JPH10178270A - Manufacture of circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable circuit board for a power module by reducing the occurrence of cracks without sacrificing the corrosion resistance and dielectric strength of the circuit board by forming multiple layers of brazing materials having different compositions on a ceramic substrate and bonding the brazing material layers to each other through heat treatment. SOLUTION: Multiple layers are formed by using many kinds of brazing materials prepared by changing the compositions or composition ratios of the materials. At the time of forming the multiple layers, such a method can be applied that the paste of various kinds of brazing materials are successively applied by using various brazing material applying methods, such as a screen printing method, a roll coater method, etc. In other words, the brazing materials having difference compositions are prepared and the materials are formed in multiple layers by repeating a process for successively applying and drying the brazing materials. The bonding condition of the layers to each other is not limited to a specific one, but can be selected appropriately in accordance with the compositions of the brazing materials and a metallic circuit board 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a circuit board having a metal circuit used for a power module of an electronic component requiring high reliability and heat dissipation.

[0002]

2. Description of the Related Art Conventionally, alumina (Al2O3), aluminum nitride (Al
N), silicon nitride (Si3N4), beryllium oxide (Be)
A circuit board in which a copper (Cu) circuit board or the like is integrally bonded as a conductive layer to the surface of a ceramic sintered body substrate such as O) is widely used.

[0003] Of these, the aluminum nitride circuit board forms a circuit with a metal such as Cu having excellent heat conductivity and electric conductivity, so that the delay of the circuit operation is reduced and the life of the circuit wiring is improved.

[0004] Several methods are known as a method for manufacturing a circuit board, but a full-etch method is often used to obtain good productivity. In the full-etch method, a brazing material paste is applied to the entire surface of the ceramic substrate, a metal plate is bonded to the entire surface so as to cover the paste, and a circuit pattern is formed on the metal plate serving as a circuit surface with an etching resist.
Unnecessary portions are removed by etching. Further, the surface of the metal plate is generally covered with a plating layer of Ni or the like in order to prevent corrosion of the metal plate and to improve solder jointability.

[0005] Although the full-etch method has good productivity,
To go through the unnecessary metal and brazing material removal process of the circuit part,
There is a feature that a large tensile stress remains on the end of a circuit pattern after etching and on a ceramic substrate between circuit patterns as compared with other methods. In particular, when a ceramic substrate having low mechanical strength such as aluminum nitride is used, there is a problem that cracks are generated in the ceramic substrate due to the residual tensile stress.

In order to solve the above problems, for example, in an aluminum nitride circuit board, a copper circuit and an aluminum nitride board are required to have sufficient durability against thermal shock such as heat shock and heat cycle and damage caused by heat history. The thickness of the bonding layer interposed between
m (Japanese Patent Laid-Open No. 6-162828) has been proposed.

[0007]

However, if the thickness of the bonding layer is increased, it becomes difficult to remove unnecessary brazing material,
Therefore, there are still problems to be solved, such as a problem of insulation failure due to the remaining brazing material and an increase in stress generated in the bonding layer. Therefore, the occurrence of residual stress is small,
If we can provide a method of manufacturing a circuit board that forms a good bonding layer, it will be generated on the ceramic substrate at the edge of the metal circuit and the ceramic substrate between the metal circuits due to the thermal stress during the mounting process on the power module and the heat cycle during use It is possible to improve the problem that cracks are reduced and the cracks are further developed, leading to destruction and a decrease in withstand voltage, thereby making the device unusable. The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a highly reliable circuit board for a power module, which reduces the occurrence of cracks without impairing the corrosion resistance and dielectric strength of the circuit board.

[0008]

The present inventors have conducted various studies on a method of joining a metal circuit board to a ceramic substrate using a brazing material. As a result, instead of forming a single layer of the brazing material as in the prior art, The present inventors have found that the formation of cracks on a circuit board can be suppressed by forming brazing materials having different compositions in multiple layers, and completed the present invention.

