JP2003152500A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the area of bumps while keeping bonding strength of a surface acoustic wave element mounted on a mounting board via a plurality of bumps in a surface acoustic wave device. SOLUTION: The surface acoustic wave device has a surface acoustic wave element provided with a piezoelectric substrate and at least one pair of comb teeth-like resonators so formed on this substrate as to intricate each other, and a mounting substrate on which the element are mounted via a plurality of bumps. The ratio of the total area of the bumps formed on the element to the mass of the elements is not less than 0.0085 mm<2> /mg.

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 having a pair of comb-shaped resonators.

[0002]

2. Description of the Related Art In recent years, mobile communication terminals such as mobile phones have been rapidly developed. This terminal is desired to be particularly small and lightweight because it is convenient to carry. In order to reduce the size and weight of terminals, it is essential that the electronic components used in them are also small and lightweight.
Therefore, a surface acoustic wave device using a surface acoustic wave element in which a plurality of surface acoustic wave resonators (SAW resonators) are formed on a piezoelectric substrate is often used in the high frequency part and the intermediate frequency part of the terminal. There is.

An important characteristic required for the surface acoustic wave device is that the insertion loss is low and the attenuation outside the pass band frequency is large. The insertion loss affects the power consumption of the device, and the lower the loss is, the longer the battery life is extended, so that the capacity of the battery can be reduced, which contributes to the reduction in size and weight. Also, if high out-of-band attenuation can be obtained with one device, it contributes to downsizing and weight reduction of equipment.

Here, in the surface acoustic wave device, a pair of comb-shaped resonators interdigitated with each other are formed on a piezoelectric substrate, and the surface acoustic wave is generated on the piezoelectric substrate by an electric field generated by applying a voltage to the resonator. , Or the generated surface acoustic wave is converted into an electric signal by a resonator.

A surface acoustic wave device in which such a surface acoustic wave element is mounted on a mounting board is assumed to be used in a mobile communication terminal, and therefore, even if it is dropped from a height of 2 m, the surface acoustic wave device is elastic. It is required that the bondability between the surface acoustic wave element and the mounting substrate is secured. The height of 2 m is the height when the mobile communication terminal is used by an ordinary person, plus a predetermined margin.

[0006]

When the surface acoustic wave device and the mounting substrate are flip-chip mounted by bumps, the bumps formed on the surface acoustic wave device are required to ensure the above-mentioned bonding performance. The area should be as large as possible.

In order to increase the bump area, the area of the piezoelectric substrate that constitutes the surface acoustic wave element must be increased.

However, it is difficult to widen the piezoelectric substrate due to the demand for smaller and lighter terminals, and therefore the area of the bump cannot be simply increased.

Therefore, the present invention provides a surface acoustic wave device capable of minimizing the bump area while maintaining the bonding strength of the surface acoustic wave element mounted on the mounting substrate via a plurality of bumps. To aim.

[0010]

In order to solve the above-mentioned problems, a surface acoustic wave device according to the present invention is provided with a piezoelectric substrate and at least one pair of comb teeth formed on the piezoelectric substrate in a mutually intertwined manner. A surface acoustic wave element having a resonator and a mounting substrate on which the surface acoustic wave element is mounted via a plurality of bumps, and the total area of the bumps formed on the surface acoustic wave element and the surface acoustic wave. The ratio with the mass of the element is 0.00
It is characterized by being 85 mm ² / mg or more.

According to such an invention, the bump area can be minimized while maintaining the bonding strength of the surface acoustic wave element mounted on the mounting substrate via the plurality of bumps.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described more specifically with reference to the drawings. Here, in the accompanying drawings, the same reference numerals are given to the same members,
Moreover, the duplicate description is omitted. It should be noted that the embodiment of the present invention is a particularly useful embodiment for carrying out the present invention, and the present invention is not limited to the embodiment.

