JPS6357393B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a multilayer wiring circuit board. Mullite (3Al ₂ O ₃ .2SiO ₂ ) ceramics have a lower dielectric constant and a smaller coefficient of thermal expansion than alumina ceramics, making them more useful as materials for multilayer wiring ceramic boards. As a method for producing mullite, US Pat. No. 3,336,108 proposes a method for producing a dense mullite sintered body by treating bauxite with water containing a dispersant to remove impurities. However, bauxite originally contains more alumina than mullite, and is a sintered body containing a mixture of mullite and alumina. Therefore, the coefficient of thermal expansion is also larger than that of mullite and close to that of alumina. For example, mullite has 28.2% by weight of SiO ₂ and 71.8% by weight of Al _{2 O 3} , while bauxite has 21.3% by weight of SiO _{2 and} 75.7% by weight _of Al ₂ O ₃ . against
21.4% by weight is also excessive. Therefore, the coefficient of thermal expansion is 50×10 ^-7 /°C or more, and the dielectric constant is as large as 6 to 7. When silicon oxide (SiO ₂ ) is added to bauxite to make it closer to a mullite composition, it becomes difficult to sinter, resulting in a sintered body with many pores. In addition, sintered products made by mixing alumina and silicon oxide in the composition ratio of mullite generally tend to have relatively large pores on the surface and inside of the sintered body, and have low mechanical strength. If this happens, there is a drawback that the conductor may be disconnected or shorted at the pores. According to Japanese Patent Application Laid-Open No. 152010/1983, mullite, alumina, and glass are mixed, and the alumina and glass are reacted during sintering to produce mullite, thereby obtaining a dense sintered body containing mullite. However, with this method, it is necessary to select a glass composition that is strictly controlled so that the composition will produce mullite, and if the firing conditions are not sufficiently controlled, the glass will soften and form before mullite can be produced from the glass. There are drawbacks such as deterioration, and when alumina and glass do not completely react, alumina remains in the sintered body, increasing the coefficient of thermal expansion and dielectric constant. An object of the present invention is to provide a multilayer wiring circuit board made of a dense mullite sintered body with few pores and an efficient manufacturing method thereof. The present invention is a method of forming a circuit with a conductive paste containing molybdenum or tungsten on a molded body having a composition excluding organic substances and having a composition of 70% by weight or more of mullite powder and glass powder, laminating a plurality of sheets, and sintering the molded body. , the glass powder is made of an oxide, contains 40% by weight or more of silicon in terms of SiO ₂ and 40% by weight or less of aluminum in terms of Al ₂ O ₃ , and the firing of a conductive paste containing molybdenum or tungsten. The present invention also provides a method for manufacturing a multilayer wiring circuit board, which has a softening temperature that allows liquid phase sintering and is characterized in that sintering is performed at that temperature. The mullite sintered body of the present invention has a softening temperature that allows liquid phase sintering at the same time as the firing of molybdenum and tungsten. By containing glass as a sintering agent, when the glass powder interposed between the mullite powders reaches a temperature higher than the softening point of the glass, the entire part softens almost simultaneously, flows, and forms the mullite powder. It is a homogeneous sintered body with no surrounding pores. A multilayer wiring circuit board is obtained.Also, by sintering with glass as a sintering aid, liquid phase sintering is performed at a relatively low temperature of 1400 to 1600°C, which is the firing temperature of molybdenum and tungsten paste. Moreover, it can be sintered by a short firing process. The glass used in the present invention may be any glass that satisfies the functions and effects described above. That is, it is a solid solution that has a softening point lower than the melting point of mullite and can flow almost simultaneously as a whole. That is, _SiO2
