JPH07193358A - Manufacture of ceramic electronic circuit board - Google Patents

Abstract

PURPOSE:To improve the joint strength, heat conductivity and heat resistance characteristics of an aluminium-ceramic composite board by a method wherein after a metal for conductive circuit formation is dissolved, a ceramic board is held and is cooled in a state that it is brought into contact directly to this molten metal. CONSTITUTION:An aluminium (ceramic) board 2, an aluminium raw material 3 and a graphite piston 4 are installed in a graphite casting mold 1 and the casting mold is put in a furnace heated to 800 to 1000 deg.C The raw material 3 is dissolved and after the molten raw material 3 intrudes into the part installed with the board 2 by the weight of the piston, the casting mold is taken out from the heating furnace and is cooled to room temperatures. The above heating and cooling are performed in a nitrogen atmosphere for the graphite casting mold from being oxidized. A composite board, which is formed in such a way and has an aluminium layer, is subjected to mechanical and electrolytic polishing. The texture of the aluminium part of such the composite board is dense and the strength of the board is 35kg/cm or stronger.

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 bonded body of metal and ceramics, and particularly to a method for manufacturing an aluminum-ceramic composite electronic circuit board suitable for mounting a high power electronic device such as a power module. It is about.

[0002]

2. Description of the Related Art A metal-ceramic composite electronic circuit board produced by bonding a metal to a surface of a ceramic substrate is used as a mounting substrate for a high power device such as a power module, and is particularly excellent in electrical and thermal conductivity. Composite substrates of copper and alumina or aluminum nitride ceramics are currently mainly used.

As a method of joining copper and ceramics, there are a direct joining method and a brazing method. The former is a technology developed for joining oxide ceramics and copper.When joining, a copper plate containing oxygen is used to heat in an inert atmosphere or to oxidize using oxygen-free copper. It is a method of joining copper and ceramics by heating in a neutral atmosphere. When joining non-oxide ceramics and copper by this method, it is necessary to previously form an oxide layer on the surface of the non-oxide ceramics. For example, as disclosed in JP-A-59-3077, about 1000
The aluminum nitride substrate is treated at a temperature of ° C to form an oxide on the surface and then the copper and aluminum nitride are bonded by the method described above. The brazing method is a method of joining copper and ceramics through a brazing material of an active metal, and in this method, an Ag-Cu-Ti based brazing material is generally used.

Although the copper-ceramic composite substrate is widely used, it has some problems during production and practical use. The most serious problem among them is the dielectric breakdown between the front and back surfaces of the substrate, which is caused by cracks inside the ceramic substrate during mounting and use of electronic components.

In order to bond a ceramic substrate and copper,
When the ceramics substrate and copper are heated to nearly 1000 ° C, and when mounting electronic components such as power modules,
The copper-ceramic composite substrate is heated to near 400 ° C. Since the coefficient of thermal expansion of copper is about an order of magnitude higher than that of ceramics, when the composite substrate is cooled to room temperature, a large thermal stress is generated inside the substrate due to the difference in coefficient of thermal expansion. Furthermore, the temperature of the substrate constantly changes due to the environment in which the electronic component is used and the heat generated during use, and the thermal stress acting on the substrate also changes accordingly. The effect of these thermal stresses causes cracks in the ceramic substrate. Therefore, heat cycle resistance, which is one of the important evaluation items for ceramics electronic circuit boards, that is, cracks are generated on the board when the board is heated and cooled repeatedly in the temperature range of -40 ° C to 125 ° C. The characteristic value evaluated by the number of repetitions until occurrence is 20 times for the copper-alumina composite substrate manufactured by the direct bonding method, but this characteristic value of the same substrate manufactured by the brazing method is 10 times or less. is there.

There has been a concept of using aluminum, which has excellent electric and thermal conductivity similar to copper, as a conductive circuit material (for example, such a concept is described in JP-A-59-121890). . Aluminum is softer than copper. Its yield strength is about 1/4 that of copper. Therefore,
If aluminum is used as a circuit material, it can be expected that the residual stress generated inside the composite substrate can be relieved significantly. However, the above-mentioned Japanese Patent Laid-Open No. 59-121890 does not disclose a specific method for joining aluminum and ceramics. Japanese Unexamined Patent Publication Nos. 3125463, 4-12554 and 4-18746 disclose methods for producing an aluminum-ceramic composite substrate by a brazing method. According to these documents, the heat cycle resistance of the manufactured aluminum-ceramic substrate is 200 times or more, which is about 10 times that of the copper-ceramic substrate.

