JPH0544200B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a multilayer circuit board that can be widely used as a high-density mounting board for circuits in electronic devices, etc., and a method for manufacturing the same.

Conventional configurations and their problems In recent years, there has been a growing demand for electronic devices to be smaller and more multifunctional. In order to meet this demand, high-density packaging of circuit components used in electronic devices and the like has become an important technology. In order to realize high-density mounting of circuit components, it is necessary to reduce the size of the circuit components and at the same time increase the wiring density of the circuit board. In order to increase the wiring density of the circuit board, it is most effective to make the circuit board a multilayer structure and form a wiring layer, that is, a conductor layer inside the board.

Conventionally, as a multilayer circuit board for high-density mounting,
A conductor layer (inner conductor layer) of a high-melting point metal such as tungsten or molybdenum and an electric insulating layer are alternately laminated on an electric insulating substrate mainly composed of alumina.
There are multilayer circuit boards manufactured by sintering in a reducing atmosphere.

In such conventional multilayer circuit boards and their manufacturing methods, when connecting such multilayer circuit boards to other components by soldering or wire bonding with metal wires or aluminum wires of semiconductor ICs and transistors, the tungsten or molybdenum is oxidized. Because it is easily damaged, it was necessary to plate a protective layer of nickel, gold, etc. on top of it. In addition, forming resistors such as glaze resistors, which are thick film components of the multilayer circuit board, generally requires sintering in air at a high temperature of 800 to 900°C, so they are formed from conductive materials that are easily oxidized, such as tungsten or molybdenum. It has been difficult to form thick film components, such as thick film resistors and thick film conductors, on multilayer circuit boards.

For this reason, in order to be able to form thick film resistors and thick film conductors in the air at high temperatures on a multilayer circuit board sintered in a reducing atmosphere as described above, the necessary parts of the uppermost insulating layer of the multilayer circuit board are That is, there is a multilayer circuit board in which small holes are provided at locations where thick film conductors and thick film resistors are to be formed, and the exposed inner conductor layer is filled with a noble metal such as platinum or palladium and sintered.

However, when forming thick film resistors and/or thick film conductors on multilayer circuit boards using precious metals such as those mentioned above, it is necessary to sinter them in air at a high temperature of 800 to 900 degrees Celsius. , as confirmed by the present inventors, platinum and/or
Also, the adhesion between palladium and an insulating layer such as an alumina layer is not sufficiently high, and
When treated at 900°C, air gradually enters the interface between platinum and/or palladium and alumina, oxidizing the internal conductor layer, that is, the molybdenum or tungsten layer, making it unsuitable for practical use. .

For this reason, one method of forming thick film resistors and thick film conductors on a multilayer circuit board is to form an internal conductor layer of tungsten or molybdenum and then sinter it in a reducing atmosphere at 500-600°C in air. A method using a special low-temperature sinterable thick film conductor and thick film resistor paste that can be sintered at a relatively low temperature;
Alternatively, there is a method of forming with a paste using a resin that hardens at around 200°C. However, these low-temperature sintered thick film resistors and resin resistors are
Compared to the thick-film resistor formed at a sintering temperature of 800 to 900°C, the resistor's electrical properties and environmental resistance are inferior, which limits its range of use as a circuit. . For this reason, the above-mentioned high temperature sintering is preferable for forming thick film resistors and thick film conductors.

OBJECT OF THE INVENTION An object of the present invention is to provide a multilayer circuit board having a thick film resistor and a thick film conductor, which does not cause deterioration of internal conductor layers and is highly reliable as a multilayer circuit board used for high-density packaging, and a method for manufacturing the same. It is about providing.

Structure of the Invention The present invention is characterized in that internal conductor layers and electrical insulating layers made of tungsten or molybdenum are alternately laminated on an electrically insulating substrate mainly composed of alumina, and a thick film conductor and In a multilayer circuit board formed with a thick film resistor, a small hole through which the internal conductor layer is exposed is provided in the outermost insulating layer, and a low melting point glass material that is not reduced by tungsten or molybdenum is provided in the small hole portion. The multilayer circuit board is provided with a conductor layer filled with a conductor material consisting of and a noble metal, and on which the thick film conductor and thick film resistor are provided.

Further, the present invention forms a bioelectrical insulating substrate mainly composed of alumina, and alternately forms internal conductor layers and electrical insulating layers made of tungsten or molybdenum on the bioelectrical insulating substrate, and at this time, the inner conductor layer and the electrically insulating layer made of tungsten or molybdenum are alternately formed. A small hole through which the inner conductor layer is exposed is provided in the outer layer, and then these are simultaneously sintered at high temperature in a reducing atmosphere, and then a low melting point glass material and a noble metal that are not reduced by tungsten or molybdenum are filled in the small hole area. A method of manufacturing a multilayer circuit board includes filling a conductor material to form a conductor layer, forming a thick film conductor and a thick film resistor thereon, and then sintering the whole in air.

