JPH10154866A - Production of ceramic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To remove unnecessary brazing material substantially perfectly by an unnecessary brazing material removing process comprising a first step for processing a board at a specified temperature using an aqueous solution containing ammonium fluoride and hydrogen peroxide, and a second step for processing the board at a specified temperature using an aqueous solution containing alkaline and hydrogen peroxide. SOLUTION: A first processing liquid contains ammonium fluoride and hydrogen peroxide and a board is processed at 20-40 deg.C. Concentration of ammonium fluoride is 5-30wt.% and concentration of hydrogen peroxide is 2-20wt.%. A second processing liquid contains alkaline and hydrogen peroxide and the board is also processed at a relatively low temperature of 20-40 deg.C in order to remove the residual brazing material thoroughly. Ammonia water is more preferable than an alkaline hydroxide metal as the alkaline. Unnecessary brazing material is removed well while suppressing dissolution of copper when the concentration of ammonia is 0.5-10wt.% and the concentration of hydrogen peroxide is 2-15wt.%.

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 for a power semiconductor module (hereinafter, referred to as a power module) which is a semiconductor device for high power. More specifically, the present invention relates to a method for manufacturing a circuit board, in which a metal plate is joined to a ceramic substrate using a brazing material containing an active metal, and then a circuit pattern is formed by etching. Regarding a certain method.

[0002]

2. Description of the Related Art In recent years, power modules such as inverters and the like used for controlling motors and uninterruptible power supplies have been increased in power and performance, and the amount of heat generated from substrates has been increasing steadily. Therefore, in order to efficiently dissipate a large amount of generated heat, the use of ceramic substrates is increasing. Further, as for the material of the ceramic substrate, the use ratio of the aluminum nitride substrate having high thermal conductivity has been increased from the conventional alumina substrate.

[0003] A circuit of a ceramic substrate for a power module is formed by joining a metal plate (eg, a copper plate) formed in advance by punching or etching to the ceramic substrate or by attaching a metal plate (eg, a copper plate) to the ceramic substrate. After joining, the method is generally performed by printing a resinous resist in a desired circuit pattern and removing an unnecessary portion (non-circuit portion) of the metal plate which is not covered with the resist by etching. The latter method is hereinafter referred to as an etching method.

[0004] There are many known methods for joining a ceramic substrate and a metal plate. As a method for directly joining without using a metallized layer, an active metal brazing method and a method in which the metal plate is a copper plate are used. DBC (d
irect bond copper) methods, and these methods are also used to form circuits on ceramic substrates for power modules.

[0005] The active metal brazing method uses an active metal (eg, Ti,
This is a method of performing heat bonding with a brazing material containing Zr, Hf, etc.) interposed therebetween. In the case of an aluminum nitride substrate, the DBC method is a method in which a substrate and a copper plate whose surfaces are oxidized are heated to a temperature equal to or lower than the melting point of copper and equal to or higher than the eutectic temperature of Cu-O without using a brazing material. is there. The active metal brazing method has a lower joining temperature and a smaller residual stress due to a difference in the coefficient of thermal expansion between the substrate and the metal plate (this difference is larger in an aluminum nitride substrate than in an alumina substrate) as compared with the DBC method. Since the material is a ductile metal, it is advantageous in that it is resistant to thermal shock and has improved durability when subjected to a thermal cycle.

In the above-mentioned etching method, when the metal plate is a copper plate or a copper alloy plate, a ferric chloride solution or a cupric chloride solution is generally used for etching the metal plate. When the unnecessary portion (non-circuit portion) of the metal plate is removed by etching in this manner, when the metal plate is brazed to the ceramic substrate, the surface of the non-circuit portion from which the metal plate has been removed has
The brazing material used for brazing is exposed. The brazing material is metallic and conductive, and if it remains in the non-circuit portion, it causes a short circuit. Therefore, it is necessary to substantially completely remove the unnecessary brazing material from the non-circuit portion. In addition, since a resist which is an insulating substance is adhered on the metal plate of the circuit portion remaining after the etching, this resist is also subjected to an appropriate treatment (e.g., peeling treatment using an organic solvent or an alkaline aqueous solution). Remove.

