JPH0227834B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a multilayer circuit board suitable for high-density mounting of thick film circuit components, ICs, LSIs, and the like. Conventional Technology In recent years, the demand for smaller devices and multi-functionality has become stronger over the years, and in order to meet these demands, high-density mounting of circuit components has become an important technology. In particular, with the development of ICs and LSIs and the development of thick film technology for resistors, capacitors, etc., the mounting of circuit components is becoming increasingly dense. In order to realize high-density mounting of components, it is important to reduce the size of the components and simultaneously increase the wiring density of the board. The most effective way to increase the wiring density of a board is to make the board a multilayer structure and form the wiring layers inside the board. Conventional multilayer substrates include alumina and tungsten (W), or alumina and molybdenum (Mo).
There is one in which insulating layers and conductive layers are laminated alternately. Problems to be Solved by the Invention However, the above substrate has the following problems. (i) To enable soldering of components, it is necessary to plate the tungsten or molybdenum conductor layer on the surface of the multilayer board with nickel, gold, or the like. (ii) In order to form glazed resistor elements and capacitor elements as thick film elements, it is necessary to process them in air at high temperatures (800 to 900°C), but conductive materials that are easily oxidized such as tungsten and molybdenum are Since it cannot be processed in an oxygen atmosphere, it is not suitable as a circuit board on which thick film elements are directly formed. For these reasons, sufficient conditions have not been provided for an alumina multilayer wiring board. Means for Solving the Problems In order to solve the above problems, the multilayer circuit board of the present invention includes a laminated portion formed by alternately laminating insulating layers mainly composed of alumina and conductive layers made of tungsten metal; A conductive covering material made of low melting point glass and noble metal that is not reduced to tungsten and formed on the exposed conductor part provided in the uppermost insulating layer of the laminated part so as to be electrically conductive with the inner conductor layer, and the uppermost insulating layer material. Consisting of a thick film resistance element provided on the layer and using the extended portion of the covering material as an electrode, a silver-palladium conductor pad for mounting electronic components electrically connected to the extended portion, and a wiring pattern. It is what was done. Effects The present invention has the above-described structure, and since a low melting point glass that is not reduced to tungsten is used as the glass component of the conductive filler, the conductor sintered layer (tungsten or molybdenum) is not oxidized even under high temperatures in the air. Excellent electrical conductivity is obtained, and by using the filler, thick film elements such as resistors and capacitors can be formed on the top layer in air, and in addition, laser trimming of thick film resistors can also be performed on the base layer. Since it has high alumina, it can be carried out stably. Furthermore, since the coating material contains an appropriate amount of Pt, which is a highly active oxidation catalyst, the binder burns efficiently when the coating material is fired, preventing the formation of pores during glass softening, and preventing unburned resin from forming. The generation of carbide residues is prevented, the coating effect is increased, and a highly reliable multilayer substrate can be provided. Embodiments Examples of the present invention will be described below with reference to the drawings. Figure 1 shows an embodiment of the present invention, in which 1, 2, and 3 are alumina insulating layers, 4 and 5 are tungsten or molybdenum conductor layers, and 6 is a low-melting glass and noble metal that cannot be reduced to tungsten or molybdenum. 7 and 9 are silver-palladium conductors, and 8 is a ruthenium-based thick film resistance element. Next, a specific example will be shown. A green sheet made of inorganic powder mainly composed of alumina with a sintering aid added, PVB (poly vinyl butyral), and a plasticizer was created using the doctor blade method. Alternatively, a conductor paste made by adding and kneading an appropriate amount of Ethocel vehicle to a conductor mixture containing molybdenum as a main component and a conductor sintering aid, and an alumina paste having the same inorganic composition as the green sheet are alternately printed to form a multilayer structure. . In this step, a 300 μm square hole was formed in the upper alumina layer to expose a portion of the lower tungsten conductor layer. this
It was fired in a reducing atmosphere at 1550-1650°C. The shrinkage rate of the substrate after sintering was about 16%. Next, the softening point of the surface pores of the sintered multilayer structure is approximately
A paste consisting of glass powder and silver powder mainly composed of B ₂ O ₃ and BaO is screen printed at 540℃ to cover the pores of the top alumina layer and has an extension that serves as an electrode for the resistor element. formed a pattern. This has a bell-shaped temperature profile,
It was passed through a thick film firing furnace with a peak temperature of 850°C. Next, a ruthenium-based glaze resistive film and a silver-palladium conductive film were printed and formed into a required pattern, and passed through the thick film firing furnace. In the circuit board thus obtained, the conductive layer of the covering material made of silver-glass material was firmly adhered to the surface of the substrate, and electrical continuity with the lower conductive layer was sufficiently ensured. When the electrical resistance (Rc) between the lower conductor layer and the upper electrode (between 4 and 7 in FIG. 2) was evaluated, it was about 3 to 5 mΩ. Furthermore, a ruthenium-based resistance element formed using the extended portion of the covering material as an electrode showed approximately the same resistance value as that using a conventional Ag-Pd electrode, and exhibited extremely good matching properties. Also available for cladding and mounting.
The electrical conductivity at the Ag-Pd electrode interface also showed extremely good characteristics, and no phenomenon of increased resistance was observed at the interface. Furthermore, in order to investigate the stability of the coating part of this circuit board, a pressure-cutting car test (121℃ 2
48 hours later, the electrical resistance Rc was measured.
Table 1 shows the Pt content of samples obtained in specific examples,
and the electrical resistance Rc (Ω) between the electrode layers. Note that sample numbers 2 to 4 correspond to Examples of the present invention. As shown in Table 1, when the covering material of Sample No. 1 or Sample No. 5 is provided, conduction with low resistance is obtained at the initial value, but the resistance value increases after the pressure cutter test. The resistance is sometimes as high as several tens of kilohms.

