JPS6367359B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for bonding metallic copper to the surface of a ceramic substrate. Conventionally, to bond ceramic and metallic copper,
The following methods are known. According to the method described in U.S. Pat. No. 3,744,120,
Metallic copper is placed on ceramic, and the melting point of copper (1083℃) is heated in a reactive gas (e.g., nitrogen containing oxygen).
The bonding process is performed by heating to a temperature (1065°C), which is lower than that, but still high enough to generate a eutectic between copper and gas. This method had the following drawbacks. (i) In order to place copper metal on ceramic, it is necessary to use a copper foil that is thick enough not to be significantly deformed by the weight of the metal copper. For this,
Since the heating temperature was lower than the melting point of copper, the copper foil did not come into sufficient contact with the ceramic surface, and after cooling, the copper foil "bulged" and a non-bonded area was created. (ii) In order to place metallic copper on ceramic, both must be flat plates. Therefore, it is not possible to three-dimensionally join a plane and a side surface at the same time, and its uses are limited. (iii) Reactive gas (inert gas containing a large amount of oxygen)
During heating, the copper metal placed on the ceramic is oxidized, so the copper bonded to the ceramic after cooling is copper oxide. For this reason, the conductivity was poor. The method described in Japanese Patent Publication No. 52-37914 is an improvement of the method described in the above-mentioned US Pat. No. 3,744,120. This method involves placing a binder (i.e., copper oxide) on top of the ceramic, and then placing copper metal on top of the ceramic to form an oxidized material in an inert gas that is lower than the melting point of copper (1083°C), but Bonding is performed by heating at a temperature sufficiently higher than the eutectic temperature of copper (1065°C). This method is characterized by the inclusion of a binder between the ceramic and the metal copper, and as a result, the drawback shown in item (iii) above can be solved. However, essentially the U.S. patent no.
Same as No. 3744120, it was not possible to solve the drawbacks shown in items (i) and (ii) above. Furthermore, the following important drawbacks are common in the prior art. When using a ceramic-metallic copper bonded body as an electronic circuit board, it is necessary to form the metallic copper into a circuit pattern. This necessity has the following drawbacks. (iv) Copper foil punched into a circuit pattern is laminated on a ceramic substrate and heated and bonded using the method described above, but this method has the disadvantage that the circuit pattern cannot be made finer. Another possibility is to form a pattern by etching the copper foil bonded to the ceramic, but the thickness of the copper foil (approx.
200 μm), it was not possible to form fine patterns, and the conventional technology had limitations in its application. The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a ceramic substrate in which copper metal can be bonded to the three-dimensional surface of ceramic without causing "bulges" without placing metal copper on the ceramic surface. and copper bonding method. The method for bonding a ceramic substrate and copper according to the present invention for the above purpose includes a first layer made of a noble metal that forms a solid solution with copper on the surface of a ceramic substrate, preferably containing divalent palladium and hydrochloric acid as essential components. A first layer of a noble metal made of metallic radium is formed by immersion in a treatment solution of The second layer is made of copper oxide plating.
layer, preferably divalent copper ions, tartaric acid or an alkali metal salt of tartaric acid as a complexing agent for divalent copper ions, formaldehyde as a reducing agent for divalent copper ions, monovalent copper ions as a complexing agent for monovalent copper ions. A second layer formed by chemical copper oxide plating by immersion in a chemical copper oxide plating solution containing as an essential component a complexing agent that forms a tetrahedral complex with copper ions. to form a substrate, and heat the substrate at a temperature of 500 to 1083° C. in an inert gas containing oxygen to form the second layer of conductive metallic copper, and the conductive metallic copper and the ceramic substrate. It consists of joining. According to the method of the present invention, metallic copper can be bonded with sufficient bonding strength without causing "blurring" even on the surface of a ceramic substrate having a three-dimensional surface. The present invention is based on a method of chemically oxidized copper plating. First, a solid solution with copper is formed on the entire surface of the ceramic substrate so that the entire surface of the ceramic substrate can be plated with chemical oxidized copper. A noble metal is deposited on the entire surface of the substrate.
