JPH0320914B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Use The present invention relates to a ceramic multilayer wiring in which semiconductor ICs, chip parts, etc. are mounted and interconnected, and a method for manufacturing the same.

Conventional Structures and Problems There are currently three types of ceramic multilayer substrates, classified according to the method of forming multilayer wiring. it is,
These methods include the thick film method, green sheet printing method, and green sheet lamination method. The method will be briefly described below. First, the thick film printing method, typified by hybrid ICs, involves screen printing a thick film paste of a conductor or insulator onto a sintered ceramic substrate, and then repeating firing each time to form a pattern. It's a method. This method is easy to obtain thick film paste,
Since the construction method itself is simple and can be manufactured relatively easily, it is currently in practical use in many fields.
However, since this thick film printing method uses glass for the insulating layer, it is not easy to create multiple layers (3 to 4 layers at most), and baking is performed each time after printing, which increases equipment costs and leads to It has drawbacks such as a long time, and furthermore, it is difficult to process through holes because it uses a sintered substrate, so it is not a suitable method for double-sided wiring or multilayer wiring. do not have. Next is the green sheet printing method, which involves adding an organic binder, plasticizer, and solvent to ceramic powder (for example, containing alumina, beryllia, etc. as the main ingredients) and making it into a slurry using a ball mill. This method uses a membrane formed into a sheet (called a green sheet) using the blade method.

The conductor paste is mainly made of a high melting point metal such as W or Mo, and a paste containing an inorganic component having the same composition as the green sheet material is used as the insulating layer paste. The green sheet printing method is a method in which conductive paste and insulating paste are alternately printed and laminated on the green sheet to form a multilayer.
After repeated printing and drying, firing is completed in one go. This firing is performed in a reducing atmosphere in which the high melting point metals W and Mo are not oxidized. For example, the firing temperature is 1600℃, some water vapor is included, and the hydrogen gas concentration is about 10
% in a nitrogen gas atmosphere.

This method of using green sheets has many advantages and is expected to be adopted by an increasing number of manufacturers in the future. Its advantages are: firstly, it only needs to be fired once after printing and laminating, which reduces manufacturing time; and secondly, since the insulating layer has the same composition as the substrate material and is fired at the same time, it improves heat dissipation and airtightness. Excellent. Second, since a green sheet is used, it is easy to process through holes, etc., and it is said that printability is also good. Third, since metals such as W and Mo are used, the material cost is lower than that of gold or silver-palladium conductor materials. Fourth, due to shrinkage during sintering, it is actually denser than when printed. Fifth, the adhesive strength of the conductor is greater than that of thick film printing.

However, the disadvantages are that it is not easy to make major design changes, and it is dangerous because it requires high temperatures and a hydrogen atmosphere, which also increases equipment costs. Regarding conductors, compared to Au, Ag, Cu, etc., conductor resistance is higher and soldering is not possible, and the surface is easily oxidized, so Au, etc.
Examples include the need for post-treatment to coat with Ni, etc.

The final green sheet lamination method is almost the same as the green sheet printing method, but when creating multiple layers, conductors are printed and via holes are processed.
This is a method in which a large number of green sheets are laminated and pasted together, and the advantages of the above-mentioned green sheet printing method can be directly applied. This method has a large number of laminated layers and is advantageous when printing in large quantities, but it requires many molds and jigs for processing via holes in the green sheet, and there is less freedom to change the design, so the green sheet It is not as common a method as the printing method. Next, looking at the metallized conductive materials used in ceramic substrates, the thick film method
Au, Ag-Pd, Cu, etc. are used, and in the green sheet method, W, Mo, Mo-Mn, etc. are used. Although Au and Ag-Pd can be baked in air, they are precious metals and are therefore expensive.
The green sheet method has problems such as the fact that only high melting point metals such as W and Mo can be used because the temperature at which the ceramic substrate is sintered is as high as 1500° C. or higher.

