Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-04-18
2003-06-24
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S089160, C156S064000
Reexamination Certificate
active
06582541
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to monolithic ceramic substrates, to manufacturing and designing methods therefor, and to electronic devices including such a monolithic ceramic substrate. In particular, the present invention relates to an improvement for reducing warpage of the monolithic ceramic substrate.
2. Description of the Related Art
Monolithic ceramic substrates include a plurality of ceramic layers laminated together to define a laminate body. In the monolithic ceramic substrate having the structure described above, various wiring conductors are provided. As wiring conductors, for example, internal conductive films extending along predetermined interfaces between ceramic layers and via hole conductors extending so as to penetrate predetermined ceramic layers are provided inside a monolithic ceramic substrate, and external conductive films are arranged to extend on the external surfaces of the monolithic ceramic substrate.
Monolithic ceramic substrates are used for mounting semiconductor chip units, other chip units, and other electronic components, and are used for interconnection of these electronic units. The wiring conductors described above define electric pathways for the interconnection described above.
In addition, passive units, such as capacitors, and inductors, may be embedded in monolithic ceramic substrates in some cases. In the case described above, these passive units are defined by parts of the internal conductive films and the via hole conductors used as the wiring conductors described above.
Monolithic ceramic substrates are used for, for example, LCR hybrid high frequency components in the field of terminal apparatuses for mobile communication. In addition, in the field of computers, monolithic ceramic substrates are used for forming hybrid components including active units, such as semiconductor integrated circuit (IC) chips, and passive units, such as capacitors, inductors, and resistors, or are used for merely forming semiconductor IC packages.
In particular, laminated ceramic electronic components are widely used for constituting various electronic devices, such as PA module substrates, RF diode switches, filters, chip antennas, various package devices, and hybrid devices.
In order to improve the multi-functionality, mounting densities, and performances of the monolithic ceramic substrates, it is effective to form wiring conductors having finer pattern densities.
However, in order to form a monolithic ceramic substrate, a sintering step must be performed. In the sintering step mentioned above, sintering of the ceramic causes shrinkage, and the shrinkage does not occur uniformly over the entire monolithic ceramic substrate, whereby undesired deformation and warping of the wiring conductors may be generated. The deformation and warping of the wiring conductors interfere with the improvement in wiring density of the wiring conductor.
Accordingly, a so-called non-shrinking process is proposed for use in manufacturing of monolithic ceramic substrates, in which the shrinkage of the monolithic ceramic substrate in the direction along the main surface can be substantially constrained during a sintering step.
In a method for manufacturing monolithic ceramic substrates in accordance with the non-shrinking process, in addition to a low-temperature sinterable ceramic material which can be sintered at, for example, 1,000° C. or less, an inorganic particle is prepared which constrains the shrinkage and which is not sintered at a sintering temperature of the low-temperature sinterable material described above. When a green laminate is prepared which forms a predetermined monolithic ceramic substrate by sintering, constraining green layers containing the inorganic particle are disposed so as to be in contact with the main surfaces of predetermined layers of a plurality of base green layers which are laminated with each other and which contain the low-temperature sinterable ceramic material. In addition, conductive paste bodies for forming wiring conductors are provided for the base green layers.
The green laminate thus obtained is then fired. During this sintering step, reaction layers having a thickness of approximately about 2 &mgr;m to about 3 &mgr;m are formed at the interfaces between the base green layers and the constraining green layers, and the reaction layer adheres the base green layer to the constraining layer adjacent thereto. In addition, since the inorganic powder material contained in the constraining green layers is not substantially sintered, substantial shrinkage is unlikely to occur in the constraining green layers. Accordingly, since the constraining green layers constrain the shrinkage of the base green layers, the base green layers substantially shrink only in the thickness directions thereof, and the shrinkage in the directions along the main surfaces is constrained. As a result, since irregular deformation is difficult to occur in the monolithic ceramic substrate formed by sintering the green laminate, unwanted deformation and warping hardly occur, whereby a higher pattern densities of the wiring conductors can be achieved.
However, even though the shrinkage of the base green layer can be constrained in the direction along the main surface thereof, the shrinkage cannot be reduced to 0%, and since binders are lost which are contained in the base green layer and the constraining green layer, shrinkage of at least 2 to 3% inevitably occurs.
In addition, the shrinkage described above varies in accordance with the characteristics of the base green layer and the constraining green layer. For example, when the thickness of the base green layer is increased, it becomes difficult for the constraining force of the constraining green layer to work on the base green layers, and as a result, the base green layer is more likely to shrink. Furthermore, the thinner the constraining green layer, the weaker the constraining force for constraining the shrinkage. Consequently, the base green layer is more likely to shrink.
Accordingly, in a green laminate including a plurality of types of base green layers having different thicknesses in the range of, for example, 25 &mgr;m to 300 &mgr;m, in the case in which constraining green layers having the same characteristic are formed so as to be in contact with the main surfaces of the base green layers, the shrinking rates thereof may vary in the lamination direction of the laminate body when a monolithic ceramic substrate is formed by sintering the green laminate, and as a result, the laminate body may be warped. Furthermore, in a serious case, cracking and separation may occur in the laminate body. Consequently, the accuracy of positions at which the wiring conductors are provided for the laminate body is degraded, whereby formation of the wiring conductors having finer wiring density is prevented, and hence, reliability of the monolithic ceramic substrate thus obtained is decreased.
In the description of the related art above, the difference in thickness of the base green layers is exemplarily described as a factor which causes differences in the shrinking rates of the green layers. However, in addition the difference in thickness, the shrinking rates of the base green layers may differ from each other due to the difference in composition or type of material constituting the base green layers, the difference in wiring density distribution or distribution of the wiring conductors provided for the base green layers, or other factors.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a greatly improved monolithic ceramic substrate, manufacturing and designing methods therefor, and an electronic device including the novel monolithic ceramic substrate described above.
According to a preferred embodiment of the present invention, a monolithic ceramic substrate formed by sintering a green laminate includes a plurality of base ceramic layers which contain a low-temperature sinterable cer
Baba Akira
Nishide Mitsuyoshi
Sakai Norio
Keating & Bennett LLP
Mayes Curtis
Murata Manufacturing Co. Ltd.
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