A chemical copper oxide plating film containing copper and cupric oxide as the main components is applied to form a substrate, and the substrate is heated in an inert gas containing a trace amount of oxygen to form a chemical copper oxide plating film on metallic copper. By heating and reducing it to form a eutectic of copper and cuprous oxide, and bonding it with ceramic,
This is a method for bonding metallic copper three-dimensionally to the ceramic surface with sufficient strength without causing any "bulges" on the entire surface of the ceramic. The present invention will be described in more detail as follows. The principle of bonding ceramic and metal copper in the prior art, which is related to the present invention, is as follows. A noble metal-free binder (i.e., copper oxide) that forms a solid solution with copper on the ceramic is prepared, and a substrate on which metallic copper is placed is prepared.
The melting point of copper (1083
When placed at a temperature lower than the eutectic point of copper monoxide (1065°C), a melt containing liquid eutectic is generated between the ceramic and the metallic copper, and the melt sufficiently absorbs the ceramic. After wetting, cooling, and solidifying, the ceramic and copper metal form a strong bond (possibly a covalent bond). British Patent No. 761045 describes a high temperature (1083~
It is known that cupric oxide converts to cuprous oxide at a temperature of 1200°C), forms a copper monoxide eutectic, and bonds with ceramic. Furthermore, U.S. Pat.
It is known that ceramic and copper monoxide eutectic bond firmly together when heated to a temperature of That is, common in the prior art,
The necessity of producing some kind of melt to wet and bond the ceramics was due to the following reasons. In other words, copper oxide, which acts as a binding agent between ceramic and copper, is produced by: (i) attaching copper oxide particles to ceramic and placing metallic copper on top; (ii) treating the surface of metallic copper to form copper oxide. , and place it on the ceramic. Therefore, there is only mechanical contact between ceramic and copper oxide, or between copper oxide and copper, but not real contact. It is necessary to increase the number of non-bonded parts. The bonding between ceramic and copper does not occur because the binder becomes a melt, but is thought to be caused by a covalent bond between the ceramic and copper oxide that involves copper oxide. If you take the time to heat it using the above), you can achieve the original purpose. The present invention differs from the above-mentioned prior art in that there is no need to use a molten binder, and copper oxide is placed by chemical plating to a thickness that is in sufficient contact with the ceramic and can serve as a binder. It is then heated and bonded in an inert gas. For this reason, three-dimensional bonding with sufficient bonding strength is possible without causing the "bulging" of the copper foil on the ceramic, which was a drawback of the prior art. Chemical copper oxide plating, which is the gist of the present invention, will be explained. It is known that in the reduction-precipitation reaction of divalent copper ions (Cu ²⁺ ), metal copper is formed through an intermediate of monovalent copper ions (Cu ⁺ ). Chemical copper plating using formaldehyde as a reducing agent for divalent copper ions is known, but in the prior art, metallic copper is obtained from divalent copper ions. The present invention differs from the prior art in that during the above Cu ²⁺ reduction reaction, Cu ⁺
The main components of chemical plating precipitates, such as cuprous oxide (Cu ₂ O) and cupric oxide (CuO), are oxidized by the oxygen or hydroxide ions in the plating solution. This is done by chemically oxidized copper plating consisting of copper. As a result of studying various plating solution compositions, the present inventors found that divalent copper ions, formaldehyde as a reducing agent for divalent copper ions, tartaric acid or an alkali metal salt of tartaric acid as a complexing agent for divalent copper ions, ,