Therefore, we are currently using Cu, which has low conductor resistance, does not cause migration, and has good solderability.
Wiring substrates using . There are also some examples of thick film printing methods that have been put into practical use. However, since it is a base metal, it also has drawbacks. Because it is a base metal, it cannot be baked in the air, and it also has excellent adhesive strength, sheet resistance, and solderability with the board.
This is because, due to the influence of the field of binders, very delicate control of the atmosphere is required, such as including a small amount of oxygen in the nitrogen atmosphere.

Furthermore, if a resistor or dielectric is to be formed after forming a Cu conductor, it is necessary to perform the baking in the same baking atmosphere as described above. However, only a few of the resistors and dielectrics that can be used for this purpose are put to practical use, and there is very little freedom in their selection.

However, the advantages of Cu are very attractive, and there is no doubt that it will gradually be put into practical use through research and development activities in various fields.

Therefore, if we consider the multilayer construction method described above, the ideal form of a multilayer wiring board would be to use copper as the conductor and use a green sheet for the multilayer construction method. In other words, it is obtained by printing or laminating an insulating layer on which a copper conductor is printed on a green sheet to form a multilayer structure, and then firing them at the same time.

However, there are some problems that need to be overcome before this Cu multilayer substrate can be put into practical use. The problems that need to be overcome are shown below.

First of all, Cu has a low melting point of 1083℃, so
In order to perform simultaneous firing with the substrate material, the sintering temperature of the substrate material itself must be lower than that. It is an essential condition that the performance required for the substrate material, such as sintered compact strength, resistance, moisture resistance, and thermal conductivity, must be satisfied. , performance is also required when multi-layered. The second problem is that it is difficult to use the binder under such firing conditions (temperature, atmosphere). In other words, organic binders, plasticizers, and
It is said that the same organic binders used in paste vehicles and the like are difficult to completely remove in non-oxidizing atmospheres and do not decompose at temperatures sometimes below the melting point of copper. It is said that if the binder cannot be completely decomposed and removed, the ceramic material itself will remain porous, and not only will sintering not progress, but the remaining carbon will only result in a darkened substrate. . It is difficult to put copper multilayer substrates into practical use for the reasons mentioned above.

Purpose of the Invention The present invention relates to a ceramic multilayer wiring board,
The present invention solves the above-mentioned problems regarding the method of forming a copper multilayer wiring board. In other words, we provide a new method for removing organic binders, which is the biggest problem in copper multilayering.
Another object of the present invention is to form a copper multilayer wiring board having a novel structure obtained by a manufacturing method including reduction and firing steps.

Structure of the Invention In order to achieve the above object, the present invention provides a ceramic substrate material (for example, a glass composition or an alumina composition substrate containing a large amount of glass) that can be fired at a temperature below the melting point of copper, an organic binder, and a plasticizer. A conductive pattern is formed on the green sheet using a paste containing cupric oxide as a main component, and the insulating layer is made of a paste consisting of the same inorganic component as the green sheet. It is formed by printing and printed repeatedly a desired number of times to form multiple layers.

Next, the binder removal method is performed at a temperature lower than that at which the sintering of the substrate material progresses, and the binder is sufficiently decomposed and removed.
Heat treatment is performed in an oxidizing atmosphere such as in oxidizing air. The main points of this method are, firstly,
The binder is removed from cupric oxide, which is the starting material for the conductive material, at a temperature at which the crystal structure does not undergo transformation and sintering does not proceed more than necessary.

Secondly, it is a prerequisite that the organic binder of the entire substrate does not remain and is thermally decomposed at a temperature lower than the sintering temperature of the substrate material.

What is important in the binder removal process performed as described above is that by controlling the heat treatment temperature, a part of the cupric oxide in the conductor paste can be diffused into the insulating layer to a desired degree. That's true. This has a remarkable effect on improving the metallization properties (adhesive strength) as a copper electrode.

Next, the cupric oxide is reduced to metallic copper in a mixed gas atmosphere of hydrogen and nitrogen (reduction step). This is a step in which heat treatment is performed at a temperature higher than the temperature required for reduction and lower than the softening point of the glass composition in the insulating composition. The method further includes a firing step in which the reduced laminate is fired in a nitrogen atmosphere at a temperature sufficient to sinter the insulating composition. Next, the reason why the present invention can be realized will be explained.

