a metal cover as in the past, making it possible to reduce the height and cost, and further improve the moisture resistance compared to the past. And to provide a highly reliable surface acoustic wave device. SOLUTION: A surface acoustic wave device S1 in which a surface acoustic wave element 1 having an excitation electrode for generating a surface acoustic wave provided on a lower surface of a piezoelectric substrate 1a is accommodated in a package 5, and is provided on an upper surface side of the piezoelectric substrate 1a. A conductive resin layer for blocking electromagnetic waves of a predetermined frequency or less is formed, and the conductive resin layer is connected to a grounding conductor pattern formed on a package.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an elastic surface such as a flip-chip type surface acoustic wave filter which is preferably used as a high-frequency element in a mobile communication device such as a cellular phone or a cellular phone in the telecommunications field. Wave device.

[0002]

2. Description of the Related Art FIGS. 7 to 9 are sectional views showing structural examples of a surface acoustic wave filter using a conventional flip chip mounting method.

A surface acoustic wave filter J1 shown in FIG. 7 is formed by mounting a surface acoustic wave element (chip) 1 having a driving electrode 1b formed of a comb-like electrode or a reflector electrode on a piezoelectric substrate 1a by flip-chip mounting. 5.

Here, the package 5 has a base 5a, an annular laminated member 5b on which the outer peripheral portion of the chip 1 is placed, an annular laminated member 5c which forms a wider space, and a joining member 10 disposed above the annular laminated member 5c. An electrode is formed outside the package 5.

The signal electrodes 2 formed on the lower surface of the chip 1 are connected to the signal electrodes 7 and the flip-chip bonding electrodes 9 formed in the package 5 via the bumps 3. . Incidentally, reference numeral 6 in the drawing denotes a conductive adhesive for bump bonding.

A surface acoustic wave filter J2 shown in FIG. 8 joins a metal lid 4 with a welding metal annular body 5e instead of the laminated member 5c and the joining member 10 in the surface acoustic wave filter J1 of FIG. Further, the area occupied by the laminated member 5b in the package 5 is reduced so that the outer periphery of the peripheral portion of the chip 1 is not mounted.

A surface acoustic wave filter J3 shown in FIG. 9 has a cover 4 joined by a metal ring 5e for welding instead of the laminated member 5c and the joining member 10 in the surface acoustic wave filter J1 of FIG. is there.

As described above, in the conventional flip chip surface acoustic wave filter, the input / output pad portion formed on the chip is wire-bonded to make electrical connection with the package. Au or Cu
And the like, and a bump is made of a conductive adhesive or solder to connect the chip to the inside of the package.

[0009]

However, the main problem of the flip chip mounting is that the metal film electrode of the surface acoustic wave element formed on the lower surface side of the chip is contaminated and short-circuited by solder or conductive adhesive. Therefore, the hermetic structure in the package and the structure for preventing external noise are hardly taken into consideration and have not been properly performed. Moreover, the conventional flip-chip mounting has been used only as a means for reducing the area, and has not improved the height of the package or the cost of the entire device.

In a surface acoustic wave device which does not require shielding of external noise (especially external electromagnetic waves), a device having a resin embedded structure for the purpose of a low profile structure has been proposed. There was a problem with the moisture resistance when using an airtight structure material. Further, a filling structure using a hydrophobic resin has also been proposed, but such a resin structure alone was insufficient in moisture resistance.

Therefore, in the present invention, external electromagnetic waves can be shielded as much as possible, so that a metal cover is not required as in the prior art, and the height and cost can be reduced, and the moisture resistance can be further improved. It is an object of the present invention to provide a surface acoustic wave device having extremely excellent reliability.

[0012]

In order to solve the above-mentioned problems, a surface acoustic wave device according to the present invention includes a surface acoustic wave element having an excitation electrode for generating a surface acoustic wave on a lower surface of a piezoelectric substrate in a package. A surface acoustic wave device housed in
A conductive resin layer for blocking electromagnetic waves of a predetermined frequency or less is formed on the upper surface of the piezoelectric substrate, and the conductive resin layer is connected to a grounding conductor pattern formed on the package.

[0013] A metal thin film and / or a hydrophobic resin layer may be provided between the piezoelectric substrate and the conductive resin layer and / or on the upper surface side of the conductive resin layer. As a result, it is possible to improve the moisture resistance and improve the lowering of the height.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a surface acoustic wave device according to the present invention will be described below in detail with reference to the drawings. First, FIGS. 1 and 2 are sectional views showing the basic structure of a surface acoustic wave filter according to the present invention.

The surface acoustic wave filter S1 shown in FIG. 1 is composed of lithium niobate (LiNbO ₃ ), lithium tantalate (LiTaO ₃ ), and lithium tetraborate (Li ₂ B).
_On the lower surface of a piezoelectric substrate 1a made of a langasite-type single crystal such as ₄ O ₇ ) or La ₃ Ga _5.5 Nb _0.5 O ₁₄ , a comb-shaped excitation electrode and reflector electrodes provided on both sides thereof are provided. A surface acoustic wave element (chip) 1 provided with an electrode pattern 1b in which a plurality of drive electrodes are connected to a lattice-type or ladder-type circuit is accommodated in a package 5 by flip-chip mounting.

