JPH10326949A - Circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance durability against heat cycle by setting the shortest interval between metal circuits, between bonding layers and between a metal circuit and a bonding layer within a specified range and setting the insulation resistance at 150 deg.C in the shortest interval at a specified value or above. SOLUTION: The circuit board comprises a metal circuit and a ceramic board bonded through a bonding layer containing an active metal. The shortest interval (c) between metal circuits, between bonding layers and between a metal circuit and a bonding layer is set within a range of 0.5-1.0 mm. Insulation resistance decreases when the shortest interval (c) is shorter than 0.5 mm and a fine pattern can not be obtained when it exceeds 1.0 mm. Furthermore, the insulation resistance at 150 deg.C in the shortest interval (c) is 1×10<11> Ω.cm or above. If the insulation resistance is lower than that value, dielectric breakdown takes place when a current of 0.5 mA flows at 5.0 kV.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board used for a power module of an electronic component.

[0002]

2. Description of the Related Art In recent years, power modules such as high-power and high-efficiency inverters have been changing with the advancement of the performance of industrial equipment such as robots and motors, and the heat generated from semiconductor devices has been increasing steadily. I have. In order to efficiently dissipate this heat, various methods have conventionally been used for power module substrates. Especially recently, ceramic substrates with good thermal conductivity have become available,
After joining a metal plate such as a copper plate on the board and forming a circuit,
A structure in which a semiconductor element is mounted as it is or after performing a process such as Ni plating has been adopted.

[0003] Such modules have initially been used in simple machine tools, but in recent years have been used in welding machines, train drives, electric vehicles and in more severe environmental conditions. Durability and further miniaturization have been required.

[0004]

To meet this demand, for example, there is an increase in the thickness of a metal circuit to increase the current density and a finer metal circuit pattern. It has been difficult to achieve this by an active metal brazing method having excellent properties. This is because, in the active metal brazing method, it is necessary to remove the brazing material when forming a metal circuit pattern.

An object of the present invention is to manufacture a circuit board having high durability against a heat cycle and realizing miniaturization of a metal circuit pattern with high productivity. The object of the present invention can be achieved by optimizing the length of the bonding layer containing the active metal protruding from the lower end of the metal circuit and the length of the metal circuit pattern interval.

[0006]

That is, the present invention provides a method in which a bonding layer containing an active metal is protruded inward and / or outward from a lower end portion of a metal circuit and the metal circuit is bonded to a ceramic substrate. The shortest distance between the metal circuits, between the bonding layers, and between the metal circuit and the bonding layer is 0.5 to 1.0 mm, and the insulation resistance at 150 ° C. in the shortest distance is 1 mm. × 10 ¹¹ Ω · cm or more.

Further, the present invention provides a method in which a bonding layer containing an active metal is protruded inward and / or outward from a lower end portion of a metal circuit so that the metal circuit is bonded to a ceramic substrate. , Between the bonding layers, and between the metal circuit and the bonding layer, the shortest distance is 0.5 to 1.
0 mm, the length of the bonding layer protruding from the lower end of the metal circuit is −50 μm (inside 50 μm) to +30 μm (outside 30 μm), and the dimensional difference between the lower end and upper end of the metal circuit is 50 to 100 μm. It is a circuit board characterized by the above-mentioned.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in more detail. The reliability of a circuit board formed by bonding a metal circuit such as copper and a ceramic substrate such as an aluminum nitride substrate via a bonding layer will be described. In addition to the thickness of the metal circuit, the peeling of the metal circuit from the ceramic substrate due to the heat cycle occurs from the edge of the metal circuit, so it is important to optimize the edge shape and reduce the thermal stress (for example, JP-A-3-261669, JP-A-4-3
No. 43287).

Conventionally, it has been recognized that the larger the etching factor, that is, the dimensional difference between the lower end and the upper end of the metal circuit, and the larger the length of the protrusion of the bonding layer from the lower end of the metal circuit, the more the thermal stress is dispersed. Therefore, it was difficult for the metal circuit to peel off. However, in order to design a metal circuit pattern having a small etching factor, it is necessary to increase the distance between the patterns. Therefore, the present inventors defined the etching factor and the length of protrusion of the bonding layer,
While maintaining reliability, miniaturization and miniaturization of metal circuit patterns were made possible.