However, there are the following problems when an aluminum-ceramic composite substrate is manufactured by the brazing method as disclosed in the above publication and when the substrate thus prepared is used.

1) Since aluminum is easily oxidized, the method disclosed in the above-mentioned publication must be carried out in vacuum or in a high-purity inert gas atmosphere.

2) The melting point of aluminum is as low as 660 ° C,
When the brazing temperature is brought close to this, all of the aluminum melts and the shape collapses, or the aluminum locally melts, causing a brazing defect called bug eating. On the other hand, when the brazing temperature is lowered, the reaction between the brazing material and the ceramics is less likely to occur, so that the strength of the joined body is weak. As shown in the examples of the present invention, when an Al-Si based brazing alloy is used, the brazing should be performed within a temperature range narrower than the temperature range of 590 ° C to 640 ° C. According to the experience of the inventor, in the case of mass production, especially when manufacturing a composite substrate in a vacuum (the heat from the heating element is transferred only by radiation and conduction, and there is no convection), the temperature in the furnace is uniformly controlled. Very difficult to do.

3) When a composite substrate is manufactured by the brazing method, the brazing temperature must be 660 ° C. or lower of the melting point of aluminum. However, at such a temperature, the wettability between the aluminum brazing material and the ceramic is not good. Therefore, when manufacturing a composite substrate by this method,
Non-contact defects are likely to occur.

4) Although an alumina substrate can be directly brazed, in the case of an aluminum nitride ceramic substrate, the surface of the aluminum nitride substrate must be previously oxidized as in the case of directly joining copper. This method not only complicates the process, but since the aluminum nitride substrate was originally developed to meet the requirement for high thermal conductivity, the formation of oxide on the surface adversely affects the thermal conductivity. Needless to say to give.

5) As in the case of the copper-ceramics composite substrate, the heat cycle resistance of the substrate produced by the brazing method is considered to be lower than that produced by the direct joining method. This is because the braze alloy used to make the substrate is harder than pure metal,
This is because plastic deformation is unlikely to occur, which adversely affects stress relaxation.

[0013]

As described above, in the process of producing an aluminum-ceramic composite substrate by the brazing method, there are problems such as stability, and the ceramic substrate is a non-oxide type. However, the manufacturing process is complicated. Further, it is considered that the composite substrate manufactured in this way is not necessarily optimum in terms of bonding strength and heat resistance.

The present invention overcomes these problems and provides a stable and convenient manufacturing method for manufacturing an aluminum-ceramic composite substrate having better bonding strength, thermal conductivity, and heat resistance. With the goal.

[0015]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found a novel manufacturing method for manufacturing an aluminum-ceramic composite substrate, and can provide the present invention. did it.

That is, according to the present invention, (1) in the production of a ceramic electronic circuit board having a metal conductive circuit on at least one surface of the ceramic substrate, (a) the metal for forming the conductive circuit is melted in advance and then cast into a mold. Melting or melting the metal in a mold,
(A) Directly contacting the ceramic substrate with the molten metal by previously disposing the ceramic substrate at a predetermined place in the mold or by inserting the ceramic substrate into the molten metal; A method for manufacturing a ceramics electronic circuit board, characterized in that the ceramics substrate and the molten metal are held in contact with each other and then cooled to directly bond the metal and the ceramics substrate; (2) The metal is aluminum or an alloy thereof. And the above-mentioned manufacturing method, wherein the ceramic substrate is a ceramic substrate suitable for mounting alumina, aluminum nitride, or other electronic devices.

[0017]

According to the previous research conducted by the inventors, when heated in the atmosphere, a thick oxide (alumina) layer is formed on the surface of aluminum, so that aluminum and ceramics cannot be joined. Although aluminum and ceramics can be bonded in a vacuum and in an inert atmosphere, a thin oxide layer is detected at the bonding interface, and aluminum and ceramics are bonded through a thin oxide film on the aluminum surface. Recognize. Since aluminum covered with alumina does not have good wettability with respect to ceramics, a non-contact portion is easily formed in the interface portion of the joined body thus produced, and the joining strength varies.

