JPS6351690A - Manufacture of ceramic wiring board - Google Patents

Abstract

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

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for manufacturing a ceramic wiring board used as a high power circuit board.

[Background technology]

In general, wiring boards used for high power applications require thick conductor layers that form conductive circuits in order to allow large currents to flow or to provide heat dissipation properties.

Conventionally, the following method has been used to manufacture ceramic wiring boards used for high power applications.

(2) A method in which a ceramic substrate and a conductive plate having a desired thickness are prepared, and then heat treated at a temperature higher than the eutectic temperature at which they form a eutectic alloy to bond them together to form a wiring board.

■ Chemically roughen the surface of the ceramic substrate, apply electroless plating to the surface to deposit a conductor layer, and
A method of applying electroplating to the desired thickness.

(2) A method of applying metal to a desired thickness by electroplating on the metal portion of a ceramic substrate that has been previously meclized by the so-called Telefunken method. However, all of these methods have the following drawbacks. That is, in method (2), it is difficult to control the temperature or atmospheric gas during heat treatment, and therefore the production yield is low. Methods (1) and (2) use electroplating to thicken the conductor layer, so the deposition rate is slow and it takes a very long time to obtain the desired thickness. In addition, it is also difficult to form a conductor layer with a uniform thickness.

Therefore, it has been desired to develop a method for efficiently depositing a thick conductor layer on the surface of a ceramic substrate.

[Purpose of the invention]

In view of the above points, it is an object of the present invention to provide a method for manufacturing a high-power ceramic wiring board and a Vil board with high productivity.

[Disclosure of the invention]

In order to achieve the above object, the present invention provides a ceramic substrate, characterized in that, when thickening a conductor layer that becomes a conductive circuit on the surface of a ceramic substrate, the conductor layer is thickened by thermal spraying a conductive material. The main topic is the manufacturing method of wiring boards.

This will be explained in detail below with reference to the accompanying drawings, one embodiment of which will be described below.

FIG. 1 shows a method for manufacturing a ceramic wiring board according to the present invention.

First, a smooth sintered ceramic substrate is prepared. The materials used for such sintered substrates include oxide ceramics such as alumina, forsterite, steatite, zircon, mullite, cordierite, zirconia, and titania, as well as various carbide and nitride ceramics. . In this case, the surface roughness of the ceramic substrate is preferably as small as possible. That is, its surface roughness Rmax is 3μ
It is desirable that it is less than m, more preferably 1.5μ
m or less. If the surface roughness of the ceramic substrate is like this, as will be explained later, when a thick conductor layer is applied to the substrate by thermal spraying, it is difficult to attach thermally sprayed metal (conductive material) to the areas with this surface roughness. This is convenient because it does not occur. Next, a base having the same pattern as the conductive circuit is formed on the surface of the ceramic substrate. This portion has an appropriate surface roughness to allow the adhesion of the sprayed metal, and is formed on the smooth surface of the ceramic substrate by chemical or physical means. For example, Cu
It is formed by screen printing the same pattern as the conductive circuit using a conductive paste containing a conductive material such as and a glass component, and then firing it. When the conductive paste is fired, the glass component contained in the paste migrates to the interface between the substrate and the base and precipitates, resulting in a rough surface.

On the other hand, the base may be formed using the so-called Telefunken method. In other words, a metal paste containing a high melting point metal is screen printed on a ceramic green sheet,
The ceramic sheet and the metal paste are fired simultaneously. In addition, as the isoelectric paste, Cu
In addition, materials containing four electrical materials such as Ag, Au, and Ag-Pd are often used, but the material is not particularly limited to any one of them. In short, it is sufficient that the paste contains a conductive material and a glass component that roughens the surface during firing.

Furthermore, the base may be formed by placing a mask having a pattern opposite to the conductive circuit pattern on the ceramic substrate and roughening the surface using a phosphoric acid solution or the like.

After forming a base on the substrate as seen above, a conductive material is sprayed onto the base using a thermal spraying method to thicken the conductor layer that will become the conductive circuit. In this case, the sprayed conductive material will adhere to the pre-formed base. That is, in this case, as seen above, since the surface roughness of the ceramic substrate is small, it is difficult for the thermal spray material to adhere to this portion. In other words, the thermally sprayed conductive material adheres only to the base portion forming the same pattern as the conductive circuit, thereby creating a ceramic wiring board. Note that the entire surface of the ceramic substrate is roughened,
A mask having a pattern opposite to the circuit pattern may be placed on the surface of the substrate, and thermal spraying may be performed from that surface.

If, for example, a power IC or the like is to be mounted on the ceramic wiring board thus produced, it is necessary to minimize the roughness of the sprayed conductor layer. In such a case, for example, as shown in the first picture, after applying electroplating to the thermally sprayed conductor layer, use a polisher to reduce the surface roughness to a smooth surface of about 1 to 2 μm. In the manufacturing method of the ceramic wiring board according to the present invention, which requires only surface preparation, as shown above, the conductor layer is thickened by thermal spraying, so it is not necessary to thicken it by electroplating as in the conventional method. This means that the desired thickness can be achieved in a much shorter period of time than would otherwise be possible. Moreover, since a normal thermal spraying method can be used as is, the work is easy and the production cost is correspondingly low.

Next, examples will be described together with comparative examples.

(Example 1) A 96% Al z O3 plate with a surface roughness Rmaxl of 5 μm was prepared as a ceramic substrate. As the thin paste, an inexpensive Cu paste was used, which contains Cu and has excellent electrical conductivity and heat dissipation. On this board,
A base was formed according to the manufacturing process shown in FIG. however,
In the figure, electroplating and surface preparation steps were not performed after thermal spraying of the conductive material. As shown in FIG. 2, a base 2 was formed on a substrate 1 by a screen printing method, and then heated and fired at 800 to 950° C. in an N2 gas atmosphere. The thickness of the base 2 after firing was about 20 μm.

Next, thermal spraying was performed on this by a conventional method to form a thermal sprayed layer 4. That is, the base 2 formed by screen printing and then baking was thickened. Cu was used as the thermal spraying material. When the thermal spraying was performed, the thermally sprayed Cu did not adhere to this part because the surface roughness of the substrate was small and smooth, but only to the base 2 on which the Cu paste was fired.

The thermal sprayed layer 4, which is a conductive layer, obtained by this thermal spraying method had a thickness of 250 μm and was uniform. The thermal spraying time required for this thickening was about 1 minute. The sprayed layer thus formed also had good heat dissipation properties.

(Example 2) In the same manner as in Example 1, a ceramic substrate was formed and fired, and then a sprayed layer was formed on the ceramic substrate.The ceramic substrate was electroplated so that electronic components such as power ICs could be mounted thereon, and its surface was Polishing (surface preparation) was performed. That is, as shown in FIG.
After lightly bonding the two thermally sprayed layers 4.4 with metal wires 6, a normal Cu plating method was performed while masking the areas other than the top surfaces of these thermally sprayed layers 4.4. That is, this substrate was energized at 3 A/dm for 7-10 minutes to form the Cu plating layer 5 only on its upper surface. Then, the metal wire 16 was removed and its surface was polished by about 2 μm using a polisher to obtain a smooth surface with a surface roughness Rmax of 2 μm.

The time required for thickening, including thermal spraying, was approximately 12 minutes. (Example 3) W-Mo paste was screen printed on a green sheet of a 96% A1zCh substrate, and A p, z Off 'S
The plate and W-Mo paste were co-fired at about 1500°C.

The surface roughness Rmax of the AA203 substrate after firing is 1.8
It was μm.

Next, Cu was thermally sprayed under the same conditions as in Example 1 to a thickness of 2.
A sprayed layer of 50 μm was obtained. The time required for thermal spraying was about 1 minute.

(Comparative Example) After appropriately roughening the surface of a ceramic substrate, Cu was deposited by electroless plating, and the surface was thickened by electroplating. The thickness of Cu plating at this time is 250
It was μm. The time required to form such a conductor layer was about 100 minutes.

As seen above, the method for manufacturing a ceramic wiring board according to the present invention takes about 1/10 to 1/100 times less time than the conventional method of thickening a conductor layer by electroplating.
I was able to shorten it to /100.

〔Effect of the invention〕

Since the method for manufacturing a ceramic wiring board according to the present invention has the above-described structure, it is possible to reliably thicken the conductor layer in a much shorter time than with conventional electroplating methods. , it is possible to manufacture high-power wiring boards with high productivity.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing an example of the method for manufacturing a ceramic wiring board according to the present invention, and FIG. bl is a partial front view of the same figure fa), FIG. It is a partial front view. 1... Ceramic substrate 4...? Reflective layer (conductor layer)
Agent Patent Attorney Takehiko Matsumoto Figure 1

Claims (2)

[Claims] (1) A method for manufacturing a ceramic wiring board, characterized in that the thickness of the conductor layer forming a conductive circuit is increased by spraying a conductive material on the surface of the ceramic substrate. (2) The surface roughness Rmax of the ceramic substrate is 3 μm or less, and a metal paste containing a glass component is screen printed on the surface in advance in the same pattern as the conductive circuit, and then this substrate is fired. A method for manufacturing a ceramic wiring board according to claim 1, wherein the ceramic wiring board is thermally sprayed.