Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-08-24
2002-02-19
Mayes, Curtis (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S089120, C310S324000
Reexamination Certificate
active
06348115
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method for producing a ceramic diaphragm structure which is used as a constitutional member of various kinds of sensors, piezoelectric/electrostrictive actuators, or the like.
A ceramic diaphragm structure has a structure in which a thin and flexible diaphragm plate is superposed on a substrate having at least one window portion so as to cover the window portion and to work as a diaphragm. Such a ceramic diaphragm structure is used for various kinds of sensors by being constituted so that a diaphragm portion detects a bending displacement originated from a subject to be measured by an adequate means, or used as a constituting member of a piezoelectric/electrostrictive actuator by being constituted so that a pressure is given to the pressure room formed inside the actuator by deformation of the diaphragm portion due to a piezoelectric/electrostrictive element.
A ceramic diaphragm structure is produced by unitarily superposing a thin ceramic green sheet (hereinafter referred to as a green sheet) on a ceramic green substrate (hereinafter referred to as a green substrate) to obtain a laminate, and subsequently firing the laminate. After firing, the green substrate becomes a substrate, and the green sheet becomes a diaphragm plate. Generally, there is used a ceramic diaphragm structure
3
having a diaphragm portion
1
formed to have a protrudent shape toward the side opposite to a window portion
8
of a substrate
2
as shown in
FIG. 1
, so as to prevent a crack or a depression in a firing step. Such a diaphragm portion
1
having a protrudent shape as described above can have a higher inherent resonance frequency in comparison with a diaphragm portion having a flat shape. Further, it is recognized that a diaphragm portion having a protrudent shape is excellent in mechanical strength and is not hindered upon sintering a film formed on the surface of the diaphragm portion
1
.
In the fields of sensor and piezoelectric/electrostrictive actuator, since a demand for high precision and densification is raised, it is required to make a diaphragm portion more minute or to increase the number of the diaphragm portions.
When a ceramic diaphragm structure having a protrudent shape is produced, there are used materials which satisfy the following formulae 1), 2), and 3):
S
(substrate)−
S
(sheet)≧−0.08
{T
70
(substrate)−
T
70
(sheet)}−1 1)
0
≦T
70
(substrate)−
T
70
(sheet)≦300, 2)
and
S
(substrate)−
S
(sheet)≦20 3)
(wherein S(substrate) and S(sheet) denote shrinkage rates(%) of the ceramic green substrate and the ceramic green sheet, respectively, and T
70
(substrate) and T
70
(sheet) denote mid-sintering temperatures (° C.) of the ceramic green substrate and the ceramic green sheet, respectively.).
JP-A-8-51238 discloses that by using such a material, a protrusion can be made in a green sheet (diaphragm plate) toward the side opposite to a window portion arranged in a substrate during firing without any crack or the like. That is, a thin ceramic portion having a protrudent shape can be formed by setting differences in shrinkage rate and mid-sintering temperature between a green substrate and a green sheet.
Incidentally, a shrinkage rate (%) means a shrinkage rate (%), in a direction of a surface, of a green substrate and a green sheet independently fired at the same temperature as the temperature at which a laminate is fired, and the shrinkage rate (%) is shown by {(length before firing−length after firing)/length before firing}×100(%). The term “a direction of surface” does not mean the direction of thickness, but means a predetermined direction on the surface where a green substrate or a green sheet is molded. A mid-sintering temperature means a firing temperature at which a shrinkage reaches 70% of the aforementioned shrinkage rate, S(substrate) and S(sheet) in a firing step, and a mid-sintering temperature is a barometer showing a sintering speed.
However, the method disclosed in JP-A-8-51238 is on the supposition that a shrinkage rate and a mid-sintering temperature of a green substrate are uniform from a portion near a green sheet to a portion apart from the green sheet. However, in this method, as shown in
FIG. 2
, a ceramic diaphragm structure
3
is constituted of a substrate
2
and a diaphragm plate
12
, and a plurality of the ceramic diaphragm structures
3
constitutes a ceramic plate
15
. Therefore, a diaphragm structure has a large waviness, and a warpage is caused wholly in a ceramic plate including diaphragm structures.
It is difficult to reform the aforementioned warpage and waviness even if the ceramic substrate is subjected to firing again with loading. When a load on the ceramic plate is too large, a diaphragm portion
1
and/or a substrate
2
damage(s). When a warpage or a waviness is left as it is, dimensional preciseness of a diaphragm structure
3
deteriorates, and therefore, preciseness in printing of a film pattern on a diaphragm plate deteriorates, and/or variance in thickness of a film formed on the diaphragm plate is caused. Accordingly, when such a diaphragm structure is used for a sensor, such a sensor brings deviation in detection preciseness, and when it is used for a piezoelectric/electrostrictive actuator, such an actuator brings deterioration or variance in displacement.
As a result of the various studies, the present inventors proposed, in JP-A-10-117024, the following method as a method for producing a ceramic diaphragm structure, which can form a diaphragm portion having a protrusion toward the side opposite to a window portion of a substrate and which can advantageously reduce a waviness of a diaphragm structure and/or a warpage of a ceramic plate including the diaphragm structures.
First, we proposed a method for producing a ceramic diaphragm structure, comprising the steps of:
superposing a thin ceramic green sheet having at least one layer on a ceramic green substrate having at least one window portion and at least one layer so as to cover the window portion to obtain a unitary laminate, and
firing the unitary laminate so that a diaphragm portion has a protrusion toward a side opposite to the window portion;
wherein the ceramic green substrate and the ceramic green sheet satisfy the formulae:
S
(substrate)−
S
(sheet)≧−0.08
{T
70
(substrate)−
T
70
(sheet)}−1 1)
0
≦T
70
(substrate)−
T
70
(sheet)≦300, 2)
and
S
(substrate)−
S
(sheet)≦20 3)
(wherein S(substrate), and S(sheet) denote shrinkage rates (%) of the ceramic green substrate and the ceramic green sheet, respectively, and T
70
(substrate) and T
70
(sheet) denote mid-sintering temperatures (° C.) of the ceramic green substrate and the ceramic green sheet, respectively.), and an average sintering temperature difference of the layers of the ceramic green substrate, shown by the following formula, is larger than 0:
4
)
∑
n
=
1
N
T
70
(
substrate
)
n
∫
tn
tn
+
1
×
ⅆ
x
(wherein N denotes the number of layers constituting the ceramic green substrate, T
70
(substrate)
n
denotes a mid-sintering temperature (° C.) of a layer positioned in the nth place from the bottom of the laminate in the ceramic green substrate having the ceramic green sheet thereon, t
n
and t
n+1
denote distances from the lower and upper surfaces, respectively, of the layer positioned in the nth place to a neutral line of the substrate after firing the unitary laminate, using (−) for a surface under the neutral line and (+) for a surface over the neutral line.).
Secondly, the inventors proposed a method for producing a ceramic diaphragm structure, comprising the steps of:
superposing a thin ceramic green sheet having at least one layer on a ceramic green substrate having at least one window portion and at least one layer so as to cover the window portion
Nanataki Tsutomu
Takeuchi Katsuyuki
Takeuchi Yukihisa
Burr & Brown
Mayes Curtis
NGK Insulators Ltd.
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