DESCRIPTION OF EMBODIMENTS Examples of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a multilayer circuit board according to the present invention.

In FIG. 1, reference numeral 1 denotes an electrically insulating substrate containing alumina as a main component. and a synthetic resin such as polyvinyl butyral as a binder and a plasticizer, which is then processed by doctor blading or other known methods to form a green electrically insulating substrate. This insulating substrate may be in the form of a sheet, a film, or a relatively thick plate, but is preferably in the form of a sheet in order to make the finished product as thin as possible.

Next, the bioelectrical insulating substrate 1 made as described above
A conductor paste consisting of tungsten powder or molybdenum powder, an organic binder such as polyvinyl butyral, and a solvent is printed on top in a desired shape to form the inner conductor layer 2, and then the same material as that used for forming the electrically insulating substrate is applied. The electrical insulating layer 3 is formed by printing. Next, the internal conductor layer 2 described above
A second inner conductor layer 2' is formed in communication with the inner conductor layer 2 in the same manner as above, and an electrically insulating layer 3' is formed in the same manner as the electrically insulating layer 3 described above. In Fig. 1, an example is shown in which the above lamination is carried out twice.
It will be appreciated that this can be constructed in many more layers or layers if desired. Although FIG. 1 shows the case where the internal conductor layers 2, 2', . . . and the electrical insulating layers 3, 3', . A conductive layer and an electrically insulating layer may be similarly formed on the opposite side of the substrate 1.

A small hole a is provided in the uppermost layer (3' in the figure) of the electrically insulating layer produced as described above to expose the underlying internal conductor layer (2' in the figure).

Next, the bioelectrical insulating substrate 1, the internal conductor layers 2, 2',
. . . and the electrical insulating layers 3, 3', .
℃ to sinter the whole.

As described above, the small holes a formed in the electrically insulating layer 3' of the multilayer circuit board sintered in a reducing atmosphere are filled with a conductive material made of a low melting point glass material and a noble metal that cannot be reduced by tungsten or molybdenum. Then, a conductor layer 4 is formed. The conductor layer 4 used here has electrical conductivity with the internal conductor layer 2' described above, and is used in the air to be used for forming the thick film conductor and thick film resistor that will be formed later on. It is necessary to have the property that it will not be oxidized during processing at high temperatures, and that it will protect the tungsten or molybdenum of the inner conductor layer 2' from being oxidized, and therefore will not be reduced by the tungsten or molybdenum.

When a commonly used lead-based glass material is used as the material for the conductor layer 4, this material causes an oxidation reaction of tungsten or molybdenum in the inner conductor layer 2' in high-temperature air, and at the same time a reduction reaction of the main component lead oxide. oxidation of the internal conductor layer 2' cannot be prevented.
It was found that electrical conductivity was impaired. Therefore, in the present invention, the glass material for forming the conductor layer 4 is made of an alkaline earth metal oxide, such as magnesium oxide, calcium oxide, or barium oxide, and a metal oxide of group 3 of the periodic table, such as boron oxide or aluminum oxide. It was found that it is better to use . Each of these may be used alone or in the form of a mixture. Such a glass material has the property of not oxidizing tungsten or molybdenum, in other words, not being reduced by tungsten or molybdenum. In the present invention, in order to obtain electrical conductivity of the conductor layer 4, the above-mentioned glass material is coated with noble metals such as silver, platinum, gold and/or
Or mix and disperse palladium powder. It has been found that by doing so, electrical conductivity can be obtained through contact between the noble metal particles, and stable electrical conductivity can be obtained without oxidation of the internal conductor layer 2'. When forming the conductor layer 4, the above-mentioned glass material and noble metal powder are added as a sintering aid.
A conductive paste consisting of SiO ₂ , a binder, and a solvent was prepared, and small holes a were filled with this by printing. After drying, it was passed through a belt furnace at a maximum temperature of 850°C and fired in air to form a conductor layer 4. In this state, the conductor layer 4 is firmly fixed to the small hole a, and electrical continuity with the inner conductor layer 2' is achieved.

Next, according to the present invention, a thick film conductor 5 is formed on the conductor layer 4 formed as described above. This thick film conductor 5 constitutes the connection and wiring parts of thick film resistors, ICs, transistors, capacitors, and other electrical components, and is made of a known silver-palladium conductor paste, such as Ag56% by weight, Formed by printing a paste containing 14% by weight of Pb and 30% by weight of glass and other materials. After drying, it is passed through a belt furnace at a maximum temperature of 850°C and sintered in air.

