JP2764087B2 - Ceramic superconductor paste and method of manufacturing ceramic superconductor wiring circuit board using the paste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a ceramic used for producing a superconductor wiring circuit board which is dense, has high adhesive strength to ceramics and metal, and has excellent moisture resistance. The present invention relates to a high-temperature superconductor paste and a method for producing the circuit board using the paste, and more particularly to a low-temperature sintering method comprising an oxide of an alkaline earth metal, bismuth and / or thallium, copper and silver and metal palladium. The present invention relates to a hardenable ceramic high-temperature superconductor paste and a method of manufacturing a circuit board using the paste.

(Prior art and its problems) Wiring boards for semiconductor integrated circuits and electronic circuits (hybrid
Ceramic substrates used for ICs (including IC substrates) are ceramic substrates such as alumina, mullite alumina, steatite, forsterite, sapphire, aluminum nitride, magnesia, and beryllia, substrates such as glass ceramic and silicon, or aluminum and iron Such as a metal core substrate in which the surface of a metal plate is coated with an inorganic insulating layer is mainly used. Metals such as copper, nickel, palladium, gold, and silver, or alloys containing these are used for the conductor layers formed on these substrates.

Recently, however, the performance of electronic devices has been remarkably improved. In particular, in order to realize high-density mounting of components (including discrete components), it is necessary to efficiently dissipate the heat generated from the components or to conduct conductor wiring. A major problem is how to suppress the heat generated due to the resistance.
Also, in computers and the like, there is a strong demand for a higher signal transmission speed. Therefore, it is an important issue to reduce the proportion of signal delay occupied by conductor wiring, and it is desired to reduce the resistance of conductor wiring. The request is very large.

As a material suitable for such a request, a superconductor wiring circuit board using a superconductor substance for a conductor layer can be considered.

A superconductor substance is a substance having a so-called superconducting critical temperature at which the electric resistance becomes zero when the temperature falls below a specific temperature. Recently, lanthanum-barium-copper oxide, lanthanum-strontium- Alkaline earth elements, yttrium and / or lanthanide elements such as copper oxide (critical temperature: 30-40K), yttrium barium copper oxide, holmium barium copper oxide (critical temperature: 80-104K) -Copper oxide, bismuth, strontium, calcium, copper oxide, thallium, strontium, calcium, copper oxide, etc. are well known. If these superconductor materials can be used as wiring circuit conductors, it is possible to solve various problems caused by signal current loss due to electric resistance and heat generation, as well as miniaturization of wiring circuit conductors, which is currently a problem. It is.

As a method of forming conductor wiring on a substrate using such a superconductor material, generally, a paste obtained by adding a binder to a superconductor material powder is printed on a ceramic substrate surface in a wiring pattern shape and baked. A so-called thick-film printed wiring method is conceivable. However, such a method involves a baking process at 900 ° C. or higher, and thus causes various unpredictable problems in the superconductor wiring circuit board. First,
Because the firing temperature is 900 ° C or higher, the superconducting substance undergoes a chemical reaction with the substrate during the firing process, the composition changes, and the critical temperature that indicates superconductivity drops, or in extreme cases, the superconductivity increases. At all.

For example, yttrium / barium / copper oxide (Y ₂ Ba ₁ C
The superconducting paste composed of u ₃ O _7-δ ) has a superconducting critical temperature (Tc) of 93 to 104 K of a bulk sintered body of the paste, but is lowered to 50 K or less on an alumina substrate. . Secondly, ceramic high-temperature superconductors which have been well known so far do not easily form a dense sintered body, and therefore have a low adhesive strength to a ceramic substrate of about 5 MPa or less and are extremely poor in practical use. As a countermeasure, it is conceivable to mix glass powder as a means of imparting adhesive strength.However, when these are mixed, the superconductor substance chemically reacts with the glass to cause a composition change, and the criticality of superconductivity is exhibited. When the temperature is, for example, yttrium / barium / copper oxide as described above, the temperature is reduced from 93 to 104K to 30 to 50K. Even more disadvantageous is that conventional ceramic superconductors deteriorate over time even if they are left in a normal state.For example, the 104K superconductor consisting of yttrium, barium, and copper oxide shown above reaches 87K after 90 days. The critical temperature may decrease. A further problem is that the superconductor material is difficult to densify, and if it is immersed in liquid nitrogen or the like and brought to a very low temperature state, it will be easily broken or peeled off from the substrate and will not be practically used due to its low reliability. It is.

