Title: Glass and conductive paste using the same
Abstract: A glass containing no lead and comprising, calculated as oxides: 40-60 wt. % ZnO, 15-35 wt. % B.sub.2 O.sub.3, 1-16 wt. % SiO.sub.2, 1-10 wt. % Al.sub.2 O.sub.3, 2-15 wt. % MnO.sub.2, and at least one selected from the group consisting of Li.sub.2 O, Na.sub.2 O and K.sub.2 O in their total of 0.5-10 wt. %, and a glass with the above-described components where a total of at least one selected from the group consisting of Li.sub.2 O, Na.sub.2 O and K.sub.2 O is 0-5 wt. %, and at least one selected from the group consisting of MgO, CaO, TiO.sub.2, Cr.sub.2 O.sub.3, ZrO.sub.2, Ta.sub.2 O.sub.5, SnO.sub.2, and Fe.sub.2 O.sub.3 is further included in their total of 0.1-5 wt. %. A conductive paste using such a glass as an inorganic binder has a superior binder removal ability and a good sinterability and can form dense conductors with excellent characteristics with respect to resistance to plating solutions, adhesive strength, resistance to thermal shocks, etc.
Patent Number: 6,841,495 Issued on 01/11/2005 to Tanaka, et al.
| Inventors:
|
Tanaka; Tetsuya (Tokyo, JP);
Morinaga; Kenji (late of Chikushi-gun, JP);
Morinaga; Nobuko (Chikushi-gun, JP);
Yamazoe; Mikio (Nishitokyo, JP);
Kawahara; Megumi (Akishima, JP)
|
| Assignee:
|
Shoei Chemical Inc. (Tokyo, JP)
|
| Appl. No.:
|
314897 |
| Filed:
|
December 9, 2002 |
Foreign Application Priority Data
| Dec 21, 2001[JP] | 2001-390611 |
| Oct 30, 2002[JP] | 2002-316884 |
| Current U.S. Class: |
501/79; 252/512; 252/513; 252/514; 252/519.52; 252/519.54; 501/19; 501/26 |
| Intern'l Class: |
C03C 003/066; C03C008/18; H01B001/14 |
| Field of Search: |
501/19,26,79
252/512,513,514,519.52,519.54
|
References Cited [Referenced By]
U.S. Patent Documents
| 3902102 | Aug., 1975 | Burn | 361/305.
|
| 4451869 | May., 1984 | Sakabe et al. | 361/309.
|
| 5306674 | Apr., 1994 | Ruderer et al. | 501/20.
|
| 5645765 | Jul., 1997 | Asada et al. | 252/519.
|
| 6123872 | Sep., 2000 | Yamazaki et al. | 252/301.
|
| Foreign Patent Documents |
| 0 926 102 | Jun., 1999 | EP.
| |
| 54-119513 | Sep., 1979 | JP.
| |
| 59-184511 | Oct., 1984 | JP.
| |
| 59-223248 | Dec., 1984 | JP.
| |
| 1-51003 | Nov., 1989 | JP.
| |
| 5-234415 | Sep., 1993 | JP.
| |
| 5-342907 | Dec., 1993 | JP.
| |
| 9-55118 | Feb., 1997 | JP.
| |
| 1791405 | Jan., 1993 | RU.
| |
Primary Examiner: Group; Karl
Attorney, Agent or Firm: Flynn, Thiel, Boutell & Tanis, P.C.
Claims
What is claimed is:
1. A glass containing no lead and comprising, calculated as oxides, 40-60
wt. % ZnO, 15-35 wt. % B.sub.2 O.sub.3, 1-16 wt. % SiO.sub.2, 1-10 wt. %
Al.sub.2 O.sub.3, 2-15 wt. % MnO.sub.2, and at least one selected from the
group consisting of Li.sub.2 O, Na.sub.2 O and K.sub.2 O in their total of
0.5-10 wt. %.
2. A glass containing no lead and comprising, calculated as oxides, 40-60
wt. % ZnO, 15-35 wt. % B.sub.2 O.sub.3, 1-16 wt. % SiO.sub.2, 1-10 wt. %
Al.sub.2 O.sub.3, 2-15 wt. % MnO.sub.2, at least one selected from the
group consisting of Li.sub.2 O, Na.sub.2 O and K.sub.2 O in their total of
0-5 wt. %, and at least one selected from the group consisting of MgO,
CaO, TiO.sub.2, Cr.sub.2 O.sub.3, ZrO.sub.2, Ta.sub.2 O.sub.5, SnO.sub.2,
and Fe.sub.2 O.sub.3 in their total of 0.1-5 wt. %.