That is, the present invention relates to a method of manufacturing a circuit board for joining a metal circuit board to a ceramic substrate using a brazing material. This is a method for manufacturing a circuit board.

Further, there is provided the above method for producing a circuit board wherein the active metal in the brazing material is Ti and / or Zr.

Further, there is provided the method for manufacturing a circuit board according to the above, wherein the active metal content in the brazing material in the layer in contact with the ceramic substrate is higher than the active metal content in the brazing material in the other layers.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Ceramic substrates used in the present invention include oxides such as alumina (Al2O3) and nitrides such as aluminum nitride (AlN) and silicon nitride (Si3N4) having a small coefficient of thermal expansion, although not particularly limited. The effect of the present invention is large in a physical ceramic substrate. More specifically, when aluminum nitride is used as a ceramic substrate, a thermal conductivity of 8
A material having a strength of 0 W / mK or more is suitable, and a material having a flexural strength of 350 MPa or more is suitable because the strength after forming the circuit board is affected. The shape of the ceramic substrate is usually rectangular in many cases, but the shape is appropriately selected depending on the application, and the present invention is not limited at all by the shape of the circuit board. The thickness of the ceramic substrate varies depending on the required strength of the circuit board.
Those having a size of 3 mm to 1.5 mm are used.

The material of the metal circuit board bonded to one side of the ceramic substrate and the metal radiator plate bonded to the back side are copper,
Pure metals or alloys such as nickel, aluminum, molybdenum, and tungsten are used. The thickness of the metal circuit or the metal radiator plate is usually 0.1 to 2.0 mm.

The thickness of the metal circuit to be joined is extremely important,
With a thickness of about 0.075 mm, in the case of joining by the active metal method, a slight load is applied at the time of joining, so that expansion of the metal plate is hindered, wrinkles may be generated on the metal plate, and mass productivity is poor. There is. Therefore, it is preferable to use one having a thickness of 0.1 mm or more.
m or less.

The brazing material used in the present invention may be appropriately selected from the composition system of the generally used brazing material depending on the material of the ceramic substrate or metal circuit board to be used. The gist of the present invention is to use many kinds of these brazing materials with different compositions or composition ratios and to form these brazing materials in multiple layers. As a method of forming a multilayer, it is possible to apply a method of sequentially applying multiple types of brazing material paste prepared in advance as generally applied using various brazing material application methods such as a screen printing method and a roll coater method. is there. That is, a brazing material having a different composition can be formed in multiple layers by preparing a brazing material having a different composition, sequentially applying the brazing material in accordance with a desired configuration, and repeating the drying process.

For example, when the ceramic substrate is a nitride-based material such as aluminum nitride or silicon nitride and the material of the metal circuit board is copper, a brazing material containing silver, copper and an active metal is preferable. Here, if the active metal brazing material used has a melting point equal to or higher than the melting point of the solder used in assembling semiconductor components,
Although not particularly limited, an active metal brazing material using a silver-copper eutectic is the most common. As active metals, Ti, Zr, and Hf have been proven and can be said to be preferable. Active metal is not just a simple metal element.
Alloys or compounds of Ti, Zr, and Hf can also be used.
For example, titanium hydride. Among them, a brazing material containing Ti and / or Zr is particularly suitable for the bonding strength and the like.
Further, it is necessary that the active metal content in the brazing material in contact with the ceramic substrate is higher than the active metal content of the brazing material in the other layers. The reason is that the active metal component in the layer in contact with the ceramic substrate has a small moving distance, so that the reaction with the ceramic substrate is performed efficiently, the bonding state becomes good, and the bonding strength is improved and the residual stress is reduced. Conceivable. The reliability of the resulting circuit board is improved. In addition,
The melting point of the Ag-Cu-based brazing filler metal containing an active metal in these brazing filler metals varies depending on the composition, but is about 800 to 900 ° C.