In order to suppress the adverse effect of such an oxide film, the present inventors have long used aluminum as an alloying element S.
i, Ti, etc. were added and the effect was investigated. Si has the effect of thinning the oxide film on the surface, and Ti plays the role of promoting the reaction at the interface. It was also confirmed that the simultaneous addition of Si and Ti is most effective in improving the strength and stability of the joined body. However, in each case, oxide was detected from the interface part of the bonded body, and it was found that aluminum and ceramics were still bonded via the oxide film.

Oxide alumina on the surface of aluminum is chemically very stable and does not easily react with other substances. Therefore,
If this is present at the interface, it is considered that the bonding between aluminum and the ceramic substrate is hindered.

In a previous study conducted by the inventors of the present invention on a sintered body of aluminum and ceramic powder, there is a portion where aluminum oxide and ceramic powder are directly joined without an oxide film interposed, and aluminum is also interposed between them. It was found that a reaction product of the and the ceramics was formed. It is considered that this is because the oxide film on the surface of the aluminum powder was broken when the powder was mixed and pressure-molded, and the aluminum and the ceramic powder were heated while being in direct contact with each other. This suggests the possibility of direct bonding between aluminum and ceramics.

The present inventors have made various attempts to remove the oxide film on the aluminum surface and produce a good quality metal-ceramic composite substrate, but it has been found that the following means is effective.

1) A relative motion was caused between the molten metal and the ceramic substrate in order to dissolve the metal and break the oxide film on the surface of the molten metal. More specifically, by placing a ceramics substrate at a predetermined location of the mold in advance and then casting the molten metal, or by inserting the ceramics substrate into the cast molten metal, Cause a relative movement between.

2) Since the oxide film on the metal surface is easily decomposed when the temperature rises, it is preferable to raise the temperature of the molten metal. However, heating the molten metal to a high temperature requires extra energy, and at the same time, unfavorable conditions such as the evaporation of the molten metal and the reaction between the molten metal and the mold become violent. Is below ℃,
A sound composite substrate can be produced in this temperature range.

3) In order to suppress the oxidation of the molten metal surface as much as possible, the molten metal is cast and the substrate is inserted as quickly as possible. The production may be carried out in the air, but it is preferable to carry out the melting and casting in a vacuum or an inert atmosphere in order to prevent oxidation.

Regarding the method of forming the pattern of the electronic circuit, the pattern of the circuit pattern is formed in advance on the mold and the circuit pattern is directly formed, or after the solid aluminum layer is formed, the circuit pattern is formed by the etching method. There is a way to do it.

[0026]

Example 1 As shown in FIG. 1, a graphite mold 1 has a thickness of 0.
A 635 mm alumina (ceramics) substrate 2, an aluminum raw material 3 and a graphite piston 4 are installed, and these are 700 ℃ (experiment 1), 800 ℃ (experiment 2), 900 ℃ (experiment 3), 1000 ℃ (experiment 4), respectively. It was placed in a furnace that was heated to room temperature. After the aluminum raw material melted and entered the portion where the alumina substrate was installed by the weight of the piston, the mold was taken out of the heating furnace and cooled to room temperature. In this example, heating and cooling were performed in a nitrogen atmosphere in order to prevent oxidation of the graphite template. 0.5mm on one side made in this way
Mechanically and electropolishing a composite substrate with a thick aluminum layer, observing the structure of the aluminum with an optical microscope,
A 4 mm wide sample for peel strength measurement was cut out from this composite substrate and a 90 ° peel strength test was conducted.

The composite substrate produced at any temperature has a very dense structure of the aluminum part,
There were no defects commonly found in castings such as cavities. Further, as shown in Table 1, since the strength of the composite substrate was 35 kg / cm or more, and the fracture occurred not in the interface but in the aluminum, it was found that the aluminum was firmly bonded to the alumina substrate. Furthermore, some non-contact defects were found in the samples prepared at 700 ° C, but were not found in the samples prepared at 800 ° C or higher.

In these examples, the alumina substrate was used to manufacture the composite substrate, but one inventor confirmed in another invention that the aluminum nitride composite substrate could be manufactured by the same method.