3. A conductive paste comprising an electrically conductive powder, a
vehicle, and a powder of the glass claimed in claim 1.
4. A conductive paste comprising an electrically conductive powder, a
vehicle, and a powder of the glass claimed in claim 2.
5. The conductive paste according to claim 3, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of copper, nickel, cobalt and an alloy or composite
containing at least one of these metals.
6. The conductive paste according to claim 4, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of copper, nickel, cobalt and an alloy or composite
containing at least one of these metals.
7. The conductive paste according to claim 3, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of silver, palladium, and an alloy or composite
containing at least one of these metals.
8. The conductive paste according to claim 4, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of silver, palladium, and an alloy or composite
containing at least one of these metals.
9. A conductive paste for forming a terminal electrode of a multilayer
ceramic component, wherein the conductive paste is according to claim 3.
10. A conductive paste for forming a terminal electrode of a multilayer
ceramic component, wherein the conductive paste is according to claim 4.
11. The conductive paste according to claim 9, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of copper, nickel, cobalt and an alloy or composite
containing at least one of these metals.
12. The conductive paste according to claim 10, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of copper, nickel, cobalt and an alloy or composite
containing at least one of these metals.
13. The conductive paste according to claim 9, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of silver, palladium, and an alloy or composite
containing at least one of these metals.
14. The conductive paste according to claim 10, wherein the electrically
conductive powder comprises at least one powder selected from the group
consisting of powders of silver, palladium, and an alloy or composite
containing at least one of these metals.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a conductive paste suitable for forming
electrodes of electronic components and conductors of thick-film circuits
and to a glass used therein. More particularly, the present invention
relates to a conductive paste that can be fired even in a non-oxidizing
atmosphere and is suitable for forming terminal electrodes of multilayer
ceramic components using a base metal such as nickel or copper for inner
electrodes and to a glass used therein.
2. Description of the Prior Art
Multilayer ceramic components such as multilayer capacitors, multilayer
inductors, and the like are typically fabricated in the manner as follows.
Unfired (green) ceramic sheets, for example, of a dielectric or magnetic
material are alternately laminated with a plurality of inner electrode
paste layers to obtain a non-fired laminate. Then, the laminate is cut and
fired at a high temperature to obtain a ceramic body (referred to as
"ceramic body" hereinbelow). Thereafter, a conductive paste in which a
conductive powder and an inorganic binder powder such as glass and the
like is dispersed, if necessary, together with other additives in a
vehicle, is coated by any of a variety of methods such as dipping, brush
coating, screen printing, and the like on the end surfaces of the inner
electrodes exposed from the ceramic body, followed by drying.
High-temperature firing is then conducted to form terminal electrodes
electrically connected to the inner electrodes. Then, if necessary, a
plated nickel layer or a plated layer of tin or alloy thereof is formed on
the terminal electrodes.
Noble metals such as palladium, silver-palladium, platinum, and the like
have been used as the inner electrode materials. But in recent years, base
metals such as nickel, copper, and the like came into use in order to save
natural resources, to reduce cost and also to prevent the occurrence of
delamination and cracking caused by oxidation and expansion of palladium.
As a result, conductive pastes of base metals such as nickel, cobalt,
copper and the like, which can easily form good electric connection to
those inner electrode materials are also used for the formation of
terminal electrodes. Because those base metal electrodes are easily
oxidized during firing, the firing has been conducted at a peak
temperature of about 700-900.degree. C. in a non-oxidizing atmosphere, for
example, an inert gas atmosphere or a reducing atmosphere, such as
nitrogen or hydrogen-nitrogen and the like.
A non-reducible glass which is stable even in firing under a non-oxidizing
atmosphere has to be used as an inorganic binder for a conductive paste to
be fired in the non-oxidizing atmosphere. A PbO component contained in
lead-containing glass frits, which have been widely used for conductive
pastes, is easily reduced. Moreover, because lead is hazardous to the
human bodies and causes environmental pollution, a glass containing no
lead is required.
Further, when a terminal electrode is electroplated, adhesive strength with
the ceramic body is sometimes greatly decreased by an acidic
electroplating solution that modifies and dissolves glass components and
breaks the glass structure. Therefore, a glass is required which has not
only a high adhesive strength, but also good resistance to acids so that
the glass is not vulnerable to attack from acidic plating solutions.