When aluminum or an alloy thereof is used for the metal circuit board, the brazing material may be Al-Si based, Al-
A brazing material generally applied to aluminum, such as an Mg-based or Al-Cu-based material, can be used. Among them, an Al-Si-based material, in particular, causes deterioration in characteristics due to diffusion of a brazing material component into a metal circuit board. Is preferred. The melting point of these brazing materials is about 600 ° C.

The bonding conditions are appropriately selected depending on the composition of the brazing material and the material of the metal circuit board, and are not particularly limited to special conditions. For example, when the joining process is performed using a brazing material containing an active metal, the joining process can be performed in a vacuum of 10 −4 torr or less at a temperature equal to or higher than the melting point of the brazing material.
As a general condition, it is safe to select a temperature about 50 ° C. above the melting point of the brazing material. Note that the application of the method of the present invention facilitates bonding, and enables formation of a favorable bonding layer in a short time.

Thereafter, as a method of manufacturing a circuit board from the joined body, in a full etching method, an unnecessary metal plate and a brazing material are removed by a method such as chemical etching in order to form a metal plate portion into a target shape. Form a metal circuit. Further, a circuit can be formed by a method such as the DBC method.

Further, after the circuit is formed by patterning, the metal portion is generally plated with Ni or the like in order to improve solder wettability and weather resistance. The plating method is not particularly limited, such as an electrolytic plating method and an electroless plating method. However, the electroless plating method is generally used because the pattern is complicated and it is difficult to set an electrode setting position.

[0021]

The present invention will be described more specifically with reference to examples and comparative examples. An aluminum nitride sintered substrate was used as a ceramic substrate. The aluminum nitride sintered substrate was prepared by mixing 18% of yttrium oxide powder with aluminum nitride powder and molding the mixture using a doctor blade method.
Thermal conductivity 15 obtained by firing in a nitrogen atmosphere at 70 ° C.
0 W / (m · K), relative density 99.9%, thickness 0.63
mm.

The preparation of a paste for forming a multi-layered brazing material layer is carried out as usual, with a commercially available raw material powder for brazing material,
Silver powder (average particle diameter 2 μm, purity 99% or more), copper powder (average particle diameter 2.5 μm, purity 99% or more), titanium hydride powder (particle diameter 10 μm or less, purity 98% or more), Zr powder (particles) (Diameter: 40 μm or less, purity: 98% or more), and were blended such that the weight ratio of the metal elements was as shown in Table 1. 15 parts by weight of terpineol and 1.5 parts by weight of a solid solution of a polyisobutyl methacrylate toluene solution as an organic binder were added to 100 parts by weight of the compounded raw material powder, and three rolls were used. The paste was sufficiently kneaded until it passed through a 250 mesh Tetron mesh to prepare a paste. The raw material powder mixed in the kneading step is pulverized and sufficiently mixed.

First, a first paste having the composition shown in Table 1 was applied on both sides of an aluminum nitride sintered substrate by screen printing and dried at 150 ° C. for 10 minutes. The coating amount at that time was adjusted by adjusting printing conditions and the like in advance so as to be the amount shown in Table 1 after drying. A second and third pastes having different compositions (different according to Examples and Comparative Examples) were successively applied and dried on this substrate in the same manner to obtain a substrate in which brazing material pastes having different compositions were formed in multiple layers. .

Next, a copper plate having a thickness of 0.3 mm for forming a metal circuit is provided on one surface of the aluminum nitride substrate coated with the brazing material paste, and a copper plate having a thickness of 0.15 mm is provided on the other surface for heat radiation. A copper plate was placed in contact. After being loaded in a BN container, put into a vacuum heating furnace, and heated at a temperature shown in Table 1 for 10 minutes under a vacuum of 1 × 10 −4 torr, and then heated at 2 ° C. /
min. The mixture was cooled at a temperature lowering rate to produce a joined body.

