Compositions: ceramic – Ceramic compositions – Glass compositions – compositions containing glass other than...
Reexamination Certificate
1999-11-29
2001-10-30
Sample, David R (Department: 1755)
Compositions: ceramic
Ceramic compositions
Glass compositions, compositions containing glass other than...
C501S017000, C501S024000, C501S026000, C501S046000, C501S047000, C501S048000, C501S049000, C501S051000, C501S052000, C501S077000, C501S079000
Reexamination Certificate
active
06309989
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a tin-borophosphate glass and to a sealing material using the same.
As a sealing material for various kinds of materials such as glass, ceramic, and metal, development has been made of a material using a sealing glass.
In order to obtain a strong bonding, it is necessary in a sealing process to heat the sealing glass to a temperature sufficient to wet a sealing surface of a sealed object. However, in sealing electronic components or parts, a sealing temperature must be kept as low as possible. Therefore, in such application, use is mainly made of a sealing material utilizing a low-melting-point lead-borate glass. Specifically, use is widely made of the material having a sealing temperature of 430-500° C. and a thermal expansion coefficient of 70−100×10
−7
/° C.
However, it is recently required that no lead is contained in the sealing glass in view of the environmental problem.
As a lead-free sealing glass, a tin-phosphate glass has been proposed. However, such a glass contains a large amount of P
2
O
5
as a main glass-forming oxide and therefore tends to exhibit following defects inherent to a phosphate glass: 1) the thermal expansion coefficient is increased, 2) the mechanical strength is decreased in comparison with existing sealing glasses, 3) the weather resistance is degraded, 4) a glass component left uncrystallized is released or eluted, and 5) heavy bubbling occurs during vitrification because phosphate is used as a raw material. As a result, practical use is not yet commenced.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a glass which does not contain a lead component but has characteristics equivalent to those of an existing sealing glass, and a sealing material using the same.
Taking the above-mentioned circumstances into consideration, the present inventor has carried out various experiments. As a result, it has been found out that the above-mentioned object is achieved by introducing B
2
O
3
as a main glass-forming oxide and satisfying a condition of B
2
O
3
/P
2
O
5
≧0.20 by mole ratio. This finding is herein proposed as the present invention.
Specifically, a tin-borophosphate glass according to the present invention contains SnO, B
2
O
3
, and P
2
O
5
as main components, consists essentially of, by mole % representation, 30-70% SnO, 5-30% B
2
O
3
, and 24.1-45% P
2
O
5
, and satisfies a condition of B
2
O
3
/P
2
O
5
≧0.20 by mole ratio.
DESCRIPTION OF THE INVENTION
Description will hereafter be made as regards the reason why the contents of SnO, B
2
O
3
, and P
2
O
5
as the main components of the glass are defined as specified above.
SnO is a component for lowering the melting point of the glass. When the content of SnO is less than 30%, the viscosity of glass is increased so that the sealing temperature becomes excessively high. When the content is more than 70%, vitrification is difficult to occur. A preferable range of SnO is 35-65%.
B
2
O
3
is a glass-forming oxide. When the content of B
2
O
3
is less than 5%, vitrification takes place, but a scum is produced by separation of the glass. When the content exceeds 30%, the viscosity is increased so that the flow is difficult. When the content of B
2
O
3
is 20% or less, the glass tends to be unstable so that the weather resistance is decreased. Accordingly, a preferable range of B
2
O
3
is 20.1-30%.
P
2
O
5
is a glass-forming oxide. When the content of P
2
O
5
is within a range of 24% or less, stability of the glass is not sufficient. When the content exceeds 45%, the weather resistance of the glass itself is deteriorated and the viscosity of the glass is increased so that the flow is difficult. A preferable range of P
2
O
5
is 25-35%.