FIG. 1 is a sectional view showing a surface acoustic wave device in which a surface acoustic wave element according to an embodiment of the present invention is packaged, and FIG. 2 is a surface acoustic wave element according to an embodiment of the present invention. FIG. 3 is a schematic diagram showing a circuit, FIG. 3 is a plan view showing a pattern of a resonator in the surface acoustic wave element of FIG. 2, and FIG. 4 is a graph showing the bump area and the peeling strength of the surface acoustic wave element in the surface acoustic wave device of FIG. FIG. 5 is a graph showing the relationship, and FIG. 5 is a schematic diagram showing a pendulum type impact tester used in the evaluation test of the surface acoustic wave device according to the present embodiment.

In the surface acoustic wave device 10 shown in FIG. 1, a surface acoustic wave element 11 having a predetermined conductive pattern formed on a piezoelectric substrate is composed of a single layer or a plurality of layers, and a predetermined wiring pattern and circuit pattern are formed. It is mounted on a mounting board 12 made of ceramic or resin. The element formation surface of the surface acoustic wave element 11 is arranged so as to face the mounting substrate 12, and the surface acoustic wave element 11 and the mounting substrate 12 are flip-chip connected via bumps 13.

Here, the piezoelectric substrate is LiNbO3, Li
It is formed of a piezoelectric single crystal such as TaO3 or quartz, or a piezoelectric ceramic such as lead zirconate titanate piezoelectric ceramics. However, ZnO on the insulating substrate
A piezoelectric substrate on which a piezoelectric thin film such as a thin film is formed may be used.

A cap 14 is bonded to the mounting substrate 12 so as to surround the surface acoustic wave element 11 to protect the surface acoustic wave element 11 from dust and mechanical shock.

As shown in FIG. 2, a resonator 15 resonating with a surface acoustic wave having a predetermined frequency is formed on the piezoelectric substrate of the surface acoustic wave element 11 mounted on the surface acoustic wave device 10. There is. The resonator 15 and the mounting substrate 12 are electrically connected to the resonator 15, and an input electrode 16, an output electrode 17, and a ground electrode 18 for inputting and outputting an electric signal to and from the resonator 15 are connected via a wiring portion 19. Are electrically connected.

The electrodes 16, 17, 18 and the mounting substrate 12 are bump-connected by ultrasonic waves by forming the bumps 13 shown in FIG. 1 on them. Therefore, in the present embodiment, the surface acoustic wave element 11 is formed with the six bumps 13. The element forming surface is arranged to face the mounting substrate 12 by such bump connection.

In the present embodiment, the electrodes 16,
Sixteen and eighteen are formed in total, and therefore six bumps 13 are also formed. However, the present invention is not limited to six electrodes, and the necessary number may be provided depending on the layout pattern of the resonator or the like. You can Therefore, the number of bumps 13 does not have to be six, and as many as the number of electrodes are provided.

Here, as shown in FIG. 3, the resonator 15 is formed in the shape of a pair of interdigitated comb teeth. When a voltage is applied to the resonator 15 on the input side to apply an electric field, a surface acoustic wave is generated on the piezoelectric substrate due to the piezoelectric effect. In addition, the mechanical distortion due to the surface acoustic waves generated in this way causes an electric field, and the resonator 1 on the output side is
At 5, it is converted into an electric signal.

Reflectors 20 for reflecting surface acoustic waves are arranged on both sides of the resonator 15.

In the present embodiment, the wiring portion 19 between the input electrode 16 and the output electrode 17 is used as a series arm, and a plurality of wiring portions 19 are arranged between the series arm and the ground electrode 18. And the ladder type circuit in which the resonators 15 are arranged in the series arm and the parallel arm is configured, but the present invention may be other than the ladder type circuit.

Here, the inventor of the present invention is directed to the surface acoustic wave device 10.
The relationship between the area of the bump and the peeling strength of the surface acoustic wave device in was examined as follows.

