Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2002-03-05
2003-03-25
Paladini, Albert W. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C331S068000, C331S10800D, C257S719000
Reexamination Certificate
active
06538208
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic device, more particularly, to an electronic device comprising a housing of an insulating material having mounted therein an electronic element such as a semiconductor element and a quartz element, and a method of producing the same. The present invention also relates to a package base for mounting an electronic element, i.e. a component part of the electronic device.
2. Description of Related Art
As is well known, various electronic devices currently have been proposed and practically used. Some examples include an IC package having an IC chip mounted thereon and a crystal resonator having a quartz element mounted thereon. These electronic devices have been generally produced by mounting an electronic element in a housing constituted of a package base and a cap, and sealing the housing.
For example, a crystal resonator is a quartz element-mounted package structure of surface mounting type utilizing a quartz element as a reference signal source of a clock or a mobile communication unit, and generally has a structure as shown in
FIG. 1. A
crystal resonator
60
comprises a quartz element
58
, a package base
50
for accommodating and bonding the quartz element
58
in a closed space (cavity)
57
, a junction member
55
for bonding the quartz element
58
and the package base
50
, a cap
59
for contacting and closing the package base
50
to thereby form the cavity
57
, and a sealing member
56
for sealing the package base
50
and the cap
59
. The interior of the cavity
57
is maintained under a vacuume condition or charged with an inert gas such as nitrogen for improving the resonation characteristic (Q value) of the quartz element
58
and reducing its variation with time.
FIG. 2
is a cross-sectional view showing the package base
50
for mounting the quartz element, used with the prior art crystal resonator shown in FIG.
1
. The package base
50
, as shown in
FIG. 2
, is constituted of a base member
51
for forming a cavity along with a cap arranged in opposed relation thereto, a wiring
54
for electrically connecting the interior and the exterior of the cavity, an internal electrode
52
for fixing and electrically connecting the quartz element, and an external electrode
53
for connecting it to an external circuit. The substrate
51
is generally formed from a ceramic such as alumina. The wiring
54
, the internal electrode
52
and the external electrode
53
are each formed by baking a conductive metal such as W, Mo, AgPd alloy or the like on the substrate member
51
, and suitably plated with Ni or Au.
In the prior method of producing the crystal resonator, a conductive adhesive has been used widely as a junction member for bonding the quartz element and the package base. However, since a heat curing process is required for the adhesive, the adhesive develops a distortion due to its shrinkage, which in turn causes stress to be exerted on the quartz element. As a result, the Q value of the quartz element is varied, thereby causing the problem of deterioration of the stability of its characteristics.
Recently, there has been a tendency for a hard metal having little variation with time to be used as a junction member for the crystal resonator, to satisfy the requirements of long lasting stability of the characteristics along with an improved Q value of the quartz element. As explained below with reference to
FIG. 3
, for example, a method has been proposed to use a AuSn alloy paste as a junction member.
In the method shown in
FIG. 3
, the first step is to coat a AuSn alloy paste
61
on a predetermined portion of an internal electrode
52
formed on a substrate
51
of a package base
50
, and then apply the quartz element
58
thereon so that they contact. The AuSn alloy paste
61
is composed of spherical particles of the AuSn alloy containing 29 atomic % of Sn dispersed in a flux. Since the AuSn alloy paste
61
is viscose, the quartz element
58
is temporarily tacked on the internal electrode
52
of the substrate
51
. Thereafter, the AuSn alloy paste
61
is melted by heating it to at least its melting point of 278° C., thereby to bond the quartz element
58
and the substrate
51
. After bonding, in order to remove the flux, the assembly is washed and dried, after which it is covered with a cap (not shown) and a vacuum is applied in a vacuum tank to obtain a sealed product. However, due to the narrow gap between the quartz element and the package base (substrate) after bonding, use of the AuSn alloy in this method makes it difficult to remove the flux by washing, and undesirably leaves a residue of flux on the quartz element. The residual flux can be the cause of the above variation with time.
Further, Japanese Unexamined Patent Publication (Kokai) No. 2000-232332, for example, discloses a method of ultrasonic bonding of a quartz element with the package base by forming an Au bump on an electrode of the quartz element, as explained below with reference to FIG.
4
.
In the method shown in
FIG. 4
, the first step is to form an Au bump
62
on the electrode (not shown) of the quartz element
58
, using a ball bonder. Then, the quartz element
58
is brought into contact with the package base
50
at a predetermined position (the internal electrode
52
on the substrate
51
) as shown, and an ultrasonic welder
63
for applying the ultrasonic vibration from above the quartz element
58
is applied to the quartz element
58
. The quartz element
58
is moved horizontally by ultrasonic waves under application of a load. The Au bump
62
and the internal electrode
52
of the package base
50
are bonded to each other by the friction generated therebetween by the ultrasonic waves. The ultrasonic junction occurs only in such a range that the Au bump
62
is in contact with the substrate
51
of the package base
50
, and therefore the junction area is limited. After complete ultrasonic bonding, a cap is applied to the assembly, which is then vacuum sealed in a vacuum tank. This method, however, suffers from the problem that the junction area is so small that insufficient bonding strength results in low shock resistance. Further, when the load for ultrasonic bonding is increased in order to increase the bonding strength, a new problem of breaking or cracking in the quartz element is caused.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the prior art problems caused using a conductive adhesive, an AuSn alloy paste, an Au bump or the like as a junction member for the electronic element in the production of an electronic device such as a crystal resonator, thereby providing an easy-to-produce electronic device having stable characteristics exhibiting little variation with time and high shock resistance, and a method of producing such a device.
Another object of the present invention is to provide a crystal resonator or package structure of a quartz element which can be produced easily, and which has stable characteristics with little variation with time and high shock resistance.
Still another object of the present invention is to provide a package base for mounting an electronic element that can be advantageously used for the production of the electronic device according to the invention.
These and other objects of the present invention will be easily understood from the following detailed description of the present invention.
According to one aspect of the present invention, there is provided a package base for mounting an electronic element, comprising an insulative substrate and an internal electrode formed at a predetermined position on the substrate, the internal electrode being bonded to the electronic element, in which a junction member comprising a junction layer composed of a junction alloy having a melting point higher than the mounting temperature and an anti-oxidation conductive layer covering the junction layer are provided on the internal electrode.
According to another aspect of the present invention, there is provid
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