We have discovered a chemical copper oxide plating solution that contains as an essential component a complexing agent that forms a tetrahedral complex with monovalent copper ions. Below, the present invention will be explained in more detail with reference to Examples and comparative examples for comparing the effects of the Examples. The following describes the test and measurement method. For the samples in the following examples, the ceramic substrate was pretreated according to (a) and (b) below. (a) Alkaline degreasing treatment Treatment liquid composition: Sodium hydroxide…100g Water…amount that makes the whole 1 Treatment conditions: 70℃, 5 minutes (b) Neutralization treatment Neutralizing liquid composition: 12N hydrochloric acid…150ml Water…the whole Conditions: room temperature, 1 minute Next, the following step (c) was performed on the ceramic substrate after the above pretreatment. (c) Plating nucleation treatment This treatment is as shown in the respective sections of the comparative example and each example. Next, the above-treated product was subjected to the following step (d). (d) Chemical plating treatment This treatment is as shown in the respective sections of the comparative example and each example. Next, the above-treated product was subjected to the following step (e). (e) Heat treatment This treatment is as shown in the respective sections of the comparative example and each example. During the treatment steps (a) to (e) above and (f) below, washing and drying steps are included as usual, if necessary. In addition, through the processing steps up to (e) above, copper was bonded to a thickness of 0.5 to 10 μm on the ceramic substrate, but in the bonding strength measurement, it was found that in order to improve solderability and strengthen the bonded copper coating, above
After the (e) process, the product was subjected to the following (f) electrolytic copper plating process. (F) Electrolytic copper plating treatment Plating solution composition: Copper pyrophosphate...90g Potassium pyrophosphate...350g Brightener...3ml Polyphosphoric acid...Amount to make pH 8.6 Water...Amount to make total 1 Condition: 3A/dm ² , 30 minutes (20 μm) The ceramic-copper substrate obtained by electrolytic copper plating with a thickness of 20 μm was etched into a 2×2 mm square with only the copper on the ceramic, and a 2 mmφ
A brass rod was soldered perpendicularly to the board, and the ceramic-copper bond was peeled off using a tensile tester to measure the bonding strength between the ceramic and copper. The components of the chemical copper plating film obtained up to step (e) above were detected by X-ray diffraction. Comparative examples and examples will be described below. Comparative Example In the sample preparation process described above, the (c) plating nucleation process, (d) chemical plating process, and (v) heat treatment process in this comparative example were each as follows. (c) Plating nucleation treatment Composition of plating nucleation liquid: Catalyst 404, manufactured by Shippray, USA Conditions: Room temperature, immersion for 5 minutes (d) Chemical plating treatment Chemical plating treatment liquid composition: CuSO ₄・5H ₂ O …10g EDTA -2Na...30g NaOH...Amount to make the pH 12.3 37%-Formalin...3ml α,α'-Diviridyl...10ml Polyethylene glycol Stearylamine...200ml Water...Amount to make the whole 1 Conditions: 70℃, 1.2h (3μm) (e) Heat treatment: 800℃ in nitrogen containing 20ppm oxygen for 30 minutes, then 1050℃ for 20 minutes The plating nucleation solution in (c) above contains metal palladium as a noble metal dispersed in the solution as a colloid. By dipping the ceramic substrate, it is adsorbed onto the entire surface to form the first layer. The chemical plating solution in (d) above is of conventional technology, and as a result of X-ray diffraction,
The plating film contained no copper oxide and was pure metallic copper. Using a ceramic substrate (thickness: 1 mm) made of Al ₂ O ₃ with a purity of 96%, perform the steps (a) to (f) of the above sample preparation.
As a result of measuring the bonding strength after performing the above treatments,
It was 81Kg/ ^cm2 . It was found that even a general epoxy resin adhesive had an adhesive strength of 250 kg/cm ² and that the peeled part was at the interface between the ceramic and copper, so it was not sufficient for the bonding strength. Example 1 In this example, in the sample preparation process described above, (c) plating nucleation process, (d) chemical plating process, and (v) heat treatment process were as follows. (c) Plating nucleation treatment Same as comparative example. (d) Chemical plating treatment Chemical plating treatment liquid composition: CuSO ₄・5H ₂ O …30g Lotsiel salt …150g NaOH …Amount to adjust pH to 13.0 37%-formalin …10ml α,α′-dipyridyl …10mg Water … ...amount with the total as 1 Conditions: 40°C, 1.5h (3μm) (e) Heat treatment Same as comparative example. In this example, whereas the above comparative example differed only in the chemical plating treatment according to the present invention, the chemical plating treatment in (d) above was made according to the present invention. α, α′-dipyridyl is used as a regular tetrahedral complexing agent for Cu ⁺ , and the resulting plating film shows Cu ₂ O, CuO as a result of X-ray diffraction.