As a method for removing the unnecessary brazing material, a method using hydrofluoric acid, a method using an aqueous solution of ammonium halide (eg, ammonium fluoride) (JP-A-4-32)
No. 2491), a method using an aqueous solution containing a fluorine compound (eg, ammonium fluoride) and hydrogen peroxide but not containing an inorganic acid (JP-A-7-235750), an ammonium halide (eg, fluoride) A method of performing a first treatment with an aqueous solution containing ammonium and an aqueous solution containing an inorganic acid (eg, sulfuric acid or nitric acid) and hydrogen peroxide.
No. -326827).

[0008]

However, the use of hydrofluoric acid alone requires a high-temperature treatment to remove the unnecessary brazing material, which is dangerous. With an aqueous ammonium halide solution, the effect of removing the unnecessary brazing material is not sufficient even if the treatment is performed at a high temperature. In an aqueous solution containing only a fluorine compound and hydrogen peroxide,
To sufficiently remove unnecessary brazing material, an aqueous solution containing 5 to 10% or more of a fluorine compound and 2 to 5% or more of hydrogen peroxide is required, and etching is performed at a relatively high temperature of 50 to 60 ° C. There is a need. The method of performing the first treatment with an aqueous solution of ammonium halide and the second treatment with an aqueous solution containing an inorganic acid and hydrogen peroxide is also preferable if both the first and second treatments are not performed at a high temperature of 50 to 60 ° C. No good brazing material removal results.

When the unnecessary brazing material is removed at such a high temperature, the processing solution etches (dissolves) the metal plate of the circuit portion in addition to the brazing material (this phenomenon is also called side etching), and the circuit pattern is not removed. There is a problem that it is difficult to maintain dimensional accuracy. In particular, in the case of the above two-stage processing method,
In the second treatment with an aqueous solution containing an inorganic acid and hydrogen peroxide, the copper has a large solubility in the second treatment, and the dimensional accuracy of the circuit pattern is significantly deteriorated.

An object of the present invention is to provide a method of manufacturing a circuit board in which a ceramic substrate and a metal plate are joined by using a brazing filler metal containing an active metal and then a circuit pattern is formed by an etching method. An object of the present invention is to provide a method capable of substantially completely removing an unnecessary brazing material at a composition and at a temperature at which the metal plate of the circuit section is less dissolved in order to maintain the same.

[0011]

Means for Solving the Problems The present inventors first treated with an aqueous solution containing ammonium fluoride and hydrogen peroxide, and then with an aqueous solution containing alkali and hydrogen peroxide. It has been found that unnecessary brazing material can be efficiently removed at a low temperature.

Here, the present invention provides a step of joining a metal plate to a ceramic substrate using a brazing material containing an active metal, and a step of forming a predetermined circuit pattern by removing unnecessary portions of the joined metal plate by etching. And a step of removing unnecessary brazing material in a non-circuit portion, wherein the step of removing the unnecessary brazing material is performed using an aqueous solution containing ammonium fluoride and hydrogen peroxide.
A first treatment at ~ 40 ° C and a second treatment at 20-40 ° C using an aqueous solution containing alkali and hydrogen peroxide,
A method for manufacturing a ceramic circuit board, comprising:

In the present invention, the unnecessary brazing material means a brazing material existing in a non-circuit portion (that is, between circuit patterns). The non-circuit portion includes both a portion where the metal plate is removed by etching and the brazing material is exposed, and a portion where the metal plate is not joined and the brazing material is exposed from the beginning.

[0014]

In the present invention, the material of the ceramic substrate is not particularly limited, and silicon nitride, aluminum nitride, boron nitride, alumina, and a composite material containing these components (eg, mullite, cordierite) etc)
At least one member selected from the group consisting of: Preferred are an alumina substrate and an aluminum nitride substrate. In particular, an aluminum nitride substrate is most suitable as a power module substrate. The thickness, shape, and method of manufacturing the substrate (whether or not a sintering aid is used and the type thereof) are not particularly limited.

The circuit can be formed on one side or both sides of the ceramic substrate. When the circuit is formed on only one side, a heat-dissipating metal plate for attaching a heat sink may be provided on the back side of the substrate (the side on which the circuit is not formed). This metal plate can also be joined to the ceramic substrate at the same time as the metal plate for circuit formation using the brazing material described below.

