JP2001244781A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device having a long chip length applicable to video applications, a low profile and high reliability against thermal shocks. SOLUTION: A piezoelectric body 1 used for an element 10 is made of a material containing lithium tantalite or lithium niobate, and a base substrate 20 is made of a material whose thermal expansion coefficient is 11-20 ppm/ deg.C. Thus, the difference between the thermal expansion coefficients of the both is small. Even when the element length is long, improper contact or bent in the base substrate is small and even when the surface acoustic wave device is subjected to a heat process, such as solder reflow, the surface acoustic wave device with high reliability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device suitable for a frequency filter of a video device such as a TV.

[0002]

2. Description of the Related Art A surface acoustic wave device is a comb-shaped electrode (IDT: Inter Digita) made of a thin film metal provided on a piezoelectric body.
l Transducer), electric signal and surface acoustic wave (SAW)
This is a device that performs the conversion to transmit and receive signals, and is widely used, including surface acoustic wave filters, surface acoustic wave resonators, delay circuits, and the like.

In recent years, particularly in the field of TVs and the like, surface acoustic wave filters have been widely used because of their advantages of being thinner and smaller. The surface acoustic wave filters used in this field are mainly of an insertion type for mounting on a circuit board such as a SIP (Single Inline Package) using a lead frame.

However, the introduction of a double-sided circuit board has been studied to reduce the size and cost of video equipment, and accordingly, a surface acoustic wave filter is also desired to be a surface mount type.

[0005] Conventional surface acoustic wave devices use a lead frame as a modified product.
ne Package) with a bent J-lead. However, such a device has a problem that the package thickness cannot be reduced. In the future, the thickness will be required to fit within the card, and DIP type surface mount products will not be able to cope.

Therefore, it has been proposed to make the surface acoustic wave element face-down bonded on a flat base substrate and cover the element with a cap so as to further reduce the thickness.

However, a surface acoustic wave element for video has a long element length, and accordingly, a base substrate having a long length is used. For this reason, the influence of thermal expansion generated in a heating step such as solder reflow cannot be ignored.

If the difference in thermal expansion coefficient between the piezoelectric body forming the element and the base substrate is large, stress is applied to bumps and the like connecting the element and the base substrate, and the connection is released by thermal shock. There is a possibility that it will.

Furthermore, since the base substrate and the cap are bonded with a sealing material, if the difference in thermal expansion coefficient between the two is large, the device will be warped.

[0010]

As described above, conventionally,
If the element length is long like a surface acoustic wave element for video,
If the difference between the coefficients of thermal expansion of the piezoelectric body forming the element and the base substrate is large, stress will be applied to the bumps connecting the base substrate and the element due to the difference in thermal expansion generated in the heating process such as solder reflow. The connection may be disconnected due to the applied thermal shock.

[0011] Similarly, since the base substrate and the cap are bonded with a sealing material, there is a problem that if the difference in the coefficient of thermal expansion is large, the device will be warped.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a thin and highly reliable thermal shock device for a surface acoustic wave device having a long chip length such as an image application. .

[0013]

A surface acoustic wave device according to the present invention comprises a surface acoustic wave element having a comb-shaped electrode and a terminal electrode formed on a piezoelectric body, and an external connection terminal and an element connection terminal on the surface. A formed base substrate, a connection body for electrically connecting the terminal electrode of the surface acoustic wave element and the element connection terminal of the base substrate, a cap covering the surface acoustic wave element, and the surface acoustic wave An element comprising: a sealing material for sealing the base substrate and the cap on which a device is mounted; and the piezoelectric body is formed using a lithium tantalate or lithium niobate material; Is characterized by having a coefficient of thermal expansion of 11 to 20 ppm / ° C.

Here, it is preferable that the difference in thermal expansion coefficient between the piezoelectric body and the base substrate is within 5 ppm / ° C.

The base substrate may be a glass substrate / epoxy resin printed wiring board, or a glass substrate / BT resin printed wiring board.
Alternatively, a ceramic substrate having a coefficient of thermal expansion adjusted to 11 to 20 ppm / ° C. may be used.

The connection body may include a metal bump, or may include a conductive adhesive.

It is desirable that the difference in thermal expansion coefficient between the piezoelectric body and the cap be within 5 ppm / ° C.

The cap has a coefficient of thermal expansion of 11 to 20.
It may be molded using a liquid crystal polymer adjusted to ppm / ° C.