Another problem is that because firing is conducted under an atmosphere
with a small content of oxygen, organic components such as solvents and
binder resins which are used as vehicles are difficult to oxidize and
decompose. If sufficient burning, decomposition, removal (referred to as
"binder removal" hereinbelow) are not conducted, the vehicle decomposition
products are encapsulated in the film and/or partly become carbon and
remain in the film. Those carbonaceous residues cause a variety of
problems, such as preventing sintering, lowering the density of the
resultant fired film due to pores formed by oxidation and gasification at
a high temperature and decreasing the strength of the ceramics such as
barium titanate constituting the ceramic body. The selection of inorganic
binder is also important in terms of resolving these problems associated
with binder removal.
Accordingly, a barium-containing glass and a zinc-containing glass have
been comprehensively studied as a reduction-resistant glass which has a
high adhesive strength with a substrate and makes it possible to provide
conductors with excellent characteristics.
For example, base metal terminal electrodes of multilayer ceramic
capacitors are known which use a reduction-resistant glass such as barium
borate glass, barium zinc borate glass, barium zinc borosilicate glass,
and the like (see U.S. Pat. No. 3,902,102). Furthermore, it is also known
to use a copper paste for terminal electrodes comprising a barium
borosilicate glass (see Japanese Patent Publication No. 5-234415), to use
a copper paste for terminal electrodes comprising a zinc borosilicate
glass of specific composition including alkali metal components and
alkaline earth metal components (see Japanese Patent Publication No.
59-184511) and to use an aluminum strontium borosilicate glass for
terminal electrodes (see Japanese Patent Publication No. 9-55118).
Further, there have been proposed a copper a paste for terminal electrodes
using a zinc borosilicate glass (see Examined Japanese Patent Publication
No. 1-51003), and a terminal electrode paste using a zinc borosilicate
glass with a superior resistance to plating solutions (see Japanese Patent
Publication No. 5-342907).
However, in recent years improvements on characteristics of terminal
electrodes have been strongly required. Accordingly, those conventional
glasses are not always fully satisfactory for terminal electrodes. In
particular, although barium-containing glass has an advantage of low
softening temperature so that it can be fired at low-temperatures even if
lead is not contained therein, it does not have a sufficient resistance to
plating solutions and permits permeation of plating solution occurring
during electroplating which reduces the adhesive strength with the ceramic
body, causes cracking and fracturing of the ceramic body, induces a
decrease in insulation resistance, and reduces reliability of the
resultant multilayer products. Another problem was that lumps or spots of
glass (referred to as "glass spots" hereinbelow) locally appeared on the
electrode surface preventing the formation of a uniform plated film and
inhibiting soldering.
On the other hand, a zinc-containing crystallizable glass is generally
known to form a reaction layer and thereby strongly adhere to the ceramic
body and has excellent strength, thermal shock resistance, resistance to
plating solutions, and resistance to water. However, such a glass
typically has a high softening point. A problem associated with a zinc
borate glass or a zinc borosilicate glass of specific composition with a
low softening point is that it is difficult to obtain a uniform glass film
from these glasses because they have a narrow range of vitrification and
are susceptible to phase separation. Moreover, because they are
crystallizable glasses, flow characteristics and crystallization behavior
in the firing process are difficult to control. Yet another problem is
that the temperature range in which firing can be conducted is narrow
because of dependence on process conditions, in particular, because of
significant variations in characteristics related to the firing
atmosphere, firing temperature, and the like.
Further, some ceramic body is also known to decrease the electrode
strength. Specifically, when the ceramic body is formed from a barium
titanate ceramic dielectric with F characteristic specified by JIS
(Japanese Industrial Standard) C6429 and C6422, which has a high
dielectric constant, the zinc-containing crystallizable glass of the
terminal reacts with the ceramic body in the interface zone therebetween,
forming a homogeneous reaction layer, strongly adhering to the substrate
and showing practically no deep permeation into the ceramic body. However,
in the case of applications to a barium titanate ceramic dielectric with B
characteristic specified by JIS, i.e., a flat capacity-temperature
characteristic, glass components present in the terminal electrode that
were melted during firing deeply permeate into the ceramic body, degrading
the strength of the ceramic body. The ceramic body so degraded may be
cracked or fractured when a stress causing the electrode film to peel off
is applied to the capacitor, for example, in a peel strength test of
terminal electrodes. As a result, the capacitor mounted on a circuit
substrate or the like has poor reliability. This is apparently due to the
difference in microstructure between the ceramics; ceramics with F
characteristic have a relatively homogeneous structure, whereas ceramics
with B characteristic has a heterogeneous structure in which the grain
boundary portions thereof have a reaction activity higher than that of
crystal portions. In prior art, terminal electrodes with excellent peel
strength could not be obtained on such barium titanate ceramics with B
characteristic.
