JPS6146097A - Multilayer circuit board - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a multilayer circuit board suitable for high-density mounting of thick film components, ICs, LSIs, and the like.

Conventional configurations and their problems In recent years, demands for smaller devices and multi-functionality have become stronger over the years.In order to meet these demands, high-density mounting of circuit components has become an important technology. There is. In particular, rc,
With the development of LSI and thick film technology for resistors, capacitors, etc., the mounting density of circuit components is becoming increasingly high. 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 an insulating layer made of alumina and molybdenum (Mo),
Some have conductor layers laminated alternately.

However, this has the following problems.

■ To enable soldering of components, nickel, nickel, or
It is necessary to plate it with gold or other material.

■ In order to form glaze resistance elements and capacitor elements as thick film elements, high temperatures (80Q to 900Q) are required in air.
'C) Processing is required, but conductive materials that are easily oxidized such as tungsten and molybdenum cannot be processed in an oxygen atmosphere, making them unsuitable as circuit boards on which thick film elements are directly formed.

For these reasons, the range of use of the alumina multilayer wiring board is limited, and the alumina multilayer wiring board does not have sufficient conditions as a board for high-density mounting.

On the other hand, in order to enable the formation of a thick film in air at high temperatures on a multilayer substrate made of alumina and tungsten or molybdenum as described above, small holes are provided at necessary locations on the top layer of the multilayer substrate. A structure has been proposed in which a conductive filler made of a low-melting glass and a noble metal that is not reduced to tungsten is formed. In this multilayer circuit board,
Since a low melting point glass that is not reduced to tungsten is used as the glass component of the conductive filler, the conductive sintered layer is not oxidized even at high temperatures in the air, and good electrical conductivity can be obtained. By using this filler material, thick film elements such as resistors and capacitors can be formed on the top layer in air, and trimming of thick film resistors using a laser is also stable because the base is made of high alumina. It offered great features such as the ability to perform

However, this conductive filler is generally printed in the form of a thick paste on the exposed surface of a sintered tungsten or molybdenum conductor and fired in air at a high temperature of around 860°C. However, the following major problems arose during firing. In other words, this coating material (synonymous with filler)
Due to the principle of air-blocking, the glass component contained in the paste must soften quickly and cover the conductor surface at as low a temperature as possible during firing, but the large amount of organic binder contained in the paste is difficult to fly away at low temperatures. If there is a large amount of Baka9 remaining, it will hinder the fluidity of the glass at high temperatures, and as a result, the coating effect of the coating material will be reduced. For this reason,
In reality, priority is given to binder combustion, and the surface of the sintered conductor layer is oxidized to some extent.

This oxidized layer (WO2) ζ~ exhibits semiconducting properties electrically, so although frequent conduction is ensured, oxidation gradually progresses and ultimately becomes the internal electrode. Conductivity between the upper layer electrodes will no longer be obtained. This tendency is particularly accelerated under harsh conditions (humidity, high temperature atmosphere).

As mentioned above, multilayer substrates are very important as substrates for mounting components, but conventional multilayer substrates made of alumina and tungsten or molybdenum are filled with glass that does not oxidize tungsten. However, the method of forming a conductive filler made of a noble metal cannot sufficiently prevent oxidation of the internal conductor layer, and therefore a highly reliable multilayer circuit board cannot be obtained.

OBJECTS OF THE INVENTION The purpose of the present invention is to realize a structure that does not require plating on soldering electrode pads as well as high-density component mounting boards, and allows the formation of thick film elements such as glaze resistor elements. Another object of the present invention is to provide a highly reliable multilayer circuit board that simplifies the manufacturing process and reduces costs.

Structure of the Invention The multilayer circuit board of the present invention has electrical insulating layers mainly composed of alumina and conductive layers made of tungsten or molybdenum metal alternately laminated, and the uppermost insulating layer has an average grain size of 3 to 70 μm. A material consisting of a low-melting glass that cannot be reduced to tungsten or molybdenum and a noble metal is formed on the exposed part of the internal conductor layer, and the uppermost wiring layer is formed using the same material. A glaze resistance element is formed on the wiring layer, and silver-palladium conductor pads for mounting components and attaching a lead frame are formed. This makes it possible to provide a highly reliable multilayer circuit board that does not require plating for soldering and is equipped with thick film elements, making it possible to produce a high-density packaging circuit module.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention. 1.2
and 3 is an alumina insulating layer, 4 and 6 are tungsten or molybdenum conductor layers, 6 is a coating material made of 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 thickness It is a membrane resistance element.

A specific example is shown next.

A green sheet consisting of an inorganic powder containing alumina as a main component and a sintering aid added thereto, PVB (polyvinyl butyral), and a plasticizer was produced by a doctor blade method. To this, an appropriate amount of ethcel-based vehicle was added and mixed into a conductor mixture containing tungsten or molybdenum as a main component and a conductor sintering aid. In this step, a hole with a diameter of 300 μm was provided in the uppermost alumina layer so as to expose a portion of the lower tungsten conductor layer. This'11660-166
It was fired in a reducing atmosphere at 0°C. The shrinkage rate of the substrate after sintering is approximately 16%, and the average sintered grain size measured by planimetric method from SEM photographs of exposed parts of tungsten and molybdenum conductors is 3 to 70 μm, indicating that the sintered state is very good. It was very detailed. .