First, in the dehindering process, since cupric oxide is used as the starting material for metallizing copper in the method of the present invention, it remains as cupric oxide even during heat treatment in air, resulting in unnecessary volume. No change occurs and thermal decomposition of the organic binder takes place. At this time, it is necessary to carry out the process at a temperature below the softening point of the glass component of the glass-ceramic composition used as the insulating material. This is because when the temperature is above the softening point, the sintering of the laminate composed of the cupric oxide and the insulating material progresses, and the cupric oxide is sealed inside the laminate and is no longer reduced in the subsequent reduction process. The second copper oxide used is preferably cupric oxide. This is because cupric oxide is stable even in air and does not undergo crystal transformation even when the temperature is raised, making it suitable for the purpose of the present invention. Note that when oxides other than those mentioned above, such as suboxide Cu ₂ O, are used, debinding in air involves a change in volume due to transformation into CuO, which causes cracks and peeling when multilayered. To remove the binder with Cu ₂ O without volume change, the atmosphere must have an oxygen partial pressure of PO ₂ .
Although it is possible to control the oxygen partial pressure within the range of 10 ^-3 to ^{10 -5} , it is difficult to control the oxygen partial pressure as described above and is not effective from the viewpoint of the purpose of the present invention.

Next, in the reduction step, it is common knowledge that copper can be sufficiently reduced at a very low temperature (200 to 400°C). Therefore, the reduction to copper can be completed at a temperature below the softening point of the glass-ceramic composition.

The final step is the firing process. In this step, since the binder has already been removed, only the insulating material and copper metallization need be considered. That is, the temperature is raised to the sintering temperature of the glass/ceramic in a nitrogen gas atmosphere. As a result, good metallization properties can be obtained by sintering the glass/ceramic and sintering the copper particles. If this firing step is performed in a reducing atmosphere like a reducing step, sufficient copper metallization cannot be obtained. This is because the firing atmosphere has a large effect on the wettability of copper and the glass-ceramic material at high temperatures. In other words, this is based on the fact that glass components in insulating materials generally have poor leakage with metal. Therefore, in order to improve wettability by providing a very thin oxide layer on the surface of the copper particles, firing is performed in a neutral atmosphere. The above is the reason why the reduction step and the firing step are performed separately.

Note that it is also possible to perform the above-mentioned binder removal, reduction, and firing steps continuously in a dual atmosphere furnace.

FIG. 1 shows the structure of the copper multilayer wiring board manufactured as described above. 1 is the above-mentioned insulating substrate material made of glass or glass and ceramic composition, 2 is the reduced copper metallized layer, 3 is the above-mentioned,
It is a layer of copper oxide diffused inside an insulating layer.

The presence of the copper oxide diffusion layer makes the bond between the copper metallized layer and the insulating layer stronger.

Description of Examples First, the ceramic substrate material according to the present invention is made of borosilicate glass powder (Corning Corporation #7059 glass average particle size 3 μm) and alumina (Al ₂ O ₃ average particle size
1.0 μm) powder in a weight ratio of 40:60. This mixed powder is used as an inorganic component of the substrate material, polyvinyl butyral is used as an organic binder, di-n-butyl phthalate is used as a plasticizer, and
Mix a mixture of toluene and isopropyl alcohol (30:70 ratio) as a solvent with the following composition.
It was made into a slurry.

Inorganic components: 100 parts Polyvinyl butyral 5 parts D-n-butyl phthalate 5 parts Toluene/isopropyl alcohol 40 parts This slurry was formed into a sheet on an organic film (Toray, Lumirror 125 μm thick) by a doctor blade method. At this time, a system was used that continuously performs each process from film formation to drying, optional punching, and through-hole processing if necessary.

