Low temperature sealing composition

A low temperature sealing composition consists essentially of 45.0 to 85.0 wt. % of PbO, 1.0 to 11.0 wt. % of B.sub.2 O.sub.3, 1.0 to 45.0 wt. % of Bi.sub.2 O.sub.3, 0.2 to 10.0 wt. % of Fe.sub.2 O.sub.3, 0 to 15.0 wt. % of ZnO, 0 to 5.0 wt. % of CuO, 0 to 5.0 wt. % of V.sub.2 O.sub.5, 0 to 3.0 wt. % of SnO.sub.2, 0 to 5.0 wt. % of SiO.sub.2 plus Al.sub.2 O.sub.3, 0 to 7.0 wt. % of BaO, 0 to 5.0 wt. % of TiO.sub.2, 0 to 5.0 wt. % of ZrO.sub.2 and 0 to 6.0 wt. % of F.sub.2. The sealing composition has a low sealing temperature of 400.degree.C. or lower and is useful for readily sealing IC packages and display panels without application of load. In order to adjust the thermal coefficient of expansion, the sealing glass composition may be used by mixing with 20 vol. % to 55 vol. % of refractory filler powder of such as lead titanate based ceramics, willemite based ceramics, cordierite ceramics, zircon based ceramics or tin oxide based ceramics.

BACKGROUND OF THE INVENTION 
This invention relates to a low temperature sealing composition, and more 
particularly, to a low temperature sealing glass composition suitable for 
hermetically sealing ceramic packages for integrated circuits (ICs) and 
quartz resonators, and sealing display panels such as vacuum fluorescent 
displays (VFDs). 
A sealing material for hermetically sealing packages for an IC or quartz 
resonators, and display panels are required to be sealable at a low 
temperature so as not to deteriorate the enclosed devices due to thermal 
effects. In addition, it is also necessary that the thermal coefficient of 
expansion (hereinafter, abbreviated to TCE) of the material is compatible 
with that of the ceramics or a display panel glass to be used. In 
particular, the IC packages should be sealed with the material that is 
high in mechanical strength besides meeting the aforementioned 
requirements. The material for sealing the IC package is also required to 
have superior insulating properties to avoid undesirable leak of signal 
currents. Further, the material for the IC package should have the least 
possible content of .alpha.-particle emitting impurities because the soft 
error often occurs when an IC chip such as DRAM and CCD is exposed to the 
.alpha.-particle. 
Various sealing materials have been proposed that meet the above mentioned 
requirements. One of such materials is a PbO-B.sub.2 O.sub.3 glass of a 
low melting temperature. It has also been proposed to use the low melting 
temperature glass as an admixture with refractory fillers. For example, 
Japanese Patent Unexamined Publication 229738/1990 discloses a sealing 
material comprising PbO-B.sub.2 O.sub.3 glass powder, lead titanate 
ceramic powder and low expansion ceramic powder. 
It is known about the PbO-B.sub.2 O.sub.3 glass that lowering content of 
B.sub.2 O.sub.3 generally lowers the glass transformation point resulting 
in a lower sealing temperature. However, sufficient content of B.sub.2 
O.sub.3 is necessary to make the glass stable, which limites glass 
composition and makes it impossible to obtain sealing materials usable 
below 400.degree. C. The sealing temperature of 400.degree. C. or lower is 
thus difficult to be achieved. This means that the sealing material of the 
type described is not suitable for sealing packages for heat sensitive 
devices such as a highly integrated IC, or quartz resonators. 
Several sealing materials have also been proposed which are sealable at the 
temperature of 400.degree. C. or lower. For example, Japanese Patent 
Publication No. 8060/1988 discloses a sealing material consisting of 
PbO-B.sub.2 O.sub.3 glass powder with Tl.sub.2 O contained therein. In 
addition, U.S. Pat. No. 4,743,302 discloses another sealing material 
comprising PbO-V.sub.2 O.sub.5 -TeO.sub.2 glass powder. However, both of 
these materials are unfavorable because of the following reasons. The 
sealing material disclosed in the Japanese Patent Publication No. 
