JPH05191038A - Ceramic board with metallic layer and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To increase the bonding strength between a board and a metallic layer by a method wherein a surface-roughened oxide layer is formed on the junctioned surface side of non-oxide base ceramic board with a metallic layer while a compound oxide layer is interposed between the oxide layer and the metallic layer. CONSTITUTION:A surface-roughened aluminum nitride board 1 is baked meeting the requirements of the temperature of 1200 deg.C for one hour in the air to form an oxide layer 2 on the surface of the aluminum nitride board 1. The oxide layer 2 on the aluminum nitride board 1 is chemically plated with copper to form a copper thin layer 3 0.5mum thick. Furthermore, the copper thin layer 3 is electrolytically plated with copper to form a copper layer 3a 5mum thick. Next, the aluminum nitride board 1 is heat-treated meeting the requirements for the temperature of 1070 deg.C for 10 minutes in atmospheric oxygen concentration of 2ppm to form another aluminum nitride board 4 having the copper layer 3a. Finally, after cooling down step, a compound oxide layer 5 made of CuAl2O4 is formed on the interface between the copper layer 3a and the aluminum nitride board 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal layer on the surface of a non-oxidizing ceramic substrate by chemical plating.

[0002]

2. Description of the Related Art When a ceramic substrate is used for circuit formation, heat sink, insulation, etc., it is necessary to form a metallized layer of metal on the surface thereof. Conventionally, as a method of forming a metallized layer, a thin film method, a thick film method, a co-firing method, a plating method and the like have been performed.

In the thin film method, a metal thin film is formed on the substrate surface by using vacuum deposition, sputtering or the like. The advantages of the thin film method are that it is highly reliable and that the metallization layer has good precision and fineness, and is suitable for high density. However, since a vapor deposition device or the like is required, it is disadvantageous in terms of productivity and cost, and since the film thickness is thin, the resistance of the metallized layer cannot be sufficiently lowered.

In the thick film method, a paste containing gold, silver, copper, etc. is printed on the surface of the substrate and then baked. The advantage of the thick film method is that it is suitable for mass production of substrates because the number of steps is small. However, since the method uses paste printing, it is not possible to sufficiently achieve high precision and high density of the metallized layer. Further, since the paste contains a glass component, the wettability of the solder to the metallized layer is deteriorated.

In the simultaneous firing method, a paste containing a refractory metal is printed on the surface of the green sheet, and then the green sheet and the paste are simultaneously fired. The advantage of the co-firing method is that it is suitable for mass production of substrates because the number of steps is small. However, since a refractory metal such as W or Mo is used, the conductor resistance of the metallized layer is high, or the wettability is poor, so that a treatment such as Ni plating is required. Furthermore, since the method uses paste printing, it is not possible to sufficiently achieve high precision and high density of the metallized layer.

As described above, the thin film method, the thick film method, and the co-firing method do not satisfy the above-mentioned various conditions, and it is inevitable to select a different forming method depending on the application of the substrate.

On the other hand, according to the plating method of plating the surface of the substrate with copper or the like, not only can the process be simplified and the substrate can be mass-produced as in the thick film method and the simultaneous firing method,
Lower resistance of the metallized layer can also be achieved. Further, the precision and density of the metallized layer can be increased similarly to the thin film method. Since the plating method can be applied to a wide range of fields in this way, it is more advantageous than the above method from the viewpoint of practicality.

In this type of plating method, for example, in the plating method disclosed in JP-A-61-63581,
The substrate is roughened with an alkali prior to plating.
Further, in the plating method disclosed in JP-A-61-270890, the surface of the substrate is roughened with an acid before plating. Then, a fine anchor is formed on the surface of the substrate by the above treatment in order to improve the adhesion with the metallized layer.

However, the above-mentioned adhesion by forming the anchor is merely physical bonding, and it has been difficult to secure sufficient adhesion strength between the substrate and the metallized layer. Further, for example, in the plating method disclosed in Japanese Patent Laid-Open No. 61-197488, heat treatment is performed in an oxygen-containing atmosphere to promote chemical bonding between the substrate and the metallized layer to improve adhesion. ..

However, in the heat treatment, only oxygen in the atmosphere is involved in the reaction, the amount of oxygen is not sufficient to promote chemical bonding, and sufficient adhesion strength between the substrate and the metallized layer is ensured. Was difficult. The present invention has been made in view of the above circumstances, and its object is to promote chemical bonding between an oxide layer and a metallized layer in addition to physical bonding by an anchor effect, thereby forming a substrate and a metallized layer. It is an object of the present invention to provide a method for manufacturing a ceramic substrate having a metallized layer capable of ensuring sufficient adhesion strength therebetween.