Thus, various types of glasses that have heretofore been developed have
respective advantages, but a glass making it possible to satisfy all of
the requirements has not yet been obtained.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a conductive paste
having all of the required characteristics, that is, containing no
hazardous components such as lead or the like, having a good binder
removal ability and sinterability even in firing in a temperature range of
about 700-900.degree. C. in a non-oxidizing atmosphere, making it possible
to form a conductor with excellent characteristics with respect to
density, resistance to plating solution, adhesive strength, resistance to
thermal shocks, and the like, having small dependence on firing process
conditions, and being capable of being fired in a wide temperature range,
and also to provide a glass used in such a conductive paste. Yet another
object of the present invention is to provide an excellent conductive
paste especially suitable for forming terminal electrodes of multilayer
ceramic capacitors. Still another object of the present invention is to
provide a conductive paste causing no degradation of ceramic bodies and
exhibiting an excellent adhesive strength with respect to a variety of
dielectric ceramic bodies, in particular, when used for terminal
electrodes of multilayer ceramic capacitors.
The present invention provides a glass containing no lead and comprising,
calculated as oxides: 40-60 wt. % ZnO, 15-35 wt. % B.sub.2 O.sub.3, 1-16
wt. % SiO.sub.2, 1-10 wt. % Al.sub.2 O.sub.3, 2-15 wt. % MnO.sub.2, and at
least one selected from the group consisting of Li.sub.2 O, Na.sub.2 O and
K.sub.2 O in their total of 0.5-10 wt. %. The present invention also
provides a glass containing no lead and comprising, calculated as oxides:
40-60 wt. % ZnO, 15-35 wt. % B.sub.2 O.sub.3, 1-16 wt. % SiO.sub.2, 1-10
wt. % Al.sub.2 O.sub.3, 2-15 wt. % MnO.sub.2, at least one selected from
the group consisting of Li.sub.2 O, Na.sub.2 O and K.sub.2 O in their
total of 0-5 wt. %, and at least one selected from the group consisting of
MgO, CaO, TiO.sub.2, Cr.sub.2 O.sub.3, ZrO.sub.2, Ta.sub.2 O.sub.5,
SnO.sub.2, and Fe.sub.2 O.sub.3 in their total of 0.1-5 wt. % (referred to
hereinbelow as "the second glass of the present invention"). The present
invention also provides a conductive paste comprising the above-specified
glass and a conductive paste for forming terminal electrodes of multilayer
ceramic components.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The glass in accordance with the present invention is a zinc borosilicate
crystallizable glass having a low softening point within a range of
500-700.degree. C. and is characterized in that it forms a homogeneous
glass in which firing hardly causes phase separation and in that it shows
appropriate crystallization behavior and flow characteristic during firing
a conductive paste containing such a glass. Using the glass in accordance
with the present invention as an inorganic binder of a conductive paste
not only makes it possible to obtain excellent characteristics of fired
films, but also decreases dependence on firing temperature and allows the
firing to be conducted within a wide temperature range.
Thus, regardless of its low softening temperature, good binder removal
capability in a low-temperature range is obtained during firing the
conductive paste. As a result, a dense conductor film with excellent
strength, resistance to thermal shocks, and resistance to plating
solutions and water can be formed without deteriorating the glass
flowability, impeding sintering of metal powder, or causing property
degradation, by residual carbon or the like. Further, because precipitated
crystals suppress a sudden drop in glass viscosity and the glass does not
move to the surface of conductor film by excess flowing even in a
high-temperature region, occurrence of glass spots is prevented. Main
precipitated crystals are supposed as Zn.sub.3 B.sub.2 O.sub.6 which
apparently precipitate mainly in the form of needles that are intertwined,
producing a network structure in the film, and producing an effect of
appropriately suppressing a flow of the glass.
The above glass component reacts with some of ceramic body components on
the interface with the ceramic body, for example, of a capacitor and the
reaction products penetrate into the dielectric. The presence of this
reaction layer increases the adhesive strength of the electrodes and can
prevent the occurrence of cracking in the ceramic body during plating or
thermal shock test.