That is, 36 ° rotation Y on the piezoelectric substrate
A resonator and a reflector made of aluminum were formed on a -X propagation lithium tantalate single crystal substrate. The frequency characteristics of the resonator are determined by the film thickness and the electrode finger pitch. The film thickness of aluminum is generally 0.1 to 0.5 μm,
Since the non-sticking variation is large when forming the gold (Au) stud bump with this film thickness, the film thickness of aluminum in the pad portion for bump formation is increased to 0.5 to 1 μm.

Six gold stud bumps were formed on the surface acoustic wave element by ultrasonic bonding of gold balls. The gold ball is a gold wire (manufactured by Tanaka Denshi Kogyo, GBC25
μm) was melted and formed by arc discharge. At this time, the diameter of the gold ball was changed by controlling the distance and current of the torch that generates the discharge.

Gold balls were pressed against the input electrode, output electrode and ground electrode on the piezoelectric substrate, and ultrasonic vibration was caused to form gold bumps. Then, the surface acoustic wave element having gold bumps was ultrasonically flip-chip mounted on a mounting substrate having pads formed of gold electrodes to prepare a sample.

These samples were flip-chip-observed from the side, the bump diameter after bonding was measured, and the bump area (total area) was calculated from the bump diameter. Then, the peeling strength between the surface acoustic wave element and the mounting substrate was measured.

The results are shown in FIG. As shown,
It was found that the peeling strength depends on the bump area and the relationship is linear.

Next, a drop test was carried out by preparing 300 samples each having the following bonding area prepared by controlling the diameter of the gold bump after bonding. At this time, a normal SAW filter ceramic package was used as the package, and a metal cap was welded and sealed to obtain the structure shown in FIG.

At this time, the number of bumps is 6 and the element volume of the surface acoustic wave element is 1.3 mm × 0.8 mm × 0.35.
mm, and the element mass has a density of lithium tantalate of 7.
From 5 g / cm ³ to 2.7 mg.

The conditions of the drop test were to drop freely on concrete from a height of 1 m, 2 m, and 3 m, and confirm the number of peeling defects at bump joints.

The test results are shown in Table 1.

[0033]

[Table 1]

From this result, in order to pass the drop test of 2 m, the diameter of the bump is 70 μm (the total area of the bump is 0.02).
It can be seen that 3 mm ² ) or more is necessary. And
When this is taken as the ratio of the total area of the bumps to the mass of the surface acoustic wave element, it is 0.023 mm ² /2.7 mg = 0.0085.
a mm ² / mg.

Next, the element volume is 1.8 mm × 1.4 mm ×
Six bumps were formed on a 0.35 mm surface acoustic wave element as described above, and a drop test was conducted under the same conditions.

The test results are shown in Table 2.

[0037]

[Table 2]

The mass of this surface acoustic wave element is 6.6 mg.
Therefore, in order to pass the drop test of 2 m, it is understood that a bump diameter of 110 μm (bump total area 0.057 mm ² ) or more is required. Then, if this is taken as the ratio of the total area of the bumps and the mass of the surface acoustic wave element, it is 0.05
Is a 7mm ² /6.6mg=0.0086mm ² / mg.

From the above results, the ratio of the total area of the bumps and the mass of the surface acoustic wave element, which can withstand the drop test from 2 m, which is a condition required for mobile communication terminals such as mobile phones, is 0.0085 mm. It was found to be ² / mg or more.

By setting the diameter of the bumps so as to satisfy this condition, the bump area can be minimized while maintaining the bonding strength of the surface acoustic wave element mounted on the mounting substrate through the plurality of bumps. Will be possible.

Here, a surface acoustic wave device 10 was produced in which a surface acoustic wave element having a bump diameter of 80 μm was flip-chip mounted on a mounting substrate and a metal cap was welded and sealed on the mounting substrate. Then, the pendulum type impact tester 21 was applied with impact acceleration to evaluate the breakage state of the surface acoustic wave element mounted by flip chip.

Pendulum type impact tester 21 used at this time
Is shown in FIG.

The pendulum type impact tester 21 shown in FIG. 5 is composed of a column 22 and a plastic arm 23 rotatably mounted on the column 22 and having a length of about 1.5 m.
And a weight 24 fixed to the tip of the arm 23 and having a weight of about 100 g, and a stage 25 arranged at a position where the arm 23 hangs down.

