JP2002033423A - Module structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-radiating component which has high reliability and superior heat radiation characteristics at low cost. SOLUTION: This is a module structure formed by joining a ceramic circuit board with an aluminum-silicon carbide composite. The yield of the aluminum- silicon carbide composite is 1.5 to 4 times as large as that of the aluminum in the aluminum-silicon carbide composite, or the Young's modulus of the aluminum-silicon carbide composite is 120 to 200 GPa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a module structure in which a ceramic circuit board on which a semiconductor element is mounted and a heat sink are joined, and more particularly to a module used in a mobile device such as a high power module or an electric vehicle. The present invention relates to a structure used, and more particularly to an improvement of a module structure in which the heat sink is made of an aluminum-silicon carbide composite.

[0002]

2. Description of the Related Art Conventionally, various insulating substrates such as a ceramic substrate and a resin substrate have been used as a circuit substrate for mounting a semiconductor element. However, miniaturization of the circuit substrate and high integration of the semiconductor element have been attempted. As the process progresses, it is desired to improve the heat radiation characteristics of the insulating material in these circuit boards. Ceramic substrates are mainly used as circuit boards, package bases, and the like that require high heat dissipation.
Materials used for ceramic circuit boards include:
Alumina (Al ₂ O ₃ ), aluminum nitride (AlN),
Silicon nitride (Si ₃ N ₄ ) and the like are known.

When a ceramic substrate is used as a circuit board, a package base, or the like, heat generated from the semiconductor element is radiated to the outside through a heat-dissipating component called a heat sink provided on the backside of the circuit board or the like, thereby increasing the temperature of the semiconductor element. And operating characteristics are ensured.

As a material for the heat sink, copper (Cu) is generally used. However, when a copper heat sink is used, the ceramic circuit board or the ceramic circuit board and the heat sink are joined by a heat cycle or the like under heating conditions or under actual use conditions due to a difference in thermal expansion between the ceramic substrate and the heat sink. Cracks and cracks may occur in the solder.

Therefore, when a ceramic circuit board is used in a field where reliability is required, a high melting point metal such as Mo or W having a small thermal expansion difference from the ceramic circuit board has been used as a heat sink. However, a heat dissipating component using a heat sink made of Mo or W is heavy because Mo or W is a heavy metal, and is not preferable for applications in which it is desired to reduce the weight of the heat dissipating component.

[0006] On the other hand, with recent advances in miniaturization of circuit boards and high integration of semiconductor elements, further improvement in heat radiation characteristics of insulating materials in these circuit boards is desired. For this reason, as a material used for the ceramic circuit board, aluminum nitride having a thermal conductivity about 10 times higher than that of alumina has been studied and put to practical use. However, even in the case of an aluminum nitride substrate, as in the case of a conventional alumina substrate, there is a problem that cracks occur in the ceramic circuit substrate and the solder at the joint due to thermal stress during use.

Further, as a material for a ceramic circuit board, silicon nitride having excellent mechanical properties such as strength and fracture toughness has been studied from the viewpoint of reliability. Conventionally, the thermal conductivity of silicon nitride has been as low as that of alumina.
Silicon nitride ceramics having about twice the thermal conductivity have been obtained.

However, although cracks in the ceramic circuit board due to thermal stress during use can be greatly reduced by using the silicon nitride substrate, the joint between the ceramic circuit board and the semiconductor element and the joint between the ceramic substrate and the heat sink are reduced. The problem that cracks occur in the solder remains.

For this reason, it has been desired to develop a heat sink material having excellent thermal conductivity and a linear thermal expansion coefficient (hereinafter referred to as a thermal expansion coefficient) close to that of a ceramic circuit board as a heat sink material. (Metal Mat) reinforced with inorganic fibers or particles
(Rix Composite) is attracting attention.

In recent years, an aluminum alloy-silicon carbide composite has been mainly studied as the composite. The aluminum alloy-silicon carbide composite has a coefficient of thermal expansion of 8 × 10
^-6 / K, which is effective in suppressing solder cracks between the heat sink and the ceramic circuit board. However, the thermal conductivity of the aluminum alloy-silicon carbide composite is 200 W
/ MK, a conventional copper heat sink (400 W / m
K), which is inferior in heat dissipation characteristics and expensive, so that practical problems remain.

