JPH04322491A - Manufacture of ceramic circuit board - Google Patents

Abstract

PURPOSE:To enhance the safety and the peeling strength of the title circuit board and to increase the productivity of the circuit board by a method wherein a ceramic board is coated with the paste of a brazing material, a metal sheet is bonded onto it, the metal is etched and remaining brazing material is removed by using an aqueous solution which contains ammonium halogenide. CONSTITUTION:Ammonium halogenide, especially ammonium fluoride, is used to remove remaining brazing material; thereby the brazing material is removed under the condition of neutrality (pH=7) or close to it. As advantages of removing the inessential brazing material at a pH close to 7, a bad effect on a human body is small and the degree of corrosion to a metal such as copper or the like used to form a metal circuit is weakened. Since a bonded layer is not corrosion, the peeling strength of the title circuit board is not lowered. The concentration of the solution of ammonium halogenide is desirably at 2 to 15wt.%.

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 ceramic circuit board used in power semiconductor modules, etc., in which a metal plate is bonded to a ceramic substrate to form a semiconductor circuit.

0002

[Background Art] In recent years, as the performance of industrial equipment such as robots and motors has improved, the use of high-power modules such as high-power, high-efficiency inverters has progressed, and the heat generated from semiconductor elements is also increasing. ing. In order to efficiently dissipate this heat, various methods have been used in the past for high-power module boards. In particular, recently, with the advent of ceramic substrates having good thermal conductivity, a structure has been adopted in which a circuit is formed by bonding a metal plate onto the substrate, and then a semiconductor element is directly mounted on the metal plate.

Conventionally, there are various methods for joining metals and ceramics, but from the viewpoint of manufacturing circuit boards, the Mo-Mn method, active metal brazing method, copper sulfide method, DBC method, copper One example is the metallization method. Among these, in the manufacture of high-power module boards, the current mainstream is to use copper as the metal and the active metal brazing method or DBC method as the bonding method to ceramics. The use of aluminum nitride as an insulating substrate is becoming popular.

Conventional methods for joining copper plates and aluminum nitride substrates include the active metal method (for example, the active metal method, in which a brazing material containing an active metal is interposed between the copper plate and the aluminum nitride substrate, and the bonded body is formed by heat treatment). Kaisho 60-1776
34 Publication), or the DBC method (for example, Japanese Patent Application Laid-Open No. 163093/1983), in which a copper plate and an aluminum nitride substrate whose surface has been oxidized are joined by heating at a temperature below the melting point of copper and above the eutectic temperature of Cu2O-O. etc. are known.

The active metal method has the following advantages over the DBC method. (1) Since the bonding treatment temperature is low, the residual stress caused by the difference in thermal expansion of Aln-Cu is small. (2) Since the bonding layer is made of ductile metal, it has great durability against heat shock and heat cycles.

[0006] The present applicant has proposed a ceramic circuit board with high productivity, which is made by applying a brazing paste to the entire surface of a ceramic substrate, bonding a metal plate to the entire surface, etching the metal, and removing unnecessary brazing material with a chemical solution. (PCT/JP90/01502).

[0007]

[Problems to be Solved by the Invention] The present invention is an improvement of the above-mentioned invention, and by using an ammonium halide aqueous solution as a chemical solution, 1) safety and 2) increased productivity with further improved peel strength, etc. The purpose is to manufacture ceramic circuit boards.

0008]

[Means for Solving the Problems] That is, the present invention applies a brazing paste to a ceramic substrate, and after bonding a metal plate thereon, etches the metal, and then uses unnecessary brazing paste in an aqueous solution containing ammonium halide. This is a method of manufacturing a ceramic circuit board characterized by removing.

The present invention will be explained in more detail below.

The greatest feature of the present invention is that ammonium halides, especially ammonium fluoride, are used as the chemical solution for removing unnecessary brazing filler metal, thereby achieving a neutral (pH=
7) or similar conditions to remove the brazing filler metal. The advantages of removing unnecessary brazing filler metal when the pH is around 7 are as follows:
It causes less harm to the human body, and the degree of corrosion against metals such as copper used in forming metal circuits is reduced. Moreover, since the bonding layer is not eroded, the peel strength does not decrease.

Examples of ammonium halides include ammonium fluoride, ammonium chloride, ammonium bromide,
Examples include ammonium iodide, but among these, ammonium fluoride also acts as a chemical polishing agent that increases metal luster. The surface can be polished to increase gloss.

The concentration of the ammonium halide aqueous solution is 2
~15% by weight is desirable. If it is less than 2% by weight, the removal effect of unnecessary brazing filler metal will not be sufficient, while if it exceeds 15% by weight, handling and safety will deteriorate.