8060/1988 includes a highly toxic component, i.e., thallium carbonate in 
the raw material for the glass. Such a toxic material should be handled 
using special protective instrument. The sealing material disclosed in 
U.S. Pat. No. 4,743,302 is more likely to be crystallized and thus 
requires application of a large load to the package to be sealed. 
SUMMARY OF THE INVENTION 
Accordingly, a primary object of the present invention is to provide a low 
temperature sealing composition which meets the requirements for sealing 
material of IC packages or display panels and which is sealable at the 
temperature of 400.degree. C. or lower without application of load during 
sealing operation. 
Another object of the present invention is to provide a low temperature 
sealing composition without use of highly toxic components. 
A low temperature sealing composition according to the present invention is 
glass powder which essentially consists of 45.0 to 85.0 wt. % of PbO, 1.0 
to 11.0 wt. % of B.sub.2 O.sub.3, 1.0 to 45.0 wt. % of Bi.sub.2 O.sub.3, 
0.2 to 10.0 wt. % of Fe.sub.2 O.sub.3, 0 to 15.0 wt. % of ZnO, 0 to 5.0 
wt. % of CuO, 0 to 5.0 wt. % of V.sub.2 O.sub.5, 0 to 3.0 wt. % of 
SnO.sub.2, 0 to 5.0 wt. % of SiO.sub.2 plus Al.sub.2 O.sub.3, 0 to 7.0 wt. 
% of BaO, 0 to 5.0 wt. % of TiO.sub.2, 0 to 5.0 wt. % of ZrO.sub.2 and 0 
to 6.0 wt. % of F.sub.2. 
In addition, a low temperature sealing glass composition according to the 
present invention comprises 45% to 80% by volume of glass powder and 20% 
to 55% by volume of refractory filler powder. The glass powder essentially 
consists of 45.0 to 85.0 wt. % of PbO, 1.0 to 11.0 wt. % of B.sub.2 
O.sub.3, 1.0 to 45.0 wt. % of Bi.sub.2 O.sub.3, 0.2 to 10.0 wt. % of 
Fe.sub.2 O.sub.3, 0 to 15.0 wt. % of ZnO, 0 to 5.0 wt. % of CuO, 0 to 5.0 
wt. % of V.sub.2 O.sub.5, 0 to 3.0 wt. % of SnO.sub.2, 0 to 5.0 wt. % of 
SiO.sub.2 plus Al.sub.2 O.sub.3, 0 to 7.0 wt. % of BaO, 0 to 5.0 wt. % of 
TiO.sub.2, 0 to 5.0 wt. % of ZrO.sub.2 and 0 to 6.0 wt. % of F.sub.2. 
DESCRIPTION OF THE INVENTION 
The present inventors have found that, as a result of tremendous studies 
and considerations, Fe.sub.2 O.sub.3 is considerably effective for 
stabilizing PbO-B.sub.2 O.sub.3 glass, in particular to PbO-B.sub.2 
O.sub.3 glass with Bi.sub.2 O.sub.3 contained therein, and that the above 
mentioned objects can be achieved with the reduced content of B.sub.2 
O.sub.3 by means of adding Fe.sub.2 O.sub.3 to the glass composition. 
Briefly, the low temperature sealing composition according to the present 
invention is obtained by means of substituting Fe.sub.2 O.sub.3 for a part 
of B.sub.2 O.sub.3 of the PbO-B.sub.2 O.sub.3 glass, thereby reducing the 
content of B.sub.2 O.sub.3. 
In the low temperature sealing composition according to the present 
invention, the ingredients of the glass powder are limited as set forth 
above because of the following reasons. 
The content of PbO ranges from 45.0 to 85.0 wt. %, and preferably, from 
50.0 to 83.0 wt. %. PbO content of lower than 45 wt. % increases the 
viscosity of the glass, impeding sufficient flow of the glass at a 
temperature of 400.degree. C. or lower. On the other hand, PbO content of 
higher than 85 wt. % causes crystallization upon sealing, which hinders 
flowing of the glass. 