In such a pendulum type impact tester 21, the surface acoustic wave device 10 is installed on the stage 25, the arm 23 is made horizontal, and the weight 24 is dropped in an arc shape from a position of 1.5 m in height. By causing the surface acoustic wave device 10 to collide with the surface acoustic wave device 10, the surface acoustic wave device 10 is instantaneously accelerated from the stationary state to the speed of the weight 24 at the time of collision. A cushion 26 is installed in the traveling direction of the surface acoustic wave device 10 that is repelled from the stage 25. Then, the installation posture of the surface acoustic wave device 10 on the stage 25 was variously changed, and the fracture state of the flip chip mounting portion was observed.

Table 3 shows the observation results.

[0046]

[Table 3]

As can be seen from Table 3, when the accelerating force is applied in the direction of peeling the surface acoustic wave element mounted by flip chip, the surface acoustic wave element is broken 100%, that is, the defect occurrence rate is 100%. .

From the results of this experiment, in the above-described drop test on concrete, when the surface acoustic wave device 10 comes into contact with concrete from the cap, a force for peeling off the flip chip mounting portion is generated at that moment, and this force causes the force. It is expected that destruction will occur. That is, the peeling strength of the surface acoustic wave element mounted by flip chip and the breakage frequency of the drop test are correlated.

Although the surface acoustic wave device 10 in which one surface acoustic wave element 11 is mounted is shown in the above description, for example, two surface acoustic wave elements having mutually different band center frequencies are mounted. And make it a duplexer,
The present invention can be applied to various types of surface acoustic wave devices.

[0050]

As is apparent from the above description, according to the present invention, the following effects can be obtained.

That is, the total area of the bump and the surface acoustic wave element.
Ratio with mass of child is 0.0085mm ^Two / Mg or more
By setting the diameter of the bumps so that
Connection of the surface acoustic wave element mounted on the mounting board via
The bump area can be minimized while maintaining the total strength.
become.

[Brief description of drawings]

FIG. 1 is a sectional view showing a surface acoustic wave device in which a surface acoustic wave element according to an embodiment of the present invention is packaged.

FIG. 2 is a schematic diagram showing a circuit of a surface acoustic wave element according to an embodiment of the present invention.

FIG. 3 is a plan view showing a pattern of a resonator in the surface acoustic wave device of FIG.

FIG. 4 is a graph showing a relationship between a bump area and a peeling strength of a surface acoustic wave element in the surface acoustic wave device of FIG.

FIG. 5 is a schematic diagram showing a pendulum type impact tester used in an evaluation test of the surface acoustic wave device according to the present embodiment.

[Explanation of symbols]

10 Surface acoustic wave device 11 Surface acoustic wave device 12 mounting board 13 bumps 14 cap 15 resonator 16 input electrodes 17 Output electrode 18 Ground electrode 19 Wiring part 20 reflector 21 Pendulum type impact tester 22 props 23 arms 24 weights 25 stages 26 cushion

Claims (4)

[Claims] 1. A surface acoustic wave element comprising a piezoelectric substrate and at least one pair of comb-shaped resonators formed on the piezoelectric substrate so as to be interdigitated with each other, and the surface acoustic wave element has a plurality of bumps. A mounting substrate mounted via the surface acoustic wave element, and a ratio of the total area of the bumps formed on the surface acoustic wave element to the mass of the surface acoustic wave element is 0.0085 mm ^2.
The surface acoustic wave device is characterized in that the surface acoustic wave device is not less than / mg. 2. The surface acoustic wave device according to claim 1, wherein the bump is a gold bump. 3. The surface acoustic wave device according to claim 1, wherein the electrode on which the bump is formed is made of aluminum having a film thickness of 0.5 to 1 μm. 4. The surface acoustic wave device is a duplexer equipped with two surface acoustic wave elements having different band center frequencies from each other. The surface acoustic wave device according to item.