On the other hand, there is also a problem that cracks occur due to thermal stress during use also in the solder portion joining the semiconductor element and the ceramic circuit board. This crack is considered to be caused by stress generated by a difference in thermal expansion between the semiconductor element and the circuit metal. In recent years, by using aluminum alloy with low elastic modulus and low yield stress as circuit metal,
It has been studied to suppress the occurrence of cracks by yielding and relaxing the stress generated in the solder portion by the aluminum alloy. However, such an aluminum circuit board still has a problem in terms of long-term reliability.

[0012]

As described above, in a conventional module structure having a joint structure between a ceramic circuit board and a heat sink, when a heavy metal material such as Mo or W is used for the heat sink, the structure of the module structure is reduced. There is a problem that the weight becomes heavy and the heat dissipation is not always sufficient. On the other hand, when using Cu, Al, etc., which are relatively lightweight and excellent in heat dissipation, as a heat sink,
In order to obtain a highly reliable structure with a large difference in thermal expansion from the ceramic circuit board, the joining structure itself becomes very complicated, leading to an increase in manufacturing cost and an increase in thermal resistance as a heat dissipating component. There was such a problem. Furthermore, even if an aluminum-silicon carbide composite having a low coefficient of thermal expansion is used as a heat sink, problems remain in terms of heat radiation characteristics and reliability. In view of the above circumstances, in a conventional module structure having a bonding structure of a ceramic circuit board and a heat sink, it is an issue to reduce the weight and simplify the bonding structure, and to improve reliability and heat dissipation. ing.

The present invention has been made in view of the above circumstances, and has high reliability in which cracks generated in a ceramic substrate are prevented, and cracks in a solder portion due to thermal stress generated in a use environment are suppressed. It is an object of the present invention to provide an inexpensive heat dissipating component having excellent heat dissipating characteristics.

[0014]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have used an aluminum-silicon carbide composite as a heat sink material, and have studied the mechanical and thermal expansion characteristics of the composite. It has been found that the heat radiation characteristics and the reliability can be improved by adjusting, and the present invention has been completed.

That is, the present invention relates to a module structure comprising a ceramic circuit board joined to an aluminum-silicon carbide composite, wherein the aluminum-silicon carbide composite has a yield strength in the aluminum-silicon carbide composite. A module structure characterized by 1.5 to 4 times the yield strength of aluminum.

Further, the present invention relates to a module structure having a ceramic circuit board bonded to an aluminum-silicon carbide composite, wherein the aluminum-silicon carbide composite has a Young's modulus of 120 to 200 GPa. This is a featured module structure.

Further, the present invention provides the above module structure, wherein the room temperature of the aluminum-silicon carbide composite is 12
The thermal expansion coefficient at 5 ° C. is 15 × 10 ⁻⁶ / K or less.

In addition, the present invention is characterized in that in the module structure, the silicon-carbide content in the aluminum-silicon carbide composite is 10 to 40% by volume.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The module structure of the present invention has a structure in which a ceramic circuit board and a heat sink are integrally joined and uses an aluminum-silicon carbide composite as the heat sink. Even if the semiconductor elements mounted on the substrate, the ceramic substrate that constitutes the ceramic circuit board, and the heat sink all have the same small coefficient of thermal expansion and are subject to thermal fluctuations that occur during the manufacturing process and actual use conditions, It has the feature that the joint is not peeled off and the ceramic substrate is not broken, and the reliability is considerably high.

However, when applying the module structure as a structure used as a module used in a mobile device such as a high-power module or an electric vehicle, if the module structure is applied to other heat dissipating parts such as heat dissipating fins and heat dissipating blocks. When tightening and fixing the module structure, the joints of the module structure may be peeled off, the ceramic substrate may be broken, or the module structure may be deformed due to thermal fluctuations that occur during the manufacturing process or actual use conditions. This may cause a phenomenon in which the fastening state with other heat radiating components is loosened, and there is a problem in long-term reliability.

