Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1994-08-04
2002-11-26
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S089160, C156S235000, C156S246000, C156S247000
Reexamination Certificate
active
06485591
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for manufacturing laminated-ceramic electronic components such as laminated-ceramic capacitors which are widely used in electronic devices such as video tape recorders, liquid crystal display televisions and OA equipment. The invention can also be widely applied to manufacturing of laminated-ceramic electronic components such as multilayer ceramic substrates, laminated varistors and laminated piezoelectric devices.
BACKGROUND ART
In recent years, the trend toward higher density of circuit boards in the field of electronic components has been imposing increasing requirements on laminated-ceramic capacitors and other components for further size reduction and higher performance. A laminated-ceramic capacitor is taken as an example in the following description.
FIG. 1
is a cross sectional view of a part of a laminated-ceramic capacitor. In
FIG. 1
, the reference numeral
1
is the ceramic layer,
2
is internal electrodes and
3
is external electrodes. The internal electrodes
2
are connected alternately to the two external electrodes
3
.
Laminated-ceramic capacitors have been manufactured by such a conventional method as follows.
Specified electrode ink is printed on ceramic greenware sheets which have been cut into a specified size. The electrode ink is dried to form an electrode ink film. Then a specified number of ceramic greenware sheets on which the electrode ink films have been formed are laminated to form a laminated body of ceramic greenware sheets which is then cut into a desired shape and sintered, to which external electrodes are then bonded for completion.
However, a direct printing of the electrode ink on the ceramic greenware sheet has drawbacks such that a solvent included in the electrode ink (solvents such as diethylene glycol monobutyl ether of about 30% by weight is included in the electrode ink available in the market) causes the ceramic greenware sheet to swell and/or corrodes it during the printing of the electrode ink onto the ceramic greenware sheet. In addition, pin holes become more likely to occur in the ceramic greenware sheet as the ceramic greenware sheet becomes thinner, resulting in a short circuit between internal electrodes.
Various approaches have been taken in an attempt to solve these problems.
FIG. 2
is a drawing explanatory of a process for printing electrode ink on the ceramic greenware sheet by means of a screen printing technique. In
FIG. 2
, the reference numeral
4
is the screen frame,
5
is the screen,
6
is electrode ink,
7
is the squeegee,
8
is the stage,
9
in the base film,
10
is the ceramic greenware sheet and
11
is the printed electrode. The arrow indicates the direction in which the squeegee moves. As shown in
FIG. 2
, a specified number of ceramic greenware sheets on which the electrode ink is printed are laminated to form a ceramic greenware lamination, which is then cut into a desired shape and then sintered, to which external electrodes are bond ed to make laminated-ceramic capacitors.
In order to increase the capacitance of the laminated-ceramic capacitor, it has been attempted to decrease the thickness of the ceramic layer. In order to decrease the thickness of the ceramic layer, thickness of the ceramic greenware sheet must be decreased. However, a decrease in the thickness of the ceramic greenware sheet leads to the decrease of its mechanical strength. Therefore, there is a problem that a ceramic greenware sheet of a thickness less than 20 micrometers cannot be handled individually (called problem
1
hereafter), which makes a reduction of thickness difficult. Moreover, during a printing of electrode ink onto the ceramic greenware sheet surface, there is a problem that the likeliness of a short circuit occurrence increases with a decrease in the thickness of the ceramic greenware sheet (called problem
2
hereafter), because the ceramic greenware sheet swells or is dissolved by the electrode ink (or by permeation of the electrode ink into minute surface irregularities of the ceramic greenware sheet).
Also, with a laminated-ceramic capacitor, an increase in the number of laminated layers causes local thickness variations or steps on the surface due to the internal electrodes. This problem will be well understood from the following description with reference to
FIGS. 3 and 4
.
FIG. 3
is a cross sectional view of a laminated-ceramic capacitor formed by multiple layers. As shown in
FIG. 3
, the thickness of the laminated-ceramic capacitor is greater at the center (where the number of internal electrodes
2
stacked is greater), called thickness A, than at the periphery (where the number of internal electrodes
2
stacked is smaller), called thickness B.
FIG. 4
is a drawing explanatory of the thickness difference between the center and the periphery with respect to the number of laminated layers. The thickness of the ceramic greenware sheet used herein is 20 micrometers, and the thickness of the internal electrode
2
is 4 micrometers. From
FIG. 4
, it can be seen that a thickness difference between the center and the periphery exceeds 20 micrometers, which is equal to the thickness of the ceramic greenware sheet which is laminated, when the number of laminated layers exceeds 10. Surface irregularities due to this thickness difference (total thickness of electrodes) make it impossible to make uniformly laminated-ceramic capacitors, causing a problem such as delamination (peel-off of layers) and crack (called problem
3
hereafter).
To solve these problems (problems
1
,
2
and
3
), various approaches have been taken.
Solutions to the problem
1
include a method, proposed in Japanese Laid-Open Patent Publication No. 62-63413, where electrode ink is printed onto the ceramic greenware sheets while the ceramic greenware sheets remain to be adhered onto base films, and they are laminated to make it easy to handle the ceramic greenware sheets. After lamination, the base films are peeled off. This method can solve problem
1
to a certain extent, but cannot solve problem
3
. Moreover, with regards to problem
2
, the solvent of the electrode ink which is absorbed in one side of the ceramic is greenware sheet cannot evaporate from the opposite side, because the opposite side (on which electrode ink is not printed) of the ceramic greenware sheet is covered by the base film, and remains in the ceramic greenware sheet. Consequently, the electrode ink remains in the ceramic greenware sheet for a longer period of time than in the case of the conventional method, thereby further aggravating the problem that the ceramic greenware sheet becomes susceptible to corrosion by the electrode ink (problem
2
).
Another method proposed in Japanese Laid-Open Patent Publication No. 59-172711 is to manufacture laminated-ceramic capacitors by embedding electrodes, which are formed on a base film, in ceramic greenware sheets, laminating the ceramic greenware sheets together with the base films, and sintering them. Although this method solves problems
2
and
3
to a certain extent, problem
1
remains unsolved. This is because the base film must be very thin, namely from 1.5 to 14 micrometers, in order to sinter the laminated-ceramic greenware sheets together with the base films. Moreover, the number of base films to be sintered increases with an increase in the number of laminated layers, which makes delamination more likely to occur. This implies that the base film thickness must be decreased with an increase in the number of laminated layers. Base films of such a small thickness are difficult to handle, weak in mechanical strength and are not practical.
Approaches to solve problem
2
include one which uses transfer of electrodes. In Japanese Laid-Open Patent Publication No. 52-15879, Japanese Laid-Open Patent Publication No. 63-31104 and Japanese Laid-Open Patent Publication No. 63-32909, such methods are proposed that electrode ink films are formed on ceramic greenware sheets while adverse effects of the solvent included in the electrode ink are being prevented
Horibe Yasutaka
Iguchi Takashi
Katoh Masahiro
Miura Yoshiyuki
Nakao Keiichi
Akin Gump Strauss Hauer & Feld L.L.P.
Matsushita Electric - Industrial Co., Ltd.
Mayes Curtis
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