The green sheet obtained as above is
A dense sintered body can be obtained by firing in air at 1000℃ for 1 hour, and its electrical properties include a relative permittivity of 7.5 and a dielectric loss of 0.15% (IMHz).
The transverse tensile strength is 20Kg/ ^mm2 . Its performance is almost satisfactory as a substrate. At this time, the substrate material may be any glass having a softening point below the melting point of copper, and is not limited to the glass of the above embodiment.

Next, a conductor pattern is screen printed on the green sheet using cupric oxide paste. The cupric oxide (CuO) used at this time is
Special reagent grade particles with an average particle diameter of 5 μm were used. The vehicle composition for preparing the paste was prepared by using turpentine as a solvent, dissolving ethyl cellulose as an organic binder, and kneading it with the cupric oxide powder described above to form a paste. On the other hand, as an insulating paste, a paste having the same composition as the inorganic material for the green sheet was used in the same manner as above, the cupric oxide paste was screen printed, and after drying, an insulating layer pattern was printed. In the case of cupric oxide paste, the printing conditions at this time are approximately 20 μm thick with a 250 mesh screen, and the insulating layer is 200 μm thick.
A mesh screen was used to obtain a thickness of approximately 30 μm. Then, the above printing was performed a desired number of times on both sides of the green sheet.

In addition, although turpentine oil and ethyl cellulose were used to prepare the cupric oxide paste and the insulating paste, the vehicle was nitrocellulose instead of ethyl cellulose, and the solvent was cellosolves such as butyl carbitol and butyl cellosolve. It is also effective to use a surfactant such as sorbitan alkyl ester or polyoxyethylene alkyl ether.

Next, the binder was removed from the printed green sheet, and this was carried out using a temperature profile as shown in FIG. 2 as an example of the binder removal system of the present invention. The atmosphere at this time is in the air,
The organic binder in the green sheet and most of the organic components in the paste are decomposed at 500°C, and the organic components are completely removed at 800°C. Note that the binder removal temperature and atmosphere settings are determined by conducting thermal analysis in advance to confirm whether the binder is completely removed. Therefore, since the decomposition temperature differs depending on the type of binder, it is natural that the temperature profile when removing the binder also differs. When the substrate after the binder was removed was observed using a scanning electron microscope, it was found that the ceramic substrate material (alumina and glass components) showed almost no change in particle size from the starting material, and only the organic components were scattered. This is because the binder was removed at a temperature below the melting point of the glass component in the substrate material, indicating that no significant sintering of the cupric oxide itself or crystal transformation accompanied by a volume change has occurred. be.

Next, this debinding substrate is reduced and fired.
FIG. 3 shows an example in which the reduction step and the firing step were performed simultaneously. The atmosphere was a nitrogen gas atmosphere containing 10% hydrogen gas (flow rate 2/min). As a result, a white ceramic substrate was obtained from the fired ceramic substrate, and the properties of the substrate itself were almost the same as those of the above-mentioned air-fired substrate.
Then, by this firing, the cupric oxide was reduced to become metallic copper, and a conductive pattern was formed. The conductor resistance at that time is about 500 μm in line width and 10 μm in thickness.
A sheet resistance of 3.7 mΩ/□ was obtained, and the conductive pattern formed inside the insulating layer also obtained a result of 4.0 mΩ/□, similar to that of the surface layer. The metallization performance of the substrate and copper was determined by a so-called tensile test, and a result of 1.5 kg/cm ² was obtained. From the above results, it is judged that the copper multilayer wiring board according to the present invention can be put to practical use, although there is some dissatisfaction with the copper metallization properties. According to the present invention, since the binder is removed in advance in the air before sintering progresses, there is no residual carbon that inhibits the progress of substrate sintering, and the carbon is reduced to copper at a stage prior to substrate sintering. Therefore, sufficient conductivity can be obtained even for internal wiring.

In the above binder removal, reduction, and sintering methods,
Since the strength of the substrate after binder removal is weak and handling is difficult, and multiple electric furnaces are required, the following example using a dual atmosphere furnace is shown.
This dual atmosphere furnace is a belt-conveyed continuous furnace that can create independent atmosphere zones using air and nitrogen as carrier gases.

