JPH0321108B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method of manufacturing a ceramic multilayer wiring board on which semiconductor LSIs, chip parts, etc. are mounted and interconnected. BACKGROUND TECHNOLOGY Ceramic multilayer substrates are currently classified into three methods depending on the method of multilayering. The first is the thick film printing method, which is typified by hybrid ICs.
This involves screen printing a thick film paste of a conductor or insulator onto a sintered ceramic substrate and repeating firing each time to create a multilayer structure. Second
is a green sheet printing method, which uses as a substrate material unfired ceramic powder made into a slurry with an organic binder, plasticizer, and solvent, and formed into a sheet-like film (called a green sheet) using the doctor blade method. It is. Conductor and insulator pastes are printed on this green sheet and firing is completed in one go. The third method is the green sheet lamination method.
This method is a method in which a desired number of green sheets with conductor patterns formed thereon are laminated and bonded together, and a multilayer board can be obtained by firing once, similar to the green sheet printing method. On the other hand, focusing on the conductive materials used in ceramic multilayer substrates, we find Au, Au-Pt, Ag-Pt, Ag,
Those using noble metals such as Ag-Pd, W, Mo,
It can be broadly classified into high melting point metals such as Mo-Mn and relatively low melting point base metals such as Cu and Ni. First, noble metal pastes are widely used because they can be processed in air and are highly reliable. However, precious metals have the problem of high cost. In addition, high melting point metals such as W, Mo, and Mo-Mn need to be fired at the same time at a high temperature of around 1600°C, that is, above the sintering temperature of the green sheet, so while they are suitable for multilayering, they also need to be fired in a reducing atmosphere. Therefore, it is dangerous. Also, the conductor resistance is high,
It has problems such as requiring Ni or Au plating for soldering. Therefore, materials such as Cu and Ni, which can be processed at low temperatures and are inexpensive, are attracting attention. Therefore, an example of a method for manufacturing a ceramic multilayer wiring board using Cu paste will be described. The method involves screen printing Cu paste on a sintered substrate such as alumina to form a wiring pattern, and after drying, the paste is heated to a temperature below the melting point of Cu (approximately 850 to 950 degrees Celsius).
The firing is carried out in a nitrogen atmosphere in which the oxygen partial pressure is controlled so that the Cu is not oxidized and the organic components in the conductor paste are sufficiently combusted. When multi-layered, the insulating layers are printed and fired under the same conditions. However, when using Cu paste as described above, there are several problems.
First of all, it is difficult to control the atmosphere during the firing process to an appropriate oxygen partial pressure.
In other words, if there is too much oxygen, Cu will be oxidized, and if there is too little oxygen, the organic binder in the paste will not be decomposed and removed, and good metallization will not be obtained. In the second case of multi-layering, it is necessary to repeat baking each time after printing each paste, resulting in problems such as a long lead time and an increase in equipment costs. Therefore, a special request was made in 1981.
No. 147833 has already disclosed a method in which a ceramic multilayer substrate is produced in three steps: a binder removal step, a reduction step, and a firing step. It uses cupric oxide as the starting material for the conductor, and the binder removal process is carried out in an oxidizing atmosphere sufficient for carbon and at a temperature sufficient to thermally decompose the internal organic binder, and is reduced to cupric oxide. It consists of a firing process in which the substrate is sintered.
This makes it easier to control the atmosphere during firing and allows a dense sintered body to be obtained. Problems to be Solved by the Invention However, the following problems have become apparent. This is because there are limits to the materials that can be used as the insulating material for the green sheet, which is the substrate material, in the production of ceramic multilayer substrates. This is because, in the production method that uses cupric oxide as a starting material and includes a heat treatment process in a reducing atmosphere as described above, the insulating material (glass-ceramic) contains a metal oxide (PbO) that is reduced. PbO + aMe → Pb + MeaO Me: Another metal reaction occurs, and the insulating layer containing metallized Pb becomes
It becomes unable to function as an insulator. Therefore, when using base metals such as Cu as conductor materials,
As an insulating material, it is thermodynamically stable and oxidized with Cu.