The present inventors have conducted various studies on ceramic high-temperature superconductor thick-film wiring circuit boards, and as a result of the fact that high adhesive strength cannot be obtained, it is difficult for ceramic superconductors to form a dense sintered body. In addition, they found that an adhesive layer might not be formed at the interface with the substrate, and the reason that the superconductor was hard to densify was that the liquid layer sintering progressed at the sintering (firing) temperature as heretofore known. It has been found that the superconductor material powder itself has a cause of the above-described problem.

(Object of the Invention) The inventors of the present invention have conducted intensive studies to solve such a problem, and as a result, desorbed oxygen during heating to the ceramic superconductor material powder, and in the sintering (firing) temperature range of the ceramic superconductor. A metal oxide forming a liquid layer, for example, silver oxide (desorbing oxygen at 390 ° C.) and the metal oxide captures the desorbed oxygen. Ceramic superconductor wiring with excellent adhesion to the substrate, high moisture resistance, dense, reliable, and excellent production stability in a wide firing temperature range of 720 to 950 ° C when mixed with a suitable metal such as metal palladium. The inventors have found that a circuit conductor can be formed, and have reached the present invention.

Accordingly, an object of the present invention is to improve the disadvantages of the conventional ceramic superconductor wiring circuit board, and to obtain a ceramic superconductor wiring circuit board which is excellent in superconductivity and has a high adhesion strength to a substrate, and which is excellent in moisture resistance. It is an object of the present invention to provide a ceramic superconductor paste used for producing a superconducting ceramic. That is, the present invention produces a liquid phase necessary for ceramic superconductor material powder to sinter at a low temperature, and releases oxygen essential for the formation of the ceramic superconductor at around the firing temperature to form a dense ceramic superconductor. It is an object of the present invention to provide a ceramic superconductor paste having a unique action that promotes the formation of a superconductor substance.

(Means for Solving the Problems) The present invention firstly provides a ceramic superconductor paste comprising a ceramic superconductor material powder, an organic binder and a solvent, wherein the paste releases its own oxygen during heating. And a metal oxide capable of forming a liquid phase at the time of firing, and a ceramic superconductor paste containing a metal powder capable of capturing the oxygen released from the metal oxide and releasing the captured oxygen during firing. Secondly, a ceramic superconductor material powder, a metal oxide capable of releasing its own oxygen during heating and forming a liquid phase during firing, and capturing the oxygen released from the metal oxide and capturing the captured oxygen A ceramic superconductor paste containing a metal powder, an organic binder and a solvent that can be separated during firing is applied to a circuit board, and the circuit board is heated and fired. And a method for manufacturing a ceramic superconductor wiring circuit board.

 Hereinafter, the present invention will be described in detail.

As the ceramic superconductor material powder that can be used in the present invention, a conventional powder can be used as it is, but it is preferable to use a powder prepared by the following method. That is, an oxide or carbonate of an alkaline earth metal and an element of yttrium and / or a lanthanide is formed in a dispersion medium composed of an organic solvent, and then a solid or a coprecipitate is separated from the dispersion medium to obtain a superconductor raw material powder. Next, this was calcined at a temperature of 950 ° C. or less, and bismuth oxide (Bi ₂ O ₃ ) ₇ and strontium carbonate (SrCO ₃ ) and calcium carbonate (CaCO ₃ )
Is dispersed in a dispersion medium composed of an organic solvent, and then copper oxalate is formed in the dispersion medium.The solid content or the coprecipitate is separated from the dispersion medium to obtain a superconductor material powder.
It is fired in the range of 720 to 900 ° C to obtain ceramic superconductor material powder.

The superconductor material powder containing copper oxalate as a coprecipitate is produced, for example, by dispersing a powder of a component other than copper in a dispersion medium composed of an organic solvent and generating copper oxalate in the dispersion medium. can do. That is, powder of the above-mentioned oxide such as yttrium and / or carbonate such as strontium carbonate is dispersed in a dispersion medium at a predetermined molar ratio to form a slurry, and the slurry contains oxalic acid in an amount equivalent to or more than copper used. Then, a predetermined amount of a copper salt is added thereto, and the oxalic acid and the copper salt are reacted in the dispersion medium to easily obtain a superconductor material powder containing copper oxalate as a coprecipitate.
In addition, the superconductor material powder can also be obtained by mixing salts or oxides of the respective components of the superconductor at a predetermined molar ratio and firing the mixture in the air. In the present invention, the superconductor raw material powder may be produced by a method other than the above as long as the superconductivity is not adversely affected.