As described above, since the difference in the coefficient of thermal expansion between the piezoelectric body and the base substrate is small, the difference in thermal expansion between the two is small even in a heating step such as solder reflow, so that the connecting member may come off, It is possible to suppress the occurrence of warpage of the source substrate or the like.

[0020]

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

The surface acoustic wave device according to the present embodiment will be described with reference to FIGS.

As shown in FIG. 1A, a surface acoustic wave element 10 is formed by providing a comb-like electrode 2 and a terminal electrode 3 on the surface of a piezoelectric body 1. Obtained surface acoustic wave device 10
2A is as shown in FIG. 2A, but as described above, the chip length is long for the video application, and the distance between the terminal electrodes 3 is also long.

As shown in FIG. 2B, the surface acoustic wave element 10
The sound absorbing material 5 that absorbs the reflected wave from the end face is applied to both end portions by screen printing or the like.

As shown in FIG. 1C, a convex conductive material 4 such as a metal bump is formed on the terminal electrode 3 of the surface acoustic wave device 10.
Is formed by bonding, screen printing, or the like.

On the other hand, as shown in FIG. 3, on the flat base substrate 20 on which the external connection terminals 12 and the element connection terminals 13 are formed in advance, the element connection terminals 1 are formed by screen printing or the like.
3 is coated with a conductive adhesive 14.

As shown in FIG. 4A, the surface acoustic wave element 10 is face-down bonded to the base substrate 20. Thereafter, the conductive adhesive 14 is subjected to a heat process.
Is cured, and the element 10 is fixed on the base substrate 20 and electrically connected.

As shown in FIG. 4B, the cap 21 is attached to the base substrate 2 using an adhesive so as to cover the outside of the element 10.
Then, the base substrate 20 is cut into individual pieces to obtain a surface acoustic wave device as shown in FIG.

FIG. 5 shows the appearance of the obtained surface acoustic wave device. FIGS. 5A to 5D are a plan view, a front view, a bottom view, and a right side view, respectively.

Conventionally, an alumina ceramic substrate has been generally used as a base substrate of a surface acoustic wave device. However, the thermal expansion coefficient of the alumina-based ceramic substrate is around 7 ppm / ° C. The piezoelectric material used for forming the element has a lithium tantalate content of 16 ppm / ° C. and a lithium niobate content of 15.4 ppm / ° C. Therefore, there is a difference in thermal expansion coefficient of 8 ppm / ° C. or more between the two.
Therefore, the peak temperature in the solder reflow from room temperature to 24
When the temperature changes to 0 ° C., a dimensional difference of 18 to 20 μm occurs in the base substrate for an element having a length of about 10 mm.

The bump and the conductive adhesive are usually 100 to 2
If the gap is about 00 μm (Φ or □) and the gap between the element and the base substrate is about 40 to 50 μm, this dimensional difference cannot be absorbed.

As a result, a connection body made of bumps or the like comes off, and a defect that electrical connection is not ensured occurs.

A high adhesive strength is obtained between the base substrate and the cap by using a sealing material in a ring shape along the end face of the cap, and the cap is usually not peeled off.
The device sometimes warped.

In the above-described embodiment, the piezoelectric body 1 is L
iNbO3 (coefficient of thermal expansion 15.4ppm // ° C) or LiTaO3
(Coefficient of thermal expansion 16 ppm / ° C.).

The base substrate 20 is made of FR-4, FR
-5 resin or equivalent glass substrate / epoxy resin printed wiring board (coefficient of thermal expansion: 14 to 16 ppm / ° C) or BT resin (glass substrate, printed using BT resin containing bismaleimide and triazine as basic components) The wiring board is formed using a coefficient of thermal expansion of 13 to 16 ppm / ° C.). Therefore, the difference in the coefficient of thermal expansion between the two is within the range of 5 pp / ° C.

Further, the cap 21 is formed using a molded product of a liquid crystal polymer. The liquid crystal polymer has a different thermal expansion coefficient between the flow direction X of the resin during molding and the vertical direction Y (longitudinal direction) thereof.

The thermal expansion coefficient in the X direction is 10 ppm / ° C., and the thermal expansion coefficient in the Y direction is 26 ppm / ° C. In order to obtain a desired coefficient of thermal expansion during this time, by setting the pouring gate position of the resin at the time of molding substantially at the center position, a coefficient of thermal expansion close to the base substrate 20 of 11 to 20 ppm /
° C can be obtained.

According to the present embodiment, since the coefficient of thermal expansion between the piezoelectric body and the base substrate is within the range of 5 ppm / ° C., even in the heating step such as solder reflow, the heat between the piezoelectric body and the base substrate is maintained. The difference in expansion can be suppressed small.
Thus, it is possible to prevent a problem such as disconnection of the connection body, occurrence of electrical connection failure, and occurrence of warpage of the base substrate.