The present inventors have conducted various experimental studies on the aluminum-silicon carbide composite used for the heat sink, and found that the Young's modulus and the yield stress of the aluminum-silicon carbide composite have important functions. In particular, with regard to the latter, it has been found that when the yield strength of the aluminum-silicon carbide composite and the yield strength of aluminum in the aluminum-silicon carbide composite have a specific ratio, the above problem can be solved, and the present invention has been achieved. Things.

In the present invention, the Young's modulus of the aluminum-silicon carbide composite is 120 to 200 GPa. There are many unclear points as to the reason why the Young's modulus of the aluminum-silicon carbide composite is limited to the above specific range, but the present inventor has found that if the Young's modulus is too small, it is tightened to other heat radiating components. The force is small, the thermal contact between the module structure and other heat dissipating components is poor, and the heat dissipation characteristics of the module structure are degraded. Due to the fluctuation of
The contact position between the other heat dissipating components and the module structure is likely to be displaced, and long-term reliability cannot be maintained. It is speculated that the specific range is limited because a very large clamping force is required to improve the contact state, and sometimes the ceramic substrate is broken.

Further, in the present invention, the yield strength of the aluminum-silicon carbide composite and the yield strength of aluminum in the aluminum-silicon carbide composite are limited to a specific ratio, and based on the experimental results of the present inventors. , Aluminum
The yield strength of the silicon carbide composite is 1.5 to 4 with respect to the yield strength of aluminum in the aluminum-silicon carbide composite.
When the ratio is double, preferably 2-3 times, the object of the present invention can be achieved. When the ratio is 1.5 times or less, the module structure is deformed due to heat fluctuation when the module structure is fastened and fixed to another heat radiating component, and high reliability can be maintained for a long time. If the ratio exceeds 4 times, the stress cannot be relieved at the joint between the module structure and other heat radiating components due to the deformation of the heat sink, and as a result, long-term reliability is secured. become unable.

In the present invention, the coefficient of thermal expansion of the aluminum-silicon carbide composite from room temperature to 125 ° C. is 1
It is preferably at most 5 × 10 ⁻⁶ / K. As described above, the semiconductor element mounted on the circuit of the ceramic circuit board, the ceramic substrate, and the heat sink all have the same small coefficient of thermal expansion. Although desirable because it hardly occurs, the semiconductor element is generally made of silicon (coefficient of thermal expansion;
2.6 × 10 ⁻⁶ / K), and aluminum nitride or silicon nitride is generally selected as a ceramic substrate for large current applications, and their thermal expansion coefficients are generally about 6 to 8 The upper limit is selected because it is × 10 ⁻⁶ / K. Further, there is no technical reason to determine the preferable lower limit of the thermal expansion coefficient. In addition, from the usage, the coefficient of thermal expansion may be considered from room temperature to 125 ° C.

As an embodiment of the present invention, aluminum-
Silicon carbide content in the silicon carbide composite is 10 to 40% by volume
And more preferably 20 to 30% by volume. If it is less than 10% by volume, the coefficient of thermal expansion of the obtained aluminum-silicon carbide composite will increase, and the yield strength ratio will decrease. On the other hand, 40% by volume
When the ratio exceeds the above range, the yield strength ratio tends to increase, and the cost of the aluminum-silicon carbide composite increases, which is not practical.

Hereinafter, the present invention will be described in more detail by exemplifying a method of manufacturing the module structure of the present invention.

The method of obtaining the aluminum-silicon carbide composite used in the present invention includes a method of adding silicon carbide powder and fiber to molten aluminum and a method of obtaining a porous molded body from silicon carbide powder and fiber. A method of infiltrating or impregnating the molten aluminum in the void portion of the molded body later,
Conventionally known methods such as a method of mixing aluminum powder or lump with silicon carbide powder or fiber at a desired ratio and heating the mixture in a mold can be applied. Among them, the high-pressure forging method is a method of obtaining a porous compact from silicon carbide powder or fiber and then infiltrating or impregnating the molten aluminum into the voids of the compact.
Since a high pressure of 0 to 100 MPa is applied, the adhesion between silicon carbide and the aluminum alloy in the obtained aluminum-silicon carbide composite is excellent, and a composite having high thermal conductivity is obtained.

