JP2008187561A - Surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element which can be directly bumped on a wiring pattern. <P>SOLUTION: The surface acoustic wave element has a piezoelectric substrate (4), interdigital electrodes (6, 16) which have a function to convert between surface acoustic waves that occur on the piezoelectric substrate and electric signals, wiring patterns (8, 18) that are formed by extending the interdigital electrodes on the surface of the piezoelectric substrate, and solder balls (10, 20) which are directly provided on the wiring patterns and connected to electrodes of a package board. The interdigital electrode and the wiring pattern are mainly composed of a copper and silver alloy, and the solder ball includes tin and silver, or tin and zinc. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

  The present invention relates to a surface acoustic wave element used for a surface acoustic wave device.

2. Description of the Related Art In recent years, surface acoustic wave devices (SAW (Surface Acoustic Wave) devices) have been adopted as electronic devices and communication devices such as mobile phone devices and television receivers as resonators and band filters.
This type of device is configured by hermetically sealing a surface acoustic wave element, and this element has a comb electrode (IDT: Interdigital Transducer), a wiring pattern, a wiring pad, and the like formed on the surface of the piezoelectric substrate. (For example, see Patent Documents 1 and 2).

Specifically, as shown in FIG. 4, layers of comb-tooth electrodes 60 and 160 and wiring patterns 80 and 180 are formed on the piezoelectric substrate 40, and this layer is composed mainly of aluminum (Al). Yes. Next, wiring pads 90 are formed on this layer by sputtering or the like, and bumps (for example, solder balls) 100 are formed on the pads as protruding electrodes. When the pad is composed mainly of gold (Au) or the like, the comb electrode and the wiring pattern whose main component is Al are protected from the bumps.
When the wiring pad is also composed mainly of Al, as shown in FIG. 5, a UBM (Under Bump Metal) is provided below the pad 90 located below the bump (eg, gold bump) 200. 92 is provided to protect the comb electrode, the wiring pattern and the wiring pad.

JP 2000-299355 A JP 2002-343827 A

  However, when the comb electrode and the wiring pattern layer are mainly composed of Al, at least a wiring pad is required, which increases the manufacturing period of the surface acoustic wave device and reduces the manufacturing cost. There is a problem that becomes difficult. Therefore, measures for omitting the wiring pads are necessary, but no special consideration is given to this point in the prior art.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a surface acoustic wave device capable of solving the above-described problems and providing bumps directly on a wiring pattern.

  A first invention for achieving the above object includes a piezoelectric substrate, a comb electrode formed on the surface of the piezoelectric substrate, and having a function of mutually converting a surface acoustic wave and an electric signal generated on the piezoelectric substrate; A wiring pattern formed by extending a comb-tooth electrode on the surface of the piezoelectric substrate and a solder ball provided directly on the wiring pattern and connected to the electrode of the package substrate. The pattern is composed mainly of a copper-silver alloy, and the solder ball is composed of tin and silver.

  According to the first invention, the comb electrode and the wiring pattern are composed of the same component mainly composed of a copper silver alloy, and the copper silver alloy has good compatibility with the solder, and the comb electrode and the wiring pattern. This layer need not be protected as compared with the case where the layer is composed mainly of Al. As a result, wiring pads and UBMs are completely unnecessary between the solder balls and the wiring pattern as in the prior art, and the manufacturing cost of the surface acoustic wave device can be reduced.

According to a second aspect of the present invention, in the configuration of the first aspect, the solder ball further includes copper, the copper content is 0.45 mass% to 0.85 mass%, and the silver content is 2.8 mass% to 3.2 mass%. %, And tin is composed of a residual rate.
According to the second invention, in addition to the action of the first invention, the solder ball is composed of tin, silver and copper, and is very compatible with the comb electrode and wiring pattern mainly composed of a copper-silver alloy. Therefore, the bonding strength between the wiring pattern and the solder ball is improved.

As in the first invention, the third invention comprises a piezoelectric substrate, comb electrodes, wiring patterns, and solder balls, wherein the comb electrodes and wiring patterns are mainly composed of a copper-silver alloy. The solder ball is configured to contain tin and zinc.
Also according to the third invention, the comb electrode and the wiring pattern are composed of the same component mainly composed of a copper silver alloy, and this copper silver alloy has a good compatibility with the solder. It is not necessary to protect the layer as compared with the case where the layer is composed mainly of Al. As a result, wiring pads and UBMs are completely unnecessary between the solder balls and the wiring patterns as in the prior art, and the manufacturing cost of the surface acoustic wave device can be reduced.
In addition, since the melting point can be lowered by using the solder, the comb electrodes and the wiring pattern can be protected.

