JP2017041567A - Method of manufacturing ceramic circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic circuit board having excellent crack resistance against ultrasonic bonding.SOLUTION: Provided is a method of manufacturing a ceramic circuit board in which both main surfaces of a ceramic substrate and a metal plate are joined via a silver-copper brazing material layer, in which the composition of the silver-copper brazing material is 75 to 98 parts by mass of the silver powder and 2 to 25 parts by mass of the copper powder, the ceramic circuit contains at least one active metal selected from titanium, zirconium, hafnium, niobium, tantalum, and vanadium, and tin, and is bonded at a degree of vacuum of 1×10Pa or less, a bonding temperature of 780°C to 850°C, and a holding time of 10 to 60 minutes, and the difference in thickness of the brazing material layer after bonding is smaller than 50 μm. The ceramic substrate is made of aluminum nitride.SELECTED DRAWING: None

Description

  The present invention relates to a method for manufacturing a ceramic circuit board having excellent crack resistance against ultrasonic bonding.

Power modules that require high voltage and large current operation, such as those for electric railways, vehicles, and industrial machines, are mounted with a semiconductor element bonded on a ceramic circuit board. In order to extract the output from the ceramic circuit board to the outside, it is common to provide a copper electrode and install it in a form protruding from the outside of the ceramic circuit board.

  Conventionally, solder has been used to join a ceramic circuit board and a copper electrode, but there has been a problem that solder cracks are generated due to heat and vibration generated when used as a power module, and reliability is lowered. For this reason, ultrasonic bonding that directly bonds a metal circuit board and a copper electrode has been used. Ultrasonic bonding is a technique in which the copper plate and the copper electrode of the circuit board are integrated by applying ultrasonic vibration in the horizontal direction while applying a load in the vertical direction to the ceramic substrate.

Ceramic substrates used for ceramic circuit boards use aluminum nitride sintered bodies and silicon nitride sintered bodies with high thermal conductivity in response to the increase in heat generation due to higher output and higher integration of semiconductor elements. ing. In particular, since the aluminum nitride substrate has a higher thermal conductivity than the silicon nitride substrate, it is suitable as a ceramic circuit substrate for mounting a high heat dissipation electronic component.

However, while the aluminum nitride substrate has high thermal conductivity, its mechanical strength and toughness are low, so the cracks occur on the surface of the aluminum nitride plate directly under the joint due to vibration during ultrasonic bonding, resulting in module reliability. There was a problem of damaging. In order to prevent the occurrence of cracks in the ceramic substrate, the following proposals have been made.

  Patent Document 1 states that the occurrence of cracks in the ceramic substrate can be prevented by optimizing the position at which the copper electrode is ultrasonically bonded and the bonding strength between the copper electrode and the metal circuit board.

JP 2002-164461 A

  However, Patent Document 1 does not improve the ceramic circuit board itself, and has not yet reached a fundamental solution for preventing the occurrence of cracks.

  An object of this invention is to obtain the ceramic circuit board which has the outstanding crack resistance with respect to ultrasonic bonding in view of the said subject.

As a result of intensive studies to achieve the above object, the present inventor has found that crack resistance at the time of ultrasonic bonding can be improved by suppressing the difference in thickness of the brazing material layer after bonding of the ceramic circuit board. Is obtained.

That is, the present invention is a ceramic circuit board in which both main surfaces of a ceramic substrate and a metal plate are bonded via a silver-copper brazing material layer, and the silver-copper brazing material has a silver powder 75- 98 parts by mass, 2 to 25 parts by mass of copper powder, and a total of 100 parts by mass, including at least one active metal selected from titanium, zirconium, hafnium, niobium, tantalum and vanadium and tin, and a degree of vacuum of 1 × 10 ⁻³ The ceramic circuit board manufacturing method is characterized in that bonding is performed at Pa or less, a bonding temperature of 780 ° C. to 850 ° C., and a holding time of 10 to 60 minutes, and the difference in thickness of the brazing filler metal layer after bonding is smaller than 50 μm.

  According to the present invention, it is possible to manufacture an aluminum nitride circuit board in which cracks are not generated by ultrasonic bonding.