As the silicon carbide used in the present invention, powder made of high-purity green silicon carbide is used because of its high thermal conductivity and high fluidity even at low temperatures when contained in molten aluminum metal. In particular, the average particle size is 30 to 200
A powder of about μm is preferred.

The aluminum used in the present invention is a metal containing aluminum as a main component, and any aluminum-silicon carbide composite may be used as long as it satisfies desired characteristics. However, based on experimental studies by the present inventors, an aluminum alloy containing 20% by mass or less of silicon (Si) is preferable. Si content is 2
If it exceeds 0% by mass, the yield strength of the aluminum alloy in the obtained aluminum-silicon carbide composite becomes too large, and it becomes difficult to obtain a module structure having desired characteristics.

The aluminum alloy may contain iron (Fe) or copper (Cu) as an impurity in an amount of 1% by mass or less. This is because the presence of the impurity exceeding 1% by mass causes a decrease in thermal conductivity, and in the former case, the strength is reduced, and in the latter case, the yield strength is excessively increased. Further, in the aluminum alloy, the oxygen content in the obtained aluminum-silicon carbide composite is 1% by mass or less for the purpose of enhancing the adhesion between silicon carbide and the aluminum alloy and for the purpose of increasing the thermal conductivity. It is preferable to contain 3% by mass or less of magnesium (Mg).

When it is assumed that the module structure is obtained, for example, 6% by mass of Si and 0.5% by mass of Mg
The aluminum alloy contained is melted, and the mixture containing 10 to 40% by volume of silicon carbide powder is poured into a mold made of a material which is difficult to react with aluminum, such as graphite, ceramics or iron. Generally, a flat plate having a thickness of 2 to 10 mm is formed by a method of cooling and solidifying. At this time, for the purpose of accelerating the release of the mold and the flat plate, it is preferable to use a release agent composed of fine powder such as graphite, boron nitride, and alumina.

The obtained flat plate is subjected to machining or polishing as it is or as necessary, and if necessary, a metal layer of Ni or the like is provided on a desired portion by plating or the like to form a heat sink having a desired shape. It will be called a heat dissipation component.

On the other hand, the ceramic circuit board used in the present invention may be any ceramic circuit board having a structure in which a circuit is provided on one main surface of a ceramic substrate made of alumina, aluminum nitride, silicon nitride or the like. Absent. However, as a ceramic substrate, a semiconductor element mounted on the ceramic circuit substrate has a small thermal expansion coefficient.
Aluminum nitride and silicon nitride are preferred because they are made of i and because the heat dissipation of the obtained module structure can be increased. Generally, a plate thickness of 0.3 to 2 mm is selected in consideration of mechanical properties such as electric insulation, heat dissipation, and strength.

Further, regarding the circuit of the ceramic circuit board, since a module structure having a low electric resistance, a high thermal conductivity and a high reliability can be obtained, Cu,
Al or an alloy thereof is preferable. Further, the circuit on the back surface of the ceramic substrate (main surface for the heat sink) may or may not be provided. The circuit and the ceramic substrate, or the metal plate for heat dissipation and the ceramic substrate are generally joined by brazing using a copper-based or silver-based brazing material. It is preferable to use a brazing material containing a so-called active metal, such as Ti or Zr, because a strong bonding force can be obtained.

Next, the ceramic circuit board is bonded onto the heat sink and integrated to form a module structure. At the time of joining, a commercially available brazing material may be used, but when a circuit is provided on the back surface, joining may be performed using solder.

[0036]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[Examples 1 to 3, Comparative Examples 1 and 2]
After heating 5 kg of an aluminum alloy containing 70% by mass to a temperature of 700 ° C. in an electric furnace, the average particle size is 70% with stirring.
20 μm by volume of μm silicon carbide powder was added. Furthermore, Mg
Was added at 1% by mass to produce an aluminum alloy containing silicon carbide powder. 100 g of the obtained molten alloy is
80mm x 120m pre-heated to 50 ° C and coated with release agent
m, and was immediately press-molded at a pressure of 50 MPa and cooled to produce a composite 1. Also, complex 2
Is Mg for the composite 1 as an aluminum alloy.
Was prepared by the same method except that the content of silicon carbide powder was 30% by volume. Table 1 shows the results of evaluating various properties of the obtained composite.

