JPH09116373A - Saw chip and production of saw device using the chip - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the easy breakage of electrical connection between a bump and a pad film even when the stress is applied to the junction part between the bump and the pad film by forming an electrode film containing Al on the surface of a piezoelectric substrate and also forming the pad film containing Au and no Al which is laminated on the electrode film only at a part with another part remaining as it is with no lamination. SOLUTION: A pad film 14A containing Au partly overlaps an electrode film 12 containing Al. For this purpose, the shapes, the sizes and the positions of both films 14A and 12 are set respectively. Therefore, an Al-Au alloy layer 18A that is generated due to Al of the film 14A never exists at the junction part related to a bump 16. If the layer 18A is generated at the contact/ lamination part between the films 12 and 14A, the layer 18A is distant away from the bump 16. As a result, the shearing stress is not caused at the layer 18A even though the difference of heat expansion coefficients is caused between a substrate 10 and a package. Therefore, the junction part related to the bump 16 is not substantially impaired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SAW chip having an electrode structure composed of at least an electrode film and a pad film, and a SAW chip using this SAW chip.
The present invention relates to a device, a method for manufacturing the device, and applied equipment such as a mobile phone using the SAW device.

[0002]

2. Description of the Related Art Acoustic waves propagating on a surface of a substrate having piezoelectricity or a relatively shallow portion are generally surface acoustic waves (SA).
W). Devices using SAW (SA
W devices) include filters, resonators, delay lines, etc.,
This type of device is widely used in various wireless devices and high-frequency devices including simple mobile phones such as PHS. For example, in the RF stage of a mobile phone, a SAW filter is used in a known manner such as an antenna duplexer.
In addition, application devices such as mobile phones are generally required to be small and low-priced. Therefore, similar improvements are always required for SAW devices used in this type of device. . So-called flip-chip type SAW
The device is an S developed to meet such demands.
A chip which is an AW device and has a structure in which predetermined electrodes are provided on a piezoelectric substrate in a package having a structure capable of face-down bonding on an external circuit substrate (S
AW chip) is mounted or housed and both are electrically and mechanically connected by bumps containing metal.

FIG. 3 shows the structure of a flip-chip type SAW filter, especially the SAW chip. On the surface of the piezoelectric substrate shown by reference numeral 10 in the drawing, two pairs of electrode films 12 having finger-intersectioned electrode finger groups are arranged so as to respectively constitute a wave-transmitting electrode or a wave-receiving electrode. Electrode film 12
A pad film 14 that is electrically and mechanically connected to the bumps 16 is provided on the upper and lower rectangular portions in FIG. 3A. The bump 16 electrically connects a pad film 22 on the package 20 described later and the electrode film 12 on the SAW chip via the pad film 14, and
It has a function of mechanically fixing the AW chip to the package 20.

Here, the electrode film 12 is generally an Al film added with Cu in order to secure strength against stress migration. That is, the material of the electrode film 12 is Al
-Cu alloy (reference: "High Power SAW Filte
r for Antenna Duplexer ”, Y.Kinoshita, A.Nakagoshi,
H.Kojima and M.Hikita, IEEE 1983 Ultrasonic Symposi
um, pp.83-86). The suitable film thickness of the electrode film 12 depends on the frequency band used, and in the SAW filter used at a frequency of 800 MHz or higher, the electrode film 12 is generally 100
It must be a very thin film such as nm-200 nm. The reason for providing the pad film 14 in FIG. 3 is that such thin electrode film 12 cannot be bonded to the bump 16 using an ultrasonic bonder or the like. As is clear from this purpose, the thickness of the pad film 14 must be a thickness (for example, 1 μm) to which an ultrasonic bonder or the like can be applied, and the material thereof is a material suitable for connection with the bump 16 or the electrode film 12. (Eg Al) must be used.

[0005]

When an Au bump formed mainly of Au is used as the bump 16, A at the contact portion between the bump 16 and the pad film 14 is used.
The formation of the l-Au alloy joins the two. However, this Al-Au alloy has the property of being hard and brittle. Therefore, the bump 16 and the pad film 14 after bonding
When the Al—Au alloy grows into an Al—Au alloy layer 18 having a non-negligible thickness due to metal interdiffusion between the bumps 16 (see FIG. 4), the bumps 16 are electrically connected to the pad film 22 on the surface of the package 20. In addition, when mechanically connecting (see FIG. 5), the Al—Au alloy layer 18, and hence the bump 16 and the electrode film 12 are sheared by the shear stress caused by the difference in thermal expansion coefficient between the piezoelectric substrate 10 and the package 20. The indirect connection between them is destroyed, which causes a failure or a failure.

One of the objects of the present invention is to improve the electrode structure so that the electrical connection between the bump and the electrode film is less likely to be lost even if some stress is applied to the bonding portion between the bump and the pad layer. Is to Another object of the present invention is to realize a sufficiently high yield and a sufficiently low failure rate even if there is a difference in thermal expansion coefficient between the piezoelectric substrate and the package. Another of the objects of the present invention is to make it possible to realize the above-mentioned object by a simple means and thus at a low cost.