The content of B.sub.2 O.sub.3 ranges from 1.0 to 11.0 wt. %, and 
preferably, from 2.0 to 10.0 wt. %. B.sub.2 O.sub.3 content of lower than 
1.0 wt. % makes the glass unstable to cause crystallization upon sealing. 
Such crystallization behavior also hinders flowing of the glass. B.sub.2 
O.sub.3 content of higher than 11.0 wt. % increases the viscosity of the 
glass, impeding the glass from sufficient flow at a temperature of 
400.degree. C. or lower. 
Bi.sub.2 O.sub.3 has the effect of stabilizing the glass without increasing 
the viscosity and the content thereof is between 1.0 and 45.0 wt. %, and 
preferably, between 1.2 and 35.0 wt. %. The above mentioned effect cannot 
be achieved by Bi.sub.2 O.sub.3 of less than 1.0 wt. %. Bi.sub.2 O.sub.3 
of more than 45 wt. % is responsible for the increased viscosity of the 
glass, inhibiting sufficient flow of the glass at a temperature of 
400.degree. C. or lower. 
Fe.sub.2 O.sub.3 has the significant effect for stabilizing the glass and 
the content thereof is within the range of 0.2 to 10.0 wt. %, and 
preferably, 0.2 to 9.0 wt. %. Fe.sub.2 O.sub.3 of less than 0.2 wt. % 
produces no effect of glass stabilization, so the glass significantly 
crystallizes upon heating. On the other hand, Fe.sub.2 O.sub.3 of more 
than 10.0 wt. % is responsible for the increased viscosity of the glass, 
inhibiting sufficient flow of the glass at a temperature of 400.degree. C. 
or lower. 
The content of ZnO ranges from 0 to 15.0 wt. %, and preferably, from 0 to 
13.0 wt. %. While ZnO contributes to stabilizing the glass as well as 
improving water-resistance thereof, ZnO of more than 15.0 wt. % causes 
crystallization of the glass to inhibit sufficient flow of it. 
The content of CuO ranges from 0 to 5.0 wt. %, and preferably, 0 to 4.0 wt. 
%. While CuO is known to be the component capable of stabilizing the glass 
without increasing the viscosity, CuO content of higher than 5.0 wt. % 
results in precipitation of crystals upon sealing. 
V.sub.2 O.sub.5 contributes to reducing surface tension of the glass and 
improves flowability thereof. The content of V.sub.2 O.sub.5 is between 0 
and 5.0 wt. %, and preferably, between 0 and 3.0 wt. %. V.sub.2 O.sub.5 of 
more than 5.0 wt. % causes the glass to be crystallized significantly and 
makes the glass difficult to flow. 
SnO.sub.2 favorably affects on stabilization of the glass and is contained 
therein ranging from 0 to 3.0 wt. %, and preferably, from 0 to 2.0 wt. %. 
SnO.sub.2 of more than 3.0 wt. % also causes the glass to be crystallized 
significantly and makes the glass difficult to flow. 
The content of SiO.sub.2 and Al.sub.2 O.sub.3 in total ranges from 0 to 5.0 
wt. %, and preferably, from 0 to 3.0 wt. %. SiO.sub.2 and Al.sub.2 O.sub.3 
can be effectively used to avoid crystallization of the glass. However, 
the total content thereof exceeding 5.0 wt. % increases viscosity of the 
glass, which makes the glass to flow only at a temperature higher than 
400.degree. C. 
The content of BaO ranges from 0 to 7.0 wt. %, and preferably, 0 to 5.0 wt. 
%. While BaO has the effect of preventing the glass from being 
crystallized, its content of higher than 7.0 wt. % results in the 
increased viscosity of the glass. The higher viscosity is responsible for 
insufficient flow thereof at a temperature of 400.degree. C. or lower. 
TiO.sub.2 exhibits the effect of stabilizing the glass when being contained 
in the amount between 0 to 5.0 wt. %, and preferably, between 0 and 1.0 
wt. %. With the higher content of TiO.sub.2 than 5.0 wt. %, the glass 
shows significant tendency to be crystallized and to hardly flow. 