According to a fourth invention, in the configuration of the third invention, the solder ball further includes bismuth, wherein the bismuth is 2.5 mass% to 3.5 mass%, and the zinc is 7.5 mass% to 8.5 mass%. %, And tin is composed of a residual rate.
According to the fourth invention, in addition to the action of the first invention, the solder ball is made of tin, zinc and bismuth, and the melting point is further lowered. Thereby, when bonding to the electrode of the package substrate, stress (distortion) due to thermal expansion to the wiring pattern can be reduced, so that the bonding strength between the wiring pattern and the solder ball is more reliably maintained. .

According to a fifth aspect of the present invention, in the surface acoustic wave device according to the first to fourth aspects of the present invention, the surface acoustic wave element is used for a filter of a transmitter.
According to the fifth invention, in addition to the action of the first invention, the surface acoustic wave device used for the filter of the transmitter can generate a large amount of power and generate heat. Is composed of a copper-silver alloy as a main component, and is therefore excellent in power durability and suitable.

  ADVANTAGE OF THE INVENTION According to this invention, the surface acoustic wave element which can achieve reduction in the manufacturing cost of an element can be provided.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.
1 and 2 show a surface acoustic wave device 2 of the present embodiment. This element 2 is an element built in a SAW device described later.
The element 2 includes a piezoelectric substrate 4, and the substrate 4 is made of, for example, LT (lithium tantalate: LiTaO ₃ ) or LN (lithium niobate: LiNbO ₃ ).

  On the surface of the substrate 4, layers of comb electrodes 6 and 16 and wiring patterns 8 and 18 are formed. The comb electrodes 6 and 16 are mainly composed of a copper-silver alloy (Cu alloy). The comb electrode 6 includes a base portion 6 b and comb teeth extending from the base portion 6 b along the surface of the substrate 4 in a comb shape. Part 6a. The comb electrode 16 has substantially the same configuration as the comb electrode 6, and includes a base portion 16 b and each comb tooth portion 16 a extending from the base portion 16 b along the surface of the substrate 4 in a comb shape. The comb teeth 6a and the comb teeth 16a are alternately arranged with a constant interval.

These comb-tooth electrodes 6 and 16 use the electrostrictive effect to convert between mechanical quantities and electric quantities.
On the other hand, the wiring patterns 8 and 18 are wirings that are formed on the surface of the substrate 4 and are referred to as conductive so-called outer peripheral patterns, and extend the base portions 6b and 16b of the comb electrodes 6 and 16, respectively. Like the comb electrodes 6 and 16, the copper silver alloy (Cu alloy) is used as a main component.
In addition, Cu alloy which comprises the layer of these comb-tooth electrodes 6 and 16 and the wiring patterns 8 and 18 contains a small amount of silver (Ag), tin (Sn), etc. in copper (Cu). For example, about 2.6 wt% to about 3.0 wt% of Ag, Sn, or the like is added.

Also, solder balls 10 and 10 are provided directly on the patterns 8 and 18 without forming the above-described wiring pads. Each ball 10 is composed of lead-free solder composed of Sn and Ag.
More specifically, the ball 10 of this example further includes Cu in addition to Sn and Ag, and is represented by the following composition formula.

aSn-bAg-cCu
Here, a: residual ratio, 2.8 wt% <b <3.2 wt%, 0.45 wt% <c <0.85 wt%.

  This is because, if Ag is less than 2.8 wt%, it is difficult to maintain the bonding strength between the wiring patterns 8 and 18 and the solder ball 10, while if Ag is more than 3.2 wt%, it becomes expensive. This is because a shrinkage nest, that is, a nest such as an elongated crack is likely to occur on the fillet surface of the ball 10 immediately after the ball 10 is bonded to an electrode of a package substrate described later.

Further, when Cu is less than 0.45 wt%, the melting point is hardly lowered, whereas when Cu exceeds 0.85 wt%, copper is eroded, that is, the comb electrodes 6, 16 and the wiring patterns 8, 18. This is because the copper component is easily dissolved into the ball 10 and it becomes difficult to maintain the bonding strength.
The optimum values (a: b: c) of these Sn, Ag and Cu are 96.5: 3: 0.5, and the melting point of the ball 10 is in the range of 217 ° C. to 219 ° C. in the atmosphere.

By the way, the pair of reflectors 22 are configured by arranging a plurality of elongated electrodes extending in a direction substantially perpendicular to the propagation direction of the surface acoustic wave, and the comb-like electrodes 6 and 16 are viewed in the propagation direction of the surface acoustic wave. Adjacent to each other. The propagation direction means a main direction in which the surface acoustic wave propagates on the surface of the substrate 4.
Here, the above-described solder ball 10 is connected to an electrode of a package substrate, which will be described later, and a high-frequency signal is input to one of the comb electrodes 6 and 16 from this electrode.

  Specifically, when a high-frequency signal is supplied to the comb-teeth electrode 16 via, for example, the wiring pattern 18, the comb-teeth portion 16 a causes an inverse piezoelectric effect due to the electric field generated by the high-frequency signal and displaces the surface of the substrate 4. Cause it to occur. Next, surface acoustic waves are generated on the substrate 4 and propagate mainly along the propagation direction. The pair of reflectors 22 reflects the propagating surface acoustic waves and prevents the energy of the surface acoustic waves from escaping to the outside.

  Subsequently, the surface acoustic wave is transmitted to the comb tooth portion 6a paired with the comb tooth portion 16a, and the comb tooth portion 6a is subjected to the piezoelectric effect based on the displacement of the surface of the substrate 4 by the transmitted surface acoustic wave. A frequency signal in a specific band corresponding to the displacement is detected. This frequency signal is extracted from the wiring pattern 8 via the base 6b.

  In the surface acoustic wave device 2 configured as described above, first, a Cu alloy film of several tens to several hundreds of nanometers is formed on the substrate 4. In this film forming process, after forming a thin Cr film, the Cu alloy film may be formed, and then a TiN film or a Cr film may be formed. Next, the Cu alloy film is etched, and the comb-tooth electrodes 6 and 16, the wiring patterns 8 and 18, and the reflector 22 are formed. Then, solder balls 10 are formed at appropriate positions on the wiring patterns 8 and 18 of the substrate 4 to form the element 2 described above.

Thereafter, as shown in FIG. 3, the element 2 is turned over, and the solder ball 10 and the electrode 34 of the package substrate 32 are overlapped and joined. Specifically, by irradiating ultrasonic waves while pressing the ball 10 against the electrode 34, the ball 10 is bonded to the electrode 34 and chip mounting is performed.
Then, the metal lid 36 is overlaid on the package substrate 32, and the element 2 is hermetically sealed by brazing the substrate 32 and the lid 36, whereby the SAW device 1 is obtained. Thereby, even if the comb-tooth electrodes 6 and 16 and the wiring patterns 8 and 18 are mainly composed of a Cu alloy, the same corrosion resistance as in the prior art can be obtained. In addition to this metal sealing, resin sealing may be used.

Thus, the surface acoustic wave element 2 becomes the SAW device 1 by hermetic sealing, and the device 1 of this embodiment is used for a filter of a transmitter.
By the way, the solder ball 10 described above may be composed of lead-free solder composed of tin (Sn) and zinc (Zn).
More specifically, the ball 10 of this example further includes bismuth (Bi) in addition to Sn and Zn, and is represented by the following composition formula.

aSn-bZn-cBi
Here, a: residual rate, 7.5 wt% <b <8.5 wt%, 2.5 wt% <c <3.5 wt%.

This is because when Zn is less than 7.5 wt%, the melting point is difficult to decrease, whereas when Zn is more than 8.5 wt%, it is easy to deteriorate and the above-mentioned bonding strength is difficult to maintain, and the spread of solder, etc. This is because the wettability shown decreases and becomes spherical on the surface, causing corrosion.
Also, if Bi is less than 2.5 wt%, the melting point is difficult to decrease and wettability is reduced. On the other hand, if Bi exceeds 3.5 wt%, the bonding interface is biased or non-uniform during solidification of the solder. This is because segregation in which a layer is formed easily occurs and the above-described bonding strength is difficult to maintain.

  The optimum values (a: b: c) of these Sn, Zn and Bi are 89: 8: 3, and the melting point of the ball 10 is suppressed to a range of 189 ° C. to 199 ° C. in a nitrogen atmosphere. Moreover, if it implements in nitrogen atmosphere, Zn will not oxidize, a zinc oxide layer will not be formed, and the fall of joint strength will be suppressed.

  As described above, the present invention pays attention to the point that the solder is directly formed on the layer made of the Cu alloy and the chip is mounted.

