JP2738840B2 - Ceramic-metal composite substrate - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic-metal composite substrate manufactured by bonding a ceramic and a metal used for mounting a semiconductor, for example, and more particularly to a semiconductor-ceramic composite substrate. It relates to a substrate structure to be prevented.

[Prior Art] FIG. 5 is a cross-sectional view showing a conventional composite board for mounting a semiconductor in which a ceramic insulating base and a metal member are directly joined, for example, as disclosed in Japanese Patent Application Laid-Open No. 60-155580. In (1), an alumina member of a ceramic insulating base material, (2)
A) and (2B) are metal members formed on the alumina member (1), for example, a tough pitch electrolytic copper plate for forming an electric circuit, and (7A) and (7B) are alumina members (1) and a copper plate (2A). , (2B) are directly joined.

FIG. 6 is a perspective view showing an embodiment using a conventional semiconductor mounting substrate, and shows an example of a module structure on which a semiconductor is mounted. In the figure, (4) is a semiconductor, (5) is a solder for mounting the semiconductor (4) on the copper plate (2b),
(6a) (6b) is another copper plate (2a) electrically insulated from the copper plate (2b) to operate the semiconductor (4) respectively
This is a bonding wire made of, for example, aluminum connected to (2c).

When the semiconductor of the module configured as described above, particularly a high-power semiconductor, is operated, the semiconductor (4) generates a large amount of heat. Of course, the above modules are used repeatedly. Therefore, the following is required for the semiconductor mounting substrate. The heat generated from the semiconductor (4) can be sufficiently released, and the operation of the semiconductor (4)
The semiconductor (4) should not be destroyed by the thermal expansion and contraction of the substrate caused by the heat cycle accompanying the non-operation, and the alumina member itself should not be destroyed by this heat cycle.

[Problems to be Solved by the Invention] However, in the above substrate structure, the ceramic insulating base material (1) generally has a small coefficient of thermal expansion, and is 7 × 10 ⁻⁶ in the alumina ceramic of the above embodiment. Therefore, when directly joined to a copper plate (2A) (2B) having a thermal expansion coefficient of 17 × 10 ⁻⁶ , stress was generated near the joint surfaces (7A) and (7B) due to the difference in thermal expansion coefficient. When such a bonded body is subjected to a heat cycle, large stress is repeatedly generated in the vicinity of the bonded surfaces (7A) and (7B), and the hard but brittle alumina member (1) cannot withstand the stress and cracks. At last there was a problem of separation. FIG. 7 typically shows a crack shape in a cross-sectional view. (8A) (8B) (8C) (8D) are cracks.
Thus, the cracks (8A) to (8D) occurred from the corners of the ceramic insulating substrate (1) and the copper plates (2A) (2B) where stress was concentrated.

Further, since the copper plates (2A) and (2B) are firmly joined to the alumina part (1), their thermal expansion coefficients are smaller than those of copper alone, but the thermal expansion coefficients are 5 × 10 ^{− 6}
When the small silicon semiconductor (4) is mounted by, for example, soldering, there is a problem that the semiconductor (4) is also cracked. These problems became remarkable when the thickness of the copper plates (2A) and (2B) was increased in order to increase the operating current of the semiconductor (4) or when the semiconductor (4) having a large area was mounted.

Although the above cracks can be slightly improved by increasing the thickness of the alumina member (1), the heat radiation characteristics from the semiconductor (4) are deteriorated due to the high thermal resistance of the alumina member (1). For example, by increasing an alumina member (1) having a thickness of 0.4 mm to 0.63 mm, the temperature becomes -40 ° C to 150 ° C.
Although the heat cycle resistance of this material is improved by about 1.2 times, the thermal resistance value that prevents heat from escaping is about 1.6 times higher, and the functions of the semiconductor (4) and the cost of the ceramic insulating substrate (1) are taken into consideration. If not a valid way.

Therefore, in order to avoid these problems, the copper plate (2A), (2B)
It is necessary to take measures such as reducing the mounting density by making it thinner and wider, and this has been a major obstacle to higher functionality and higher density of the module.