[0029]

[Table 1] From the contents described in the present specification, it will be easily understood that the method shown in the above-mentioned embodiment is not the only method and should not be limited to the conditions shown in this embodiment.
High pressure casting, die casting, it is possible to produce a composite substrate by various methods such as continuous casting, the holding time at the production temperature is lengthened, an alloying element useful in the decomposition and activation of surface oxides in aluminum, Alternatively, if alloying elements that lower the melting point, such as Si, Ge, Ti, and Mg, are added to make the sintering aid in the ceramic substrate a composition that easily reacts with aluminum, and measures are taken to increase the amount, It is easily conceivable that the composite substrate can be produced at a lower temperature.

[0030]

[Comparative Examples 1 to 6] For comparison, an aluminum-ceramic composite substrate was produced by a brazing method.

The aluminum plate and the ceramic substrate were set so that the two aluminum plates having a thickness of 0.5 mm sandwich the ceramic substrate having a thickness of 0.635 mm from above and below via the brazing material. A weight was further placed on this, and it was held in a vacuum of 10 ⁻⁵ at 650 ° C. for 20 minutes to braze the aluminum plate and the ceramic substrate. The ceramics substrates used were two types, alumina and aluminum nitride substrates, and the brazing material was three types of Al-Si-Ti alloy foil with a thickness of 0.2 mm. Its composition is shown in Table 2. The evaluation of the composite substrate was performed by the same method as shown in the examples.

[0032]

[Table 2] Table 1 also shows the evaluation results of the composite substrate. HS
In the composite substrate brazed with the brazing material, the aluminum plate itself melted and the shape collapsed. In the composite substrate brazed with the MS and LS brazing material, the aluminum plate was not entirely melted, but a considerable part was melted, and a worm-eating soldering defect was generated. The peel strength of these samples is 30 kg / cm
Below, especially in the case of aluminum nitride substrate, the brazing strength is
2.5 kg / cm or less, peel strength required as a substrate
It was lower than 5 kg / cm. In addition, the area of the non-contact portion of these composite substrates was approximately 10% or more.

[0033]

[Comparative Examples 7 to 8] In order to prevent dissolution of the aluminum plate,
The brazing temperature was lowered by 10 ° C. to 640 ° C., and an aluminum-alumina composite substrate was tried to be produced by using LS and MS brazing material. However, as shown in Table 1, at this temperature LS
Brazing with brazing material was not possible. Although brazing with the MS brazing material was possible, the brazing strength was lower than that at brazing at 650 ° C, and the above-mentioned insect biting and non-contact defects still occurred. Lowering the temperature may eliminate bug-eating defects, but there may be more non-contact defects.

[0034]

Comparative Examples 9 to 10 An attempt was made to produce an aluminum-alumina composite substrate by lowering the brazing temperature to the melting temperature of the HS brazing material (about 580 ° C). However, at such a low temperature, the ceramic substrate and the brazing material were not joined. Again 590
In the case of brazing at ℃, a part of the aluminum plate was melted to cause a bug-eating defect. It was found that the temperature cannot be raised any higher.

As can be seen from the above comparative examples, the aluminum-ceramic composite substrate manufactured by the brazing method has a lower bonding strength and a higher probability of non-contact defects than those manufactured by the direct bonding method of the present invention. .

[0036]

According to the method of the present invention as disclosed in the present specification, a soldering defect such as non-contact in the case of manufacturing by the conventional brazing method is eliminated, and high reliability of aluminum and a ceramic substrate is obtained. High strength bonding can be realized. by this,
A good quality aluminum-ceramics composite substrate with excellent heat cycle resistance can be manufactured.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an aluminum-based structure according to an embodiment of the present invention
It is a sectional view of a mold at the time of producing a ceramics composite substrate.

[Simple explanation of symbols]

 1 Graphite Template 2 Ceramics Substrate 3 Aluminum Raw Material 4 Graphite Piston

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 23/12 H05K 3/00 R

Claims (2)

[Claims] 1. In the production of a ceramic electronic circuit board having a metal conductive circuit on at least one surface of a ceramic substrate, the metal for forming the conductive circuit is melted, and then the ceramic substrate is held in direct contact with the molten metal. A method for manufacturing a ceramics circuit board, characterized in that the metal and the ceramics board are directly joined by cooling with cooling. 2. The method for manufacturing a ceramic electronic circuit board according to claim 1, wherein the metal is aluminum or an aluminum alloy, and the ceramic substrate is one selected from alumina and aluminum nitride.