As a metal plate to be bonded to a ceramic substrate for forming a circuit, Cu, Ni, Al, an alloy thereof, or the like is used. In the case of a substrate for a power module, a copper plate, especially in the case of brazing An oxygen-free copper plate is most suitable. The thickness of the metal plate is usually 0.1 to 1.0 mm, preferably 0.2 to 0.6 mm.

The metal plate to be joined to the ceramic substrate may be a solid metal plate having no circuit formed at all and the same thickness as a whole. A half-etch metal plate with a reduced thickness can also be used.

In the method of the present invention, the joining between the ceramic substrate and the metal plate is performed by an active metal brazing method using a brazing material containing an active metal. The active metal of the brazing filler metal is not particularly limited as long as it reacts with the ceramic substrate to ensure the wettability of the brazing filler metal, but is preferably Ti, Zr, or H.
f, and alloys containing these as main components, and metal compounds which are decomposed by heating to produce these active metals (these are precursors of the active metals, but are included in the present invention in the active metals). Titanium hydride (Ti
H ₂ ) and zirconium hydride (ZrH ₂ ).

The metal components other than the active metal of the brazing material include Ni, Cu, Ag, an alloy of Ag and Cu or Ni, Cu
Alloy of Ag and Sn, alloy of Ag, Cu and Sn, etc. can be used,
Ag-Cu alloy with low melting point, especially 72% by weight of eutectic Ag / Cu
An alloy composition of about 28% by weight is preferable. Specific alloy systems of brazing filler metals containing active metals include Ag-Cu-Ti, Ag
-Cu-Zr, Ag-Cu-Ti-Sn, Cu-Zr-Sn, Ag-Cu-Hf and the like.

The brazing material contains 0.5 to 40 parts by weight of the active metal (in the case of a precursor, the amount of the metal) per 100 parts by weight of the metal other than the active metal. The brazing filler metal is generally used in the form of a paste containing an organic solvent (eg, cellosolves, terpineol, etc.) and optionally an organic binder (eg, cellulose derivative, acrylic resin, etc.) in addition to these metal components. Is done. The brazing material may further contain a small amount of ceramic powder.

The joining with the brazing material is performed by applying the brazing material to one or both of the ceramic substrate and the metal plate, and then heating the brazing material to a temperature at which the active metal in the brazing material reacts with the ceramic substrate. It is performed by The coating can be performed by roll coating, screen printing, or the like. The heating is preferably performed in an inert gas atmosphere or in a vacuum. The heating temperature is about 800 to 850 ° C. when the main component of the brazing material is an Ag—Cu alloy having a eutectic composition. By this heating, the active metal of the brazing material reacts with the ceramic substrate to generate a nitride or an oxide thereof, thereby ensuring the wettability of the molten brazing material to the ceramic substrate.

Unnecessary portions of the metal plate bonded to the ceramic substrate are etched to form a predetermined circuit pattern on the metal plate. The formation of the circuit pattern by this etching may be performed by printing a resist on a predetermined circuit pattern as in the conventional case.

As the resist, a resist mainly composed of a thermosetting resin or an ultraviolet curing resin can be used, and the resist is usually printed by screen printing. However, when the metal plate is a half-etch plate, the resist can be applied only to the circuit portion by roll application. After the resist is cured by heating or ultraviolet irradiation, unnecessary portions of the metal plate that are not covered with the resist are removed by etching. The etchant may be any liquid that can dissolve the metal plate. However, when the metal plate is a copper plate or a copper alloy plate, as described above, ferric chloride or chloride
An aqueous solution containing copper as a main component is used.

Thereafter, the resist remaining on the metal plate of the circuit pattern and the unnecessary brazing material exposed on the ceramic substrate of the non-circuit portion from which the metal plate has been removed are removed to obtain a ceramic circuit substrate.

The resist can be removed by dissolving or swelling the cured film of the used resist.
The material used for the treatment is not particularly limited, but usually an aqueous alkali solution (eg, an aqueous solution of sodium or potassium hydroxide) is used.

According to the present invention, the removal of the unnecessary brazing
It is performed by the processing of the steps. That is, after a first treatment using an aqueous solution containing ammonium fluoride and hydrogen peroxide (hereinafter, also referred to as a first treatment liquid), an aqueous solution further containing an alkali and hydrogen peroxide (hereinafter, a second treatment liquid) (Also referred to as a second process) to remove the unnecessary brazing material. All treatments are performed at a temperature of 20 to 40C, preferably at a temperature of 25 to 35C.