  The ceramic substrate used for the ceramic circuit board of the present invention is not particularly limited, and nitride ceramics such as silicon nitride and aluminum nitride, oxide ceramics such as aluminum oxide and zirconium oxide, silicon carbide, etc. It can be used for carbide ceramics, boride ceramics such as lanthanum boride. However, since the metal plate is bonded to the ceramic substrate by the active metal method, non-oxide ceramics such as aluminum nitride and silicon nitride are preferable, and an aluminum nitride substrate is more preferable from the viewpoint of excellent thermal conductivity.

The thickness of the ceramic substrate of the present invention is not particularly limited, but if it exceeds 1.5 mm, the thermal resistance increases, and if it is less than 0.2 mm, the durability is lost, so 0.2 to 1.5 mm is preferable.

  The metal used for the metal plate of the present invention is not particularly limited as long as it is a metal to which the active metal method can be applied, such as copper, aluminum, iron, nickel, chromium, silver, molybdenum, cobalt, or an alloy thereof, but in particular, Copper is preferable from the viewpoints of conductivity and heat dissipation.

  The purity of the copper plate of the present invention is preferably 90% or more. When the purity is lower than 90%, when the ceramic substrate and the copper plate are joined, the reaction between the copper plate and the brazing material becomes insufficient, or the copper plate is hard. Therefore, the reliability of the circuit board may be reduced.

The thickness of the copper plate of the present invention is not particularly limited, but is generally 0.1 to 1.5 mm, particularly preferably 0.2 mm or more from the viewpoint of heat dissipation, and 0.5 mm from the viewpoint of heat cycle characteristics. The following is preferred.

  The brazing material of the present invention is composed of a silver-copper brazing material containing at least one active metal selected from titanium, zirconium, hafnium, niobium, tantalum, and vanadium and tin in the brazing material. The composition ratio of the silver-copper brazing material is preferably set to a composition ratio at which eutectic composition is likely to be generated, and in particular, a composition considering the penetration of copper from the circuit copper plate and the heat dissipation copper plate (of silver powder and copper powder). In total 100 parts by mass, 75 to 98 parts by mass of silver powder and 2 to 25 parts by mass of copper powder) are preferable. When the amount of the silver powder is other than 75 to 98 parts by mass, the melting temperature of the brazing material is increased, so that the thermal stress derived from the difference in thermal expansion coefficient at the time of bonding is increased, and the heat cycle resistance is easily lowered.

In order to adjust the melting temperature of the brazing material at the time of joining, 0.1 to 20 parts by mass of tin is preferably added to the brazing material layer of the present invention. If the amount is less than 0.1 parts by mass, the effect is not obtained. If the amount exceeds 20 parts by mass, the melting temperature becomes too low, and problems such as the brazing material flowing out during joining occur.

The thickness of the brazing material of the present invention is 5 to 40 μm on a dry basis. Is preferred. If the thickness of the brazing material is less than 5 μm, an unreacted portion may occur. On the other hand, if the thickness exceeds 40 μm, the time for removing the bonding layer may become long and productivity may be reduced. The coating method is not particularly limited, and a known coating method such as a screen printing method or a roll coater method that can be uniformly coated on the substrate surface can be employed.

The bonding temperature of the ceramic circuit board according to the present invention is preferably 780 ° C. to 850 ° C., more preferably less than 800 ° C. in a vacuum furnace having a degree of vacuum of 1 × 10 ⁻³ Pa or less. Further, the holding time is desirably 10 to 60 minutes. If the bonding temperature is lower than this, or if the holding time is shortened, the Ti compound may not be generated sufficiently, so that it may not be possible to partially bond. Conversely, if the bonding temperature is high or the holding time is too long Therefore, the difference in thickness of the brazing filler metal layer after joining becomes too large, and cracks due to ultrasonic joining tend to occur.

  The thickness difference of the brazing material layer of the ceramic circuit board of the present invention is preferably less than 50 μm, more preferably less than 35 μm. When the thickness difference of the brazing material layer is large, the stress generated at the time of ultrasonic bonding tends to concentrate locally, and cracks are likely to occur.

  In order to form a circuit pattern on the bonded ceramic circuit board, an etching resist is applied to the metal plate and etched. There is no restriction | limiting in particular regarding an etching resist, For example, the ultraviolet curing type and thermosetting type generally used can be used. There is no restriction | limiting in particular about the coating method of an etching resist, For example, well-known coating methods, such as a screen printing method, are employable.