The ceramic superconductor paste of the present invention contains an organic binder and a solvent, a metal oxide and a metal powder in addition to the ceramic superconductor material powder. The organic binder plays a role of binding the components relatively weakly,
For example, ethyl cellulose or the like can be used. The solvent is for imparting fluidity as a paste, and various organic solvents, particularly higher alcohols having relatively high viscosity, can be preferably used.

The metal oxide is an oxide that releases its own oxygen at a relatively low temperature region of the paste baking step, for example, at a temperature of 200 ° C., and forms a liquid phase at a relatively high temperature region, for example, at a temperature of 600 ° C. or higher, Usually, silver oxide is preferably used. The silver oxide is uniformly mixed with the superconductor material powder to form a paste.When the paste is heated, oxygen is released at 380 ° C. or higher to form metallic silver, and the metallic silver forms a liquid phase in the firing step of the ceramic superconductor paste. Generate. However, the generated metallic silver does not react with the ceramic superconductor powder and the like, enabling the liquid phase sintering of the superconductor powder and the like. It is considered that segregation occurs at the bonding interface of the ceramics, and eventually promotes the densification of the ceramic superconductor and the improvement of the adhesive strength with the substrate.

It is considered that such a function other than silver oxide has a similar effect as long as it releases oxygen in a relatively low temperature region to form a liquid phase and is an oxide that wets well with the ceramic superconductor component and the substrate. The metal oxide in the present invention is not limited to silver oxide.

In addition, the above-mentioned metal powder contained in the ceramic superconductor paste of the present invention captures oxygen released from the metal oxide, for example, silver oxide, at the initial stage of sintering of the superconductor, that is, in a low temperature range. When the temperature is close to the temperature at which sintering is possible, on the contrary, it exhibits an action of releasing oxygen and supplying oxygen from the inside of the sintered body to the ceramic superconductor, and as the metal powder, the use of metal palladium is most preferable. It is not limited to palladium, and other metals and palladium-based alloys can be used.

Metallic palladium captures oxygen at a temperature of 600 ° C. or less to become palladium oxide, and at around this temperature, oxygen released from silver oxide or the like is fixed in the form of the palladium oxide. Thereafter, when the firing temperature rises to 600 ° C. or higher, the palladium oxide releases oxygen in reverse, and is reduced to metallic palladium.

What is particularly needed in ceramic superconductors is to supply oxygen from the inside in a temperature range where the superconductor composition is formed in a timely manner, thereby greatly improving the composition of the ceramic superconductor and, hence, its stability. It is known that it can be done.

As the ceramic superconductor paste of the present invention is heated, the metal oxide releases oxygen at 390 ° C. for silver oxide, for example. And the metal powder such as metal palladium
At a temperature of 600 ° C. or less, the metal oxide captures the released oxygen and becomes a stable metal oxide such as palladium oxide. Thereafter, when the firing temperature further rises to 600 ° C. or higher, the palladium oxide releases and releases oxygen again. Therefore, the released oxygen plays the role of "supplying oxygen from the inside in a timely manner", and a ceramic superconductor whose physical properties, particularly stability, are greatly improved can be obtained.

In other words, in the ceramic superconductor paste of the present invention,
Metal oxides, such as silver oxide, mixed in the ceramic superconductor raw material powder are converted to the corresponding metals by releasing their oxygen in a relatively low temperature range of 200 ° C or higher, and 600 ° C.
In the above, a liquid phase is formed to enable the liquid phase sintering of the superconductor, thereby improving the adhesion to a substrate or the like, and a metal powder such as a metal palladium contained in the ceramic superconductor material powder in the same manner. Captures oxygen released from the silver oxide or the like, and releases it at a higher temperature, and supplies oxygen in a timely manner from the inside during sintering of the superconductor to form a superconductor material having excellent physical properties such as stability. It becomes possible to give.

In this specification, the heat treatment of the paste is described using two types of terms, “sintering” and “sintering”, but the former means the heat treatment received by the paste itself, and the latter is performed from outside. It means a heat treatment for the paste, and there is no substantial difference between the two.

(Example) An example of the present invention will be described below, but the present invention is not limited to the example.

