Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
2000-02-02
2001-10-23
Sample, David R. (Department: 1775)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S017000, C501S024000, C501S025000, C501S026000, C501S044000, C501S046000, C501S047000, C501S048000, C501S049000, C501S052000, C501S077000, C501S079000
Reexamination Certificate
active
06306783
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tin borophosphate glass and to a sealing material using the glass.
2. Description of the Related Art
Materials using glasses have been developed as sealing materials for glass, ceramics, metals, and other materials.
To obtain a strong bonding, such a sealing glass must be heated to a sufficiently high temperature to wet the surface of a subject to be sealed in a sealing process. The sealing temperature should be, however, decreased as low as possible in the sealing of electronic parts. Sealing materials are mainly used in such applications and contain a lead-borate low-melting glass. Especially, sealing materials in wide use have a sealing temperature of 430° C. to 500° C. and a thermal expansion coefficient of 70×10
−7
/° C. to 100×10
−7
/° C.
However, demands have been made in recent years to provide lead-free sealing glasses from the viewpoint of environmental issues.
A tin borophosphate glass has been proposed as such a lead-free sealing glass. This type of glass contains, however, large amounts of P
2
O
5
as a main glass forming oxide and shows various disadvantages specific to a phosphate glass and has not yet been used in practice. The disadvantages of phosphate glasses include 1) an increased thermal expansion coefficient, 2) a deteriorated mechanical strength as compared with conventional sealing glasses, 3) a deteriorated weatherability, 4) exuding of a remaining matrix glass when crystallized, and 5) vigorous foaming in a glass forming reaction due to a material phosphoric acid.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a lead-free glass of equal quality to conventional sealing glasses.
It is another object of the invention to provide a sealing material using the glass.
Under these circumstances and after intensive investigations, the present inventors found that the above objects can be achieved by restricting the content of P
2
O
5
to 24% by mole or less and using B
2
O
3
as a main glass forming oxide instead of P
2
O
5
. The invention has been accomplished based on the above findings.
According to one aspect of the present invention, there is provided a tin borophosphate glass which comprises, by mole, 30 to 80% of SnO, 5 to 60% of B
2
O
3
, and 5 to 24% of P
2
O
5
as main components.
According to another aspect of the present invention, there is provided a sealing material which includes, by volume, 50 to 100% of a powdered tin borophosphate glass and 0 to 50% of a powdered refractory filler. The powdered tin borophosphate glass contains, by mole, 30 to 80% of SnO, 5 to 60% of B
2
O
3
, and 5 to 24% of P
2
O
5
as main components.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention will now be described in more detail. The term “%” as used herein means “% by mole” unless specifically defined otherwise.
In the invented glass, the contents of main components, SnO, B
2
O
3
, P
2
O
5
are specified to the above ranges for the following reasons.
SnO serves to lower the melting point of the glass. When the content of SnO is less than 30%, the glass is to have an excessively high viscosity and an excessively high sealing temperature. In contrast, when the content exceeds 80%, the materials cannot be vitrified. The content of SnO preferably ranges from 40% to 65%.
B
2
O
3
serves as a glass forming oxide. When the content of B
2
O
3
is less than 5%, the materials cannot be vitrified. In contrast, when the content exceeds 60%, the glass is to have an excessively high viscosity. The content of B
2
O
3
preferably ranges from 10% to 40%.
P
2
O
5
serves as a glass forming oxide. When the content of P
2
O
5
is less than 5%, the materials cannot be vitrified. In contrast, if the content exceeds 24%, a resulting glass significantly exhibits the disadvantages specific to a phosphate glass, such as an excessively increased thermal expansion coefficient. The content of P
2
O
5
preferably ranges from 10% to 23%.
A molar ratio B
2
O
3
/P
2
O
5
is preferably 0.25 or more, and more preferably 0.4 or more. When the molar ratio is less than 0.25, the disadvantages specific to a phosphate glass are liable to occur.
The invented glass can further comprise additional components in addition to the main components. These additional components include, but are not limited to, ZnO, Al
2
O
3
, SiO
2
, WO
3
, MoO
3
, Nb
2
O
5
, TiO
2
, ZrO
2
, R
2
O, CuO, MnO, R′O, and other components for stabilizing glass, where R is Li, Na, K, and/or Cs, and R′ is Mg, Ca, Sr, and/or Ba. The total content of the stabilizing components should be preferably 40% or less. This is because, a resulting glass contrarily becomes unstable and is liable to devitrify in molding when the total content exceeds 40%.
The stabilizing components for use in the invention preferably have the following contents for the following reasons.
ZnO serves to stabilize the glass and to lower the thermal expansion coefficient. The content of ZnO is preferably 0 to 25%, and more preferably 0 to 15%. When the content of ZnO exceeds 25%, the glass is liable to crystallize to an excessive extent and the fluidity is thereby deteriorated.
The contents of Al
2
O
3
and SiO
2
are each preferably 0 to 10%, and more preferably 0 to 5%. When each of the contents of these components exceeds 10%, the glass is liable to have an excessively high viscosity.
The contents of WO
3
and MoO
3
are each preferably 0 to 20%, and more preferably 0 to 10%. When each of these contents exceeds 20%, the glass is liable to have an excessively high viscosity.
Nb
2
O
5
, TiO
2
and ZrO
2
each preferably have a content of 0 to 15%, and more preferably 0 to 10%. When each of these contents exceeds 15%, the glass is liable to crystallize excessively.
The content of R
2
O is preferably 0 to 35%, and more preferably 0 to 15%. If the content of R
2
O exceeds 35%, the glass is liable to crystallize excessively.
The contents of CuO and MnO are each preferably 0 to 10%, and more preferably 0 to 5%. When each of these contents exceeds 10%, the glass is liable to become unstable.
The content of R′O is preferably 0 to 15%, and more preferably 0 to 5%. If the content exceeds 15%, the glass is liable to become unstable.
The glass can further comprise F
2
to lower the melting point of the glass. In this case, a mole ratio F
2
/(F
2
+O
2
) should preferably be 0.3 or less, and more preferably 0.1 or less. If the ratio F
2
/(F
2
+O
2
) exceeds 0.3, the glass is liable to become unstable.
The glass having the above composition has a glass transition point of 280° C. to 380° C. and shows a satisfactory fluidity at temperatures of 500° C. or lower. The glass has a thermal expansion coefficient of about 90×10
−7
/° C. to about 150×10
−7
/° C. at temperatures ranging from 30° C. to 250° C.
The invented tin borophosphate glass has the above characteristics and can be used alone as a sealing material for materials having a compatible thermal expansion coefficient. In contrast, the glass can be compounded with a powdered refractory filler comprising a low-expansion material and can be used for the sealing of materials not having a compatible thermal expansion coefficient. Such materials not having a compatible thermal expansion coefficient include, for example, alumina (70×10
−7
/° C.) and a flat window glass (80×10
−7
/° C). The powdered refractory filler can be also added to improve the mechanical strength, as well as to adjust the thermal expansion coefficient.
In the case a powdered refractory filler is added, the glass should comprise, by volume, 50 to 100% of a powdered glass and 0 to 50% of the powdered filler. When the proportion of the powdered filler exceeds 50% by volume, the proportion of the glass becomes relatively low, and a fluidity required as a sealing material cannot be obtained. Materials of the powdered refractory filler include, but are not limited to, cordierite, zircon, tin oxide, niobium oxide, zirconium phosphate, willemite, mullite, and o
Nippon Electric Glass Co. Ltd.
Sample David R.
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