was found to be the main component. This film was black. Using the same ceramic substrate as in the comparative example, processes (a) to (f) in the sample preparation process were performed, and the bonding strength was measured, and a value of 505 Kg/cm ² was obtained. In this case, the ceramic substrate was destroyed without peeling off at the interface between the ceramic and copper. Therefore, using this chemical plating,
That is, it was found that according to the present invention, the bonding strength between ceramic and copper was sufficient. Example 2 In this example, in the sample preparation process described above, (c) plating nucleation process, (d) chemical plating process, and (e) heat treatment process were as follows. (c) Plating nucleation treatment The treatment method was as shown in the comparative example, but the treatment solution composition and conditions were as follows. Composition of plating nucleation solution: PtCl ₄ ...0.1g Ethanol ...amount that makes the total 1 Conditions: room temperature, soaking for 5 minutes (d) Chemical plating treatment Chemical plating treatment solution composition: CuSO _{4.5H 2} O ... 30g Lotsiel's salt...150g NaOH...Amount to set the pH to 13.0 37%-Formalin...10ml O-Fenatroline...30mg Water...Amount to set the total to 1 Conditions: 40℃, 1.5h (3μm) (E) Heat treatment Comparative example and The same. The plating nucleation solution (c) above uses platinum as the noble metal, and a first layer of platinum chloride is formed by immersing the ceramic substrate under the above conditions and then drying it. The chemical plating solution (d) above uses O-phenanthroline as a tetrahedral complexing agent for Cu ⁺ , and it was confirmed that a plating film similar to that in Example 1 was formed. It was done. Using the same ceramic substrate as the comparative example, we performed the processes (a) to (f) in the sample preparation process, and measured the bonding strength. As a result, we obtained a value of 482Kg/ ^cm2 , and the bonding was so strong that the ceramic substrate was destroyed. It was very strong. In addition, only the composition of the plating nucleation liquid in (c) is as follows.
The same bonding strength as above was obtained with the liquids shown in (a) and (b). (a) Composition: PdCl ₂・2H ₂ O...0.1g Acetone...Amount to make a total of 200ml (b) Composition: AuCl ₃ ...0.1g Ethanol...Amount to make a total of 200ml Note that plating allows chemical plating. It has been confirmed that copper and other metals with a smaller ionization tendency, such as gold, platinum, and palladium, can be used as the core. It was also confirmed that nitrogen-containing heterocyclic compounds such as cuproine, bathocuproine, and neocuproine have remarkable effects as complexing agents that form tetrahedral complexes with Cu ⁺ . Example 3 In the same manner as in Example 1, however, the thickness of the chemical plating was changed, that is, the relationship between the bonding strength and the plating time was determined. The results are shown in Table 1, and the copper oxide plating thickness
At 0.3 μm (No. 1) or less, the copper on the heated ceramic had no electrical conductivity, and the electrolytic copper plating described in (f) in the above sample preparation could not be performed, making it impossible to measure the bonding strength. In addition, the plating thickness of copper oxide
When the thickness exceeded 10 μm (No. 7, No. 8), the black plating film peeled off during plating, and the entire surface of the ceramic could not be plated. Therefore, the appropriate plating thickness for chemically plating ceramic with copper oxide is 0.4.
It was found to be ~8.0 μm. With this plating thickness, it was possible to obtain a bonding strength of approximately 300 kg/cm ² or more.