Al ₂ O ₃ is a metal oxide that does not undergo a reduction reaction,
B ₂ O ₃ , BaO, SiO ₂ , CaO, Na ₂ O, MgO,
It should be selected from Ta ₂ O ₅ , Nb ₂ O ₅ , etc. On the other hand, low-temperature sintered substrate materials containing PbO, TiO ₂ , etc. are considered unusable. However, substrate materials made of non-PbO-based oxides as described above have many disadvantages. For example, the above materials tend to have low insulation resistance and poor dielectric loss (tan δ). In addition, it is known that the softening point tends to be relatively high, and such systems have problems such as difficulty in lowering the sintering temperature and difficulty in short-term firing. . On the other hand, since cupric oxide is used as a starting material for the top layer wiring of the multilayer body after sintering, a reduction in volume (CuO → Cu) occurs during the reduction process, which causes many cracks to occur on the electrode surface. It cannot be said that it is a dense electrode. CuO as a starting material is not optimal for the top layer wiring, which requires the highest reliability. Means for Solving the Problems In order to solve the above problems, in the method of manufacturing a ceramic multilayer wiring board of the present invention, it is possible to use lead-based glass, which is highly reliable and easy to mass-produce, as an insulating material. This can be obtained by configuring the manufacturing process conditions as possible. In other words, the purpose of this study was to examine in detail the conditions of each step in the manufacturing process and achieve both non-reduction of lead oxide and reduction of cupric oxide. Further, the conductor paste for the uppermost layer wiring is mainly composed of metallic copper, and is formed after the reduction of the multilayer body, and the firing of the multilayer body and the firing of the uppermost layer conductor are performed simultaneously in nitrogen. Effect The present invention consists of the manufacturing method and manufacturing process conditions as shown below. This is a ceramic multilayer substrate that enables the use of materials such as The operation of the present invention will be explained below. First, to explain the manufacturing method of the present invention, there is a process of forming a multilayer body using cupric oxide as a conductive material and a low-temperature sintered material containing lead-based glass as an insulating material, and a process of removing the binder. The process consists of a reduction process in which CuO is reduced to Cu, a top layer Cu conductor printing process in which the top layer wiring is formed using Cu paste, and finally a firing process in which the multilayer body and the top layer wiring are simultaneously fired. In the binder removal step, the organic binder within the substrate is decomposed and removed in an oxidizing atmosphere such as air at a temperature below the softening point of the insulating glass. Then, in the reduction step, cupric oxide is reduced. As described above, since heat treatment in a reducing atmosphere is included in the manufacturing process, it has conventionally been said that insulating materials containing metal oxides that are reduced by heat treatment in a reducing atmosphere cannot be used. However, as a result of repeated studies from various viewpoints, the inventors found that by setting the conditions for each process of reduction and firing to certain values, it is possible to prevent lead oxide from being reduced to metallic lead and to reduce it to copper. I found out. In other words, after removing the binder from the unsintered multilayer body in which a conductive pattern was formed using cupric oxide, we determined through experiments the temperature at which it could be reduced to metallic copper in the air. In an atmosphere containing hydrogen, the reduction reaction occurred at approximately 250°C. Also, at this temperature, the PbO contained in the multilayer body
was not reduced to Pb. Next, when the reduction temperature was gradually raised in the same atmosphere, it reached approximately 600℃.
From the above, it was found that Pb reduction occurs at the same time as Cu reduction. In addition, when reducing at 250°C, depending on the heat treatment time, some parts may remain that are not reduced to copper; conversely, if the temperature is high, the glass softening point may be exceeded and cupric oxide may remain before being sufficiently reduced to copper. Since it may result in being incorporated into the inner layer, the practically effective range is between 300 and 500°C. After sufficient reduction has been completed, the top layer wiring is made of metal Cu.
Print with a paste whose main ingredient is powder. and,
In the firing process, the Cu paste and the insulating material are fired simultaneously in a neutral atmosphere such as nitrogen. As a result, PbO in the insulating material is not reduced and exhibits a good insulating function. Furthermore, the top Cu layer, which is co-fired with the insulating material, is dense and provides good metallization. Examples are shown below. Examples First, 96% alumina (96Al ₂ O ₃ ) was used for the ceramic sintered substrate according to the present invention. (thickness 0.8mm
^t ) Next, the conductor paste for the inner layer is made by adding 5wt% of glass frit (manufactured by Corning, #70593μm average particle size) to cupric oxide powder (average particle size 3.0μm) to improve adhesive strength. Then, ethyl cellulose, which is an organic binder, was added together with a vehicle dissolved in terpineol, and the mixture was kneaded using three-stage rolls to obtain an appropriate viscosity. Next, the insulating paste used was one in which the insulating material having the composition shown in Table 1 including lead-based glass was used as an inorganic component, and a vehicle was added and kneaded in the same manner as the conductive paste.

[Table] The method for producing the insulating material is to first melt it at a high temperature so that it has the glass composition shown in Table 1, then drop it into water to rapidly cool it, and then crush it in a wet process to an average particle size of about 2 μm. Furthermore, as a ceramic material, alumina powder with an average particle size of 0.8 μm is mixed to form an inorganic powder. A multilayer body is produced using the inner layer conductive paste produced as described above and the insulating paste. In this method, a wiring pattern is formed on the alumina substrate by screen printing using a conductive paste for the inner layer, and after drying, an insulating paste is further screen printed on top of the wiring pattern. This step is repeated a predetermined number of times to produce a multilayer body. At this time, the uppermost layer wiring is not printed, and an insulating layer with via holes for necessary connections is formed on top. A cross-sectional view of the multilayer body thus obtained is shown in FIG. In the figure, 1 is a CuO layer, 2 is an insulating layer, and 3 is an alumina substrate. Next, the binder from this unsintered multilayer body is removed. The softening points of the insulating glasses used in this example are 626°C, 619°C, and 630°C, respectively, and it is necessary to remove the binder at a temperature below the softening point.