Thus, even when the chip length is long, such as a device for video, a surface acoustic wave device that is thin and has high reliability against thermal shock can be obtained.

The above embodiment is merely an example and does not limit the present invention. For example, the materials of the base substrate, the piezoelectric body, and the cap are not limited to those used in the above embodiment. Other materials such as a ceramic material may be used as long as the combination of the base substrate and the piezoelectric material, or desirably, the difference between the coefficients of thermal expansion of the base substrate, the piezoelectric material and the cap is within the range of 5 ppm / ° C. You may.

In the above-described embodiment, the bump and the conductive adhesive are used in combination as the connection body between the base substrate and the element. However, the present invention is not limited to this, and another material may be used.

By the way, the base substrate is usually formed in a large number of pieces, and after mounting the elements, it is often cut into individual pieces.

In many cases, the surface acoustic wave element is cut into individual pieces from the state of a wafer and then subjected to face-down bonding to a base substrate. However, the present invention does not limit the timing of the cutting step. Therefore, after the base substrate is formed in multiple pieces, it may be cut into individual pieces before mounting, or the surface acoustic wave element may be cut into individual pieces from the wafer state before being cut into individual pieces. Face-down bonding may be performed.

[0043]

As described above, in the surface acoustic wave device of the present invention, the piezoelectric body is formed from a material containing lithium tantalate or lithium niobate, and the base substrate has a thermal expansion coefficient of 11 to 20 ppm /. ° C., the difference between the two thermal expansion coefficients is small, even if the element length is long,
When a heating process such as solder reflow is performed, poor connection and warpage of the base substrate do not occur, and a highly reliable surface acoustic wave device can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an element showing a configuration of a surface acoustic wave device according to an embodiment of the present invention and a method of manufacturing the same in each step.

FIG. 2 is a plan view showing a plane configuration of an element used in the surface acoustic wave device according to the embodiment.

FIG. 3 is a vertical cross-sectional view of the element showing the configuration of the surface acoustic wave device according to the embodiment and a method of manufacturing the same in each step.

FIG. 4 is a longitudinal sectional view of the element showing the configuration of the surface acoustic wave device according to the embodiment and the method of manufacturing the same in each step.

FIG. 5 is a plan view, a front view, a bottom view, and a right side view showing the appearance of the surface acoustic wave device according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric body 2 Comb-shaped electrode 3 Terminal electrode 4 Metal bump 5 Sound absorbing material 10 Surface acoustic wave element 11 Flat plate 12 External connection terminal 13 Element connection terminal 14 Conductive adhesive 20 Base board 21 Cap

Claims (9)

[Claims] A surface acoustic wave element having a comb-shaped electrode and terminal electrodes formed on a piezoelectric body; a base substrate having external connection terminals and element connection terminals formed on a surface; A connection body for electrically connecting the terminal electrode and the element connection terminal of the base substrate; a cap covering the surface acoustic wave element; and the base substrate on which the surface acoustic wave element is mounted. A sealing material for sealing the cap, wherein the piezoelectric body is formed using a lithium tantalate or lithium niobate material, and the base substrate has a thermal expansion coefficient of 11 to 20 ppm / ° C. A surface acoustic wave device characterized by the above-mentioned. 2. The surface acoustic wave device according to claim 1, wherein a difference in thermal expansion coefficient between the piezoelectric body and the base substrate is within 5 ppm / ° C. 3. The printed circuit board according to claim 1, wherein said base substrate is a glass substrate / epoxy resin-based printed wiring board.
Or the surface acoustic wave device according to 2. 4. The surface acoustic wave device according to claim 1, wherein said base substrate is a glass base material / BT resin printed wiring board. 5. The base substrate has a coefficient of thermal expansion of 11 to 2.
3. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is a ceramic substrate adjusted to 0 ppm / ° C. 6. The surface acoustic wave device according to claim 1, wherein the connection body includes a metal bump. 7. The surface acoustic wave device according to claim 1, wherein the connection body includes a conductive adhesive. 8. The surface acoustic wave device according to claim 1, wherein a difference in thermal expansion coefficient between the piezoelectric body and the cap is within 5 ppm / ° C. 9. The cap has a coefficient of thermal expansion of 11 to 20.
The surface acoustic wave device according to any one of claims 1 to 8, wherein the device is formed using a liquid crystal polymer adjusted to ppm / ° C.