[0011]

In order to solve the above problems, in the present invention, a non-oxide ceramic substrate (1) having a metal layer (3) on at least a part of its surface is used.
In addition, an oxide layer (2) having a roughened surface is formed on the joint surface side of the non-oxide ceramic substrate (1) with the metal layer (3), and the oxidation is performed. A ceramic substrate provided with a metal layer, characterized in that a composite oxide layer (5) is interposed between the material layer (2) and the metal layer (3); After roughening with an alkali, etc., an oxide layer is formed on the surface of the ceramic substrate, metal plating such as chemical copper plating is applied on the oxide layer, and the plated substrate is placed in an oxygen-containing inert atmosphere. Proposes a method for heat treatment.

The reason why such a structure is desirable will be described by taking the case of chemical copper plating as an example. After forming an oxide layer (M _x O _y ) on the surface of a non-oxide ceramic substrate and performing chemical copper plating, the temperature is set to a temperature higher than the eutectic temperature of copper oxide and copper and lower than the melting point of copper. The heat treatment is performed to form a Cu—MO composite oxide at the interface between copper and the oxide layer (M _x O _y ). The Cu-MO compound layer formed by this reaction has an excellent chemical bond and can secure sufficient adhesion strength.

The method for manufacturing a ceramic substrate having a metal layer according to the present invention will be described below based on steps. In the present invention, the surface of the ceramic substrate is roughened by using a basic solution such as an alkali metal hydroxide and immersing the substrate in this aqueous solution. LiOH, KOH, NaOH or the like can be used as the alkali metal hydroxide. Next, an oxide layer is formed on the surface-roughened ceramic substrate. Examples of the oxide layer forming method include heat treatment (in air), UV ozone treatment, and oxygen plasma treatment. It is also effective to generate a hydroxide. This is because it changes into an oxide during the heat treatment for the eutectic reaction.

The thickness of the oxide layer is 0.1 μm to 20 μm.
It is desirable that it is m. The thickness of the oxide layer is 0.1 μ
This is because if it is less than m, the amount of oxygen is insufficient to form a composite oxide, and it is difficult to secure a satisfactory adhesion strength. On the other hand, when it exceeds 20 μm, stress is generated at the interface due to the difference in thermal expansion between the ceramics and the oxide layer, and as a result, the adhesion strength deteriorates.

After that, chemical copper plating is applied on the ceramic substrate. After chemical plating, if necessary, thick plating is performed by chemical plating or electrolytic plating. After plating, heat treatment is performed in an inert atmosphere to form a complex oxide layer. The heat treatment atmosphere preferably has an oxygen concentration of 25 ppm or less. This is because when the oxygen concentration exceeds 25 ppm, the metallized layer is oxidized and does not function sufficiently as a conductor layer.

The heating temperature is preferably higher than the eutectic temperature of copper and copper oxide and lower than the melting point of copper. The eutectic temperature here is 1065 ° C., and the melting point is 1083 ° C.
If the temperature is lower than 1065 ° C, the formation of the complex oxide layer is insufficient, and it is difficult to secure a satisfactory adhesion strength. on the other hand,
At 1083 ° C or higher, copper will melt.

A heating time of several minutes is sufficient. When the heat treatment is carried out for a long time, the metallized layer is oxidized and the metallized characteristics deteriorate. If the metallized layer is formed according to the above procedure, a ceramic substrate having excellent adhesion strength can be easily and reliably manufactured.

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the present invention will be described in detail below with reference to the drawings.

Example 1 After adding 5.0% by weight of Y ₂ O ₃ powder as a sintering aid, 36% by weight of a solvent and 11% by weight of a binder to aluminum nitride powder having an average particle size of 1.1 μm, The mixture was kneaded to prepare a slurry. Then, after producing a green sheet from the slurry by a sheet forming method, degreasing was performed at 400 ° C. for 12 hours. Then, the degreased green sheet is placed in a crucible and heated at 1830 ° C.
Firing was performed for 5 hours to obtain an aluminum nitride substrate 1.

The aluminum nitride substrate 1 is placed at 60.degree.
It was immersed in a 0% sodium hydroxide aqueous solution for 10 minutes to dissolve only the aluminum nitride particles on the outermost surface layer of the substrate. A large number of anchors A are formed in the marks where the particles are dissolved by the roughening treatment.

