JP2002223092A - Cooling structure of circuit substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cooling structure of a circuit substrate whose durability is not damaged and heat dissipation property is good. SOLUTION: In a circuit substrate wherein a circuit (2) is provided to a surface of an aluminum nitride substrate (3) and housing (5) is formed to enable a rear of the aluminum nitride substrate to come into direct flow contact with coolant, a alumina hydrate layer (7) is formed in an aluminum nitride substrate surface in contact with coolant. It is preferable that the hydrated alumina layer is a 2 to 20 μm-thick boehmite layer and a plurality of good heat conductive projections (4) are provided to a surface in contact with coolant of an aluminum nitride substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board cooling structure.

[0002]

2. Description of the Related Art As the output of power modules increases,
One of the important issues in a small and lightweight module is how to efficiently and quickly release heat generated from electronic components such as semiconductor elements to the outside of the system.

The conventional cooling structure of a power module is an indirect method in which a cooling plate through which cooling water flows is brought into contact with the module (see, for example, Japanese Patent Application Laid-Open No. 7-154082). And the module temperature could not be lowered to a temperature at which the electronic components could operate satisfactorily. In order to solve this problem, there has been proposed a structure in which a lower portion of a ceramic substrate is housed, a coolant such as water is circulated therein, and a direct contact can be made with the back surface of the ceramic substrate.

However, when the ceramic substrate is an aluminum nitride substrate suitable for a power module,
It has not been solved that the solvent and the refrigerant are hydrolyzed and the durability of the circuit board may be impaired. That is, since most of the refrigerant is water or an antifreeze aqueous solution such as ethylene glycol, an alumina hydrate layer such as a boehmite layer is formed by a hydrolysis reaction on the contact surface of the aluminum nitride substrate with the refrigerant. Since the substance itself is extremely unstable and progresses unevenly, the strength may be reduced due to the falling off of the alumina hydrate layer and the falling off of the aluminum nitride particles, and the durability of the circuit board may be impaired. Was.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a cooling structure for a circuit board which has excellent heat dissipation characteristics without the above-mentioned durability being impaired.

[0006]

That is, according to the present invention, a circuit (2) is provided on the surface of an aluminum nitride substrate (3), and a housing is provided so that the back surface of the aluminum nitride substrate can directly contact the refrigerant. (5) The circuit board cooling structure according to (5), wherein an alumina hydrate layer (7) is formed on a surface of the aluminum nitride substrate that comes into contact with the refrigerant. In this case, the alumina hydrate layer is a boehmite layer, and its thickness is 2 to 2
It is preferable that a plurality of good thermal conductive protrusions (4) are provided on the surface of the aluminum nitride substrate (3) that contacts the refrigerant.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in more detail with reference to the drawings of embodiments.

FIG. 1 is a schematic sectional view showing an example of a circuit board cooling structure of the present invention, and FIGS. 2 and 3 are perspective views showing an example of a good heat conductive projection. In the figure, 1 is a semiconductor, 2 is a circuit, 3 is an aluminum nitride substrate, 4 is a thermally conductive protrusion, 5 is a housing, and 7 is an alumina hydrate layer.

There are various methods for forming the circuit (2) on the surface of the aluminum nitride substrate (3). In the present invention, the conductive paste is drawn into a circuit pattern and then dried and sintered. A thick film paste method, a pattern mounting method of joining a metal circuit pattern to an aluminum nitride substrate, an etching method of joining a metal plate to an aluminum nitride substrate, and then forming a circuit pattern by etching can be adopted (for example, International Publication WO91 /
16805).

[0010] In addition, it is desirable to employ an etching method as a method for forming the good heat conductive projections (4) on the back surface of the aluminum nitride substrate (3). As shown in FIG. 2, the shape of the projection is a square or plate having a series of grooves, or a simple square or plate as shown in FIG. In the present invention, in the configuration shown in FIG. 2, a series of grooves may be provided with irregularities such as a lattice, a rib, a gimble, and a depression. The planar shape of the projection or the unevenness is a cross, an ellipse, a circle,
It can be a rhombus shape or the like, and the side shape of the projection or the unevenness may be a non-slope shape like a prism, a cylinder, etc. It may have a slope shape.