[Table] This is a low-softening point glass, and among the resin components in the vehicle mixed with silver powder and Pt powder to make a paste, the resin components near the interface (between the coating material and the internal conductor layer) soften the glass. Since the glass tends to burn and scatter later, many pores are generated inside the glass after firing. It is thought that this is because these pores promote oxidation and corrosion of the internal conductor layer near the interface in high temperature and high humidity environments. In comparison, the multilayer substrate according to the present invention contains Pt, a highly active oxidation catalyst, in the coating material from 0.5 to 0.5%.
By containing 5.0 wt%, the paste-like binder (resin component) is burned and scattered before the glass softens, and then the glass softens and covers the internal conductor layer before oxidation progresses. Therefore, even under severe conditions such as the pressure-cutting test, the coating material and the internal conductor can maintain good conductivity while preventing oxidation, corrosion, etc. of the internal layer conductor. In the embodiment, the internal conductor layers 4 and 5 are made of tungsten, but molybdenum may also be used. Also, since the internal conductor layer and the covering material are in contact,
Pt and other metals (Pd, Co,
A similar effect can also be obtained by adding Ni, Mn, Ru). Effects of the Invention As explained above, the present invention includes a laminated part formed by alternately laminating an insulating layer mainly composed of alumina and a conductive layer made of tungsten metal, and a conductor provided on the top layer of the laminated part. A conductive coating material made of a low-melting glass that cannot be reduced to tungsten and a noble metal mainly composed of Ag, formed on the exposed part so as to be electrically conductive with the internal conductor layer, and a conductive coating material for mounting electronic components connected to the coating material. In a multilayer circuit board characterized by comprising a conductor pad and a wiring pattern, 0.5 to 0.5 to 0.5% of Pt, a highly active oxidation catalyst, is contained in the conductive coating formed on the exposed conductor.
By containing 5.0 wt%, the binder (resin component) in the paste is sufficiently burned and scattered before the glass softens, and then the glass softens and covers the internal conductor layer before oxidation progresses. Therefore, it is possible to form a dense structure in the firing process with less penetration of outside air and moisture that can cause oxidation and corrosion of the inner conductor.
This makes it possible to form thick film resistive elements and capacitor elements in the outermost layer, which are fired at temperatures (°C). Moreover, since the internal wiring layer is multilayered with tungsten and molybdenum, it is inexpensive, and it is possible to mount not only thick film elements but also chip parts and ICs at high density. In particular, in the present invention, since the covering material is dense and highly stable, a highly reliable multilayer substrate can be provided.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a multilayer circuit board according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of a main part of the same board. 1, 2, 3... Alumina insulating layer, 4, 5... Tungsten conductor, 6, 10... Covering material composed of low melting point glass and noble metal that cannot be reduced to tungsten, 7, 9... Ag-Pd conductor , 8... Ruthenium-based thick film resistance element, 11... Noble metal element.

Claims (1)

[Claims] 1. A laminated part formed by alternately laminating an insulating layer mainly composed of alumina and a conductive layer made of tungsten metal, and an inner layer on an exposed conductor part provided on the top layer of the laminated part. Low melting point glass that is not reduced to tungsten and Ag formed to be electrically conductive with the conductor layer
A conductive coating material made of a precious metal whose main component is
A multilayer circuit board comprising a conductor pad for mounting electronic components connected to the covering material and a wiring pattern. 2. The multilayer circuit board according to claim 1, wherein the conductor layer is made of molybdenum. 3. The multilayer circuit board according to claim 1, which is made of a non-reducible oxide containing (BaO-B ₂ O ₃ ) as the low melting point glass. 4 Pt as a noble metal in the conductive coating material from 0.5 to
The multilayer circuit board according to claim 1, characterized in that it contains 5.0 wt%. 5 Pt, Pd, Co, Ni, Mu,
The multilayer circuit board according to claim 4, which contains Ru.