The present invention has been made in order to solve the above-described problems, and even under a severe use environment, for example, releases heat generated from a semiconductor, and has high reliability in which a ceramic insulating substrate is not broken. It is intended to obtain a ceramic-metal composite substrate.

[Means for Solving the Problems] A ceramic-metal composite substrate of the present invention is a composite substrate for mounting a semiconductor formed by bonding a copper or copper alloy member to a ceramic insulating base material. A restraining member made of any one of them and having a thickness of 1/20 to 1/3 of the thickness of the copper or copper alloy member is provided so as to be connected to the copper or copper alloy member.

[Action] In the present invention, 1 / th of the thickness of the copper or copper alloy member is used.
By providing a restraining member with a thickness of 20 to 1/3, the thermal conduction and electric conduction characteristics of the substrate are ensured, and the stress applied to the ceramic insulating substrate and the semiconductor to be mounted, for example, is reduced. And destruction of semiconductors.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view showing a ceramic-metal composite substrate according to one embodiment of the present invention. In the figure, (1) is a ceramic insulating base material, in this case, a plate-like alumina member, and (2A) is an alumina member. (1) a first copper member directly joined to one surface,
(2B) is a second copper member directly bonded to the other surface of the alumina member (1), and (2C) is a third copper member added to one surface side of the alumina member (1) to increase the capacity of the semiconductor. As a member, a semiconductor (not shown) is mounted on the third copper member (2C) similarly to the conventional substrate. (3) is a restraining member. In this case, 1 / th of the total thickness of the first and third copper members (2A) and (2C) joined between the first and third copper members (2A) and (2C). It is a molybdenum member having a thickness of 20 to 1/3.

When a substrate configured as described above undergoes a heat cycle due to a change in temperature environment or operation of a semiconductor, a copper member having a large coefficient of thermal expansion (2A) (2B) due to a difference in coefficient of thermal expansion like a conventional substrate (2C) tends to expand and contract more than the alumina member (1). However, this embodiment employs a structure in which a thin molybdenum member which is a member having a low expansion coefficient, high strength, low thermal resistance, and which can be integrated with other members is added as (3) a restraining member. Molybdenum has a coefficient of thermal expansion of about 5 × 10 ⁻⁶ (/ ° C.) and about 17 × 10 ^{−6 of} copper.
(/ ° C), and a large stress is generated at the joint interface between the two during heating and cooling. However, since the yield strength of molybdenum, especially that of a thin rolled material is 50 kg / mm ² or more, copper ( A proof stress of about 10 kg / mm ² ) is immediately plastically deformed, and molybdenum acts as a restraining member (3) to prevent a large stress from being applied to the alumina member (1). Although the stress applied to the bonding interface between molybdenum and copper is higher than that of the conventional example, no cracking occurs because both are metal materials of the extending material.

In order to firmly integrate the molybdenum member (3) as a substrate constituent material, for example, the molybdenum member (3)
After joining the first and third copper members (2A) and (2C) with a method such as explosion welding, the composite material is converted to an alumina member (1).
For example, a joining method using a DBC method or the like disclosed in Japanese Patent Application Laid-Open No. 60-155580 is adopted.

Further, even if the substrate structure is a symmetrical structure centering on the ceramic insulating base material (1) as in the conventional example, the effect on cracking of the ceramic insulating base material (1) and the like appears. However, problems such as an increase in the number of components, an increase in material cost, and an increase in thermal resistance due to the provision of a new restraint member arise. On the other hand, it is the copper member on the semiconductor side that needs to be increased in volume as the capacity of the semiconductor increases. The thickness of the copper member on the semiconductor side is required to be 0.3 mm or more in total, 5 mm or less is appropriate, and the range of 0.3 mm to 1 mm is desirable.