  And according to each Example, the comb-tooth electrodes 6 and 16 and the wiring patterns 8 and 18 are comprised by the same component which has Cu alloy as a main component, and this Cu alloy has good compatibility with the solder ball 10, and As compared with the case where the comb electrode layer and the wiring pattern layer are mainly composed of Al, it is not necessary to protect. Therefore, unlike the prior art, no wiring pad or UBM is required between the solder ball and the wiring pattern, the manufacturing period of the surface acoustic wave element 2 is shortened, and the manufacturing cost can be reduced. However, if the device 2 is hermetically sealed, the reliability of the element 2 can be secured.

  Further, since the ball 10 is made of Sn, Ag and Cu, or Sn, Zn and Bi and has good compatibility with the comb electrodes 6 and 16 and the wiring patterns 8 and 18 mainly composed of a Cu alloy, these wirings are used. The bonding strength between the patterns 8 and 18 and the ball 10 is improved.

  Moreover, if the ball 10 composed of the latter Sn, Zn, and Bi is used, the melting point can be lowered as compared with the ball composed of Sn, Ag, and Cu, so that the comb electrodes 6, 16 and the wiring pattern 8, 18 is also protected, and stress (distortion) due to thermal expansion on the wiring patterns 8 and 18 can be reduced when bonded to the electrode 34 of the package substrate 32. The bonding strength with 10 is more reliably maintained.

Furthermore, although large electric power flows through the element 2 used for the filter of the transmitter and heat can be generated, since the comb electrodes 6 and 16 and the wiring patterns 8 and 18 are mainly composed of a Cu alloy, Compared with the case where Al is the main component, the resistance is reduced and the power durability is excellent. That is, even if a high voltage is applied, the pattern is not affected, which is preferable.
The present invention is not limited to the above embodiment, and various modifications can be made without departing from the scope of the claims.

  For example, in the above embodiment, the surface acoustic wave element is embodied in a filter of a transmitter. However, the surface acoustic wave element of the present invention is used in electronic devices and communication devices such as a mobile phone device and a television receiver. Of course, the present invention can also be applied to resonators and bandpass filters.

It is a top view of the surface acoustic wave element concerning a present Example. It is the II-II sectional view taken on the line of FIG. It is sectional drawing of the SAW device using the surface acoustic wave element of FIG. It is sectional drawing of the conventional surface acoustic wave element. It is sectional drawing of the other conventional surface acoustic wave element.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 SAW device 2 Surface acoustic wave element 4 Piezoelectric substrate 6 Comb electrode 8 Wiring pattern 10 Solder ball 16 Comb electrode 18 Wiring pattern 20 Solder ball 32 Package substrate 34 Electrode

Claims (5)

A piezoelectric substrate;
A comb-like electrode formed on the surface of the piezoelectric substrate and having a function of mutually converting a surface acoustic wave generated in the piezoelectric substrate and an electrical signal;
A wiring pattern formed by extending the comb electrodes on the surface of the piezoelectric substrate;
A solder ball provided directly on the wiring pattern and connected to an electrode of a package substrate;
The comb electrode and the wiring pattern are mainly composed of a copper-silver alloy,
The surface acoustic wave device, wherein the solder ball includes tin and silver. The surface acoustic wave device according to claim 1,
The solder ball further includes copper, the copper is 0.45% by mass to 0.85% by mass, the silver is 2.8% by mass to 3.2% by mass, and the tin is constituted by a residual ratio. A surface acoustic wave device. A piezoelectric substrate;
A comb-like electrode formed on the surface of the piezoelectric substrate and having a function of mutually converting a surface acoustic wave generated in the piezoelectric substrate and an electrical signal;
A wiring pattern formed by extending the comb electrodes on the surface of the piezoelectric substrate;
A solder ball provided directly on the wiring pattern and connected to an electrode of a package substrate;
The comb electrode and the wiring pattern are mainly composed of a copper-silver alloy,
2. The surface acoustic wave device according to claim 1, wherein the solder ball includes tin and zinc. The surface acoustic wave device according to claim 3,
The solder ball further includes bismuth, the bismuth is 2.5 mass% to 3.5 mass%, the zinc is 7.5 mass% to 8.5 mass%, and the tin is constituted by a residual ratio. A surface acoustic wave device. In the surface acoustic wave device according to any one of claims 1 to 4,
A surface acoustic wave device used for a filter of a transmitter.

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