In order to join a circuit, a good thermal conductive protrusion or a metal plate which becomes a good thermal conductive protrusion by etching and an aluminum nitride substrate, a method of metallizing the aluminum nitride substrate and then joining the aluminum nitride substrate A DBC method in which an aluminum nitride substrate having a surface oxidized and a copper plate are brought into direct contact to form a eutectic (for example, JP-A-56-1630).
No. 93), group IV element metals such as titanium, zirconium and hafnium, which are called active metals, are used as copper, silver and silver.
Active metal brazing method using a joining material contained in a brazing material such as a copper alloy (for example, Japanese Patent Application Laid-Open No. Sho 60-177634).
And the like.

In the present invention, an aluminum nitride substrate on which an alumina hydrate layer is formed is used. Even in such a case, the above-described bonding method can be employed. However, it is desirable to remove the alumina hydrate layer before joining the aluminum nitride substrate to the joining portion of the above members. As a method of removing the alumina hydrate layer, a method of performing surface polishing after masking a portion other than the joint portion or a method of decomposing by acid treatment or the like can be used.
Alternatively, the alumina hydrate layer may be formed only on the surface of the aluminum nitride substrate that contacts the refrigerant.

The material of the circuit and the high thermal conductive protrusion is generally copper or an alloy thereof, or aluminum or an alloy thereof, but is not limited thereto. When the good thermal conductive protrusion is provided, the thermal conductivity is preferably 100 W / mK or more higher than that of the aluminum nitride substrate. The thickness of the circuit is usually designed to be thinner than that of the aluminum nitride substrate. Further, the thickness of the good heat conductive projection may be approximately the same as the thickness of the circuit.

The aluminum nitride substrate used in the present invention preferably has a thermal conductivity of 100 W / mK or more in order to sufficiently enhance the reliability of the power module against the thermal history. The thickness of the aluminum nitride substrate is 0.2 to 3
mm is common. As such an aluminum nitride substrate, a commercially available product can be used.

The present invention is characterized in that an alumina hydrate layer (7) is formed on the aluminum nitride substrate surface in contact with the refrigerant. An alumina hydrate layer may or may not be formed on the surface of the aluminum nitride substrate that is not in contact with the refrigerant. By forming the alumina hydrate layer, even if the refrigerant is water, it is possible to prevent the durability of the circuit board from being impaired by hydrolysis.

The alumina hydrate used in the present invention is not particularly limited. For example, boehmite (α-Al ₂ O ₃ .H ₂
O), diaspore (β-Al ₂ O ₃ .H ₂ O), alumina trihydrate (Al ₂ O ₃ .3H ₂ O), and the like.
Boehmite layers that are relatively easy to form are preferred.

The boehmite layer is formed by replacing the portion of the aluminum nitride substrate on which the boehmite layer is formed with deionized water, and then removing ammonia, amine, alcoholamine,
90-100 ° C, 20-6 in a weak alkaline bath such as amide
Zero minute processing can be mentioned. Thereafter, by further performing a pressurized steam treatment, a dense layer having more excellent hydrolysis resistance can be formed. The thickness of the boehmite layer is preferably 2 to 20 μm, particularly preferably 4 to 10 μm, which can be adjusted by the temperature of the weak alkaline bath or the treatment time.

Another feature of the present invention resides in a structure for cooling a circuit board. The conventional structure is a structure in which a heat sink is attached to the back surface of the ceramic substrate and attached to a heat sink by soldering or the like, or a plate-shaped cooling pipe is in contact with the back surface of the ceramic substrate and water is passed through the cooling pipe. It was a water-cooled structure.

On the other hand, the cooling structure of the present invention, as shown in FIG. 1, directly supplies cooling water or the like to the back surface of the aluminum nitride substrate (3) on which the alumina hydrate layer (7) is formed. A housing (5) is provided so as to be in flow contact with the refrigerant. In this case, one or more of the good thermal conductive protrusions (4) may be provided on the back surface of the aluminum nitride substrate in the housing. Although not shown, the housing may be divided into small rooms.

In forming the housing, as shown in FIG. 1, the contact surface between the metal part (6) and the housing (5) is provided with a series of projections such as a series of projections or flat cones. It is preferable to perform the fitting by press-fitting with a screw or the like. By doing so, the seal portion is extremely stable against stress caused by pressure at the time of tightening and temperature change under the use environment, compared with the case where a conventional rubber O-ring or the like is used. An excellent seal is formed. In addition, since components such as O-rings are not used, the number of components is reduced and the productivity is improved, which is effective in reducing the cost of the module.

The material of the housing is copper, aluminum,
It may be any of metals such as stainless steel, various ceramics and plastics, and may have a structure in which these materials are appropriately combined. In the present invention,
When the metal portion (6) is deformed to form the seal portion, it is preferable that the material is harder than the material of the metal portion, particularly, stainless steel, copper, hard plastic, or the like.