[0007]

In order to achieve such an object, the SAW chip according to the present invention is provided with a substrate having piezoelectricity and elasticity propagating on the substrate surface or a relatively shallow portion. An electrode film which is arranged on the surface of the substrate so as to form a wave transmitting / receiving electrode for transmitting / receiving a wave, and an Al-containing electrode film, only a part of which is laminated with the electrode film and the other part of which is left without being laminated. And a pad film containing Au and containing no Al. Further, the method for manufacturing a SAW device according to the present invention is
A step of preparing a SAW chip according to the present invention and a package on which the SAW chip is mounted or housed; a step of providing a bump containing Au on a portion of the surface of the pad film that is not laminated with the electrode film; A step of mounting or accommodating a SAW chip having bumps formed on the surface of a pad film in a package, and a step of electrically and mechanically connecting a conductive portion on the package surface and a pad film on the substrate surface via the bumps. It is characterized by having.

As described above, in the present invention, since the pad film does not contain Al, the Al—Au alloy layer does not grow at the bonding portion between the pad film and the bump. Therefore,
Since defects or failures due to stress generated at the bonding portion between the bump and the pad layer are less likely to occur than in the past, a high yield and a low failure rate can be used as the above-mentioned simple means even if there is a difference in the thermal expansion coefficient between the substrate and the package. Can be realized. Although an alloy layer may be generated at the contact portion between the electrode film and the pad film, since the bump is bonded to the pad film at a portion that does not overlap the electrode film, stress is unlikely to occur in this alloy layer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. As shown in FIGS. 1 and 2, in the present embodiment, the pad film 14A has a structure in which a part of the pad film 14A rides on the electrode film 12.
The shape, size and position of the electrode film 12 are set. Further, in the present embodiment, the pad film 14A is made of Au. As described above, in the present embodiment, the pad film 14 formed of Al is entirely covered with the electrode film 12.
It is different from the conventional technology that overlaps with. Note that, here, the same or corresponding configurations as those of the conventional technique shown in FIGS. 3 to 5 are denoted by the same reference numerals and the description thereof is omitted.

As described above, since the pad film 14A is made of Au, according to the present embodiment, Al- as shown in FIG.
The Au alloy layer 18 does not occur at the bonding site of the bump 16. Further, although the Al-Au alloy layer 18A is generated at the contact / lamination site between the electrode film 12 and the pad film 14A, the Al-Au alloy layer 18A is located away from the bump 16, and therefore the cause shown in FIG. Shear stress does not occur in this layer 18A. Therefore, even if there is a difference between the coefficient of thermal expansion of the substrate 10 and the coefficient of thermal expansion of the package 20, the bonding portion related to the bump 16 is hardly damaged, and as a result, the yield is improved and the defect / failure rate is reduced. As a result, the product price can be reduced. In addition, FIG.
The structure shown in FIG. 2 and FIG. 2 can be manufactured using basically the same manufacturing equipment as the structure shown in FIGS.

It should be noted that even if it is possible to manufacture using basically the same manufacturing equipment as in the prior art, it immediately means that "the improvement according to the present invention is merely a design choice". Note that it does not mean that. That is, factors such as the arrangement, shape, and material of the electrodes are one of the factors that determine the performance and manufacturing conditions of the SAW device, and it is inappropriate for this technical field to neglect these improvements as mere design choices. Is.

[0012]

[Addendum] The present invention also relates to a SAW device manufactured by the manufacturing method according to the present invention, and a SAW device according to the present invention.
It can be understood as a mobile phone equipped with a device. Further, although the SAW filter is taken as an example in the above-described embodiment, the present invention can be applied to other types of SAW devices. Further, although the electrode film 12 constitutes a so-called normal type transmission / reception electrode in the figure, the electrode film 12 may constitute a weighted electrode according to various methods.

[Brief description of the drawings]

FIG. 1 is a diagram showing a SAW chip according to an embodiment of the present invention, particularly an electrode structure thereof, in which (a) is a top view,
(B) is a vertical side view, and (c) is a horizontal side view.

FIG. 2 is a cross-sectional view showing a structure around a bump bonding portion in this embodiment.

3A and 3B are diagrams showing a SAW chip according to a conventional technique, particularly an electrode structure thereof, FIG. 3A is a top view, FIG. 3B is a vertical side view, and FIG. 3C is a lateral side view.

FIG. 4 is a cross-sectional view showing a structure around a bump bonding portion in this conventional technique.

FIG. 5 is a side view in which the problems of the conventional technique are slightly exaggerated.

[Explanation of symbols]

10 piezoelectric substrate, 12 electrode film (Al-Cu), 14A
Pad film (Au), 16 bumps (Au), 18A
Alloy layer (Al-Au), 20 package, 22 Pad film on package side.

Claims (2)

[Claims] 1. A substrate having piezoelectricity, and a transducing electrode for transmitting and receiving an elastic wave propagating on a substrate surface or a relatively shallow portion are provided on the substrate surface and contain Al. An electrode film, and a pad film which is arranged on the surface of the substrate such that only a part of the electrode film is laminated with the electrode film and the other part is left without being laminated, and the pad film contains Au and does not contain Al. SAW chip to do. 2. The SAW chip and the S according to claim 1.
A step of preparing a package for mounting or housing an AW chip, a step of providing a bump containing Au on a portion of the surface of the pad film which is not laminated with the electrode film, and a bump formed on the surface of the pad film SAW device, comprising: mounting or housing the formed SAW chip in a package; and electrically and mechanically connecting a conductive portion on the package surface and a pad film on the substrate surface via bumps. Manufacturing method.