FIG. 1 and FIG. 2 are partial schematic sectional views showing an example of the shape of the circuit board of the present invention. FIG. 1 shows an example in which the bonding layer protrudes outside from the lower end of the metal circuit, and FIG. 2 shows an example in which the bonding layer protrudes outside and inside. In the figure, 1 is a metal circuit, 2 is a bonding layer, 3 is a ceramic substrate,
In addition, t is the thickness of the metal circuit, a is the length of the protruding bonding layer (+ indicates that it protrudes outside, and-indicates that it protrudes inside), b
Is the dimensional difference between the lower end and the upper end of the metal circuit, and c is the shortest distance among the metal circuits, between the bonding layers, and between the metal circuit and the bonding layer.

A prerequisite of the circuit board of the present invention is that the metal circuit and the ceramic substrate are joined by a joining layer containing an active metal, which can be manufactured by an active metal brazing method. In this case, as a method of forming a metal circuit on one surface of the ceramic substrate and a metal radiator plate on the other surface, a method of etching a joined body of the ceramic substrate and the metal plate, a metal circuit punched from the metal plate, It can be performed by a method of joining the pattern of the heat dissipating metal plate to the ceramic substrate or the like.

[0012] As a joining method of metal and ceramics,
In addition to the active metal brazing method, the Mo-Mn method, the copper sulfide method,
Although there are a DBC method, a copper metallization method, and the like, the reason why the active metal brazing method is employed in the present invention is that this method is excellent in durability against heat cycles and productivity.

The active metal brazing method is described in, for example, JP-A-60-177634. The metal component of the brazing material in the active metal brazing method contains silver and copper as main components, and uses the active metal as a sub-component in order to ensure wettability with the ceramic substrate during melting. The active metal component reacts with the ceramic substrate to generate an oxide or a nitride, thereby strengthening the bond between the brazing material and the ceramic substrate. Specific examples of the active metal include titanium, zirconium, hafnium, niobium, tantalum, vanadium, and compounds thereof. As a ratio of these, silver 80 to
The active metal is 1 to 7 parts by weight per 100 parts by weight of the total of 95 parts by weight and 20 to 5 parts by weight of copper. The joining temperature is 800 ~
840 ° C. is desirable. The thickness of the bonding layer formed of the brazing material is preferably about 10 to 20 μm.

Next, in the circuit board of the present invention, the thickness t of the metal circuit is 0.3 mm or more, especially 0.3 to 0.5 m.
m is preferred. If it is thinner than 0.3 mm, it cannot meet the demand for high current density. When a metal heat sink is formed, its thickness is preferably 0.2 mm or more. The material of the metal circuit and the metal radiator plate is generally copper or a copper alloy, but is not limited thereto.

In the present invention, the shortest distance c among the metal circuits, between the bonding layers, and between the metal circuit and the bonding layer is 0.5 to 1.0 mm. If the shortest interval c is smaller than 0.5 mm, the insulation resistance decreases,
If it is wider than 1.0 mm, it can no longer be said to be a fine pattern.

Further, in the present invention, the shortest interval c
The insulation resistance at 150 ° C. is 1 × 10 ¹¹ Ω · cm or more. If the insulation resistance is smaller than this, insulation breakdown occurs when a current of 5.0 kV and 0.5 mA flows.

In order to achieve such an insulation resistance, the shortest distance c is set to 0.5 mm or more, and the length a of the bonding layer protruding from the lower end of the metal circuit is -50 μm (extending inward by 50 μm). Meaning) to +30 μm (meaning protruding 30 μm outside), preferably -20 μm
To +20 μm. Note that the insulation resistance can be further increased by protruding the bonding layer further inside than -50 μm, but in this case, minute foreign matters easily enter the gap between the ceramic substrate and the metal circuit, and the The heating causes the foreign matter to go out, causing a problem or deteriorating the durability to a heat cycle.

Further, in the circuit board of the present invention, it is preferable that the dimensional difference b between the lower end and the upper end of the metal circuit indicating the etching factor is 50 to 100 μm. 5
If it is smaller than 0 μm, the thermal stress concentration is large and there is a problem in the durability of the circuit board. If it is larger than 100 μm, the width of the metal circuit surface on which a silicon chip or the like is actually mounted becomes narrow, resulting in fine patterning. This will hinder the miniaturization.

The material of the ceramic substrate used in the present invention is silicon nitride, aluminum nitride, alumina or the like, but aluminum nitride is suitable for the power module. When the thickness of the ceramic substrate is too large, the thermal resistance increases, and when the thickness is too small, the durability is lost. Therefore, the thickness is preferably about 0.5 to 0.8 mm.