Therefore, in this embodiment, the first and third copper members (2A) and (2C) and the molybdenum member (3) only on the side on which the semiconductor is mounted.
Are laminated, and the other side is a structure of the second copper member (2B) alone, as shown in FIG. The result is a simple, inexpensive structure with good performance. The second copper member (2B) is provided for soldering in a later process, and when the second copper member (2B) is not provided, the molybdenum member (3) must be slightly thicker for balancing. I have. The thickness is suitably 0.3 mm or less to prevent cracking of the alumina member (1), and it is necessary to select the thickness in consideration of the thickness of the molybdenum member (3). For example, when the thickness of the first and third copper members (2A) and (2C) on the semiconductor side is 0.3 mm and the thickness of the molybdenum member (3) is 0.1 mm, the second copper member (2B) on the opposite side is formed. ) Is suitably 0.1 mm thick. By using a composite substrate having such a structure, a substrate that does not warp during heating and cooling of the substrate can be obtained. As described above, according to this embodiment, with a simple structure, even under a severe use environment, heat generated from a semiconductor is released,
A highly reliable ceramic-metal composite substrate that can be used as a large-capacity power transistor module substrate that does not cause damage to the alumina member (1) or the like can be obtained.

FIG. 2 is a characteristic diagram showing an example of the relationship between the thickness of the molybdenum member (3) according to the present invention and the number of heat cycles. The abscissa indicates the thickness of the molybdenum member (3), and the ordinate indicates the number of heat cycles (the number of heat cycles until the alumina member (1) cracks). This figure shows the results of a heat cycle test of a ceramic-metal composite substrate having a symmetrical structure. The total thickness of a copper member composed of two layers with a molybdenum member (3) interposed is 1.0 mm and the thickness of an alumina member (1) Is 0.63mm, heat cycle condition is -40 ℃ ~ 150 ℃
It is. From FIG. 2, the thickness of the molybdenum member (3) was set to 0.05.
It can be seen that the heat cycle resistance was sharply improved by setting the thickness to at least mm.

Thus, by absorbing the stress generated between molybdenum and copper by the deformation of copper, the stress between copper and alumina is reduced, and the molybdenum member (3) having a thickness of about 1/10 of the thickness of the copper member can be reduced. It has been proved that the heat cycle resistance can be improved by more than 10 times only by adding. This effect
Needless to say, this is not true only when the thickness of the copper member is 1.0 mm.

The thickness of the molybdenum member (3) is suitably 1/20 to 1/3 of the total thickness of the copper member. By changing the molybdenum thickness within this range, the heat cycle resistance and heat Resistance and substrate cost can be changed. With a molybdenum member (3) having a thickness of 1/20 or less, the heat cycle resistance cannot be sufficiently improved, and with a molybdenum member (3) having a thickness of 1/3 or more, the thermal resistance becomes high. Insufficient heat dissipation is inconvenient for higher functionality, and the cost of the substrate is higher, which lowers its industrial value. Further, if the thickness of the second copper member (2B) disposed on the opposite side is 0.3 mm or more, warpage occurs, which is a problem.

As a method of relieving internal stress due to a difference in thermal expansion in a structural material in which ceramic and steel are joined, a relatively soft metal layer such as aluminum or copper, niobium, or niobium / niobium may be provided between both joining surfaces. A method of providing a laminated intermediate layer of molybdenum and niobium / tungsten by several mm has been proposed. (Magazine: Metal, May 1986, 45-50
However, as described above, providing an intermediate layer of several mm as a substrate for mounting a semiconductor is a problem because heat dissipation becomes extremely poor, and a large capacity and high functionality cannot be achieved.

Although the molybdenum member (3) is provided between the first and second copper members (2A) and (2C) having the same thickness in the above embodiment, the first and second copper members (2A) and (2C) are provided. The same effect can be expected even if the thicknesses are different. Similar effects can be expected by integrating the first and second copper members (2A) and (2C) and disposing the molybdenum member (3) on the surface of a single copper member or between the copper member and the alumina member. it can.