[Table] Example 4 The relationship between the bonding strength and the heating conditions was determined in the same manner as in Example 1, except that the heat treatment conditions were changed. Table 2 shows the results of changing the atmospheric conditions at 800°C for 30 minutes and then at 1073°C for 5 minutes.As for the oxygen content in nitrogen, there is no bonding strength if it is less than 3ppm, and if it is more than 300ppm, there is no bonding strength. The copper oxide plating film is not sufficiently heated and reduced to metallic copper,
It is not electrically conductive and therefore makes it difficult to prepare samples.
(f) Electrolytic copper plating could not be performed and the bonding strength could not be measured. Therefore, it has been found that the appropriate oxygen content is 5 to 200 ppm. In addition, the atmospheric conditions were nitrogen containing 20 ppm of oxygen, and the temperature conditions were as shown in the table.
℃, after 30 minutes) The results of changing the temperature conditions in the table are shown in Table 3. When the heating temperature is below 400℃, no large bonding strength can be obtained even if heated for a long time, and the copper At temperatures above the melting point of 1083°C, copper oxide is thermally reduced to metallic copper and then melts into particles, which no longer completely cover the ceramic surface. Therefore, it was also found that 500 to 1083°C is an appropriate temperature. It was also found that the lower the heating temperature, the longer the heating time.

【table】

[Table] As described above, the effects of the present invention could be demonstrated. The bonding strength between ceramic and copper is thought to be due to the covalent bond between the ceramic and copper oxide, but in the present invention, the noble metal that forms a solid solution with copper is present as the first layer on the ceramic. Nevertheless, the present inventors consider the reason for obtaining the bonding strength as follows. The noble metal adsorbed and applied to the ceramic becomes metal through the reduction action of formaldehyde during chemical plating. Copper oxide is chemically plated onto this, and when heated in an inert gas, the copper oxide is thermally reduced to metallic copper, and the noble metal diffuses into the metallic copper. As a result, metallic copper and copper oxide substantially come into contact at the ceramic interface in a short period of time. In fact, according to the alloy phase diagram, gold, platinum, and palladium are completely dissolved in solid solution with copper. As described above, according to the present invention, the first layer of precious metal is provided so that the entire surface of the ceramic substrate can be plated with chemical copper oxide, and then the second layer of copper oxide is formed by chemical copper oxide plating. By heating the substrate in an inert gas containing a trace amount of oxygen to reduce the second layer to metallic copper and firmly bonding the ceramic and copper, It has become possible to bond the entire surface of the ceramic at the same time, which was impossible, and it has been possible to eliminate the "bulging" of copper on the ceramic, which was a drawback of the prior art.

Claims (1)

[Claims] 1. A first layer made of a noble metal that forms a solid solution with copper is provided on the surface of a ceramic substrate, and further, on the first layer, cuprous oxide and cupric oxide as main components are provided. A second layer made of chemical copper oxide plating containing copper oxide as a substrate is provided, and the substrate is heated at a temperature of 500 to 1083° C. in an inert gas containing oxygen to form a conductive metal copper layer. A method for bonding a ceramic substrate and copper, characterized in that the conductive metal copper and the ceramic substrate are bonded. 2. The first layer made of the noble metal is made of metallic palladium formed by immersion in a treatment solution containing divalent palladium and hydrochloric acid as essential components. A method of bonding ceramic substrates and copper. 3. The second layer made of chemical copper oxide plating is 2
Tartaric acid or an alkali metal salt of tartaric acid as a complexing agent for valent copper ions, divalent copper ions, formaldehyde as a reducing agent for divalent copper ions, and monovalent copper ions and regular tetrahedrons as complexing agents for monovalent copper ions. Claims 1 or 2, wherein chemical copper oxide plating is formed by immersion in a chemical copper oxide plating solution containing as an essential component a complexing agent that forms a complex. The described method for joining a ceramic substrate and copper.