JPH0466688B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field] The present invention relates to a method for manufacturing a ceramic circuit board, which is formed by forming a Cu layer on an oxide-based ceramic substrate such as alumina, and is used as an electronic circuit board or a heat sink thereof. [Background technology] Conventionally, circuit boards for electronic circuits, etc., have either a Cu layer formed on a plastic substrate or a Cu layer formed on a metal substrate with an insulating layer interposed between them, as seen in hybrid ICs. There are things etc. However, as electronic circuits have become lighter, thinner, shorter, and smaller in recent years, there has been a demand for higher reliability, such as higher density mounting of electronic components, multilayer mounting, dimensional stability against changes in temperature and humidity, and improved heat resistance. From these viewpoints, there has been a demand for the use of ceramic substrates that have high thermal conductivity and small thermal dimensional changes. Therefore, ceramic substrates (generally alumina substrates of oxide ceramics)
Various methods of forming circuits thereon have been tried. Here are the 5 currently proposed or actually implemented
We will explain two methods. The first is the Ag-Pd paste method or the Au paste method. this is
A circuit is formed by mixing Ag, Pd, or Au metal fine powder with glass frit and an organic vehicle to form a paste, screen printing it on a ceramic substrate, and then firing it at a temperature that melts and bonds the glass frit to the ceramic substrate. be. This method can only form circuits with a thick line width of 70 to 100 μm at most, making it difficult to form fine patterns.The circuit has high resistance, making it unsuitable for fine wiring.A glass layer is likely to form on the circuit surface. Therefore, there are disadvantages such as poor solder adhesion and a tendency to cause defects and failures during use. The second is
This is a Cu paste method, in which Cu and a small amount of copper oxide, glass frit, and an organic vehicle are mixed to form a paste, which is _then screen printed onto a ceramic substrate. It is fired at a temperature that allows it to be melted and bonded to the substrate to form a circuit. The disadvantages of this method are that it is not suitable for fine patterns because the circuit resistance is large, that it requires atmosphere firing, which increases the firing cost, and as with the first method, the solder adhesion is poor due to the glass layer. Third
The method is the high melting point metal method (Telefunken method),
This is made by printing Mo or Mo-Mn into a paste on a ceramic substrate and heating it at 1300 to 1700°C in humidified hydrogen or humidified facing gas (H ₂ /N ₂ ).
The reaction of Mn + H ₂ O → MnO + H ₂ occurs.
Then, the generated MnO dissolves into the glass phase at the ceramic grain boundaries, lowering the glass viscosity and forming a metallizing layer on the ceramic surface.
This surface is plated with Ni and bonded to a Cu plate using a brazing material to form a circuit. In this method, the adhesion is strengthened, but the strength of the ceramic is reduced because the ceramic grain boundaries are eroded. Since layers are formed, there are drawbacks such as poor high frequency characteristics. Fourth
This is the W, Mo method, in which a circuit is drawn on an alumina green ceramic sheet before firing using a W, Mo slurry, and the circuit is fired as a unit in a reducing atmosphere. This method is also unsuitable for fine patterns because the circuit resistance is large. One way to form a circuit on an alumina substrate is to bond a Cu conductor onto the substrate, which has excellent conductivity, bonding strength with the substrate, solder adhesion, etc., and is inexpensive compared to other conductive materials. There is a high demand for methods for forming circuits. However, due to the difference in thermal expansion coefficient between ceramics and Cu, strong bonding is difficult.
It is quite difficult, and what is being attempted is
This is the fifth copper oxide method. This can be done by firing Cu and a ceramic substrate in an atmosphere containing a small amount of oxygen, by oxidizing the surface of the Cu plate and bringing it into contact with the ceramic substrate and firing it in an inert gas atmosphere, or by firing a Cu plate containing oxygen such as tough pitch copper. By heating Cu and ceramics in a reactive atmosphere, such as by firing in an inert gas atmosphere, a eutectic melt is generated and then cooled to form a ceramic substrate.
This is a method of joining Cu plates. These methods are
JP57-13515, JP50-132022, JP52-
37914, JP 53-77212, JP 57-82181, JP 57
−36892, JP 58-67095, JP 58-67096, JP
58-137285, JP-A No. 59-13677, JP-A No. 59-3076, etc. This copper oxide method has the advantage of providing strong adhesion with a single operation and having a low-resistance layer at the interface.