Aluminum silicate as a material containing 40% by weight or more of silicon in terms of Al ₂ O ₃ and 40% by weight or less of aluminum in terms of Al 2 O 3 and having a softening temperature that allows liquid phase sintering at the same time as molybdenum or tungsten sintering. Glasses mainly composed of aluminum and magnesium silicate are used. Particularly desirable is one having a coefficient of thermal expansion comparable to or smaller than that of mullite. Specifically, it has a coefficient of thermal expansion of about 10 to 45×10 ⁻⁷ /°C. This makes it possible to obtain a sintered body whose coefficient of thermal expansion approximates that of a silicon semiconductor element when used as a substrate for a semiconductor element. If the coefficients of thermal expansion of the ceramic substrate and silicon are the same, the stress when silicon is soldered to the ceramic substrate can be reduced and the reliability of the soldered joint can be increased. The amount of glass to be used is the amount necessary for sintering, but generally a range of 2 to 30% (by weight) is appropriate. If an extremely excessive amount is used, there is a risk that the adhesive may adhere to the baking table used during baking or the shape may be significantly deformed. Mullite powder and glass powder with smaller particle sizes are generally more useful. Generally, it is preferable to use a material that passes 325 meshes. Of course, it is not limited to this. If large particles are used, the contact area between the mullite powder, glass powder, and mullite powder will decrease, reducing reactivity and sinterability, so it is necessary to increase the firing temperature or increase the firing time. . In addition, pores interposed between particles tend to remain. Firing can be satisfactorily achieved in the range of 1400 to 1600°C. The lower the softening point of the glass used, the lower the firing temperature can be. In the present invention, a mixture of mullite powder and a sintering aid containing glass powder may be pressurized prior to firing, if necessary, so that a more dense sintered body can be obtained. The above mixture also contains a binder commonly used in the production of ceramics,
Plasticizers, solvents, etc. can be used.
For example, as a binder, polyvinyl alcohol,
Synthetic resins such as polyvinyl butyral and polymethacrylic acid, dioctyl phthalate as plasticizers,
Methanol, trichlene, toluene, etc. are used as the solvent. Next, a method for manufacturing a multilayer wiring circuit board will be explained. First, mullite powder and glass powder are weighed out in a predetermined ratio, and a binder, a solvent, etc. are added thereto to form a slurry. Next, the slurry is applied onto a support such as a polyester film, adjusted to a desired thickness using a doctor blade, etc., and dried to form a so-called green sheet. This green sheet is provided with through holes for connecting conductor circuits, and molybdenum or tungsten paste as conductor circuits is printed on the inner surface of the through holes and in accordance with the circuit pattern. The green sheets thus produced are stacked and fired in a neutral or reducing atmosphere. The reason for firing in a reducing atmosphere is to prevent tungsten or molybdenum used in the conductor circuit from being oxidized and volatilized. Generally, it is appropriate to use a forming gas that is a mixture of nitrogen and hydrogen. Further, when additives such as binders or plasticizers are used for molding, it is desirable to include water as an oxidation source in the gas in order to oxidize and decompose the additives. When firing in a reducing atmosphere, if glass powder containing an oxide that is easily reduced, such as lead oxide or titanium oxide, is used, there is a risk that the insulation of the sintered body, that is, the substrate, will be reduced. Therefore, it is preferable that the glass powder is substantially free of such compounds. Ceramic multilayer wiring circuit boards manufactured by firing include ICs,
LSI and other electronic components are incorporated. Next, examples of the present invention will be shown. In each of the following examples, "part" means part by weight, and "%" means weight %. Example 1 Mullite powder passed through 325 mesh (3Al ₂ O ₃
2SiO ₂ , thermal expansion coefficient 45×10 ^-7 /℃) 90 parts, glass powder having the following composition (thermal expansion coefficient 30×10 ^-7 /℃)
Place 10 parts in a ball mill and dry mix for 3 hours.
Furthermore, 5.9 parts of polyvinyl butyral, 2.4 parts of dioctyl phthalate, 23 parts of trichlorethylene,
Add 9 parts perchlorethylene and 6 parts butyl alcohol and mix for 3 hours to form a slurry.