Further, the second glass of the present invention contains at least one
component selected from among MgO, CaO, TiO.sub.2, Cr.sub.2 O.sub.3,
ZrO.sub.2, Ta.sub.2 O.sub.5, SnO.sub.2, and Fe.sub.2 O.sub.3. When a
conductive paste containing the second glass is applied to ceramics with F
characteristic, the glass and ceramic body form a homogeneous reaction
layer, whereas when the conductive paste is applied to ceramic bodies
having portions with high reactivity, such as ceramic bodies made of
ceramics with B characteristic, a terminal electrode with a high adhesive
strength can be also formed without degrading the ceramic body strength.
This is apparently because the glass comprising those components in
specific quantities has lower crystallinity and reactivity than a glass
containing no such components and the reaction with the grain boundary
portions of the ceramic body and subsequent permeation into the ceramic
body are suppressed appropriately. Therefore, terminal electrodes with a
high adhesive strength and a high peel strength can be obtained regardless
of the type of dielectric ceramic body.
The composition range of the glass in accordance with the present invention
will be described below. In the description hereinbelow, the symbol % will
represent percent by weight, unless stated otherwise.
ZnO forms a glass network in cooperation with B.sub.2 O.sub.3 and also
becomes a constituent of precipitated crystals. In addition, it improves
adhesion strength with the substrate. The content outside the range of
40-60% is undesirable because softening point of the glass becomes too
high. If the paste is fired at a high temperature in a non-oxidizing
atmosphere, ZnO is usually easily sublimated and/or reduced under the
effect of residual carbon. However, in accordance with the present
invention, because the binder removal ability is very good, no such
problem arises despite a high content of ZnO.
B.sub.2 O.sub.3 is a network-forming oxide and also used as a flux. If the
content thereof is less than 15%, the glass is devitrified, and if the
content is above 35%, the chemical resistance of the glass decreases
significantly. It is preferred that ZnO and B.sub.2 O.sub.3 be mixed so
the molar ratio thereof is 55:45-65:35.
SiO.sub.2 is a network-forming oxide and produces an effect of expanding
the vitrification range and an effect of improving chemical resistance.
The content of more than 16% is undesirable because the softening point
becomes too high. The preferred content is no more than 13%. It is
desirable that the total content of B.sub.2 O.sub.3 and SiO.sub.2 be no
more than 40 wt. %.
The drawback of the ZnO--B.sub.2 O.sub.3 --SiO.sub.2 glass of the
above-described composition is that phase separation easily occurs
therein. Al.sub.2 O.sub.3 prevents such phase separation so that a
homogeneous glass can be formed. As a result, process dependency can be
reduced. Furthermore, similarly to SiO.sub.2, Al.sub.2 O.sub.3 improves
chemical resistance. If the content of Al.sub.2 O.sub.3 is above 10%,
softening point becomes too high and the glass is devitrified. The
preferred content of Al.sub.2 O.sub.3 is no more than 8%.
The Mn component is present in the glass with a valence of 2 or 3 and
apparently has the following effect. In a non-oxidizing atmosphere the
valence changes causing release of oxygen which is then bonded to residual
carbon originating from the vehicle present in the paste and drive off it
as CO.sub.2 to the outside of the film. Further, the Mn component also
effects an increase in the reactivity of the glass with metallic copper.
If the mixing quantity is less than 2%, calculated as MnO.sub.2
equivalent, the effect is small, and if it is more than 15%, the glass is
devitirified in the production process and stable glass cannot be
obtained. The preferred content is 2-10%.
At least one alkali metal oxide selected from among Li.sub.2 O, Na.sub.2 O,
and K.sub.2 O is a network-modifying oxide which decreases the softening
temperature of the glass. If the content thereof exceeds 10%, the chemical
resistance of the glass decreases significantly. This component also
affects the precipitation of crystals and if the content is small, the
crystals do not precipitate sufficiently. Further, the form of
precipitated crystals can be changed by selecting the type of alkali metal
oxide. When Li.sub.2 O is used alone, needle crystals cannot be
precipitated. Therefore, it is preferred that Na.sub.2 O and/or K.sub.2 O
be used therewith. With certain compositions of dielectric used for the
ceramic bodies, there is a risk of Na.sub.2 O degrading the capacitor
characteristic. In such cases, using Na.sub.2 O should be avoided.
However, sufficient water resistance is not obtained when K.sub.2 O is
used alone. Therefore, it is preferred that a combination of Li.sub.2 O
0.1-3% and K.sub.2 O 1-8% be employed. In the second glass of the present
invention comprising at least one component selected from among MgO, CaO,
TiO.sub.2, Cr.sub.2 O.sub.3, ZrO.sub.2, Ta.sub.2 O.sub.5, SnO.sub.2, and
Fe.sub.2 O.sub.3, addition of the above-mentioned alkali metal oxides is
not always required. Even when they are added, the total content is
preferably within a range of 5% and below.
Introducing a small amount of a component selected from among MgO, CaO,
TiO.sub.2, Cr.sub.2 O.sub.3, ZrO.sub.2, Ta.sub.2 O.sub.5, SnO.sub.2, and
Fe.sub.2 O.sub.3 in the glass comprising the above-described components
has an effect of changing the crystallization behavior and reactivity of
the glass in the above-described manner and is especially effective in
applications to ceramic bodies with B characteristic. The desired effect
cannot be obtained if those components are outside the range of a total
content of 0.1-5%.
The glass in accordance with the present invention can additionally contain
small amounts of other oxides within ranges which do not affect properties
of the glass.
The glass in accordance with the present invention can be produced by a
usual method comprising mixing the starting material compounds of the
respective components, melting, rapidly cooling, and grinding and also by
other methods such as a sol-gel method, a spray pyrolysis method, an
atomization method, and the like. It is especially preferred that the
glass be produced by a spray pyrolysis method because fine spherical glass
particles of uniform size can be obtained and it is not necessary to
conduct grinding when using the glass for a conductive paste.
No specific limitation is placed on the electrically conductive powder used
in the conductive paste in accordance with the present invention. Thus,
powders of base metals such as copper, nickel, cobalt, iron, and the like
which require firing to be conducted in a non-oxidizing atmosphere,
powders of alloys or composite powders containing one or more of those
metals, as well as electrically conductive powders of noble metals such as
silver and palladium or alloys or composites containing one or more of
these metals can be used. The above-mentioned conductive powders can be
used singly or in combination of two or more thereof. No specific
limitation is placed on the mixing ratio of the electrically conductive
powder and glass powder, and this ratio can be appropriately adjusted
within the usually used range according to the object and the intended
use.
No specific limitation is also placed on the vehicle. Any vehicle prepared
by dissolving or dispersing a resin binder that is usually employed, for
example, an acrylic resin, cellulose, and the like, in an aqueous or
organic solvent may be appropriately selected and used according to the
object or intended use. If necessary, a plasticizer, a dispersant, a
surfactant, an oxidizing agent, an organometallic compound, and the like
can be added. No limitation is also placed on the mixing ratio of the
vehicle, and the vehicle can be used in an appropriate amount allowing the
inorganic components to be retained in the paste and depending on the
intended use or coating method.
If necessary, metal oxides, ceramics, and the like which are usually used
may be added as other inorganic binders or additives.
The conductive paste in accordance with the present invention is especially
suitable for the formation of terminal electrodes of multilayer ceramic
components, such as multilayer capacitors, multilayer inductors, and the
like, but it can be also used for forming electrodes on other electronic
components, for forming conductor layers on multilayer ceramic substrates,
or for forming thick-film conductors on ceramic substrates, for example,
from alumina or the like.
The present invention will be described hereinbelow in greater detail based
on examples thereof.
EXAMPLE 1
Starting materials were prepared to obtain oxide compositions shown in
Table 1, melted at a temperature of about 1150.degree. C. in a platinum
crucible, poured out onto graphite and air cooled to obtain a glass which
was finely ground with alumina balls, to obtain glass powders A-K, X and
Y. Powders X and Y are outside the range of the present invention. Glass
transition temperature (Tg), softening point (Ts), and crystallization
temperature (Tc) were measured by thermal analysis for each of glass
powders. The results are shown in Table 1.
Water resistance was evaluated for each glass powder in the manner as
follows. A vehicle prepared by dissolving an acrylic resin in terpineol
was mixed with each glass powder to prepare a glass paste which was coated
on an alumina substrate and fired at a temperature of 850.degree. C. in a
nitrogen atmosphere with an oxygen concentration of no more than 5 ppm to
form a glass film. The sample obtained was immersed for 2 hours in pure
water boiled at a temperature of 100.degree. C., then removed therefrom,
thoroughly washed with water, while being scrubbed with a brush, and
dried, followed by measuring the film weight. The film residual ratio is
shown in Table 1.