Next, an ultraviolet-curable etching resist is pattern-printed on the copper plate of the joined body by a screen printing method, unnecessary copper portions are dissolved and removed using a cupric chloride solution, and the remaining copper is left outside the pattern. The unnecessary brazing filler metal and reaction products were dissolved and removed with a 10% ammonium fluoride solution at 60 ° C. Thereafter, the etching resist was stripped with a 5% caustic soda solution to obtain a circuit board having a desired shape. This was subjected to an electroless Ni-P plating treatment to form a plating film on the copper circuit portion, thereby obtaining joined body samples shown in Examples and Comparative Examples in Table 1.

A heat cycle test was performed on these circuit boards. Heat cycle test is JIS-C-0025
According to the temperature change test method, hold at -40 ° C for 30 minutes, +
The heating / cooling operation of heating at 125 ° C. for 30 minutes was defined as one cycle, and 150 cycles were performed. After the heat cycle test, the copper circuit board and the brazing material were dissolved and removed by the same method as that used to form the circuit, and the length of cracks generated in the aluminum nitride sintered substrate below the copper circuit board Was measured.

The crack due to the residual stress at the time of joining is as follows:
Along the edge of the circuit, within 3 mm from the edge of the circuit to the side of the circuit copper plate, it occurs parallel to the edge of the circuit. Therefore, the length of the cracks was obtained by observing the lengths of the cracks running in parallel under a stereoscopic microscope with a magnification of 50 times, and calculating the total. On the other hand, a value obtained by summing the lengths of the edges of the circuit board (entire circumference) was determined as the circuit circumference. Since the circuit patterns in the example and the comparative example were all the same, the circuit circumference was constant in any of the examples. The crack occurrence rate was determined by (crack length / circuit circumference) and the results are shown in Table 1.

In order to make it easier to understand in Table 1, Examples 1 to 6 and Comparative Examples 1 to 6 are experiments corresponding to the same numbers. That is, in Comparative Examples 1 to 6, in order to know the metal composition ratio of the entire multilayer paste of each of Examples 1 to 6, at the stage of coating and drying, the multilayer paste is dissolved in an organic solvent, sampled, and the composition is analyzed. In preparing a paste for a comparative example (not a multilayer, one-time paste printing application), raw materials were blended using the analysis value of the metal composition ratio. Comparative Example 7 is an example in which pastes having the same composition are printed in multiple layers.

From Table 1, it can be seen that the examples according to the present invention have a lower crack generation rate and better heat cycle resistance than the comparative examples.

[0030]

[Table 1]

[0031]

As shown in the present invention, by forming brazing materials having different compositions in multiple layers, the joining of the brazing material and the ceramic substrate becomes easy, and the heat cycle resistance and the like of the obtained circuit board are improved. The characteristics are improved. Further, it can also be expected as a method for forming a gradient functional layer.

[Brief description of the drawings]

FIG. 1 is a conceptual cross-sectional view in which pastes having different compositions are applied in multiple layers.

[Explanation of symbols]

 1: Ceramic substrate 2: Paste composition 1: 3: Paste composition 2: 4: Paste composition 3: 5: Metal circuit board

Continued on the front page (72) Inventor Ryuichi Terasaki 3-5-1 Asahicho, Machida-shi, Tokyo Denki Kagaku Kogyo Co., Ltd.

Claims (3)

[Claims] 1. A method for manufacturing a circuit board, comprising joining a metal circuit board to a ceramic substrate using a brazing material, wherein a brazing material having a different composition is formed in multiple layers on the ceramic substrate and then joined by heat treatment. A method for manufacturing a circuit board, comprising: 2. An active metal component in a brazing filler metal, Ti and / or
The method according to claim 1, further comprising Zr. 3. The circuit board according to claim 1, wherein the active metal content of the brazing material in the layer in contact with the ceramic substrate is higher than the active metal content of the brazing material in the other layers. Manufacturing method.