The firing temperature range is limited between the melting point of 1083°C and the eutectic temperature of 1065°C, and the firing time is 5 to 60 minutes, so the firing conditions are harsh and it is difficult to obtain a thin film.・There are disadvantages such as it is not suitable for patterns, the pattern moves during firing, and the circuit position is unstable. [Purpose of the Invention] This invention was made in view of the above-mentioned current situation, and relates to an oxide ceramic substrate and a Cu
When bonded to a conductor, it is a low-resistance conductive layer with high density and strength, good solder adhesion, and does not create cavities or bubbles on the bonding surface. Moreover, the firing conditions are gentler, reducing costs. A method for manufacturing a ceramic circuit board is provided. [Disclosure of the Invention] In order to achieve the above object, the present invention is directed to bonding a Cu layer to an oxide-based ceramic substrate.
This is a method of forming a eutectic alloy layer of Ti and/or Zr and Cu as the intermediate bonding layer. After forming a thin film of Ti and/or Zr and Cu as the intermediate bonding layer, the eutectic alloy is formed by firing. The gist of this paper is a method for manufacturing ceramic circuit boards characterized by the formation of layers. In other words, this invention uses Ti and Zr, which are metals that easily combine with oxygen in oxide ceramics and have very high activity at high temperatures, to be interposed between the ceramic substrate and the Cu layer, thereby improving the bond between the ceramic substrate and the Cu layer. At the same time as measuring adhesion, a eutectic alloy layer (eutectic composition phase) with Cu is generated, and the wetting effect of this liquid phase is used to strengthen the adhesion. This will be explained in detail below. First, a thin film of Ti and/or Zr is formed on a ceramic substrate. This film is preferably formed in close contact with the fine structure of the substrate, and is preferably formed by vapor deposition using a PVD method, a CVD method, or the like. This method makes it possible to form a film that is in close contact with the substrate, so that no bubbles or cavities are generated at the interface even after firing. Next, a Cu layer of the thickness required for the circuit is formed on top of it. usually,
The Cu layer used as a circuit requires a thickness of 3 μm or more, so it is appropriate to form it by wet electroplating or chemical plating, but if it is thin, it can be formed by PVD or CVD. You may. After that, the above ceramic substrate was coated with Ti and/or
Alternatively, it is fired at a temperature higher than the eutectic temperature of Zr and Cu and lower than the melting point of Cu. The firing is preferably performed in an inert gas atmosphere such as N ₂ . Under the firing conditions of this invention, there is a width of about 300°C between the melting point of Cu and these eutectic temperatures, which makes management very easy.
During this firing, a eutectic alloy phase of Cu and each metal is formed as a liquid phase intermediate bonding layer between the ceramic substrate and the Cu layer, and thoroughly wets the interface between the substrate and the Cu layer to bond them together. Increase strength. In this way, a circuit is formed on the ceramic substrate.
A Cu layer can be formed quickly. The thickness of the first layer (intermediate bonding layer) is usually extremely thin, about 200 Å, and only forms a solid solution with Cu in a very small thickness at the interface, so the resistance value of the circuit is lower than that of Cu. Similarly, it can be kept extremely small. In reality, the sheet resistance of Cu is 5 mΩ/□, which is about as small as that of Ag. In addition to the above embodiments, first a thin film of Cu is formed on the substrate by a vapor deposition method such as PVD or CVD in close contact with the microstructure, and then a thin film of Ti or/and Zr is formed by the same method. After forming a Cu layer, a ceramic circuit board with good adhesion can be manufactured even if firing is performed under the above-mentioned firing conditions. Alternatively, Cu and Ti can be formed by PVD, CVD, etc.
and/or Zr are simultaneously deposited to form a mixed film of Cu, Ti, and/or Zr, and then Cu
After forming the layer, it may be fired in the same manner under the above-mentioned firing conditions. In this case, the liquid phase progresses best, and a ceramic circuit board with the strongest adhesion and quality stability is produced. Note that when forming the Cu layer by electroplating, the first layer is Ti.
When the film is made only of Zr and/or Zr, it is common to form a Cu thin film of about 1000 Å on or below it in advance. Next, an embodiment of the method for manufacturing a ceramic circuit board according to the present invention will be described together with a comparative example. (Example 1) Triclean degreasing of 50 x 50 x 0.635 (mm) was performed.
On a 96% pure Al ₂ O ₃ substrate, 99.9% pure Ti (degassing reagent for vacuum evaporation) was deposited to a thickness of 200 Å by vapor deposition method, and then 99.9% pure Cu (degassing reagent for vacuum evaporation) was deposited to a thickness of 200 Å. A gas reagent) was deposited to a thickness of 1000 Å using the same method. On top of that, by electroplating method
A Cu layer with a thickness of 70 μm was formed. Continued above
The Al ₂ O ₃ substrate was fired at 1000°C for 10 minutes in a N ₂ stream. Note that the vapor deposition method was performed without heating the substrate, and under conditions of a surface temperature of 100° C. or less. (Example 2) On the same Al ₂ O ₃ substrate used in Example 1,
Using the same method as in Example 1, 99.9% pure Ti and
99.9% Zr was simultaneously deposited to a thickness of 200 Å. On top of this, Cu with a purity of 99.9% was added by the same method as in Example 1.
was deposited to a thickness of 1000 Å. On top of that, a 70 μm thick Cu layer was formed by electroplating, and Example 1
It was fired under the same firing conditions. (Example 3) Cu with a purity of 99.9% was deposited to a thickness of 1000 Å on an Al ₂ O ₃ substrate similar to that used in Example 1 by sputtering.
It was deposited to a thickness of . Next, Zr with a purity of 99.9% was deposited to a thickness of 200 Å using a sputtering method, and a 70 μm Cu layer was formed thereon by an electroplating method, and fired under the same firing conditions as in Example 1. (Example 4) On an Al ₂ O ₃ substrate similar to that used in Example 1, Ti with a purity of 99.9% was deposited using the same method as in Example 1.
Cu with a purity of 99.9% was simultaneously deposited to a thickness of 1000 Å.
Fluorescent X-ray and XMA surface analysis confirmed that a mixed metal film of Cu and Ti was formed. after that,
On top of that, a 70μm thick layer was coated by electroplating.
A Cu layer was formed and fired under the same firing conditions as in Example 1. (Example 5) On an Al ₂ O ₃ substrate similar to that used in Example 1,
In the same manner as in Example 1, Ti with a purity of 99.9%, purity
99.9% Zr and 99.9% pure Cu were co-deposited to a thickness of 1000 Å. It was confirmed by fluorescent X-ray and XMA surface analysis that a mixed metal film of Cu, Ti, and Zr was formed. Thereafter, a Cu layer with a thickness of 70 μm was formed thereon by electroplating, and Example 1
It was fired under the same firing conditions. (Comparative Example 1) On the same Al ₂ O ₃ substrate as used in Example 1,
Cu was deposited to a thickness of 1000 Å, and using this as a pole, a Cu layer was formed to a thickness of 70 μm by electroplating, and fired under the same conditions as in Example 1. (Comparative Example 2) On the same Al ₂ O ₃ substrate used in Example 1
A 20 μm Ti foil and a 50 μm Cu foil were stacked, pressed down with an aluminum titanate sintered body from above, and baked at 1050° C. for 3 hours in a N ₂ stream under pressure to bond the foils onto the substrate. Next, the above Examples 1 to 5 and Comparative Examples 1 and 2
The center part of the substrate obtained was cut out to a width of 10 mm, and the peel strength was measured. The results obtained are shown in the table below, together with the results before firing.

〔Effect of the invention〕

This invention involves forming a thin film of Ti and/or Zr and Cu to serve as an intermediate bonding layer when forming a bonding layer between a ceramic substrate and a Cu layer using a eutectic alloy layer of Ti and/or Zr and Cu. After that, a eutectic alloy layer is formed by firing, so that a ceramic circuit board with extremely high adhesion and good solder adhesion can be manufactured.
By simultaneously depositing Cu, Ti and/or Zr,
The method of forming and firing these mixed metal films is as follows:
In particular, it has excellent adhesion and the width of the adhesion layer is constant, making it possible to provide products with high quality stability.

Claims (1)

[Claims] 1. When bonding a Cu layer to an oxide ceramic substrate, between the Cu layer and the ceramic substrate,
This is a method of forming a eutectic alloy layer of Ti and/or Zr and Cu as the intermediate bonding layer. After forming a thin film of Ti and/or Zr and Cu as the intermediate bonding layer, the eutectic alloy is formed by firing. A method for manufacturing a ceramic circuit board characterized by forming layers. 2 Ti and/or Zr on ceramic substrate
A Cu layer is formed after evaporating Ti and/or
The method for manufacturing a ceramic circuit board according to claim 1, wherein a eutectic alloy layer is formed by firing at a temperature higher than the eutectic temperature of Zr and Cu and lower than the melting point of Cu. 3 After depositing Cu on the ceramic substrate, Ti
A eutectic alloy layer is formed by depositing Zr and/or Zr, forming a Cu layer thereon, and firing this at a temperature higher than the eutectic temperature of Ti and/or Zr and Cu and lower than the melting point of Cu. A method for manufacturing a ceramic circuit board according to claim 1. 4 After simultaneously depositing Cu, Ti and/or Zr on a ceramic substrate, a Cu layer is formed thereon, and this is heated at a temperature above the eutectic temperature of Ti and/or Zr and Cu and below the melting point of Cu. A method for manufacturing a ceramic circuit board according to claim 1, wherein a eutectic alloy layer is formed by firing the ceramic circuit board. 5. The method for manufacturing a ceramic circuit board according to any one of claims 1 to 4, wherein the oxide ceramic substrate is an alumina substrate.