[0013] The term "unnecessary brazing material" as used in the present invention means a brazing material existing between metal circuit patterns. Such unnecessary brazing filler metal may be brazing filler metal that originally exists between metal circuit patterns (this occurs, for example, when brazing filler metal is placed over the entire surface of a ceramic substrate), or it may be the brazing filler metal that originally exists between the metal circuit patterns (this occurs, for example, when brazing filler metal is placed over the entire surface of a ceramic substrate), or the metal This is the brazing filler metal that protrudes between the circuit patterns. The components of unnecessary brazing filler metal include not only the brazing filler metal components adjusted at the time of use, but also a nitride layer formed when the active metal component of the filler metal reacts with ceramics, and an alloy layer formed when metal and ceramics react. be.

The metal components of the brazing filler metal used in the present invention are:
These include one or more active metal components such as a Ti component, a Zr component, and a Hf component, and one or more metal components other than the active metal components such as a copper (Cu) component and a nickel (Ni) component. A silver (Ag) component may further be present in order to lower the melting point of the brazing filler metal.

In the present invention, when the Ag component, which is the most suitable metal component other than the active metal component, and the Cu component are used in combination, a composition of 60 to 85% by weight of the Ag component and 40 to 15% by weight of the Cu component is desirable. From the viewpoint of reducing the bonding strength and increasing the bonding strength, a so-called eutectic composition of 72% by weight of Ag and 28% by weight of Cu is optimal.

The brazing material paste used in the present invention is composed of the metal component of the brazing material described above and an organic solvent, and may further contain an organic binder for ease of handling. The metal component is supplied in a suitable form among metal powder, alloy powder and compound. Specific examples of combinations of metal components are as follows. That is, Ag-Cu-
Ti, Ag-Cu-Zr, Ag-Cu-Hf, Ag-C
u-TiH2, Cu-Ti, Cu-Zr, Ni-T
i, Ni-Zr, Ni-ZrH2, Ni-TiH2
, Cu-TiH2, Ag-Cu-Zr-Ti, Ag
-Cu-Zr-TiH2, etc. However, in the case of a compound of active metal components, it decomposes by the bonding temperature and T
It must be capable of liberating active metals such as i, Zr, and Hf.

The paste used in the present invention contains AlN, Si3N4, A
It is also possible to contain one or more ceramic powders selected from l2O3 and boron nitrogen (BN). By containing ceramic powder, unnecessary brazing material, which tends to occur when a paste is applied to a metal circuit pattern, is less likely to occur. For this reason,
The present inventors believe that this is because the ceramic powder consumes excess active metal components and suppresses excessive wetting with the ceramic substrate, making it easier to prevent unnecessary brazing filler metal (reaction product layer) from forming outside the metal circuit pattern. is thinking.

Considering that the thickness of the applied paste is usually 10 to 40 μm, the particle size of the ceramic powder is preferably 30 μm or less, especially 20 μm or less, since it is not good if the maximum diameter exceeds 50 μm. be. Also, regarding the average particle size, it is not desirable to have an average particle diameter of more than 15 μm, as if it is too large, the amount of ceramic powder added will increase, which will adversely affect the bonding condition.
The thickness is preferably 10 μm or less, particularly 5 μm or less.

In order to prepare a brazing paste using the above-mentioned metal components and ceramic powder as required, a mixer such as a roll, kneader, Banbury mixer, or universal mixer is used together with an organic solvent or an organic solvent and an organic binder. Mix using a grinder, a grinder, etc. The organic solvent used in this case is
Methyl cellosolve, ethyl cellosolve, terpineol, isophorone, toluene, etc. are used, and as the organic binder, ethyl cellulose, methyl cellulose, polymethyl methacrylate (PMMA), polyisobutyl methacrylate (PIBMA), etc. are used.

Regarding the quantitative ratio of the brazing paste components, it is preferable that the amount of active metal component used is 3 to 40 parts by weight of the active metal component and 0 to 10 parts by weight of the ceramic powder per 100 parts by weight of the metal components other than the active metal component. 5 to 35 parts by weight less than 10 to 30 parts by weight, especially 1 to 9 parts by weight, especially 2 to 8 parts by weight, organic solvents 10 to 30 parts by weight
30 parts by weight, and 0 to 5 parts by weight of the organic binder. The viscosity of the brazing paste is 1,000 to 20,000 cp
s is desirable.

The materials of the ceramic substrate used in the present invention include aluminum nitride (AlN), silicon nitride (S
The main component is at least one or two or more selected from aluminum oxide (Al2O3), aluminum oxide (Al2O3), mullite, etc., and aluminum nitride, which has high thermal conductivity, is preferred.

As the aluminum nitride substrate, those manufactured by known methods can be used without any inconvenience; examples include those sintered by a hot press method without adding a sintering aid, yttrium oxide, I such as cerium oxide, samarium oxide, calcium oxide, magnesium oxide, etc.
IIa Sintering aids such as metal oxides, rare earth element oxides, and alkaline earth metal oxides are added to aluminum nitride powder, which is then molded and then sintered under normal pressure.