The roughened aluminum nitride substrate 1 is fired in air at 1200 ° C. for 1 hour to form an oxide layer 2 on the surface of the aluminum nitride substrate 1.
(Alumina) was formed. The oxide layer 2 has a thickness of 10 μm
It was m.

Oxide layer 2 of the aluminum nitride substrate 1
Chemical copper plating is applied on top, and a copper thin layer with a thickness of 0.5 μm 3
Formed. Furthermore, electrolytic copper plating is applied on the thin copper layer 3,
A copper layer 3a having a thickness of 5 μm was formed.

Then, the aluminum nitride substrate 1 provided with the copper layer 3a was subjected to an oxygen concentration of 2 ppm in the atmosphere,
Heat treatment was performed at 1070 ° C. for 10 minutes to obtain an aluminum nitride substrate 4 having a copper layer 3a. After cooling, copper layer 3
It was confirmed that CuAl ₂ O ₄ , which is the complex oxide layer 5, was formed at the interface between a and the aluminum nitride substrate 1.

Example 2 The same aluminum nitride substrate 1 used in Example 1 was used,
Roughening treatment was performed under the same roughening condition, and the oxide layer 2 was formed to a thickness of 3 μm by heat treatment. Example 1 on the oxide 2
After forming the copper layer 3a in the same manner as above, the oxygen concentration in the atmosphere is 5p.
Under pm, heat treatment was performed at 1070 ° C. for 10 minutes to obtain an aluminum nitride substrate 4 having a copper layer 3a. After cooling, at the interface between the copper layer 3a and the aluminum nitride substrate 1, CuAl, which is the complex oxide layer 5, is formed as in Example 1.
Formation of ₂ O ₄ was confirmed.

Example 3 The same aluminum nitride substrate 1 used in Example 1 was used,
Roughening treatment was performed under the same roughening condition, and the oxide layer 2 was formed to a thickness of 5 μm by heat treatment.

A copper layer 3 was formed on the oxide 2 as in Example 1.
After forming a, the copper layer 3 is heat-treated at 1075 ° C. for 10 minutes under an oxygen concentration of 5 ppm in the atmosphere.
An aluminum nitride substrate 4 having a was obtained. After cooling, Example 1 was formed on the interface between the copper layer 3a and the aluminum nitride substrate 1.
Similarly to the above, formation of CuAl ₂ O ₄ , which is the composite oxide layer 5, was confirmed.

Comparative Example 1 The same aluminum nitride substrate 1 as that used in Example 1 was used.
A roughening treatment was performed under the same roughening conditions. After the copper layer 3a was formed on the aluminum nitride substrate 1 having the roughened surface in the same manner as in Example 1, the copper layer 3a was heat-treated at 1070 ° C. for 10 minutes under an oxygen concentration of 5 ppm in the atmosphere. An aluminum nitride substrate 4 provided with was obtained.

Comparative Example 2 The same aluminum nitride substrate 1 as that used in Example 1 was used,
Roughening treatment was performed under the same roughening condition, and the oxide layer 2 was formed to a thickness of 10 μm by heat treatment. After forming the copper layer 3a on the oxide 2 as in Example 1, the oxygen concentration in the atmosphere was set to 4
Under 0 ppm, heat treatment was performed at 1070 ° C. for 10 minutes to obtain an aluminum nitride substrate 4 having a copper layer 3a.

Comparative Example 3 The same aluminum nitride substrate 1 as that used in Example 1 was used.
Roughening treatment was performed under the same roughening condition, and the oxide layer 2 was formed to 30 μm by heat treatment. After forming the copper layer 3a on the oxide 2 in the same manner as in Example 1, the oxygen concentration in the atmosphere is set to 2
Heat treatment was performed under ppm at 1070 ° C. for 10 minutes to obtain an aluminum nitride substrate 4 having a copper layer 3a. After cooling, at the interface between the copper layer 3a and the aluminum nitride substrate 1, CuAl, which is the complex oxide layer 5, is formed as in Example 1.
Formation of ₂ O ₄ was confirmed.

In order to evaluate the physical characteristics of the aluminum nitride substrate 4 manufactured by the above method, the following tests were conducted. The adhesion strength between the aluminum nitride substrate 1 and the copper layer 3a was evaluated by the vertical pull strength. In this test, when the wire soldered to the 1 × 1 mm pattern is pulled in the vertical direction, the strength (kg / mm) at which the pattern is peeled from the aluminum nitride substrate 1
² ) was measured. Further, the thermal conductivity (W / mK) of the aluminum nitride substrate 1 accompanying the surface oxidation was also measured. The results are shown in Table 1.