Air bubbles are removed from the slurry by vacuum degassing. The slurry was then deposited onto a linear saturated polyester film support using a doctor blade.
Coat to a thickness of mm and dry using an infrared lamp to create a green sheet. this sheet
After cutting to a size of 70 x 70 mm, through holes are punched at predetermined positions, and a conductive paste having the composition shown below is printed in a predetermined circuit pattern using a screen printing method. The conductive paste was also filled into the through holes for connection between layers. The composition of the glass powder is SiO ₂ : Al ₂ O ₃ : MgO=51.3:
34.9:13.8 (weight ratio), the composition of the conductor paste is molybdenum powder: nitrocellulose: ethyl cellulose: polyvinyl butyral: trichlene = 100:
The weight ratio was 3:1:2:23. Six of the above green sheets printed with conductive paste were stacked with the guide holes aligned, and heated to a temperature of 90°C.
Pressure was applied and bonded at ℃. Next, the stacked green sheets are placed in a firing furnace in a nitrogen atmosphere containing 3 to 7% by volume of hydrogen and a trace amount of water vapor.
It was fired at a maximum temperature of 1550°C for 1 hour. In this way, a multilayer wiring circuit board having six conductor layers was manufactured. The coefficient of thermal expansion of this circuit board is 38×
10 ^-7 /℃, the dielectric constant of ceramics is 5.5,
The state of bonding between each layer was also good. There were no disconnections or shorts in the conductor circuit due to the generation of pores during firing, and the mechanical strength was sufficient. Furthermore, since the thermal expansion coefficients of the ceramic substrate and the semiconductor element (silicon chip) are similar, the reliability of the joint is extremely high when the semiconductor element is directly joined to the circuit board by soldering. Example 2 Mullite powder: 70 parts Glass powder: SiO ₂ 55%, Al ₂ O ₃ 30%, MgO 9%,
CaO6%, thermal expansion coefficient 42×10 ^-7 /℃30 parts Conductor paste: 100 parts tungsten powder, 3 parts nitrocellulose, 1 part ethyl cellulose,
2 parts of polyvinyl butyral, 23 parts of trichlorethylene Thickness of green sheet: 0.25 mm Number of stacked green sheets: 10 Firing conditions: 1550°C, 1 hour Example 1 except for the above changes.
A ceramic multilayer wiring circuit board was manufactured in the same manner as described above. The obtained circuit board had a thermal expansion coefficient of 44×10 ^-7 /°C and a ceramic dielectric constant of 5.9, and a dense circuit board with good bonding between each layer was obtained. Example 3 Ceramic substrates were prepared in the same manner as in Example 1, considering various compositions of glass and the mixing ratio of mullite and glass. The measurement results of thermal expansion coefficient and dielectric constant are shown in the table below.

[Table] As is clear from the table, the coefficient of thermal expansion of the circuit board (sintered body) is 38 to 45 × 10 ^-7 /°C, and the reliability of the joint when the element is directly bonded with solder is close to that of a silicon semiconductor element. It also has a low dielectric constant of 6 or less, making it possible to speed up signal transmission in circuits.
Furthermore, it is sufficiently satisfactory as a ceramic material for multilayer wiring circuit boards in terms of electrical insulation, mechanical strength, and density. For example, the bending strength is 1100 to 1500
It is high at Kg/cm ² .

Claims (1)

[Claims] 1. A method in which a circuit is formed using a conductive paste containing molybdenum or tungsten on a molded body having a composition excluding organic substances and containing 70% by weight or more of mullite powder and glass powder, and a plurality of sheets are laminated and sintered, the method comprising: The powder consists of oxides, converted to SiO ₂
Contains 40% by weight or more of silicon and 40% by weight or less of aluminum in terms of Al ₂ O ₃ , has a softening temperature that allows liquid phase sintering at the same time as the firing of the conductive paste containing molybdenum or tungsten, and at this temperature A method for manufacturing a multilayer wiring circuit board characterized by sintering.