TABLE 1
Glass
Powder A B C D E F G H I J
K X* Y*
Compo- ZnO 48.0 48.0 48.0 48.0 48.0 48.0 47.5 48.0 48.0 48.0
48.0 20.0 63.7
sition B.sub.2 O.sub.3 26.0 26.0 27.0 29.0 29.2 29.2 27.0 26.2
29.2 29.2 29.2 20.0 36.3
(wt. %) SiO.sub.2 6.7 6.7 7.0 6.7 7.5 7.5 11.5 10.5 7.5
7.5 7.5 7.0 --
Al.sub.2 O.sub.3 6.3 6.3 6.0 6.3 6.3 6.3 5.0 6.3
6.3 6.3 6.3 4.0 --
MnO.sub.2 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0 6.0
6.0 6.0 8.0 --
Li.sub.2 O 1.8 0.3 -- -- -- -- -- -- --
-- -- -- --
Na.sub.2 O -- -- 5.0 -- -- -- -- -- --
-- -- -- --
K.sub.2 O 5.2 6.7 1.0 7.0 2.0 2.0 -- 2.0 2.0
2.0 2.0 -- --
MgO -- -- -- -- 1.0 -- -- -- -- --
-- -- --
CaO -- -- -- -- -- 1.0 -- -- -- --
-- -- --
TiO.sub.2 -- -- -- -- -- -- 2.0 -- --
-- -- 4.0 --
Cr.sub.2 O.sub.3 -- -- -- -- -- -- 1.0 1.0
-- -- -- -- --
ZrO.sub.2 -- -- -- -- -- -- -- -- 1.0
-- -- -- --
Ta.sub.2 O.sub.5 -- -- -- -- -- -- -- --
-- 1.0 -- -- --
SnO.sub.2 -- -- -- -- -- -- -- -- --
-- 1.0 -- --
BaO -- -- -- -- -- -- -- -- -- --
-- 31.0 --
Cu.sub.2 O -- -- -- -- -- -- -- -- --
-- -- 3.0 --
Co.sub.2 O.sub.3 -- -- -- -- -- -- -- --
-- -- -- 3.0 --
Tg (.degree. C.) 467 484 471 484 532 534 555 527 542 531
541 510 545
Ts (.degree. C.) 524 535 535 535 649 641 675 645 629 635
647 593 578
Tc (.degree. C.) 599/ 637/ 639/ 637/ 813 788 881 813 806 785
797 644 692
805 809 807 808
Water 98.4 85.6 95.4 42.3 97.2 94.5 97.1 96.0 96.3 96.0
96.8 54.8 72.0
Resistance (%)
*outside the range of the present invention
EXAMPLE 2
Conductive pastes were prepared in the following manner by using the glass
powders produced in Example 1. Each conductive paste was produced by
blending 12 weight parts of the glass powder and 40 weight parts of a
vehicle in which an acrylic resin was dissolved in terpineol with 100
weight parts of a copper powder and mixing the components in a three-roll
mill. The paste was then coated by a dipping method, so as to obtain a
film thickness after firing of about 120 .mu.m, on end surfaces of inner
electrodes exposed from a fired ceramic body of a multilayer ceramic
capacitor with a flat surface size of 3.2 mm.times.1.6 mm which had been
prepared using, as a dielectric, a ceramic comprising barium titanate as a
main component and having F characteristic specified by JIS and nickel as
inner electrodes. Then multilayer ceramic capacitors with sample numbers
of 1 to 12 were produced by drying each body for 10 minutes at a
temperature of 150.degree. C. in a hot-air drier, followed by firing for a
total of 1 hour with a peak temperature retention time of 10 minutes at a
peak temperature shown in Table 2 in a nitrogen atmosphere with an oxygen
concentration of no more than 5 ppm by using a belt-type muffle furnace.
Samples with numbers 11 and 12 are outside the range of the present
invention.
Film density was studied for the obtained samples by observing the polished
cross section of the terminal electrodes with a scanning electron
microscope. The results are shown in Table 2. The following criteria were
used for evaluation: .largecircle.--dense fired film without pores,
.DELTA.--film in which small amount of pores are observed, .times.--other.
Further, a nickel plated film and a tin plated film were successively
formed on the terminal electrode surface by electroplating and thermal
shock resistance tests and measurements of adhesive strength and peel
strength were conducted in the manner as follows. The results are shown in
Table 2.
Thermal shock resistance test: each plated sample was rapidly immersed in a
solder bath at a temperature of 300.degree. C., retained therein for 7
seconds, removed, and naturally air cooled. If cracks appeared on the
ceramic surface of no more than one of 30 samples, symbol .largecircle.
was used, if cracks appeared in no less than two samples, symbol .times.
was used.