Either the removal of the resist or the removal of the brazing material may be performed first, but the removal of the resist is more effective if the processing liquid for removing the brazing material, particularly the second processing liquid, becomes dirty. It is preferable because the amount is small and the life of the processing solution is prolonged. Alternatively, since the second processing solution is alkaline and can dissolve the resist, the resist removing process is omitted, and the second process of the brazing material removal is also performed as the resist removing process.
The present invention may be implemented to simultaneously remove both the brazing material and the resist that have not been completely removed in the first process.

The first processing solution for removing the unnecessary brazing material contains ammonium fluoride and hydrogen peroxide. Preferably, the concentration of ammonium fluoride is 5-30% by weight,
It is more preferably 10 to 20% by weight, and the concentration of hydrogen peroxide is 2 to 20% by weight, more preferably 5 to 10% by weight.
An organic substance (inhibitor) that suppresses the dissolution of copper may be added to the first treatment liquid. Since an etching solution containing ammonium fluoride, hydrogen peroxide, and an inhibitor is commercially available, the first treatment may be performed using the etching solution.

In the first treatment, the first treatment liquid penetrates into the brazing filler metal and the reaction products (nitrides, oxides, etc.) of the active metals (Ti, Zr, etc.) contained in the brazing filler metal and peels or dissolves them. Make it easier. However, since the treatment is performed at a low temperature, copper hardly dissolves.

Since it is difficult to completely remove the unnecessary brazing material by the treatment in the above-mentioned temperature range with the first treatment liquid, the present invention comprises, as the second stage treatment, a treatment containing alkali and hydrogen peroxide. Using a second processing solution that is
At a relatively low temperature to completely remove the remaining brazing material. As the alkali, aqueous ammonia (ammonium hydroxide) is preferable to an alkali metal hydroxide such as sodium hydroxide. The ammonia concentration is 0.5 to 10 as a range that suppresses the dissolution of copper and has a good effect of removing unnecessary brazing material.
% By weight, and the concentration of hydrogen peroxide is preferably in the range of 2 to 15% by weight. More preferably, the ammonia concentration is 1 to 5% by weight,
The hydrogen peroxide concentration is 5 to 10% by weight.

Since the unnecessary brazing material is easily peeled or dissolved in the first-stage treatment, if the second-stage treatment is performed with an alkaline treatment solution, the unnecessary brazing material can be completely dissolved without leaving any residue. it can. A commercially available hydrogen peroxide decomposition inhibitor may be added to the second treatment liquid.

The processing time for both the first processing liquid and the second processing liquid is preferably in the range of 5 to 60 minutes, particularly preferably 15 to 45 minutes. This 2
By the step treatment, dissolution of copper forming the circuit pattern is suppressed to, for example, about 10 μm or less, and unnecessary brazing material (including brazing material reacted with the ceramic substrate) can be substantially completely removed. Thereafter, in order to protect the circuit surface formed from the metal plate and from which the resist has been removed, electroless nickel plating is usually performed on the circuit.

[0033]

EXAMPLES The present invention will be specifically described with reference to examples. In the examples, parts and% are parts by weight and% by weight, unless otherwise specified.

In 72 parts of Ag powder and 28 parts of Cu powder, 5 parts of titanium hydride powder, which generates titanium as an active metal by heating, or 5 parts of zirconium powder of active metal is used.
, And a paste was prepared with an appropriate amount of a terpineol and acrylic resin solution to prepare a brazing filler metal.

The brazing material in the form of a paste was used for 37 mm × 55 mm ×
The entire surface of both sides of an aluminum nitride substrate having a thickness of 0.8 mm was applied using a screen printing machine. The coated brazing material is heated to 140 ° C. in the atmosphere for 5 minutes and dried, and then applied to both surfaces.
A copper plate of mm × 55mm × 0.30mm thickness is placed in contact, heated to 500 ° C in a high-purity nitrogen gas stream and degreased (removing organic components), and then at 850 ° C in a high vacuum of 1 × ^10-5 Torr. By heating for 10 minutes, the copper plate was bonded to both surfaces of the aluminum nitride substrate.