[0023] There are no particular restrictions on the material of the metal plate used in the present invention, and copper, nickel, copper alloy, and nickel alloy are usually used. Further, there is no particular restriction on the thickness, and even a thin one called metal foil can be used, and a thickness of 0.1 to 1.0 mm, preferably 0.2 to 0.5 mm is usable. used. Regarding the shape of the metal plate, the following three types are used.

(1) A metal plate that includes at least a metal circuit pattern and has a larger area than the metal circuit pattern (hereinafter, this metal plate is referred to as a solid metal plate). When using a solid metal plate, the brazing paste includes at least the metal circuit pattern and is placed on the ceramic substrate over a wider area. Therefore, the brazing paste can be placed over the entire surface of the ceramic substrate, or can be placed in the same shape as the metal circuit pattern.

(1) A metal plate consisting of a metal circuit portion and a portion other than the metal circuit having a thickness thinner than the metal circuit portion (hereinafter, this metal plate will be referred to as a half-etched metal plate). In order to form portions other than the metal circuit (thin wall portion), it is desirable to dissolve the metal by chemical etching, and it is also desirable to arrange the brazing material in the same shape as the metal circuit pattern.

The advantages of using half-etched metal plates are as follows. i) When forming a metal circuit pattern by etching, a simple and highly productive method such as a roll coater can be used to apply the etching resist. ii) Etching resist can be applied to the entire surface of the ceramic substrate by screen printing. iii) During etching, since the etching resist coating film is not applied to the parts (thin parts) of the half-etched metal plate other than the metal circuit, it becomes easy to separate the metal circuit part from the part other than the metal circuit. iv) Unnecessary brazing material generated outside the metal circuit pattern is
It can be easily removed by treatment with an ammonium halide aqueous solution after etching.

■A metal plate consisting of a metal circuit part and a part other than the metal circuit, which can be easily separated by applying mechanical force.
Hereinafter, this metal plate will be referred to as a pushback metal plate). The pushback metal plate can be manufactured, for example, as follows. i) Remove the metal circuit part from the metal plate and then put it back in its original state. ii) Provide a groove until just before the metal circuit part falls off. iii) In ii) above, most of the groove is penetrated to separate the metal circuit portion from most of the portions other than the metal circuit. In the methods i) to iii) above, the thickness of the metal circuit portion and the portion other than the metal circuit may be the same or different. As a method for forming the metal circuit portion, a press mold, a saper, a milling cutter, etc. having a metal circuit pattern may be used, or chemical etching may be used.

When using a pushback metal plate, it is desirable that the brazing material be arranged in the same shape as the metal circuit pattern, and after bonding the pushback metal plate to the ceramic substrate, the metal parts other than the metal circuit should be separated. A metal circuit pattern can be easily formed by this method. Unnecessary brazing material generated outside the metal circuit pattern is removed by treatment with an aqueous ammonium halide solution.

After the metal plate is bonded to the ceramic substrate, an etching resist is applied to the metal plate and a metal circuit pattern is formed by etching. This operation is not necessary when using pushback metal plates. Examples of the etching resist used in the present invention include ultraviolet curing type and thermosetting type. Further, as the etching solution, if the metal plate is a copper plate or a copper alloy plate, a solution such as a ferric chloride solution, a cupric chloride solution, sulfuric acid, or hydrogen peroxide is used. Preferably, a ferric chloride solution or a cupric chloride solution is used. On the other hand, if the metal plate is nickel or a nickel alloy, a ferric chloride solution is usually used.

The present invention uses the above-mentioned materials to form a ceramic circuit through the steps of arranging a brazing material paste on a ceramic substrate, joining metal plates, forming a metal circuit pattern, and removing unnecessary brazing material. A substrate is manufactured.

[0031] In order to arrange the brazing paste on the ceramic substrate, a screen printing method or a coating method using a roll coater is adopted, but when the paste is to be coated on the entire surface of the substrate, the latter is preferable from the viewpoint of productivity.

The ceramic substrate coated with the brazing paste is heat-treated after a metal plate having a sufficient width to cover the paste is placed. Appropriate conditions for heat treatment vary depending on the type of metal plate and brazing filler metal, but the heat treatment must be performed at a temperature below the melting point of the metal plate. To give an example of specific conditions, the metal component of the brazing filler metal is 830 °C or higher for Ag-Cu-active metal system, and 92 °C for Cu-active metal system.
0° C. or higher, and 1000° C. or higher for Ni-active metal systems. The heat treatment atmosphere may be an inert gas atmosphere such as Ar or He, but a vacuum atmosphere is preferable from the viewpoint of wettability of the brazing material. By cooling after the heat treatment, a joined body of the metal plate and the ceramic substrate can be obtained. Since there is a large difference in the coefficient of thermal expansion between the ceramic substrate and the metal plate, if the cooling rate after heat treatment is increased, cracks or defects may occur in the resulting joined body due to residual stress. Therefore, in the present invention, in order to reduce residual stress as much as possible, it is desirable to set the cooling rate to 5° C./min or less, particularly 2° C./min or less.