Example Bismuth oxide having an average particle size of 0.6 μm and a purity of 99.9%, strontium carbonate having an average particle size of 1.0 μm and a purity of 99.5%, and calcium carbonate having an average particle size of 1.2 μm and a purity of 99.5% were mixed (Bi / Sr
/ Ca) are weighed and mixed so that the molar ratio of (2/3/3) and (1/1/1) become 10% with a ball mill using ethanol as a dispersion medium.
The mixture was wet-mixed for hours to obtain a mixed powder. Then the above mixed powder 10
0 g was dispersed in 200 ml of ethanol, and oxalic acid was further mixed so that the molar ratio of (Bi / Sr / Ca / oxalic acid) became (2/3/3/4) and (1/1/1/2). Stirring produced a uniform slurry. Separately, 1 mol of 99.3% pure copper nitrate was added to 1000 ml of ethanol to form a solution. In the slurry, the molar ratio of (Bi / Sr / Ca / oxalic acid / Cu) is (2/3/3/4/4) and (1/1/1/2/2),
The above-mentioned ethanol solution of copper nitrate was dropped at a rate of 150 ml / min to form a coprecipitate. The precipitate is left to age for about 12 hours, washed with excess ethanol, dried and then ground and mixed for 3 hours using zirconia balls to form bismuth, strontium, calcium, and 0.8 μm in average diameter. A mixed powder containing copper oxalate was obtained. This mixed powder
Heating and heating at a rate of 80 ° C / hr.
It was fired in the air for 5 hours to obtain a ceramic superconductor.
The obtained ceramic superconductor was measured for electrical resistance from room temperature to liquid nitrogen temperature, and after confirming superconductivity, coarsely crushed,
Next, the powder was wet-pulverized in ethanol for 1 to 20 hours using zirconia balls to obtain a ceramic superconductor material powder having an average particle size of 0.5 to 1 μm.

0.5 to 20 parts by weight of a mixed powder (mixing molar ratio: 1/1) of silver oxide having an average particle diameter of 0.8 μm and palladium metal having an average particle diameter of 0.5 μm was mixed with 100 parts by weight of the ceramic superconductor material powder. . Next, 100 parts by weight of the mixed powder was mixed with ethyl cellulose (manufactured by Hercules Co., USA, product number N-
7) was added in an amount of 5 parts by weight, a mixed solvent of an equal amount of terbineol and ethylene glycol / monobutyl ether was added, and the mixture was mixed for 1 to 10 hours with a grinder to obtain a ceramic superconductor paste. Next, this paste was screen-printed on a magnesia ceramic substrate (1 mm thick),
It was fired in the air at a temperature of 0 ° C. for 0.1 to 5 hours to produce a ceramic superconductor wiring circuit board.

FIG. 1, FIG. 2 and Table 1 were prepared by firing at 780 ° C. for 3 hours and then ball milling for 10 hours (Bi / Sr / Ca / C).
u) using a superconductor material powder having a molar ratio of (2/3/3/4), mixing silver oxide and metal palladium powder with the above-described method to form a thick film paste; This shows the temperature characteristics of the electrical resistance and the bond strength between the conductor and the substrate of a ceramic superconductor wiring circuit board obtained by screen printing on a ceramic substrate and then firing the printed substrate at 780 ° C. or 830 ° C. for 2 hours. Fig. 1 shows 780
The temperature characteristics of the electrical resistance of the circuit board fired at
The figure shows the temperature characteristics of the electric resistance of the circuit board fired at 830 ° C., and Table 1 shows the adhesive strength of the circuit board fired at each temperature. (1) and (2) in FIG. 1 and FIG. 2 respectively show the temperature characteristics of the electric resistance of the superconductor wiring substrate by the paste prepared without mixing the silver oxide and the metal palladium powder by the conventional method, and the present embodiment. Mixes silver oxide and metal palladium powder The temperature characteristics of the electric resistance of the superconductor wiring board by the paste produced in this manner are shown.

780 ° C or 830 ° C by mixing silver oxide and metallic palladium powder
The electrical resistances of the wiring substrates fired in the above steps all began to decrease at 90K and became zero at 77K. On the other hand, the electric resistance of the wiring board due to the paste in which silver oxide and metallic palladium powder were not mixed did not become zero at 77K, and a slight residual electric resistance was observed.

The adhesive strength is 15 to 35 MPa for the former, and 0 to 5 for the latter.
MPa.

