Firing jig for electronic element

Details Firing jig for electronic element Firing jig for electronic element

2001-11-08

2003-09-09

Jones, Deborah (Department: 1775)

Stock material or miscellaneous articles

Web or sheet containing structurally defined element or...

Including a second component containing structurally defined...

C428S336000, C428S446000, C428S697000, C428S698000, C428S701000, C428S702000, C219S444100, C219S548000

Reexamination Certificate

active

06617017

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
This invention relates to a firing jig for an electronic element, which has a long life and allows production with a low cost.
The surface of a firing jig for an electronic element used in firing functional ceramics has been coated with a dense and less reactive coating material for preventing deterioration in properties of a material to be fired due to reaction of a component in the firing jig with the material or absorption of a component in the material in the firing jig.
A frequently used substrate for a firing jig is based on Al
2
O
3
—SiO
2
. The material is inexpensive and also highly resistant to thermal shock to allows a firing jig to have a longer life, so that it has been widely used as a substrate of a firing jig for an electronic element.
However, although the outer surface of the jig is coated with a dense coating film, repeated firing may cause penetration of SiO
2
component in the substrate through the film structure and may remain in the surface of the jig. Thus, the SiO
2
component may contaminate a material to be fired and then may adversely affect the properties of an electronic element.
In an alumina-based firing jig, as an Al
2
O
3
content increases, a coefficient of thermal expansion increases, so that the jig becomes less resistant to thermal shock, leading to a shorter life.
Japanese Patent Laid-Open No. 10-158081 has disclosed that a zirconia flame coating film as a coating film may be formed to a thickness of 300 &mgr;m on the surface of an Al
2
O
3
—SiO
2
-based substrate with an Al
2
O
3
content of 65% or higher to improve durability; specifically, detachment of the flame coating layer in the jig may be reduced even after repeated cycles of heating and cooling as a firing jig. Such a configuration may prevent detachment of the flame coating layer, but properties of the electronic element placed and fired on the firing jig may be unstable, resulting in little or no increase in a jig life.
In view of the problems in the prior art described above, an objective of this invention is to provide a reliable firing jig for an electronic element by forming two or more spray coating layers on the surface of the substrate in the firing jig and defining some factors such as the contents of required materials for the substrate and individual spray coating layers for improving durability of the firing jig and stabilizing performance of the electronic element placed and fired on the firing jig.
SUMMARY OF THE INVENTION
This invention provides a firing jig for an electronic element comprising a substrate made of a ceramic and a spray coating layer made of a material less reactive to a material to be fired on the substrate, wherein two or more spray coating layers are formed on the surface of the substrate, and at least a spray coating layer adjacent to the substrate and a spray coating layer adjacent to the material to be fired are made of different materials.
In a firing jig for an electronic element according to this invention, it is preferable that the substrate is mainly based on Al
2
O
3
—SiO
2
, Al
2
O
3
—SiO
2
—MgO or SiC; the spray coating layer adjacent to the substrate is mainly based on Al
2
O
3
—SiO
2
, Al
2
O
3
—MgO, Al
2
O
3
—ZrO
2
or Al
2
O
3
; and the spray coating layer adjacent to the material to be fired is mainly based on ZrO
2
, Al
2
O
3
or Al
2
O
3
—MgO. An Al
2
O
3
content is preferably 70 to 95 wt % for the substrate, 98 wt % or more for the spray coating layer adjacent to the substrate and 72 to 96 wt % for the total in the substrate and the spray coating layer adjacent to the substrate.
An SiO
2
content is preferably 0.5 wt % or less for the spray coating layer adjacent to the substrate and 0.05 to 0.5 wt % for the spray coating layer adjacent to the material to be fired.
In a firing jig for an electronic element according to this invention, a porosity in each of the spray coating layers is preferably 16% or less. The spray coating layers preferably have a crack penetrating each of these layers with a width of 1 to 5 &mgr;m. The total thickness of the spray coating layers is preferably 50 to 1000 &mgr;m. A particle size in each of the spray coating layers is preferably 300 &mgr;m or less.
This invention also provides a firing jig for an electronic element comprising a substrate made of a ceramic and a spray coating layer, wherein a surface adjacent to the substrate is the spray coating layer and the surface of the spray coating layer is a flame coating layer.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
A firing jig for an electronic element according to this invention is based on an alumina-silica material, in which performance of the electronic element to be placed and fired on the firing jig may be stabilized by forming two or more spray coating layers on the surface of a substrate and defining the contents of the components required for the substrate and the individual spray coating layers to minimize the amount of SiO
2
entering into the coating layer. This invention will be described with reference to, but of course not limited to, embodiments below.
The term, “a firing jig for an electronic element” as used herein means a member used for firing of an electronic element made of a ceramic such as a ceramic capacitor, a thermistor and ferrite, which may comprise, for example, a setter, a case, and a plate for placing a material to be fired.
A firing jig of this invention comprises two or more spray coating layers on the surface of a substrate, where these layers are made of different materials. Thus, the surfaces adjacent to the surface of the substrate and to the material to be fired are spray coating layers with a smaller porosity than that in a flame coating layer to prevent a component adversely affecting a work property or deteriorating the substrate from transferring. Furthermore, if forming a flame coating layer, it may be formed by coating with melted ceramic particles, and thus the layer is a solid hard layer so that expansion or shrinkage cannot be absorbed in the layer, causing detachment. On the other hand, in a spray coating layer, particles are mutually sintered to form a soft layer, allowing intralayer relaxation. When a spray coating layer is formed on the surface of the substrate, the layer can prevent a reactive component in the substrate from being in contact with the material of the electronic element, allowing a silica-alumina material including silica adversely affecting the properties of the electronic element to be used as a substrate.
The term “spray coating” as used herein refers to a process of preparing a ceramic powder slurry for spraying or applying the slurry on the surface of the substrate before firing. The term “work property” refers to dispersion of a dielectric constant generated in an electronic element when firing the electronic element using the firing jig. A good work property in a firing jig means that dispersion property of a dielectric constant is good in an electronic element fired using the firing jig.
The spray coating layers are preferably mainly based on Al
2
O
3
—SiO
2
, Al
2
O
3
—SiO
2
—MgO or SiC. It is preferable that the spray coating layer adjacent to the substrate is mainly based on Al
2
O
3
—SiO
2
, Al
2
O
3
—MgO, Al
2
O
3
—ZrO
2
or Al
2
O
3
while the spray coating layer adjacent to the material to be fired is mainly based on ZrO
2
, Al
2
O
3
or Al
2
O
3
—MgO. Such a configuration may provide a firing jig comprising a substrate with good spall resistance and vent resistance, an intermediate layer preventing a component adversely affecting a material to be fired from transferring and the outer layer less reactive to the material to be fired.
In this invention, an Al
2
O
3
content is preferably 70 to 95 wt % for the substrate. If the Al
2
O
3
content of the substrate is less than 70%, a thermal conductivity of the substrate is so reduced that a temperature in the firing jig may significantly vary, leading to an uneven work property on the jig. If the Al
2
O
3
content of the substrate is more than 95%, a thermal ex

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