Next, a desired metal circuit pattern is formed using an etching resist. When a half-etched metal plate is used, it is desirable to apply the etching resist using a roll coater. This is because even if the etching resist is applied to the entire surface of the Haas-etched metal plate using a roll coater, it will not be applied to the thin parts other than the metal circuit, making it easier to remove the thin parts.
This is because productivity increases. When a pushback metal plate is used, it is not necessary to apply an etching resist except in special cases. Next, after removing unnecessary parts of the metal by etching, the etching resist film is peeled off to obtain a ceramic substrate having a metal circuit pattern. By mechanically separating the portion of the pushback metal plate other than the metal circuit, a ceramic substrate with a metal circuit pattern is obtained. At this stage, the originally placed brazing filler metal components, their alloy layers, nitride layers, or unnecessary brazing filler metal protruding outside the metal circuit patterns still remain between the metal circuit patterns, so they will be removed in the next process. remove.

The ceramic substrate on which the metal circuit pattern has been formed is treated with an ammonium halide aqueous solution to remove unnecessary brazing material, resulting in the ceramic circuit substrate of the present invention. Processing time is 3-30 minutes, processing temperature is 20-30 minutes.
80°C is preferred. It is also effective to apply ultrasonic waves simultaneously with the treatment and/or in the cleaning step after the treatment.

[0035]

[Examples] The present invention will now be explained in more detail with reference to Examples.

Example 1 Comparative Example 1 A brazing filler metal paste was prepared by mixing 72 parts of silver powder, 28 parts of copper powder, 20 parts of metallic zirconium powder, and 15 parts of terpineol in weight proportions. This is 60mm x 30
The coating was applied to both sides of an aluminum nitride substrate measuring mm x 0.65 mm using a roll coater. The coating amount was 7 to 10 mg/cm2.

After drying the brazing paste-coated substrate, solid copper plates of 60 mm x 30 mm x 0.25 mm were placed on both sides in contact with each other, and then placed in a furnace and heated for 920 minutes in a high vacuum.
After heating at 0.3°C for 0.3 hours, the composite was cooled at a rate of 2°C/min to produce a bonded body. The number of samples was 10 for each.

Next, an ultraviolet curing type etching resist is applied to the circuit pattern on the copper plates of these joints by screen printing, and then an etching process is performed with a ferric chloride solution to remove unnecessary copper plate parts, and then the etching resist is removed. was peeled off.

In the obtained bonded body, there was still some brazing material between the copper circuit patterns, so in order to remove this,
15% with a 5% ammonium fluoride aqueous solution (Example 1) at 40°C or a 5% hydrofluoric acid aqueous solution (Comparative Example 1) at 40°C.
The process was carried out for 1 minute.

Regarding the obtained ceramic circuit board,
The peel strength of the copper circuit pattern was measured using a commercially available measuring instrument. The results are shown in Table 1.

[0041]

[Table 1]

Examples 2 to 8 Comparative Examples 2 to 7 72 parts of silver powder, 28 parts of copper powder, and zirconium powder or titanium powder were mixed in the weight proportions shown in Table 2 or Table 3,
Further, 15 parts of terpineol and 1 part of PIBMA were mixed to prepare a brazing paste, which was applied to an aluminum nitride substrate in the same manner as in Example 1.

[0043] Copper plates similar to those in Example 1 were placed on top of these substrates in contact with each other, and 10 of each were placed in a furnace and heated in a high vacuum at a temperature of 880°C for 0.2 hours.
A joined body was produced by cooling.

Next, the unnecessary copper plate portions were removed by etching in the same manner as in Example 1, and the unnecessary brazing filler metal remaining between the circuits was removed under the conditions shown in Table 2 to produce a ceramic circuit board. The peel strength was measured. The results are shown in Tables 2 and 3.

[0045]

[Table 2]

[0046]

[Table 3]

[0047]

According to the present invention, it is possible to obtain a joined body of a metal plate and a ceramic substrate that does not cause a significant decrease in peel strength, and the yield in the process is greatly improved and safety is also enhanced.

Claims (1)

[Claims] 1. Ceramics characterized by applying a brazing material paste onto a ceramic substrate, bonding a metal plate thereon, etching the metal, and then removing unnecessary brazing material with an aqueous solution containing ammonium halide. Method of manufacturing circuit boards.