Next, a thick film resistor 6 is formed on the thick film conductor 5.
The thick film resistor 6 is a resistor component made into a thin film in order to obtain a highly reliable, compact, and high-density multilayer circuit board.
The material is a well-known ruthenium oxide paste that is printed, dried, and sintered in the air through a belt furnace with a maximum temperature of 850°C.

As described above, a multilayer circuit board according to the present invention is manufactured.

Note that the multilayer circuit board produced as described above may be provided with a protective coating of glass or resin.

The material used for the thick film conductor 5 is silver-
In addition to palladium, other known materials such as silver, silver-platinum, and gold can also be used. When sintering the conductor layer 4, thick film conductor 5, and thick film resistor 6, the maximum temperature of 850°C is shown as an example, but the maximum temperature of 600 to 900°C may be used as appropriate depending on the respective conductor paste materials and resistor paste materials. It could be selected and sintered in air without any negative effect on the properties of the finished multilayer circuit board.

Effects of the Invention As explained above, the present invention provides a conductor made of a low-melting glass and a noble metal that is not reduced by tungsten or molybdenum in a small hole in an insulating layer provided so that a necessary part of an internal conductor layer made of tungsten or molybdenum is exposed. Filled with materials, the tungsten or molybdenum in the inner conductor layer is not oxidized during high temperature sintering in air when forming thick film conductors and thick film resistors, making it extremely common, An excellent effect can be obtained in which thick film conductors and thick film resistors can be formed in a conventional manner with stable process control.

Furthermore, in the multilayer circuit board according to the present invention, since the wiring is multilayered with internal conductor layers, the wiring density can be extremely increased, and the resistance components are formed as a film using thick film resistors, so it is small and has high performance. It is a high-density circuit board, and has a large effect in contributing to the miniaturization and high density of electronic devices.

Furthermore, unlike conventional reduction-fired multilayer circuit boards, the multilayer circuit board of the present invention does not require plating for solder connection of components and wire bonding of semiconductor ICs. In addition, unlike the case where a thick film resistor is formed on an insulating layer made of a glass material such as in a conventional thick film multilayer circuit board, the resistor can be formed easily and stably, and the insulating layer can be formed by laser trimming the resistor. There is no damage to the process, process conditions are extremely easy to control, and productivity is greatly improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a multilayer circuit board according to the present invention. 1 is an electrically insulating substrate, 2, 2', ... are internal conductor layers, 3, 3', ... are electrically insulating layers, a is a small hole, 4
5 is a conductor layer, 5 is a thick film conductor, and 6 is a thick film resistor.

Claims (1)

[Claims] 1. On an electrically insulating substrate mainly composed of alumina,
In a multilayer circuit board in which internal conductor layers and electrical insulating layers made of tungsten or molybdenum are alternately laminated, and a thick film conductor and a thick film resistor are formed on the outermost layer of the insulating layer, the outermost layer insulating layer is A small hole through which the internal conductor layer is exposed is provided in the layer, a conductor layer filled with a conductor material made of a low-melting glass material and a noble metal that is not reduced by tungsten or molybdenum is formed in the small hole portion, and a conductor layer is formed on the layer. A multilayer circuit board, characterized in that the above-mentioned thick film conductor and thick film resistor are provided. 2. The multilayer circuit board according to claim 1, wherein the low melting point glass is composed of an alkaline earth metal oxide and a Group Group metal oxide of the periodic table. 3 Group metal oxide of the periodic table is boron oxide and/or
The multilayer circuit board according to claim 2, which is aluminum oxide. 4. The multilayer circuit board according to claim 1, wherein the noble metal is silver, platinum, gold and/or palladium. 5 A bioelectrical insulating substrate containing alumina as a main component is formed, and internal conductor layers and electrical insulating layers made of tungsten or molybdenum are alternately formed on the bioelectrical insulating substrate, and at this time, the outermost layer of the insulating layer is A small hole is provided through which the inner conductor layer is exposed, and then these are simultaneously sintered at high temperature in a reducing atmosphere, and then a conductor material made of a low-melting glass material and a noble metal that cannot be reduced by tungsten or molybdenum is placed in the small hole area. 1. A method for manufacturing a multilayer circuit board, comprising: filling the conductor layer with a conductor layer, forming a thick film conductor and a thick film resistor thereon, and then sintering the entire body in air. 6. The method for manufacturing a multilayer circuit board according to claim 5, wherein the in-air sintering is performed at 600 to 900°C. 7. The method for manufacturing a multilayer circuit board according to claim 5 or 6, wherein the low melting point glass is comprised of an alkaline earth metal oxide and a periodic table group metal oxide. 8 The periodic table group metal oxide is boron oxide and/or
or aluminum oxide, the method for manufacturing a multilayer circuit board according to claim 7.