JP2003032070A - Surface acoustic wave element and surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To standardize a bump pad position of a surface acoustic wave chip and to enhance joining performance with a package substrate. SOLUTION: The surface acoustic wave device includes a package substrate whose front side has connection terminals and a surface acoustic wave chip mounted on the package substrate, having comb-line electrodes opposed to each other and a metallic bump joined with the connection terminals. The connection terminals of the package substrate are placed in a substrate region where a bent of the package substrate is 15% of the height of the metallic bump or below and the metallic bump is placed at the inside of the opposed comb-line electrodes.

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 in which a surface acoustic wave element is bonded to a wiring board by flip chip bonding.

[0002]

2. Description of the Related Art In recent years, with the spread and miniaturization of mobile communication devices such as mobile phones, surface acoustic wave devices used in RF filters arranged in the front end and IF filters used in IF stages have become even more popular. Miniaturization is required.

Accordingly, a surface acoustic wave device employing the so-called flip chip bonding technique has been put into practical use.

FIG. 6 is a schematic top view showing an example of a conventional surface acoustic wave element used in such a surface acoustic wave device. The surface acoustic wave element 100 has a configuration in which so-called longitudinal mode coupling type resonator filters are arranged in multiple stages, and one filter has a plurality of comb-teeth-shaped electrodes 101 along the surface acoustic wave propagation direction. is doing.

Each comb-shaped electrode has an interleaved signal electrode and ground electrode, and the signal electrode has an I / O pad (input / output terminal) 102a for connection with an external circuit.
On the other hand, the GN pad (ground terminal) 102b is connected to the ground electrode.

[0006]

However, when the conventional surface acoustic wave device is connected to the base substrate of the package by flip chip bonding, the terminals located on the outer periphery of the device may have a connection failure. In particular, if a connection failure occurs at the input / output terminal, the device will not function at all and the reliability of the product will be greatly impaired.

The present invention has been made in view of the above technical background.
An object of the present invention is to provide a surface acoustic wave device which is miniaturized by flip chip bonding and which has a highly reliable connection between an element and an external terminal.

[0008]

In a surface acoustic wave device according to the present invention, a plurality of comb-teeth-shaped electrodes are arranged on a piezoelectric substrate in a direction different from the main surface acoustic wave propagation direction of the piezoelectric substrate. At least a signal terminal of the signal terminal and the ground terminal connected to the tooth-shaped electrode is arranged at a position between the steps of the plurality of comb-shaped electrodes.

In the surface acoustic wave device of the present invention, the comb-teeth electrode formed on the piezoelectric substrate, the signal terminal connected to the signal electrode of the comb-teeth electrode and the ground electrode of the comb-teeth electrode are provided. A surface acoustic wave element having a connected ground terminal, a signal electrode connected to the signal terminal via a metal bump, and a ground electrode connected to the ground terminal via a metal bump are metallized on one main surface. A base substrate, and a position where the thickness of the metal bump connected to the signal terminal is within ± 15% with reference to the thickness of the metal bump having the minimum thickness among other metal bumps. It is characterized by being placed in.

The inventors of the present invention have earnestly analyzed the cause of connection failure in the conventional surface acoustic wave device. As a result, it has been recognized that the connection failure is caused by the warp of the base substrate itself on which the surface acoustic wave element is mounted.

That is, a metallized layer for connecting to the electrode terminals of the surface acoustic wave element is formed on the surface of the base substrate, but the substrate is bent due to the tension of the metallized layer. For example, in a base substrate in which alumina ceramic is used as a base substrate and copper is metallized on the base substrate, when the metallized surface is used as the upper surface, the base substrate warps downward toward the peripheral portion.

It is extremely difficult to correct the warp of the base substrate, and the warp does not change even if it passes through the thermocompression bonding process when mounting the surface acoustic wave device on the base substrate, and as a result, especially the outer circumference of the device is reduced. It was found that sufficient pressure could not be applied to the metal bumps in the area, leading to defective bonding.

With respect to such a phenomenon, the inventors have come up with the idea of reviewing the arrangement itself of the electrode terminals of the surface acoustic wave element,
The present invention has been completed.

That is, in the surface acoustic wave device according to the first aspect of the present invention, the electrode terminals connected to the signal electrodes of the comb-shaped electrodes are arranged so as to be folded between the adjacent comb-shaped electrodes. ing. As a result, since the metallization layer is bonded to the opposing base substrate at a position where the amount of warpage is relatively small, sufficient pressure can be applied to the metal bumps, and good connection can be obtained.

Further, in the surface acoustic wave device according to the second aspect of the present invention, the metal bump connecting the signal terminal to the base substrate is ± 15 with respect to the thickness of the other metal bump having the smallest thickness. This signal terminal is arranged at a position where the thickness becomes%. Since the signal terminals are arranged at such positions, the manner in which the metal bumps are crushed, and thus the amount of pressure applied in the joining process is made substantially uniform, and good connection can be obtained.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION <First Embodiment> FIG. 1 is a top view of a surface acoustic wave device 10 according to a first embodiment of the present invention, and FIG. 2 shows the device of FIG. It is a figure of the surface acoustic wave device 20 which carried out flip chip bonding.
At the time of flip chip bonding, the electrode formation surface of the element shown in FIG. 1 is connected to a metallization layer (not shown) formed on the base substrate 22 with the electrode formation surface facing down (face down).

The surface acoustic wave device 10 has a structure in which so-called longitudinal mode coupling type resonator filters 30 and 31 are cascade-connected, and one filter has three comb teeth along the propagation direction of the surface acoustic wave. The electrode 11 is provided.
Further, a grating reflector 15 made of the same metal film as the electrode fingers of the comb-teeth-shaped electrodes is provided on both ends of the comb-teeth-shaped electrodes 11.
Are arranged.

Each comb-shaped electrode 11 has an interleaved signal electrode and a ground electrode, and the signal electrode has an I / O pad (signal terminal) 102 for connection with an external circuit.
On the other hand, the GN pad (ground terminal) 102b is connected to the ground electrode. The metallization layer of the base substrate (not shown) is two-dimensionally separated into a plurality of signal electrodes to which the respective signal terminals are connected and a ground electrode to which the plurality of ground electrodes are commonly connected. Also filter 3
The comb-teeth electrodes 11 on both ends of 0 and the comb-teeth electrodes 11 on both ends of the filter 31 are electrically connected by strip wiring 13.

The electrode terminal arrangement shown in FIG. 1 is characterized in that all the terminals which are conventionally located outside the comb-teeth electrode 11 are folded into the interstage positions of the two filters 30 and 31, and particularly in the operation of the surface acoustic wave device. The point is that the signal terminal 12a that plays an important role is arranged near the center of the surface acoustic wave element. FIG. 2 shows an electrode terminal when mounting the surface acoustic wave device of FIG. 1 on the base substrate 12, and a metal bump 1 bonded to the electrode terminal.
The position of 6 is indicated by a black circle. Further, for comparison, the electrode terminals of the conventional surface acoustic wave device and the positions of the metal bumps to be joined to the electrode terminals are shown by a dotted square line.

In this example, an alumina ceramic was used for the base substrate, and its surface was metallized with copper. Further, the piezoelectric substrate constituting the surface acoustic wave element was made of lithium tantalate, and the comb-teeth-shaped electrodes and electrode terminals formed thereon were all formed of a pattern of Al alloy by a known thin film process. Further, gold bumps were used as metal bumps for joining the electrode terminals of the element and the metallized layer of the base substrate.

FIG. 3 is a sectional view of a structure in which a surface acoustic wave device is mounted on a base substrate. 2 mm used in this embodiment
In the case of a 2 mm square alumina ceramic substrate, a warp (strain in the vertical direction) of about 20 μm occurs when comparing the outermost edge and the central portion.

On this alumina ceramic substrate, samples of a plurality of surface acoustic wave devices having different positions of the electrode terminals were used, and the presence or absence of connection failure was observed.

As a result, first, the bump located in the central portion of the element did not have a defective joint such as peeling, and the terminal and the metallized layer were normally electrically connected. At this time, the thickness of the bump was 35 μm.

However, in the sample in which the electrode terminals were arranged at positions near the outer edge of the surface acoustic wave element, a bonding failure such as peeling of the electrode terminals at that position from the metallized layer was detected.

Observation of the defective electrode terminals revealed that defective bonding occurred when the amount of warpage with respect to the center point of the base substrate exceeded a certain value. That is, if there is an electrode terminal at a position where the amount of warp of the substrate exceeds ± 15% from the thickness of the bump with reference to the thickness (35 μm) of the bump at the position where the bonding is normally performed, the bonding process It was found that sufficient pressure was not applied to the metal bumps, and the metallized layer was not sufficiently joined.

When the normal bonding is performed, the thickness of the bump is almost in accordance with the warp of the substrate. Therefore, if the position of the electrode terminal is defined from the viewpoint of the thickness of the metal bump, the thickness of the bump after bonding is Thickness of central bump (35 μm)
It is permissible to arrange the electrode terminals at a position where the increase is 15% (40.2 μm) with respect to the above, but if the terminals are arranged beyond this and close to the outer edge of the element, defective bonding will occur. . For the measurement of the warp of the substrate and the thickness of the bump, a micrometer (manufactured by UNION Optical Instruments, trade name Hisomet) was used.

When the surface acoustic wave element shown in FIG. 1 is used,
The thickness of the bumps on all of the signal terminals and the ground terminals was within the range of 15% based on the thickness of the bump on the ground terminal at the center. As a result, no defective joining occurred and good conduction was obtained.

Such arrangement of the electrode terminals can deal with not only the vertical strain of the base substrate 22 but also the horizontal strain due to the difference in thermal expansion coefficient between the surface acoustic wave element and the base substrate. can do. A lithium tantalate substrate is used as the piezoelectric substrate 15 of the surface acoustic wave device 10 of FIG. 1 and an alumina ceramic substrate is used as the base substrate 22, and a horizontal strain (expansion) at each point on the chip at a process temperature of 270 ° C. ) Was measured. As a result, it was found that peeling of the metal bump from the connection terminal (not shown) started at a point where the amount of strain exceeded 1.5% of the diameter of the metal bump 16.

FIG. 4 shows the metal bump 16 and the base substrate 22.
Shows the state of joining with. The metal bump 16 has a disk-shaped base portion having a diameter of about 120 μm at the time of joining, and an upper portion that bulges in a convex state from here. In the state before flip chip bonding, the diameter of the base is about 110 μm, and the bulge at the top is more tapered and has a higher height, but as a result of crimping,
It was crushed and finally had a height of 35 μm and a diameter of 120 μm. In this state, the amount of strain, that is, the difference between the expansion of the piezoelectric substrate and the expansion of the base substrate 22 is 1.
The metal bump 16 peels off at a point exceeding 8 μm. Such strain increases as the distance from the center of the chip increases.

When the electrode terminal is arranged at a position where the deviation of the thickness of the metal bump is within ± 15%, the difference between the expansion of the element and the expansion of the base substrate is less than the above value at the terminal position, which is good. It was confirmed that a good bond was obtained. In particular, according to the arrangement of the bump pads 12 shown in FIG. 1, since all the bump pads on the chip 10 are provided at the positions where the amount of strain in the horizontal direction is within the range described above, the bumps are removed in the lateral direction. The reliability of the operation is further improved.

FIG. 5 shows a modification of the element structure of FIG.
The element structure of FIG. 5A differs from the element structure of FIG. 1 in that the filter 30 and the filter 31 are connected by strip wiring on the piezoelectric substrate in FIG.
In the structure of FIG. 5A, the electrode terminals 17 connected to the comb-shaped electrodes 11 on both ends of the filters 30 and 31 are separately provided, and the electrode terminals 17 are connected to each other by the metallized layer on the base substrate. is there. Even in this case, the terminal 17
If the formation position of is a position where the thickness of the metal bump on the terminal 17 is within 15% of the thickness of the metal bump on the terminal 12a at the central portion, good bonding can be obtained.

FIG. 5B shows a structure in which the strip wiring 13 for connecting the filters 30 and 31 is laid out along the outer circumference of the element. With this configuration, it is not necessary to arrange strip wiring in the central portion of the element where the electrode terminals are densely arranged, and since there is no joint portion with the base substrate in the outer peripheral portion of the element, the comb-teeth-shaped electrode and the electrode terminal The arrangement gives a degree of freedom.

[0033]

According to the present invention, it is possible to obtain a surface acoustic wave device which is miniaturized by flip chip bonding and has a highly reliable connection between an element and an external terminal.

[Brief description of drawings]

FIG. 1 is a diagram showing a layout of element surfaces of a surface acoustic wave chip according to an embodiment of the present invention.

2 is a diagram of a surface acoustic wave device in which the surface acoustic wave chip of FIG. 1 is mounted on a package substrate.

FIG. 3 is a cross-sectional view taken along the line AA in FIG. 1, showing a bending portion of a package substrate and a joint portion of a surface acoustic wave chip to be mounted.

FIG. 4 is an enlarged view of the metal bump in the joined state in FIG.

5 is a diagram showing a modification of the surface acoustic wave chip shown in FIG.

FIG. 6 is a diagram showing an arrangement configuration of bump pads of a conventional surface acoustic wave chip.

[Explanation of symbols]

10 Surface acoustic wave device 11 Comb-shaped electrode 12 electrode terminals 13 Strip wiring 15 Piezoelectric substrate 16 metal bumps 17 Strip wiring 22 Base substrate 35 grating reflector

Claims (8)

[Claims] 1. A surface acoustic wave device in which a plurality of comb-teeth-shaped electrodes are arranged on a piezoelectric substrate in a direction different from a main surface acoustic wave propagation direction of the piezoelectric substrate, and a signal connected to the plurality of comb-teeth-shaped electrodes. At least a signal terminal of a terminal and a ground terminal is arranged at a position between the steps of the plurality of comb-teeth-shaped electrodes. 2. The surface acoustic wave element according to claim 1, wherein both the signal terminal and the ground terminal are arranged at the interstage positions of the plurality of comb-teeth-shaped electrodes. 3. The surface acoustic wave device according to claim 1, wherein the plurality of comb-teeth-shaped electrodes are cascade-connected. 4. A comb-shaped electrode formed on a piezoelectric substrate,
A surface acoustic wave device having a signal terminal connected to the signal electrode of the comb-shaped electrode and a ground terminal connected to the ground electrode of the comb-shaped electrode; and a signal connected to the signal terminal via a metal bump. An electrode and a base substrate metallized on one main surface with a ground electrode connected to the ground terminal via a metal bump, wherein the signal terminal is connected to the signal terminal with a different thickness of the metal bump. The surface acoustic wave device is arranged at a position within ± 15% based on the thickness of the metal bump having the minimum thickness among the metal bumps. 5. The surface acoustic wave device according to claim 4, wherein the metal bump is a gold bump. 6. The surface acoustic wave device according to claim 5, wherein the base substrate is made of a ceramic material. 7. The surface acoustic wave device according to claim 6, wherein the ceramic material is an alumina ceramic. 8. The surface acoustic wave device according to claim 4, wherein the piezoelectric substrate is made of lithium tantalate.