Metal working – Piezoelectric device making
Reexamination Certificate
2000-06-17
2004-04-13
Tugbang, A. Dexter (Department: 3729)
Metal working
Piezoelectric device making
C029S832000, C029S840000, C029S740000, C029S743000
Reexamination Certificate
active
06718604
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for mounting electronic device elements, and more particularly, the present invention relates to a method for mounting surface acoustic wave devices on mounting substrates by applying an ultrasonic wave thereto and pressing surface acoustic wave devices on the mounting substrates.
2. Description of the Related Art
Corresponding to recent miniaturized and thin electronic components, a flip chip bonding method has been developed as a method of mounting electronic device elements on substrates. The flip chip bonding method is a mounting method that positions a functional surface of an electronic device element relative to a substrate such that the functional surface opposes the substrate, then affixes the electronic device element thereon. The method is used to electrically and mechanically connect metal bumps formed on electrodes of an electronic device element and electrode patterns on the substrate. Further, the method is used to connect metal bumps located on electrode patterns provided on a substrate to electrodes of an electronic device element. Flip chip bonding methods currently in use include a method that applies an ultrasonic wave at the time of connection, and a method that simultaneously applies an ultrasonic wave and heat at the time of connection. These methods are used to increase the strength of the connections between the metal bumps and the electrode patterns provided on the mounting substrate.
In the flip chip bonding method that uses only the ultrasonic wave, increasing the ultrasonic wave power that is applied increases the strength of the connections between the metal bumps and the electrode patterns provided on the mounting substrate. However, when an ultrasonic wave power is excessively increased, a great deal of stress is exerted on the electrodes on the element and the substrate that defines the element, thereby causing cracks in the electrodes and the substrate.
Japanese Unexamined Patent Application Publication No. 8-330880 discloses a method as shown in
FIGS. 14A and 14B
that causes the above-mentioned problems. More specifically, as shown in
FIG. 14A
, although the direction of a load exerted by a bonding tool
67
is perpendicular to an electrode surface of an electronic device element
61
, the ultrasonic-wave-oscillation direction is horizontal. Therefore, a resultant force of the load and the ultrasonic wave, as shown in
FIG. 14B
, is exerted onto the electronic device element
61
. As a result, the level of a side portion of the electronic device element
61
is significantly lower than the level of the central portion. Accordingly, energy is concentrated on a metal bump
64
positioned on a side portion of the electronic device element, and the metal bump
64
collapses more than a metal bump
65
located in the central portion, thereby causing cracks in the metal bump
64
and an electrode pad
62
.
To solve the aforementioned problems, Japanese Unexamined Patent Application Publication No. 8-330880 suggests that dummy bumps be provided on the electronic device element. Specifically, as shown in
FIG. 15
, dummy pads
73
and dummy bumps
74
are provided farther away from the central portion in the ultrasonic-wave-oscillation direction than electrode pads
72
and metal bumps
75
provided on an electronic device element
71
, thereby allowing stress to be concentrated on the dummy pads
73
and the dummy bumps
74
. This prevents the cracks from forming on the electrode pads
72
and the metal bumps
75
that provide the necessary electrical conduction to a mounting substrate provided on the element
71
.
However, the method wherein the dummy bumps are provided for preventing the aforementioned cracks from forming is plagued by the following problems. According to the above-described method, since the dummy pads and the dummy bumps must be additionally provided, the size of the substrate of the electronic device element must be increased. This causes a problem in that the size of the overall electronic component is increased. Further, when cracks occur in the dummy pads, pieces of pads may be separated from the dummy pads. If the pieces adhere to the surface of the electronic device element, electrical characteristics of the electronic component and the reliability thereof deteriorate.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide a method of mounting electronic device elements for producing small electronic components that have a high reliability in coupling between an electronic device element and a package and excellent electrical characteristics.
A preferred embodiment of the present invention includes the steps of providing an electronic device element having metal bumps provided on a surface thereof, providing a bonding tool having a pressing surface, providing a mounting substrate, keeping the pressing surface of the bonding tool in contact with a reverse surface of the electronic device element, and applying an ultrasonic wave to the bonding tool, thereby mounting the electronic device element on the mounting substrate, wherein the maximum length of the pressing surface of the bonding tool in the ultrasonic-wave-oscillation direction is greater than approximately half the maximum length of the reverse surface of the electronic device element in the ultrasonic-wave-oscillation direction.
In this way, by increasing the length of the pressing surface of the boding tool in the ultrasonic-wave direction, the length of a surface wave acoustic wave device in the oscillation direction in contact with the bonding tool is increased. Thus, at the time of packaging, even when a resultant force of the load and the ultrasonic wave is momentarily exerted in a tilted orientation, the surface acoustic wave device is not tilted with respect to the horizontal direction of the mounting substrate nor does stress concentrate on metal bumps in specific positions in the electronic device element. Therefore, occurrence of cracks in the metal bumps and electrode pads is greatly reduced, thereby providing stable and reliable coupling with excellent electrical characteristics between the electronic device element and the mounting substrate.
Another preferred embodiment of the present invention provides that the shape of the pressing surface of the bonding tool is substantially the same as the shape of the reverse surface of the electronic device element. In this way, by selecting the shape of the pressing surface of the bonding tool to be substantially the same as the shape of the reverse surface of the electronic device element, the length of the electronic device element in contact with the bonding tool is further increased in directions other than the ultrasonic-wave-oscillation direction. That is, the element has a large area in contact with the boding tool such that stable contact is provided. As a result, stress is not concentrated on metal bumps in specific positions in the element. As a result, occurrence of cracks on metal bumps and electrode pads is greatly reduced, thereby further improving the coupling of the electronic device element to the substrate.
Further, in another preferred embodiment of the present invention, the maximum length of the pressing surface of the bonding tool in the ultrasonic-wave-oscillation direction is substantially equal to or less than the maximum length of the reverse surface of the electronic device element in the ultrasonic-wave-oscillation direction.
By arranging the maximum length of the pressing surface of the bonding tool in the ultrasonic-wave-oscillation direction to be substantially equal to or less than the maximum length of the reverse surface of the electronic device element in the ultrasonic-wave-oscillation direction, when the electronic device element is packaged in the package, interference with sidewalls of the package when the ultrasonic wave is applied is prevented without increasing the size of the package as compared to the si
Kita Ryoichi
Shimoe Kazunobu
Taga Shigeto
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
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