The package 5 is composed of a base member 5a made of glass ceramics or ceramics such as alumina (Al ₂ O ₃ ), and a ring-shaped laminated member which is made of the same material as the base member 5a and on which the outer peripheral portion of the chip 1 is mounted. 5b, an annular laminated member 5c that forms a space wider than the laminated member 5b with similar members, and a conductor pattern 8 for grounding is formed inside or outside the package 5 in a planar or castellated shape. . Also, inside the package 5,
That is, the signal electrode 7 is also provided in a predetermined area on the upper surface of the base 5a.
And an electrode 9 for flip chip bonding.

An electrode pattern 1 is provided on the lower surface of the chip 1.
The signal electrode 2 connected to the electrode b is formed, and the signal electrode is connected to the signal electrode on the package 5 side and the flip-chip bonding electrode 9 via the bump 3.

Further, the back side of the chip 1 (piezoelectric substrate 1a)
A conductive resin layer 11 that completely covers the upper surface and side surfaces of the piezoelectric substrate 1a is formed on the upper surface side of the piezoelectric substrate 1a by a dropping or injection forming method. The conductive resin layer 11 has a thickness of about 1 mm or less and a resistance value of 10 Ω · cm or less. For example, the conductive resin layer 11 has a predetermined aspect ratio in a resin such as an epoxy-based, urethane-based, silicon-based, or polyimide-based resin. And a conductive filler forming a distribution is dispersed, and is not more than a predetermined frequency (not less than a predetermined wavelength: not less than λ / 3, where λ is elasticity) determined by the thickness of the conductive resin layer 11, the aspect ratio of the conductive filler, and the like. (Wavelength of surface wave). Here, as the conductive filler, A
For example, u, or Ag, or an Ag-Pd alloy, or Ni, for example, a flake-like filler may be used. By appropriately setting the particle size of the flake-like filler, it is possible to block electromagnetic waves of a predetermined frequency or less.

According to the surface acoustic wave filter S1, the conductive resin layer is connected to the grounding conductor pattern formed inside and outside the package. It is possible to provide a surface acoustic wave filter that can be cut off and has good filter characteristics without the influence of external noise.

The surface acoustic wave filter S2 shown in FIG. 2 is different from the surface acoustic wave filter S1 shown in FIG. 1 in the structure for holding the chip 1, and has a large space forming area of the laminated member 5b. By placing the chip 1 in the above, an effective configuration can be obtained when the bump formation accuracy cannot be sufficiently obtained.

The surface acoustic wave filter S3 shown in FIG. 3 is a further development of the surface acoustic wave filter S2 shown in FIG.
The moisture resistance is improved by interposing a hydrophobic resin layer 12 such as a metal thin film, a urethane-based resin, or a silicone resin on the upper surface. According to this configuration, in particular, the moisture entering through the conductive resin layer 11 can be cut off as much as possible by overcoating the upper surface of the conductive resin layer 11 which is likely to become porous after curing with a hydrophobic layer. A surface acoustic wave filter having excellent properties can be provided.

The surface acoustic wave filter S4 shown in FIG. 4 is obtained by applying the laminated structure on the back side of the chip 1 of the surface acoustic wave filter S3 shown in FIG. 3 to the configuration of the surface acoustic wave filter S1 shown in FIG. There is an effect similar to that of the surface acoustic wave filter S3 in terms of moisture resistance.

The surface acoustic wave filter S5 shown in FIG. 5 is an extension of the configuration of the surface acoustic wave filter S1 shown in FIG. 1 on the back side of the chip 1, and completely covers the top and side surfaces of the piezoelectric substrate 1a. The hydrophobic resin layer 12 has a thickness of 50 to 100.
.mu.m, and a conductive resin layer 11 for blocking external noise is provided on the hydrophobic resin layer 12, and the hydrophobic resin layer 12 is formed on the conductive resin layer 11 to a thickness of 150 to 500 .mu.m.
By providing the conductive resin layer 11 at m degrees, it is possible to prevent the conductive resin layer 11 from being directly provided on the back surface side of the chip 1, and thereby it is possible to more effectively prevent the conductive surface of the chip 1 from being contaminated with the conductive resin. In order to relieve the stress on the back side of the chip 1, it is preferable to use a urethane resin for the hydrophobic resin layer 12.

The surface acoustic wave filter S6 shown in FIG. 6 is obtained by improving the back side of the chip 1 of the surface acoustic wave filter S5 shown in FIG. By forming a metal thin film of aluminum or the like on the surface, infiltration of moisture due to the moisture permeability of the resin can be more favorably prevented.