[0022]

The present invention will be described more specifically below with reference to examples and comparative examples.

Examples 1-4 Commercially available aluminum nitride substrates (80 × 58 mm square,
Thickness 0.635mm, thermal conductivity 150W / mK)
After immersion in deionized water at 5 ° C. for 5 minutes to replace the surface of the aluminum nitride substrate, the substrate was immersed in a 0.5% solution of triethanolamine at 90 ° C. for 10 to 60 minutes to obtain a layer having a thickness shown in Table 1. An alumina hydrate layer was formed on the entire surface. X-ray diffraction analysis confirmed that almost all of the alumina hydrate layer was composed of boehmite.

Next, after polishing and removing all the alumina hydrate layer formed except for the portion where the refrigerant comes into contact, a circuit (0.4 m thick) is formed at the center of the surface of the aluminum nitride substrate.
m), and a metal part (edge width 7 mm) and a thermally conductive protrusion (a protrusion height of 0.4 mm, the number and shape of the protrusions are shown in Table 1) on the back surface edge. It was formed by etching a solid metal plate joined to an aluminum nitride substrate by a metal brazing method. That is, after applying a brazing filler metal to the polished and removed portion of the alumina hydrate layer, a solid metal plate is superimposed on the front and back surfaces of the aluminum nitride substrate, and after heating and joining, etching is performed, and the circuit, the metal portion and Good thermal conductive protrusions A protrusion was formed. These materials were copper in Example 2, but all others were aluminum. The joining brazing material used was a silver-copper alloy containing zirconium.

Then, a semiconductor (13 mm ×
13 mm), and wire bonding was performed, and a stainless steel housing was screwed to the back surface of the aluminum nitride substrate with a fitting structure (fitting portion depth 0.2 mm) shown in FIG. Screwing was performed by screwing a screw over an overhang (not shown) at the surface edge of the aluminum nitride substrate and an overhang provided on the housing.

Comparative Examples 1 and 2 A cooling structure for a circuit board was manufactured according to Example 1 or Example 3, except that no alumina hydrate layer was formed on the aluminum nitride substrate.

In order to evaluate the heat radiation characteristics of each cooling structure obtained above, water was passed through the housing at a flow rate of 1.5 m / s using a 30% aqueous solution of ethylene glycol at 65 ° C. as a refrigerant, and electricity was supplied to the semiconductor (150 W). Then, the surface temperature of the semiconductor and the cooling water temperature were measured with a thermocouple, and the thermal resistance was calculated.
Table 2 shows the results.

Further, in order to evaluate the durability of each cooling structure, a cooling water at 65 ° C. was introduced into the housing at a flow rate of 1.5 m / s.
After passing water for 1000 hours at
The sheet was cut into a size of 0 × 10 × 1 mm, and the bending strength was measured by a three-point bending test. Table 2 shows the results.

[0029]

[Table 1]

[0030]

[Table 2]

From Tables 1 and 2, it can be seen that the circuit board cooling structure of the present invention has excellent heat radiation characteristics and durability.

[0032]

According to the present invention, there is provided a cooling structure for a circuit board which is excellent in heat radiation characteristics without danger of losing durability.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an example of a circuit board cooling structure of the present invention.

FIG. 2 is a perspective view showing an example of a good heat conductive projection used in the present invention.

FIG. 3 is a perspective view showing another example of a good heat conductive projection used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor 2 Circuit 3 Aluminum nitride substrate 4 Good thermal conductive protrusion 5 Housing 6 Metal part 7 Alumina hydrate layer

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E322 AA05 AA11 5E338 AA01 AA18 BB71 CC01 CD11 EE02

Claims (3)

[Claims] 1. A circuit board, comprising: a circuit (2) provided on a front surface of an aluminum nitride substrate (3); and a housing (5) provided so that a back surface of the aluminum nitride substrate can directly contact a refrigerant. A cooling structure for a circuit board, wherein an alumina hydrate layer (7) is formed on a surface of an aluminum nitride substrate in contact with a refrigerant. 2. The circuit board cooling structure according to claim 1, wherein the alumina hydrate layer is a boehmite layer and has a thickness of 2 to 20 μm. 3. The circuit board according to claim 1, wherein a plurality of high heat conductive projections are provided on a surface of the aluminum nitride substrate contacting the refrigerant. Cooling structure.