[0038]

[Table 1]

A silicon nitride sintered body having a thickness of 0.6 mm and a size of 70 mm × 40 mm (thermal conductivity: 70 W / mK,
Three-point bending strength: 650 MPa, fracture toughness: 7 MPa
^1/2 ) and aluminum nitride sintered body (thermal conductivity: 130)
W / mK, three-point bending strength: 400 MPa, fracture toughness:
An active metal-containing brazing material (Ag-Cu-Ti: 80-15-5 (mass ratio)) was screen-printed on both surfaces of 3 MPam ^1/2 ) as a joining brazing material at a thickness of 50 μm, and the materials shown in Table 2 were used. And a metal plate having a thickness of 10 ^-3 Pa and heated at a temperature of 850 ° C. for 30 minutes in a vacuum atmosphere of the order of 10 ⁻³ Pa. For this composite, the circuit metal side was polished, a patterning resist was printed, cured, and then etched to form a pattern. Furthermore, in order to remove the bonding material remaining between the circuits, the circuit boards were immersed in an aqueous solution of ammonium ammonium fluoride and then washed with water to produce a circuit board having a pattern formed thereon. The obtained circuit board was joined by soldering with a combination of a heat sink material (80 mm × 120 mm × 3 mm) shown in Table 2 and the circuit board, and then a silicon chip was mounted with eutectic solder to produce a module structure. The manufactured module structure was subjected to a heat cycle of −40 ° C. to 125 ° C. 3000 times, and then observed. Table 3 shows the results.

In Comparative Example 1, a module structure was manufactured in the same manner as in Example 1 except that a copper (metal 1) was used as a heat sink and an aluminum nitride substrate was used as a ceramic substrate. In Comparative Example 2, a module structure was manufactured in the same manner as in Example 1 except that Metal 1 was used as a heat sink and a silicon nitride substrate was used as a ceramic substrate. Table 3 shows the evaluation results.

[0041]

[Table 2]

[0042]

[Table 3]

[Embodiments 4 to 6] In Embodiments 4 and 5, a ceramic circuit board and a heat sink having the combinations shown in Table 4 were used.
After the i-type alloy paste is applied and dried, the ceramic circuit board is placed, and a load is applied to the ceramic circuit board in a vacuum at a temperature of 60 ° C.
Heat bonding was performed at 0 ° C. for 1 hour. In Example 6, the ceramics and the heat sink were directly joined without using the circuit on the back surface. A silicon chip was mounted on the obtained structure by eutectic solder to produce a module structure. The obtained module structure was subjected to a heat cycle of −40 ° C. to 125 ° C. 3000 times, and the state was evaluated. As a result, no crack or crack was observed at any point.

[0044]

[Table 4]

[0045]

According to the module structure of the present invention, the ratio of the Young's modulus and the yield strength of the heat sink has a specific value, and as a result, it has extremely high heat dissipation characteristics and extremely high reliability. It can be suitably used for mobile devices such as electric railways, automobiles, and electric vehicles, and is extremely useful in industry.

Claims (4)

[Claims] 1. A module structure comprising a ceramic circuit board joined to an aluminum-silicon carbide composite, wherein the aluminum-silicon carbide composite has a yield strength of aluminum in the aluminum-silicon carbide composite. A module structure that is 1.5 to 4 times as large as the module structure. 2. A module structure comprising a ceramic circuit board joined to an aluminum-silicon carbide composite, wherein the aluminum-silicon carbide composite has a Young's modulus of 120.
A module structure characterized by being at most 200 GPa. 3. The module structure according to claim 1, wherein the aluminum-silicon carbide composite has a coefficient of thermal expansion from room temperature to 125 ° C. of 15 × 10 ⁻⁶ / K or less. 4. The module structure according to claim 1, wherein the silicon carbide content in the aluminum-silicon carbide composite is 10 to 40% by volume.