The surface acoustic wave device of the present invention is not limited to the surface acoustic wave filter having the above-described structure, but can be applied to a surface acoustic wave resonator or the like. Between, and / or on the upper surface side of the conductive resin layer,
It is sufficient that a metal thin film and / or a hydrophobic resin layer are provided,
In particular, the types of the constituent members and the layer configuration on the back (top) side of the chip can be appropriately changed and implemented without departing from the gist of the present invention.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a surface acoustic wave filter S3 shown in FIG. 3, an excitation electrode composed of a comb-shaped electrode is formed on a piezoelectric substrate composed of a single crystal of lithium tantalate (LiTaO ₃ ) propagating in a 42 ° rotated Y-cut X direction as a substrate. A chip formed by connecting a plurality of surface acoustic wave resonators constituted by reflector electrodes provided on both sides thereof to a lattice circuit, and arranging a common electrode for connection of these resonators and a common electrode for bump formation is made of glass. It was connected by flip chip bonding in a ceramic or Al ₂ O ₃ ceramic package.

Here, the chip has a center frequency of about 900M.
Hz band, 60 pairs of excitation electrodes, 15
λ (λ: wavelength of surface acoustic wave), the material of the electrode is aluminum formed by vapor deposition, and the thickness is 410 nm.
And The electrode finger width and the electrode finger distance are each 1
μm. Au was used as a bump.

When high reliability is required for mechanical strength for the purpose of use in a mobile communication terminal or the like, the thickness of the above-mentioned aluminum electrode film is increased to about 1 μm only for the common electrode portion for bump formation. It may be designed.

Although the allowable distance between the chip and the package differs depending on the viscosity of the conductive resin to be used, the mechanical position accuracy of the die bonding apparatus used at the time of flip chip mounting is about 300 μm. Considering this, there is no problem if the viscosity of the conductive resin used is 100 cp or more.
mm silicone resin was used.

Au was used as the conductive filler dispersed in the conductive resin, and its average particle size was about 100 μm. Also, the gap between the fillers is considered to be about 100 μm at the maximum, and unless the conductivity of the resin is impaired,
From the distance between the fillers, the cutoff frequency of the external noise is f = 3
× 10 ⁸ / (1 × 10 ⁻⁴ × 3) = 1000 (GHz)
(Electromagnetic wave speed 3 × 10 ⁸ m / sec, cutoff frequency 1 /
(Three wavelengths), so that noise having a frequency of 1000 GHz or less could be cut off, and cutoff characteristics could be sufficiently secured up to high frequencies.

Further, a thin metal film of aluminum was overcoated on the conductive resin layer to a thickness of about 0.5 μm by a vapor deposition method, so that the moisture resistance could be remarkably improved. If the thickness of the metal thin film is at least about 0.1 μm, the moisture resistance can be sufficiently improved. Preferably, the thickness is 0.1 to 0.8 μm.

[0032]

According to the surface acoustic wave device of the present invention, the conductive resin layer is connected to the grounding conductor pattern formed inside and outside the package. It is possible to provide a surface acoustic wave device that can block electromagnetic waves and has good characteristics without the influence of external noise.

In addition, since a metal thin film and / or a hydrophobic resin layer are provided between the piezoelectric substrate and the conductive resin layer and / or on the upper surface side of the conductive resin layer, the conductive resin is particularly likely to become porous after curing. Moisture entering through the layer can be cut off as much as possible, and a highly reliable surface acoustic wave device having excellent moisture resistance can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating one embodiment of a surface acoustic wave device according to the present invention.

FIG. 2 is a sectional view illustrating another embodiment of the surface acoustic wave device according to the present invention.

FIG. 3 is a cross-sectional view illustrating another embodiment of the surface acoustic wave device according to the present invention.

FIG. 4 is a sectional view illustrating another embodiment of the surface acoustic wave device according to the present invention.

FIG. 5 is a cross-sectional view illustrating another embodiment of the surface acoustic wave device according to the present invention.

FIG. 6 is a cross-sectional view illustrating another embodiment of the surface acoustic wave device according to the present invention.

FIG. 7 is a cross-sectional view illustrating an example of a conventional surface acoustic wave device on which flip chip mounting is performed.

FIG. 8 is a cross-sectional view illustrating an example of a conventional surface acoustic wave device on which flip chip mounting is performed.

FIG. 9 is a cross-sectional view illustrating an example of a conventional surface acoustic wave device on which flip chip mounting is performed.

[Explanation of symbols]

 1: chip (surface acoustic wave element) 1a: piezoelectric substrate 1b: drive electrode 2: bonding electrode 3: bump 5: package 5a: substrate 5b, 5c: laminated member 6: conductive adhesive for bump bonding 7: signal Electrode 8: Grounding electrode (grounding conductor pattern) 9: Flip chip bonding electrode 11: Conductive resin layer 12: Hydrophobic resin layer 13: Metal thin film S1 to S6: Surface acoustic wave device

Claims (2)

[Claims] 1. A surface acoustic wave device in which a surface acoustic wave element comprising an excitation electrode for generating a surface acoustic wave is provided on a lower surface of a piezoelectric substrate and housed in a package. A surface acoustic wave device, wherein a conductive resin layer for blocking electromagnetic waves is formed, and the conductive resin layer is connected to a grounding conductor pattern formed on the package. 2. A metal thin film and / or a hydrophobic resin layer is disposed between the piezoelectric substrate and the conductive resin layer and / or on the upper surface side of the conductive resin layer. 2. The surface acoustic wave device according to 1.