After an ultraviolet-curable etching resist is printed on a circuit pattern by a screen printer on the copper plate of the obtained joined body, the resist is cured by irradiating ultraviolet rays of 600 to 800 mJ / cm ^{2 in} a UV curing furnace. This operation was performed on each side, and a resist pattern was formed on both sides.

Thereafter, using a spray-type etching machine, a commercially available etching solution containing ferric chloride is sprayed on the surface of the copper plate of the substrate at 45 ° C. for about 8 minutes to perform etching, and the resist is not covered with the resist. Unnecessary portions (non-circuit portions) of the copper plate were removed and washed with water.

Next, the etched substrate is heated at 40 ° C. for 2%.
After immersing in an NaOH aqueous solution for about 3 minutes to remove the etching resist and washing with water, unnecessary brazing materials remaining between circuit patterns were immersed under various conditions shown in Table 1. After each treatment of removing the unnecessary brazing material, washing was performed with water. After the completion of the brazing material removal process, the water on the substrate was replaced with alcohol, and then dried with hot air at 80 ° C. In some comparative examples, since the dissolution of copper was remarkable, the etching resist was removed after removing the unnecessary brazing material.

The state of removal of the unnecessary brazing material from the ceramic circuit board thus obtained (the state of the brazing material remaining between the circuits) was visually observed. In addition, the thickness of the copper plate of the circuit portion was measured, and the melting thickness (difference from the thickness before treatment of 300 μm) was obtained. The above results are also shown in Table 1.

[0040]

[Table 1]

As can be seen from the comparative examples shown in Table 1, the treatment solution for removing the brazing material was ammonium fluoride alone, ammonium hydrogen fluoride (ie, ammonium fluoride + hydrofluoric acid), or ammonium fluoride + peroxide. In the case of hydrogen, even if the processing temperature was increased to 60 ° C., the removal of the unnecessary brazing material was incomplete (Test Nos. 4, 5, 6). On the other hand, when a processing solution obtained by further adding hydrogen peroxide to ammonium hydrogen fluoride is used, the removal of the brazing material is incomplete even at a processing time of 1 hour in a low-temperature processing at 25 ° C. (Test No. 7 ), When the high-temperature treatment of 60 ℃, the removal of unnecessary brazing material was complete in 30 minutes of treatment, but the copper plate of the circuit part was significantly dissolved (Test No.
8). Therefore, while the resist was left on the copper plate of the circuit part, first, unnecessary brazing material was removed under the conditions of 60 ° C × 30 minutes, and then the resist was peeled off (Test No. 9)
The unnecessary brazing material could be completely removed in the same manner, but the dissolution of the copper plate in the circuit portion was still as large as 48 μm, and the dimensional accuracy of the circuit pattern was reduced due to side etching.

On the other hand, according to the present invention, when the first treatment liquid of ammonium fluoride + hydrogen peroxide and the second treatment liquid of alkali (ammonium hydroxide) + hydrogen peroxide are subjected to two-stage treatment at a low temperature, unnecessary treatment is required. The brazing material could be completely peeled off, and the dissolution of the copper plate could be suppressed within 10 μm. Therefore, according to the method of the present invention, it is possible to remove the unnecessary brazing material while substantially maintaining the dimensional accuracy of the circuit pattern.

[0043]

According to the present invention, the melting of the metal circuit pattern formed on the ceramic substrate is suppressed to a very small amount,
Unnecessary brazing material remaining in the non-circuit portion can be completely removed. As a result, the dimensional accuracy of the circuit pattern of the manufactured ceramic circuit board is improved, and the reliability is improved.

Claims (1)

[Claims] 1. A step of joining a metal plate to a ceramic substrate using a brazing material containing an active metal, a step of forming a predetermined circuit pattern by removing unnecessary portions of the joined metal plate by etching, and a step of forming a non-circuit portion. Removing the unnecessary brazing material, wherein the removing of the unnecessary brazing material is performed at 20 to 40 ° C. using an aqueous solution containing ammonium fluoride and hydrogen peroxide. A method for producing a ceramic circuit board, comprising: a treatment; and a second treatment of treating at 20 to 40 ° C. using an aqueous solution containing an alkali and hydrogen peroxide.