[0030]

[Table 1]

As is clear from the results shown in Table 1, in any of the examples, the adhesion strength between the aluminum nitride and the copper layer is excellent. As described above, this is due to Cu between the aluminum nitride and the copper layer.
This is the result of the chemical bond occurring with the formation of the Al ₂ O ₄ layer. In Comparative Example 1, the result of physical joining is simply due to the anchor effect.
Only a low adhesion strength of ² kg / mm ² was obtained.

In Comparative Example 2, the acidity concentration in the atmosphere was 40 p
pm, and an oxygen source was added from the atmosphere, but the result was that the copper layer was oxidized, and it could not be used as a metallized layer.

In Comparative Example 3, an oxide layer having a thickness of 30 μm was formed. The adhesion strength between the aluminum nitride and the copper layer is 2.1.
Although the value was as good as kg / mm ² , the fracture mode was between the oxide layer and aluminum nitride. It is considered that this is because stress was generated at the interface between the oxide layer and aluminum nitride due to the difference in thermal expansion between the oxide layer and aluminum nitride. Therefore, the reliability of the temperature cycle test and the thermal shock test becomes low, and a doubt remains as a metallized layer.

The thermal conductivity shows a good value of 170 W / mK when the thickness of the oxide layer is 10 μm, and there is no problem in use.

Summarizing the above results, it is apparent that the metal oxide layer having excellent adhesion strength can be easily obtained since the appropriate composite oxide layer is formed by the manufacturing method of each example. Further, since the present invention is basically a plating method, the thin film method and the thick film method are advantageous in that the process can be simplified, the mass production of the substrate, and the resistance, fineness and density of the metal layer can be realized. Method and co-firing method are superior. This manufacturing method solves the problem of adhesion strength that has been conventionally held, and it is no longer necessary to select a different metallization layer forming method depending on the application of the substrate, unlike the conventional method.

[0036]

As described in detail above, according to the method for producing a non-oxide ceramic substrate provided with a metal layer of the present invention, in addition to the physical bonding by the anchor effect, the interface between the metal and the oxide layer is added. In the above, since the composite oxide is formed, the chemical bond is also promoted, and there is an excellent effect that a sufficient adhesion strength can be secured between the ceramic and the metal layer.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a manufacturing process of a ceramic substrate provided with a metallized layer in Example 1.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ceramics substrate, 2 Oxide layer 3 Chemical plating layer 3a Metal layer 4 Ceramics substrate provided with a metal layer 5 Complex oxide layer A Anchor

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H05K 3/18 A 7511-4E

Claims (7)

[Claims] 1. A non-oxide ceramic substrate (1) having a metal layer (3) on at least a part of its surface, which is bonded to a metal layer (3) of the non-oxide ceramic substrate (1). On the surface side, an oxide layer (2) having a roughened surface is formed, and the oxide layer (2) and the metal layer (3) are formed.
A ceramic substrate provided with a metal layer, characterized in that a complex oxide layer (5) is interposed between the ceramic substrate and the metal oxide layer. 2. A method of metallizing a ceramic substrate, comprising a step of roughening a surface of a non-oxide ceramic substrate (1) to form an anchor (A), and an oxide on the surface of the non-oxide ceramic substrate (1). A step of forming the layer (2), a step of forming a metal layer (3) on the oxide layer (2) by chemical plating, and a step of heat-treating the metal layer (3) in an inert atmosphere. A method of manufacturing a ceramic substrate having a metal layer, comprising: 3. The method for manufacturing a ceramic substrate having a metal layer according to claim 2, wherein the oxide layer (2) is formed only on the surface of the non-oxide ceramic. 4. The method for manufacturing a ceramic substrate having a metal layer according to claim 2, wherein the chemical plating layer (3) is a copper plating layer. 5. The metal layer according to claim 2, wherein the heat treatment is performed at a treatment temperature which is equal to or higher than the eutectic temperature of the metal and its oxide and lower than the melting point of the metal. A method for manufacturing a ceramic substrate provided. 6. The heat treatment has an oxygen concentration of 25 in the atmosphere.
The method for producing a ceramic substrate having a metal layer according to any one of claims 2 to 5, wherein the treatment is performed in an inert atmosphere of ppm or less. 7. The thick plating layer (3a) according to claim 2, after the metal layer (3) is formed by chemical plating.
A method of manufacturing a ceramic substrate having a metal layer for forming a ceramic substrate.