Further, the surface properties of the ceramic substrate are important, and minute defects and dents have an adverse effect when joining a metal circuit, a metal radiator plate or a metal plate which is a precursor thereof to the ceramic substrate. It is desirable that the surface be smooth. Therefore, it is preferable that the ceramic substrate has been subjected to a honing process or a polishing process such as machining.

[0021]

The present invention will be specifically described below with reference to examples and comparative examples.

Examples 1 to 6 Comparative Examples 1 to 6 90 parts of silver powder, 10 parts of copper powder, 3 parts of zirconium powder, 3 parts of titanium powder and 15 parts of terpineol were mixed in a weight ratio, and toluene of polyisobutyl methacrylate was mixed. The solution was added and kneaded well to prepare a brazing filler metal paste.
This brazing material paste is applied to an aluminum nitride substrate (size:
60mm × 36mm × 0.65mm Flexural strength: 40k
g / mm ^{2 (} thermal conductivity: 135 W / mK). The coating amount (after drying) at that time was 9 mg / cm ² .

Next, the metal circuit forming surface is 60 mm × 36 m
An mx 0.3 mm copper plate and 60
mm × 36 mm × 0.15 mm copper plates were placed in contact with each other, and then under a vacuum of 1 × 10 ⁻⁵ Torr or less,
After heating at 830 ° C. for 30 minutes, the mixture was cooled at a temperature lowering rate of 2 ° C./min to produce a joined body.

Next, an UV-curable etching resist is applied on the copper plate of the joined body by screen printing.
Using a cupric chloride solution, etching treatment was performed for various treatment times shown in Table 1 to dissolve and remove unnecessary portions of the copper plate, and the etching resist was peeled off with a 5% sodium hydroxide solution.
In the joined body after the etching process, there is a residual unnecessary brazing material or a reactant between the active metal component and the aluminum nitride substrate between the copper circuit patterns. (NH ₄ F) and hydrogen peroxide (H ₂ O ₂ ).
The circuit board of the dimensions shown in was manufactured.

The circuit board manufactured through these series of processes was kept in the air at -40.degree. C. for 30 minutes and then at 25.degree.
Leave for 10 minutes, keep at 125 ° C x 30 minutes, then 25 ° C x
A heat cycle test in which one cycle was left for 10 minutes was performed, and the number of heat cycles at which the copper circuit or the heat-dissipating copper plate started peeling was measured.

The insulation resistance at a temperature of 150 ° C. at the shortest interval c was measured according to JIS C6481. Further, a withstand voltage test between patterns was carried out in an insulating oil under AC5.
The test was performed by applying 0 kV and a cutoff current of 0.5 mA for 1 minute. Table 1 shows the results.

[0027]

[Table 1]

[0028]

According to the present invention, a circuit board having high durability against a heat cycle and realizing a fine metal circuit pattern can be manufactured with high productivity.

[Brief description of the drawings]

FIG. 1 is a partial schematic cross-sectional view illustrating an example of the shape of a circuit board according to the present invention.

FIG. 2 is a partial schematic cross-sectional view illustrating an example of the shape of a circuit board according to the present invention.

[Explanation of symbols]

Reference Signs List 1 metal circuit 2 bonding layer 3 ceramic substrate t thickness of metal circuit a length of protruding bonding layer b dimensional difference between lower end and upper end of metal circuit c between metal circuits, between bonding layers and between metal circuit and bonding layer Shortest of the intervals between

Claims (2)

[Claims] 1. A metal circuit bonded to a ceramic substrate by protruding a bonding layer containing an active metal from a lower end portion of a metal circuit to the inside and / or the outside, wherein the metal circuit is bonded to a ceramic substrate. The shortest distance among the distances between them and between the metal circuit and the bonding layer is 0.5 to 1.0 mm, and the insulation resistance at 150 ° C. in the shortest distance is 1 × 1.
A circuit board having a resistance of 0 ¹¹ Ω · cm or more. 2. A method in which a bonding layer containing an active metal protrudes inward and / or outward from a lower end portion of a metal circuit so that the metal circuit is bonded to a ceramic substrate. The shortest distance among the distances between the metal circuits and the bonding layer is 0.5 to 1.0 mm, and the length of the bonding layer protruding from the lower end of the metal circuit is −50 μm (inside 50 μm) to +30 μm ( 30 μm on the outside), and the dimensional difference between the lower end and the upper end of the metal circuit is 50-100 μm
m.