Fig. 3 shows a molybdenum member (3) replaced with a fourth copper member (2D)
FIG. 11 is a cross-sectional view showing another embodiment of the present invention when arranged on the surface of the present invention. In this embodiment, since the molybdenum member (3) having a small thermal expansion coefficient is on the surface, the thermal expansion matching with the semiconductor (not shown) mounted thereon becomes better.

Fig. 4 shows the molybdenum member (3) being replaced with a fourth copper member (2D)
FIG. 10 is a cross-sectional view showing still another embodiment of the present invention in which the present invention is disposed between a member and an alumina member (1). In this embodiment, since the molybdenum member (3) is in contact with the alumina member (1), cracking of the alumina member (1) can be further prevented.

In addition, the molybdenum member does not need to be a single layer, in other words, if the total thickness is 1/20 to 1/3 of the copper member, if it is arranged according to the characteristics of the semiconductor and the characteristics of the ceramic insulating base material. Good.

Further, as described above, for the joining method of the ceramic-metal composite substrate, conventional methods such as explosive pressure welding and DBC method can be used. However, the substrates in the present invention may be firmly joined and restrained. Since it is necessary, it is better to avoid a joining method using a soft solder having a low melting point and a soft solder such as eutectic solder.

Furthermore, in the above-mentioned actual example, the case where an alumina member is used as the ceramic insulating base material (1) and a molybdenum member is used as the restraining member (3) has been described. A similar effect can be expected with a thin restraining member in the range of 1/20 to 1/3 of the copper member even in a brittle insulating substrate material having a small coefficient of thermal expansion. Further, instead of the molybdenum member, a tungsten member having substantially the same coefficient of thermal expansion, proof stress, and thermal conductivity can be used. In addition, the ceramic member, copper member, and restraint member do not need to be made of the same material, and the copper member and restraint member, in particular, have significant changes in physical properties such as thermal expansion coefficient, electrical conductivity, and proof stress. Unless otherwise, a synthetic substance containing the above components as a main component, for example, a copper alloy, a molybdenum alloy, or a tungsten alloy may be used.

[Effects of the Invention] As described above, according to the present invention, in a composite substrate for semiconductor mounting formed by joining a copper or copper alloy member to a ceramic insulating base material, a composite substrate for molybdenum, tungsten, or an alloy thereof is used. By providing a restraining member having a thickness of 1/20 to 1/3 of the thickness of the copper or copper alloy member connected to the copper or copper alloy member, the ceramic insulating base material which is a brittle material is provided. This has the effect of lowering the generated thermal stress and obtaining a ceramic-metal composite substrate capable of preventing the destruction of the ceramic insulating base material and the mounted semiconductor even under a severe use environment.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a ceramic-metal composite substrate according to one embodiment of the present invention, FIG. 2 is a characteristic diagram showing an example of a relationship between a heat cycle of the substrate according to the present invention and a thickness of a restraining member, FIG. 3 is a sectional view showing another embodiment of the present invention, FIG. 4 is a sectional view showing still another embodiment of the present invention, and FIG.
FIG. 6 is a sectional view showing a conventional ceramic-metal composite substrate, FIG. 6 is a perspective view showing one embodiment of a general ceramic-metal composite substrate, and FIG. 7 is a crack generated in the conventional ceramic-metal composite substrate. FIG. In the figure, (1) is a ceramic insulating substrate, (2A),
(2C) and (2D) are copper or copper alloy members, and (3) is a restraining member. In the drawings, the same reference numerals indicate the same or corresponding parts.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-72575 (JP, A) JP-A-63-179733 (JP, A) JP-A-63-206365 (JP, A) JP-A-60-1985 177634 (JP, A) JP-A-63-42152 (JP, A) JP-A-59-2150 (JP, U)

Claims (1)

(57) [Claims] 1. A composite substrate for mounting a semiconductor formed by joining a copper or copper alloy member to a ceramic insulating base material,
Molybdenum, made of any of tungsten and its alloys, that a restraining member having a thickness of 1/20 to 1/3 of the thickness of the copper or copper alloy member is provided connected to the copper or copper alloy member. Characteristic ceramic-metal composite substrate.