When both of these wiring boards were immersed in liquid nitrogen, the former showed no change, but the latter easily peeled off. The sintering state of the peeled and dropped ceramic superconductor was porous, and no adhesive layer was observed on the peeled surface. From this, the ceramic superconductor that has peeled off is incompatible with that of the substrate at the final stage of sintering, so that even if sintering proceeds, densification is suppressed and adhesion to the interface with the substrate is promoted. It was considered that the adhesive force could not be obtained because the liquid phase did not segregate. In contrast, in a superconductor to which a mixed powder of silver oxide and metallic palladium is added, oxygen, which is essential for the formation of a ceramic superconductor, can be generated near the temperature at which the superconductor sinters and supplied from the sintered body. In addition, the nascent metallic silver promotes the liquid phase sintering of the ceramic superconductor, and the volume shrinkage force due to the reduction of palladium oxide promotes densification, and at the end of sintering,
Grain boundary triple bonding point and surface layer of ceramic superconductor, and
It can be considered that segregation at the interface with the substrate resulted in improvement of densification and resistance to environmental degradation and improvement of adhesive strength.

(Effect of the Invention) The ceramic superconductor paste according to the present invention comprises a metal oxide, such as silver oxide, which releases its own oxygen during heating and forms a liquid phase during sintering, and the oxygen from which the metal oxide has been released. It contains a metal powder, such as metal palladium, which can capture and release the captured oxygen during sintering. Therefore, according to the method of the present invention in which the paste is applied to a substrate or the like by screen printing or the like and the substrate is heated and fired to produce a superconductor wiring substrate, in a relatively low temperature range, the metal oxide is reduced by reduction of the metal oxide. Free oxygen is released while being converted to the corresponding metal. The oxygen reacts with the coexisting metal powder and is converted into an oxide of the metal powder. On the other hand, the reduced metal forms a liquid phase in the firing temperature range of the ceramic superconductor, and improves the adhesive strength between the superconductor material and the substrate. Further, the metal powder oxidized as described above, for example, metal palladium releases oxygen at 500 ° C. or more, and when the superconductor is formed by sintering, conveniently supplies the oxygen necessary for the sintering smoothly from the inside. And the stability of the obtained superconductor can be improved.

[Brief description of the drawings]

FIG. 1 shows the superconductivity of the ceramic superconductor paste containing silver oxide and metal palladium in the embodiment of the present invention and the conventional ceramic superconductor paste containing no silver oxide and metal palladium fired at 780 ° C. FIG. 2 is a graph showing a temperature characteristic of electric resistance of a ceramic superconductor wiring circuit board on which a body is screen-printed, and FIG. 2 is a graph showing a temperature characteristic of each electric resistance when a similar paste is fired at 830 ° C. is there.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H01L 39/24 ZAA H01L 39/24 ZAAW H05K 1/09 ZAA H05K 1/09 ZAAA 3/12 ZAA 3/12 ZAAB (72) Invention Mikiya Ono 2270 Yokoze, Yokoze-cho, Chichibu-gun, Saitama Prefecture Mitsubishi Mining & Cement Co., Ltd. Kiyoji 5-192 Ishikawa-cho, Naka-ku, Yokohama-shi, Kanagawa Prefecture (56) References JP-A-1-192757 (JP, A)

Claims (3)

(57) [Claims] 1. A ceramic superconductor paste comprising a ceramic superconductor material powder, an organic binder and a solvent, wherein the paste is capable of releasing its own oxygen during heating and forming a liquid phase during firing, and A ceramic superconductor paste comprising a metal powder capable of capturing the oxygen released from the metal oxide and releasing the captured oxygen during firing. 2. After the ceramic superconductor material powder disperses an oxide and a carbonate in a dispersion medium composed of an organic solvent, copper oxalate is formed in the dispersion medium, and then solidified or co-precipitated. The ceramic superconductor paste according to claim 1, wherein the ceramic superconductor paste is separated from a dispersion medium and heat-treated. 3. A ceramic superconductor material powder, a metal oxide capable of releasing its own oxygen during heating and forming a liquid phase during firing, capturing the oxygen released from the metal oxide, and removing the captured oxygen. A method for manufacturing a ceramic superconductor wiring circuit board, comprising applying a ceramic superconductor paste containing a metal powder, an organic binder and a solvent that can be separated during firing to a circuit board, and heating and firing the circuit board.