In this example, BTU Engineering Co., Ltd.
MEJ-4 type was used. The temperature and atmosphere profiles are shown in FIG. 500℃, 800℃, 1000
Each holding temperature in °C serves the same purpose as described above. The performance of the wiring board obtained at this time was almost the same as that described above. In addition, when the atmosphere during the firing and temperature cooling process is only nitrogen gas that does not contain hydrogen gas, the metallization characteristics (tensile test)
improved to 2.5Kg/ ^cm2 .

Effects of the Invention As described above, the present invention provides an extremely effective means for putting into practical use a copper multilayer wiring board, which is an ideal form of a ceramic multilayer board, and can be obtained for the first time by this method. It has a highly reliable structure.

That is, according to the configuration and manufacturing method of the present invention, (1) the insulating substrate material and the conductor layer can be fired at one time, which greatly streamlines the manufacturing process.

(2) Since the green sheet method can be used, it has excellent workability and can be easily multi-layered.

(3) Since binder removal is performed in air, sufficient binder removal can be expected even without special organic binders.

Similarly, since the degree of diffusion of copper oxide can be arbitrarily controlled during binder removal, a metallized layer with good adhesiveness can be obtained. (The copper oxide layer between the insulating layer and the conductor layer becomes a strong bonding layer.) (4) The firing temperature is 900℃ to 1080℃ (especially 1000 to 1050℃)
The reliability of the insulating substrate is high because it can be carried out at a higher temperature than the thick film method. (Especially moisture resistance,
(insulation, voltage resistance, etc.) (5) Similarly, the atmosphere during firing is easy to control. (There is no need to consider carbon oxidation,
It is sufficient to consider only the reduction of Cu. ) In addition, the copper multilayer wiring board of the present invention makes full use of copper's characteristics of low conductor resistance, good solderability, and good migration resistance, making it an industrially extremely effective invention. It is.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a copper multilayer wiring board according to the present invention, FIG. 2 is a diagram showing an example of the temperature and atmosphere profile showing the heat treatment step for removing binder according to the present invention, and FIG. 3 is a diagram showing an example of the reduction/baking process according to the present invention. FIG. 4 is a diagram showing an example of the temperature and atmosphere profile showing the process, and FIG. 4 is a diagram showing an example of continuous debinding and reduction/calcination steps when a dual atmosphere furnace is used. 1... Insulating substrate material, 2... Copper metallization layer,
3...Copper oxide layer diffused into the insulating layer.

Claims (1)

[Scope of Claims] 1. An insulating substrate made of glass or a glass and ceramic composition, a conductive metallized layer mainly composed of copper formed on the insulating substrate, and an insulating layer made of ceramic, glass, or a glass-ceramic composition. 1. A ceramic multilayer wiring board comprising a copper multilayer wiring board laminated with a copper metallized layer and an insulating layer, the ceramic multilayer wiring board having a cupric oxide diffusion layer at an interface between the copper metallized layer and the insulating layer. 2. Prepare a sheet containing at least an organic binder and plasticity in glass or a composition of glass and ceramic that is sintered at a temperature lower than the melting point of copper, and apply a paste composition containing cupric oxide as a main component on the raw sheet. Alternatively, the inorganic composition of the green sheet may be used for printing the cupric oxide paste. A step of repeatedly printing an insulating paste having the same composition as the product to form a multilayer structure, and heat treating the multilayer structure in an oxidizing atmosphere sufficient for carbon and at a temperature sufficient to thermally decompose the internal organic components. After that, heat treatment is performed in a mixed gas atmosphere of hydrogen and nitrogen at a temperature below the softening point of the glass component in the insulating paste composition and above a temperature at which the cupric oxide can be reduced to metallic copper. a reduction step, and further the reduced process. 1. A method for manufacturing a ceramic multilayer wiring board, comprising the step of firing the multilayer body in a nitrogen atmosphere at a temperature necessary to sinter the insulating composition.