Furthermore, since the organic binder contained in the conductor and insulator paste used in this example is ethyl cellulose, it takes approximately
A temperature of 550℃ or higher is desired. Therefore, the binder was removed at 600°C. Its profile is shown in Figure 3. Note that if the binder is removed at a temperature above the softening point, there is a risk that the cupric oxide inside will be sealed with the insulating material, so that it will not be possible to reduce it to Cu in the subsequent reduction step. Furthermore, the decomposition and removal of ethyl cellulose, which is a binder, was carried out based on the results of thermal analysis, and it was confirmed from the results of carbon content analysis after binder removal that sufficient removal was carried out. Next, the profile of the reduction process is shown in FIG. The binder-removed laminate was inserted into a 120 mmφ tubular furnace, and nitrogen gas and hydrogen gas were introduced at a flow rate of 0.7 l/min and a flow rate of cm ² into the furnace, respectively. Reduction temperature is 200℃, 300℃, 400℃, 500℃, 600℃, 700℃
It was held at each temperature for 1 hour, and then taken out after cooling. Reduction to copper almost always occurs at temperatures other than 200℃, and at 300℃.
At ℃, there is a slight presence of cupric oxide inside. There were some parts that appeared black, and it cannot be said that the reduction was carried out sufficiently. Furthermore, at a reduction temperature of 600°C or higher, the insulating layer turned gray, indicating that PbO was reduced. From the above results, the reduction process is 300
Suitable temperature is between ℃~500℃, more specifically 400℃~
500℃ is optimal. Next, a wiring pattern was screen printed on the top layer of the reduced multilayer body using metallic copper paste (Dupon #9153) and dried (120° C. for 10 minutes). The final calcination step was carried out continuously in pure nitrogen in a mesh belt furnace. (200 manufactured by BTU Engineering Co., Ltd.
mm width belt furnace) The residual O ₂ inside the furnace was measured using an O ₂ densitometer, and the amount of O ₂ was 1 to 2 ppm.
An example temperature profile is shown in FIG. The sintering of the reduced multilayer body and the top layer Cu metallization are formed simultaneously. The structure of the multilayer wiring board obtained as described above is shown in FIG. 2, and the evaluation results are shown in Table 2. 4 is a Cu metallized layer produced according to this example.

[Table] As described above, practically sufficient results were obtained. In addition, in terms of manufacturing conditions, the firing time is short at about 1 hr, and
Since simultaneous firing is possible, it can be said that this manufacturing method is highly suitable for mass production. Among the evaluation methods, the adhesive strength was measured by placing two
A mm square Cu electrode pattern was formed, a lead wire (0.8 mmφ) was vertically soldered onto it, and its breaking strength was measured using a tensile tester. Effects of the Invention As described above, by the manufacturing method of the present invention, it is possible to obtain a ceramic-copper multilayer substrate that can be used with extremely reliable lead-based glass as an insulating material. In other words, lead-based glass generally has high insulation resistance and is said to have excellent dielectric properties, and it is also possible to lower the softening point, making it easy to bake in short times and at low temperatures, making it an extremely suitable insulation for mass production. It can be said to be a material. In addition, by forming the uppermost layer marking line after the reduction process as in the present invention, it is possible to perform the firing at the same time as the sintering of the insulating material, which improves metallization properties (adhesive strength, solderability, surface Cu wiring with excellent density can also be obtained. Furthermore, the copper metallization obtained by the manufacturing method of the present invention can fully exhibit the advantages of Cu, such as low conductor resistance, good solderability, good migration resistance, and low cost. This invention is extremely effective industrially.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a ceramic multilayer wiring board after printing and drying according to the present invention, FIG. 2 is a completed cross-sectional view of the ceramic multilayer wiring board after forming the uppermost layer wiring and firing, and FIGS. 3 and 4. , and FIG. 5 are schematic diagrams showing the temperature profiles of the binder removal process, the reduction process, and the firing process, respectively. 1...CuO layer, 2...insulating layer, 3...alumina substrate,
4...Cu metallized layer.

Claims (1)

[Claims] 1 A pattern is printed on a sintered ceramic substrate with a paste composition mainly composed of cupric oxide, and a pattern is further printed with an insulating paste made of a glass ceramic composition containing lead oxide, and the cupric oxide paste is and a step of repeating printing the insulating paste on one or both sides of the sintered ceramic substrate a desired number of times to form a multilayer; a step of pyrolysis at a temperature, and then
The mixture of hydrogen and nitrogen is also heated at 300℃ to 500℃ in the atmosphere.
a step of performing a reduction heat treatment at a temperature between A method of manufacturing a ceramic multilayer wiring board, comprising: