JPH06291448A - Circuit pattern forming method by direct joining copper - Google Patents

Abstract

PURPOSE:To efficiently manufacture the title copper-joined circuit pattern with high precision on a ceramic substrate. CONSTITUTION:A copper plate comprising the electrically isolated parts 14 in strip shape in the circuit pattern completion time and the other parts 11, 12 in the circuit pattern shape joined to a ceramic substrate 2 are heated at the temperature near the copper melting point in the atmosphere containing oxygen. Thus, the stip shape parts 14 of the copper plate are melted away while the other parts 11, 12 are fusion-welded to the ceramic substrate 2. Through these procedures, the efficiency in the circuit pattern manufacturing step can be improved simultaneously exercising the effect of enhancing the dimensional precision and insulating characteristics of the completed circuit pattern.

Description

Detailed Description of the Invention

 [Object of the Invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic substrate such as alumina or ferrite forming an electric circuit of direct current or high frequency.

[0002]

2. Description of the Related Art A so-called plane circuit using a plastic or ceramic substrate is often used because it is advantageous for miniaturization. Especially ceramic substrates have high breakdown voltage, low loss,
Widely used from direct current to high frequency range in terms of high heat resistance. Although there are various methods of forming a circuit pattern on the surface of a ceramic substrate, a typical method is a metal vapor deposition method or a metal paste sintering method, and any of them forms a circuit pattern having a desired shape using a mask. The circuit patterns obtained by these methods can electrically separate the circuit patterns 11, 12 and the like from each other as shown in FIG. Here, 2 indicates a ceramic substrate.

In recent years, in addition to the above two methods, a new circuit pattern forming method which is mass-produced and has a large bonding strength with ceramics has come into use. This utilizes the eutectic effect of copper and oxygen and controls the temperature (1065 to 1085 ° C) and the amount of oxygen (about 0.4% by weight) to melt only the surface of copper and directly bond it to the ceramic. (Less than,
This is a technology for realizing "DBC").

In order to form a circuit pattern made of a copper plate as shown in FIG. 5 by the DBC, it is necessary to set the positional relationship between the circuit patterns 11 and 12 in advance and heat them to a high temperature. A jig or the like was used for this position setting, but since it was heated to a high temperature, deformation or adhesion occurred, and a circuit pattern having a satisfactory size could not be obtained.

In order to improve this, as shown in FIG. 6, the pattern in which the circuit patterns 11 and 12 are previously integrated by the thin bridge 13 is bonded to the ceramic by the DBC. Then this joined bridge 13
Had been cut and removed with a knife or laser.

[0006]

This method requires the work of cutting and removing the unnecessary bridge 13.
If a high voltage is applied between the circuit patterns 11 and 12 in a state where copper deposits remain without being completely cut and removed, there is a drawback that dielectric breakdown occurs.

The present invention solves the above drawbacks and forms circuit patterns separated from each other among the circuit patterns formed by the DBC technique without shifting their positions and without cutting work such as a bridge. The purpose is to [Constitution of Invention]

[0008]

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above circumstances, and a copper plate in which a portion to be electrically separated upon completion has a thin shape and the other portions have a circuit pattern shape. One surface and one surface of the ceramic substrate are heated in an atmosphere containing oxygen to melt and extinguish the thin shaped portion of the copper plate, and the copper plate surface other than the thin shaped portion is melted to melt the ceramic. It is a circuit pattern forming method characterized in that it is bonded to a substrate.

[0009]

The thin pattern portion of the copper plate is melted and extinguished, and the copper plate surface of the circuit pattern shaped portion is melted and fused with the ceramic substrate to form a circuit pattern.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a bridge in which the width of the bridge 13 in FIG. 6 is narrowed to a width having a strength that does not impair the positional relationship between the circuit patterns 11 and 12 (hereinafter referred to as a fuse pattern). It is a circuit pattern made of a copper plate provided with 14. When this is put in close contact with the ceramic substrate 2 and put in a furnace that meets the DBC conditions, the fuse pattern 14 has a narrow width, so that another wide circuit pattern 1
The heat capacities are smaller than those of Nos. 1 and 12 by a slight difference, and only this part is fused. FIG. 2 shows the circuit pattern after passing through the furnace. The fuse pattern 14 is melted and drawn toward the circuit patterns 11 and 12 by surface tension. No copper deposit of the fuse pattern remains on the ceramic plate at the blowout point, and a completely insulated state is created.

The molten copper of the fuse pattern 14 attracted toward the circuit patterns 11 and 12 mixes with the molten copper only on the surface of the circuit patterns 11 and 12, and its root is rounded due to its surface tension. Shape,
The shape is convenient for insulation. The above phenomenon is
It is explained as follows. FIG. 3 shows a state diagram of copper and oxygen, in which the vertical axis represents temperature and the horizontal axis represents oxygen concentration (wt%). Region A is a liquid phase, B is a solid phase, and C and D are mixed phases of liquid phase and solid phase.

The melting point of copper is 1083 ° C., the eutectic temperature of copper and cupric oxide is 1065 ° C., and DBC is possible under the temperature of region C and oxygen concentration conditions. Looking closely at the temperature distribution of the copper plate in the furnace, if the thickness is constant, the temperature of the wide part is low and the temperature of the narrow part is higher due to the difference in heat capacity. Therefore, the narrow circuit pattern portion becomes a liquid phase and melts. However, in the wide circuit pattern portion, the copper and the ceramic on the melted surface are directly bonded to each other, and the position is not displaced.

An application of this embodiment is, for example, a trimming circuit for characteristic adjustment on an alumina substrate or a ferrite substrate used in a microwave integrated circuit. FIG. 4 shows the circuit pattern, and the main circuit pattern 15 and the trimming circuit pattern 16 are connected by a conductor piece or the like as necessary in order to correct the variations in the characteristics of the transistors used.

[0015]

According to the present invention, without using a jig,
It is possible to obtain a DBC ceramic substrate having circuit patterns separated from each other without removing the necessary displacement of the circuit pattern and without cutting off the bonded unnecessary portion pattern. As a result, the yield and position accuracy of the circuit pattern forming process can be improved, and the cutting process can be eliminated, so that a cheaper DBC ceramic substrate can be provided. In addition, the insulating property can be improved as compared with the conventional cutting method.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating an embodiment of the present invention.

FIG. 2 is a perspective view illustrating an embodiment of the present invention.

FIG. 3 is a phase diagram of a copper-oxygen system.

FIG. 4 is a perspective view showing an application example of the present invention.

FIG. 5 is a perspective view showing a conventional example.

FIG. 6 is a perspective view showing an intermediate step of a conventional example.

[Explanation of symbols]

 2 …………………… Ceramic board 11,12 ………… Circuit pattern 13 ……………… Bridge 14 ……………… Fuse pattern 15 ……………… Main circuit pattern 16 ………… ...... Trimming circuit pattern

Claims (1)

[Claims] 1. An atmosphere containing oxygen in a state where a portion to be electrically separated at the time of completion has a thin shape and the other portions have a circuit pattern shape and one surface of the copper plate and one surface of the ceramic substrate are in contact with each other. A method for forming a circuit pattern, characterized in that the thin plate-shaped portion of the copper plate is melted and extinguished by heating inside, and the surface of the copper plate other than the thin-shaped portion is melted and joined to the ceramic substrate.