Adhesive strength: lead wires were soldered to two opposing terminal
electrodes so as to be perpendicular to the electrode surface, both lead
wires were pulled in the opposite directions with a strength measurement
device, and the values at which the electrode portions have broken were
determined.
Peel strength: lead wires were soldered to two opposing terminal electrodes
so as to be parallel to the electrode surface, both lead wires were pulled
to the left and right by applying a force perpendicular to the electrode
surface with a strength measurement device, and the values at which the
electrode portions have broken were determined.
TABLE 2
Sample No. 1 2 3 4 5 6 7 8 9 10
11* 12*
Glass A A A B C D E F H I X
Y
Powder
Firing 800 830 850 830 830 830 800 800 800 800
830 830
Temperature
(.degree. C.)
Film .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .DELTA. .DELTA.
Density
Thermal .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. x .smallcircle.
Shock
Resistance
Adhesive 4.1 4.5 4.3 4.5 4.2 4.4 4.0 4.1 4.5 4.1
3.5 2.9
Strength
(kg)
Peel 3.9 4.2 4.5 4.9 4.1 5.2 4.2 4.0 4.8 4.7
3.0 2.6
Strength
(lbs)
*Outside the range of the present invention
Table 2 clearly shows that the conductive paste using the glass in
accordance with the present invention had excellent film density, high
resistance to thermal shocks, and high adhesive strength and also
demonstrated practically no changes in characteristics caused by firing
temperature.
EXAMPLE 3
Using glass powders E-K, A, X produced in Example 1, conductive pastes were
prepared in the same manner as in Example 2. Each paste was then coated by
a dipping method, so as to obtain a film thickness after firing of about
120 .mu.m, on end surfaces of inner electrodes exposed from a fired
ceramic body of a multilayer capacitor ceramic body with a flat surface
size of 2.0 mm.times.1.25 mm which had been prepared using, as a
dielectric, a ceramic comprising barium titanate as a main component and
having B characteristic specified by JIS standard and nickel as inner
electrodes. Then multilayer ceramic capacitors with sample numbers of 13
to 21 were produced by drying each body for 10 minutes at a temperature of
150.degree. C. in a hot-air drier, followed by firing for a total of 1
hour with a peak temperature retention time of 10 minutes at a peak
temperature of 800.degree. C. in a nitrogen atmosphere with an oxygen
concentration of no more than 5 ppm by using a belt-type muffle furnace.
The sample with numbers 21 is outside the range of the present invention.
The film density, thermal shock resistance, adhesive strength, and peel
strength of the terminal electrode were studied in the same manner as in
Example 2 for each of the obtained samples. The results are shown in Table
3. In all of the samples, the fracture mode in the peel strength
measurement was cracking or fracturing of the ceramic body.
TABLE 3
Sample
No. 13 14 15 16 17 18 19 20 21*
Glass E F G H I J K A X
Powder
Film .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. .DELTA.
Density
Thermal .smallcircle. .smallcircle. .smallcircle. .smallcircle.
.smallcircle. .smallcircle. .smallcircle. .smallcircle. x
Shock
Resistance
Adhesive 4.1 4.3 4.5 4.8 4.7 3.8 4.7 3.9 2.4
Strength
(kg)
Peel 1.3 1.2 1.6 1.5 1.4 1.2 1.4 0.7 0.3
Strength
(lbs)
*outside the range of the present invention
As shown in Table 3, the conductive paste using the second glass of the
present invention demonstrated excellent adhesive strength and peel
strength even with respect to a ceramic body of a ceramic dielectric with
B characteristic.
The glass in accordance with the present invention has a low softening
point, contains no hazardous components such as lead and the like, and
demonstrates appropriate viscosity characteristic and crystallization
behavior in a firing process. With a conductive paste using such a glass
as an inorganic binder, organic components can be completely removed and a
dense conductor with excellent resistance to plating solutions, adhesive
strength, resistance to thermal shocks, and reliability can be produced
even in case of firing in a non-oxidizing atmosphere. Furthermore, the
paste shows little dependence of firing process conditions and electrodes
with excellent and uniform characteristics can be formed even in firing
within a wide temperature range. Moreover, when the paste is used for
forming terminal electrodes of multilayer ceramic components, a high
terminal strength and peel strength are obtained regardless of the type of
ceramic body and ceramic components with high reliability can be obtained.
*