In order to form the circuit pattern, the copper plate is etched. There is no particular restriction on the etching solution, and generally used ferric chloride solution, cupric chloride solution, sulfuric acid, hydrogen peroxide solution, etc. can be used. A dicopper solution is mentioned. The nitride ceramic circuit board from which unnecessary metal parts have been removed by etching has the applied brazing material, its alloy layer, nitride layer, etc. remaining, inorganic acid such as aqueous solution of ammonium halide, sulfuric acid, nitric acid, peroxide It is common to remove them using a solution containing hydrogen water. The etching resist is stripped after the circuit is formed, but the stripping method is not particularly limited, and a method of immersing in an alkaline aqueous solution is common.

[Example 1]
On an aluminum nitride substrate having a thickness of 0.635 mm, 90 parts by mass of silver powder (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd .: AgC-BO) and copper powder (manufactured by Fukuda Metal Foil Powder Industry Co., Ltd .: SRC-Cu-20) 3.5 parts by mass of titanium (manufactured by Osaka Titanium Technologies: TSH-350) and 3 parts by mass of tin (Mitsuwa Chemicals: tin powder (-325 mesh)) per 100 parts by mass of 10 parts by mass Part of the active metal brazing material was applied so that the thickness after drying was 15 μm. Then, a copper plate for circuit formation (thickness 0.3 mm) is stacked on the front surface, and a copper plate for heat radiation plate formation (thickness 0.3 mm) is stacked on the back surface, and in a vacuum atmosphere (6.5 × 10 ⁻⁴ Pa) at 840 ° C. The bonded body of the copper plate and the aluminum nitride substrate was manufactured by holding for 20 minutes.

  The joined circuit board was etched with an etchant containing copper chloride to form a circuit. Further, the brazing material layer was etched with an ammonium fluoride / hydrogen peroxide etchant to produce an aluminum nitride circuit board.

Measurement of the difference in thickness of the brazing filler metal layer of the obtained aluminum nitride circuit board, ultrasonic bonding evaluation, and thermal cycle test were performed as follows.
<Measurement of thickness difference of brazing material layer>
The central part of the ceramic circuit board was cut at a width of 15 mm, and after resin embedding and cross-section adjustment, the brazing material layer was observed using SEM. The difference in thickness of the brazing material layer is obtained by averaging the difference between the maximum thickness and the minimum thickness when three cross-sections are selected at intervals of 4 mm and a range of 300 μm is observed in the horizontal direction on the joint surface. The results are shown in Table 1.
<Ultrasonic bonding evaluation>
A copper electrode material having a thickness of 1.5 mm was joined with “UP-Lite 3000 manufactured by Adwells Corporation” at a load of 1200 N, a frequency of 20 kHz, an amplitude of 50 μm, and a joining time of 0.4 seconds. After joining, the copper electrode and the copper plate of the circuit board were removed by etching, and the surface of the ceramic substrate was observed with an optical microscope. Ultrasonic bonding was performed at 32 locations, and the incidence of cracks was ranked into the following three.
A: Occurrence rate 0%, O: 0% <Occurrence rate ≤ 20%, x: Occurrence rate> 20%

[Examples 2 to 10, Comparative Examples 1 to 4]
The same operation as in Example 1 was performed except that the conditions shown in Table 1 were changed.

As described above, according to the present invention, when a copper electrode is bonded to a ceramic circuit board by ultrasonic bonding, the crack generation rate can be suppressed to 20% or less to improve the reliability of the module. A ceramic circuit board that can be provided is provided.

Claims (3)

A ceramic circuit board in which both main surfaces of a ceramic substrate and a metal plate are bonded via a silver-copper brazing filler metal layer, wherein the silver-copper brazing filler comprises 75 to 98 parts by mass of silver powder, copper powder 2 to 25 parts by mass with a total of 100 parts by mass, including at least one active metal selected from titanium, zirconium, hafnium, niobium, tantalum, and vanadium and tin, with a degree of vacuum of 1 × 10 ⁻³ Pa or less and a junction temperature of 780 A method for producing a ceramic circuit board, characterized in that bonding is performed at a temperature of 850 ° C. to 850 ° C. for a holding time of 10 to 60 minutes, and the difference in thickness of the brazing filler metal layer after bonding is less than 50 μm.   2. The method of manufacturing a ceramic circuit board according to claim 1, wherein a difference in thickness of the brazing material layer after joining is less than 15 [mu] m. 3. The method of manufacturing a ceramic circuit board according to claim 1, wherein the ceramic substrate is made of aluminum nitride.