Next, the surface pores of the sintered multilayer structure have a softening point of about 640.
Paste foam consisting of glass powder and silver powder with B2O3 and BaO'i as main components at °C! J-printing was carried out to form a pattern that covered the holes in the uppermost alumina layer and had extended portions that would serve as electrodes for resistive elements. This has a bell-shaped temperature profile with a peak temperature of 850'
It was passed through a thick film firing furnace of C. Next, a ruthenium-based glaze resistive film and an Aq-Pd conductive film were printed and formed into the required pattern, and passed through the same thick film firing furnace as above.

In the circuit board thus obtained, the conductive layer of the covering material made of silver-glass material adhered firmly to the surface of the board, and electrical continuity with the lower conductive layer was sufficiently ensured. When the electric resistance (Rc) between the lower conductor layer and the upper electrode (between 4 and 7 in FIG. 2) was completely evaluated, it was about 3 to 6 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 a conventional one using Aq-Pd as an electrode, and exhibited extremely good matching properties. In addition, Aq-Pd for covering material and component mounting
The electrical conductivity at the electrode interface also showed excellent characteristics, and no phenomenon of increased resistance at the interface was observed.

Furthermore, in order to examine the stability of the coating portion of this circuit board, the electrical resistance Rc was also measured after being left in an atmosphere of 86° C. and 86% relative humidity for an ioo period of time. Table 1 shows typical values for a conventional circuit board and a circuit board according to the present invention for comparison. Further, Table 2 shows the average particle size of the exposed conductor portion of the sample obtained in the specific example and the electric resistance Rc (Ω) between the electrode layers.

Table 1 Table 2 [- "As shown in Table 1, conventional multilayer boards initially provide low-resistance conduction, but this changes greatly when left in humidity, sometimes resulting in disconnection. .This is because the particle size is small.
This is thought to be because the neck between the tungsten or molybdenum particles is small in the sintered conductor layer, and the surface of the exposed conductor is especially rough, so the coating efficiency with low softening point glass is poor and the conductor oxide layer becomes thick. On the other hand, the particles in the conductor layer of the multilayer circuit board according to the present invention are not only large and have a high glass coating effect, but also the conductor particles themselves are less susceptible to oxidation than fine particles. Therefore, the coating layer can maintain good conductivity even under severe conditions such as being left in humidity.

This can also be confirmed from Table 2. In order to promote grain growth of tungsten particles or molybdenum particles, there is a method of adding several kinds of sintering aids (sample numbers 1 to 7), and a method of performing firing at high temperature for a long time (sample numbers 8 to 10).
However, it can be seen that there is no significant difference in the stability of the coating material. If the average particle size is 3 μm or more, the coating material will be stabilized, but 7
If it is larger than 0 μm, an imbalance in the sinterability between the conductor and the alumina substrate will occur, and the adhesion of the conductor will deteriorate, making it unsuitable for use as a circuit board.

The relationship between the average particle diameter of the conductor and the electrical resistance Rc after 100 hours at 86 DEG C. and 186% RH is shown in FIG. 3 in the shaded range for Comparative Examples and Examples.

As described in detail, according to the present invention, a multilayer structure is adopted in which dense tungsten or molybdenum with a large particle size is used as the inner conductor layer, and alumina is used as the interlayer insulating layer. The electrical conduction between the resistive element and the conductive layer formed on the surface layer is made of precious metals and glass materials that are stable even at high temperatures and in the air, and the structure also prevents air from penetrating into the internal conductive layer. Therefore, it becomes possible to form a thick film resistance element or a capacitor element, which is fired in air at high temperature (800-900°C), on the top layer. Moreover, since the internal wiring layer is multilayered with tungsten, it can be used not only for thick film elements but also for chip parts and I/O.
It is possible to implement C at high density. In particular, in the present invention, since the internal conductor layer is stabilized, a highly reliable multilayer circuit board 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. FIG. 3 is a characteristic diagram showing the relationship between the average grain size of the inner conductor layer and the humid air life. 1.2.3...Alumina insulating layer, 4,5...
...Tungsten conductor layer, 6...-Coating material composed of low melting point glass and noble metal that cannot be reduced to tungsten, 7,9...Aq-Pd conductor, 8-...
...Ruthenium-based thick film resistance element, 1o...Low melting point glass that is not reduced to tungsten, 11...
...Precious metal particles. Name of agent: Patent attorney Toshio Nakao and one other name
1 Figure 2

Claims (2)

[Claims] (1) formed on a laminated part formed by alternately laminating an insulating layer mainly composed of alumina and a conductor layer made of tungsten metal, and an exposed conductor part provided in the uppermost insulating layer of the laminated part, a conductive coating material made of a low-melting glass and noble metal that is not reduced to tungsten and conductive to the internal conductor layer; a thick film resistance element provided on the uppermost insulating layer and having an extended portion of the coating material as an electrode; It consists of a silver-palladium-based conductor pad for mounting electronic components electrically connected to the extension part, and is characterized in that the average grain size of the tungsten sintered layer in the exposed part of the conductor is in the range of 3 to 70 μm. Multilayer circuit board. (2) The multilayer circuit board according to claim 1, wherein the conductor layer is molybdenum.