In the present invention, it is important that the ratio of B
2
O
3
and P
2
O
5
satisfies a condition of B
2
O
3
/P
2
O
5
≧0.20 by mole ratio. When the value is less than 0.20, the above-mentioned defects inherent to the phosphate glass are readily caused. In particular, the weather resistance characteristic is extremely degraded. A preferable range of B
2
O
3
/P
2
O
5
is 0.40 or more.
In the glass of the present invention, various components may be added to the above-mentioned main components. For example, glass stabilizing components such as ZnO, Al
2
O
3
, SiO
2
, WO
3
, MoO
3
, Nb
2
O
5
, TiO
2,
ZrO
2
, R
2
O (R being Li, Na, K, or Cs), CuO, MnO, and R′O (R′ being Mg, Ca, Sr, or Ba) can be added to 35% or less in total. The reason why the content of these stabilizing components is limited to 35% or less is that, if the content exceeds 35%, the glass becomes unstable and is readily devitrified upon forming.
Description will hereafter be made as regards the contents of the stabilizing components (mole % representation) and the reason of limitation thereof.
ZnO has not only a function of stabilizing the glass but also an effect of lowering the thermal expansion coefficient. The content is 0-25%, preferably, 0.1-15%. When the content of ZnO is more than 25%, the tendency of crystallization of the glass is extremely increased so that the flowability is likely to be lowered.
The content of each of Al
2
O
3
and SiO
2
is 0-10%, preferably, 0-5%. When the content of each component exceeds 10%, the viscosity of the glass is readily increased.
The content of each of WO
3
and MoO
3
is 0-20%, preferably, 0-10%. When the content of each component exceeds 20%, the viscosity of the glass is likely to be increased.
The content of each of Nb
2
O
5
, TiO
2,
and ZrO
2
is 0-15%, preferably, 0-10%. When the content of each component exceeds 15%, the tendency of crystallization of the glass is likely to be extremely increased.
The content of R
2
O is 0-35%, preferably, 0-15%. When the content of R
2
O exceeds 35%, the tendency of crystallization of the glass is likely to be extremely increased.
The content of each of CuO and MnO is 0-10%, preferably, 0-5%. When the content of each component exceeds 10%, the glass is likely to become unstable.
The content of R′O is 0-15%, preferably, 0-5%. When the content of R′O exceeds 15%, the glass is likely to become unstable.
The glass having the above-mentioned composition has a glass transition point of 280-380° C., and exhibits an excellent flowability at a temperature of 500° C. or less. In addition, the glass has a thermal expansion coefficient on the order of 95-150×10
−7
/° C. at 30-250° C.
The tin-borophosphate glass of the present invention having the above-mentioned characteristics can be used alone as a sealing material for a material matched in thermal expansion coefficient. On the other hand, in order to seal a material unmatched in thermal expansion coefficient, for example, alumina (70×10
−7
/° C.) or a window panel glass (80×10
−7
/° C.), this glass can be used as a composite with refractory filler powder comprising a low-expansion material. The refractory filler powder may be added for other purposes than control of the thermal expansion coefficient, for example, in order to improve the mechanical strength.
When the refractory filler powder is mixed, the mixing ratio is preferably within a range of 50-100 vol % of the glass powder and 0-50 vol % of the filler powder. This is because, when the filler powder is more than 50 vol %, the ratio of the glass powder is relatively lowered so that the flowability necessary as the sealing material is difficult to obtain. As the refractory filler powder, use can be made of various materials, for example, cordierite, zircon, tin oxide, niobium oxide, zirconium phosphate, willemite, and mullite. Specially, NbZr (PO
4
) ceramic powder with 2 wt % MgO added thereto well matches with the tin-borophosphate glass of the present invention because phosphate is contained in the component.
In order to produce the sealing material using the tin-borophosphate glass of the present invention, a raw material is at first prepared to have the above-mentioned composition and is melted to be vitrified. It is necessary to carefully avo
Collard & Roe P.C.
Nippon Electric Glass Co. Ltd.
Sample David R
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