The content of ZrO.sub.2 ranges from 0 to 5.0 wt. %, and preferably, from 0 
to 1.0 wt. %. While ZrO.sub.2 has the effect of preventing the glass from 
being crystallized, the higher content thereof than 5.0 wt. % results in 
the increased viscosity of the glass and makes the glass to hardly flow at 
a temperature of 400.degree. C. or lower. 
The content of F.sub.2 is between 0 and 6.0 wt. %. F.sub.2 serves to lower 
the sealing temperature of the glass of a Bi.sub.2 O.sub.3 -rich 
composition. However, the content higher than 6.0 wt. % strongly 
influences the stabilization of the glass to lead the glass to 
crystallization upon sealing. As a result, the glass is reduced in 
flowability. 
Other components may be contained in the glass addition to those described 
above and the possible examples of these other components are: 5% or less, 
by weight, of Ag.sub.2 O, SrO, P.sub.2 O.sub.5, Co.sub.2 O.sub.3 and 
TeO.sub.2 ; 3% or less, by weight, of Mo.sub.2 O.sub.3, Rb.sub.2 O, 
Cs.sub.2 O, Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.3, CeO.sub.2, NiO, Cr.sub.2 
O.sub.3 and Sb.sub.2 O.sub.3 ; and rare earth oxides such as La.sub.2 
O.sub.3. However, it should be avoided to add any components using highly 
toxic element such as Tl.sub.2 O. 
The glass having the above mentioned composition is amorphous and no 
crystal will be precipitated upon sealing. With this glass composition, 
superior flowability can be achieved accordingly. In addition, the glass 
transformation point is low, i.e., 300.degree. C. or lower and the 
viscosity is low as well. The TCE of this glass at 30.degree. to 
250.degree. C. is equal to or higher than 115.times.10.sup.-7 /.degree.C. 
Thus, this glass can be used for sealing, at a low temperature, materials 
having the relatively high coefficient of thermal expansion compatible 
with that of glass. It is, however, necessary to adjust the TCE of the 
glass when the latter is used for sealing IC packages or display panels 
manufactured with materials having various TCE. For example, the TCE of 
the glass is required to be lowered for sealing alumina (having the TCE of 
70.times.10.sup.-7 /.degree.C.), aluminum nitride (having the TCE of 
45.times.10.sup.-7 /.degree.C.), or the display glass panel (having the 
TCE of 85.times.10.sup.-7 /.degree.C.). 
The TCE adaptable to seal IC packages or display panels can be obtained by 
means of adding of the refractory filler powder of an amount within the 
above mentioned range to the low temperature sealing glass composition. 
Suitable refractory filler powder may be: lead titanate based ceramic 
powder, willemite-based ceramic powder, cordierite ceramic powder, 
zircon-based ceramic powder, tin oxide based ceramic powder, 
.beta.-eucryptite ceramic powder, mullite ceramic powder or 
mixture-thereof. As other fillers than those exemplified above, silica 
glass, alumina, titanium oxide and niobium pentoxide are also applicable. 
In the present invention, the mixing ratio of the glass powder and the 
filler powder is limited as set forth above because of the following 
reasons. 
The composition with the glass component of less than 45 vol. % (i.e., with 
the refractory fillers of more than 55 vol. %) makes the mixture 
insufficient or poor in flowability, which makes the composition 
unsuitable as the sealing material used at a temperature of 400.degree. C. 
or lower. On the contrary, in the composition having the glass content of 
higher than 80 vol. % (i.e., the refractory filler content of lower than 
20 vol. %), the TCE will be lowered only by an insufficient extent and is 
never compatible with materials of the IC packages and display panels. 
Described hereinbelow is a method of manufacturing the low temperature 
sealing composition according to the present invention. Raw materials are 
blended and mixed to obtain a desired composition, thereafter, melted at 
700.degree. to 1000.degree. C. for 1 or 2 hours, and then formed into a 
plate. The plate is then ground to powder in a ball-mill or the like. The 
powder is then classified according to predetermined particle sizes to 
obtain glass powder of a desired size. If desired, the glass powder 
obtained in this manner may be mixed with refractory filler powder at a 
specific ratio. 
The foregoing features of the low temperature sealing composition according 
to the present invention will be more readily apparent in the context of a 
specifically delineated set of examples.