JP3377928B2 - Circuit board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a structure for efficiently dissipating heat in a circuit board on which an electronic component having heat generating properties such as an IC is mounted.

[0002]

2. Description of the Related Art Conventionally, a circuit board is known in which electronic parts such as ICs and resistance elements are mounted on the surface of an insulating board made of ceramics or organic resin. With the recent increase in the degree of integration of electronic components mounted on these circuit boards, for example, in electronic components such as IC elements, the heat generated when the components themselves operate is increasing,
Accordingly, the heat adversely affects the operating state of the electronic components and other electronic components that generate heat.
A major issue is how to efficiently dissipate such heat.

As a general heat dissipation structure used conventionally, as shown in FIG. 3, an electronic component 12 such as a hybrid IC is mounted on one surface of an insulating substrate 11, and a heat radiator 13 is mounted on the other surface. The heat generated from the electronic component 12 is transmitted to the heat radiator 13 via a heat transfer via-hole conductor (hereinafter referred to as a thermal via) 14 provided in the insulating substrate 11, and the heat radiator directly or bonded to the heat radiator 13. The heat radiation fins are released into the atmosphere.

[0004]

However, in a circuit board on which a plurality of IC elements are mounted, such as a hybrid IC, local stagnation of heat is scattered, so engine control for automobiles, etc. In the circuit board used for the above, the temperature of the IC part sometimes exceeds the guaranteed operating temperature. As a countermeasure, a heat sink is directly bonded to the back surface of the substrate, and most of the heat radiation is performed from the back surface of the substrate through a thermal via for heat radiation. Therefore, the number of thermal vias formed or the thermal vias formed thicker are superior in heat conductivity.

However, when a thermal via is made of a refractory metal such as W or Mo by simultaneous firing with an insulating substrate made of an alumina sintered body, the thermal expansion coefficient of the alumina substrate is 8 ppm / ° C. Since the thermal expansion coefficient of the refractory metal is different from about 5ppm / ℃, if the thermal via diameter is set to 0.5mm or more, or if too many are formed, the substrate will warp during firing, or the thermal via periphery or the thermal via There was a problem such as cracks between them.

[0006]

DISCLOSURE OF THE INVENTION The inventors of the present invention have excellent heat dissipation efficiency without increasing the diameter of a thermal via and without causing cracks even when formed by co-firing with a ceramic insulating substrate. As a result of repeated studies on the arrangement of thermal vias, electronic components were mounted on the metal conductor layer, and the heat radiator provided on the back surface of the substrate was thermally connected by three or more via hole conductors for heat transfer, and the heat transfer was performed. It was found that by arranging the via-hole conductors in a triangular lattice pattern at specific intervals, the heat dissipation efficiency can be improved and cracks can be suppressed during co-firing with the ceramic insulating substrate.

That is, the circuit board of the present invention includes a ceramic insulating substrate having a first surface and a second surface, an electronic component mounted on the first surface via a metal conductor layer, and 3 for thermally connecting the heat radiator integrally formed on the second surface with the metal conductor layer and the heat radiator
A circuit board comprising at least one heat transfer via-hole conductor, wherein the heat transfer via-hole conductor has a maximum diameter d of 0.
It is composed of a cylindrical body of 1 to 0.4 mm, and the distance between the via-hole conductors is 1.5d to 4.0d.
It is characterized in that the line segments connecting the centers of adjacent via-hole conductors are arranged so as to form an equilateral triangle. In particular, the insulating substrate is made of an alumina-based sintered body, But W (tungsten) or M
It is preferably applied when it is made of a refractory metal such as o (molybdenum).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view for explaining one embodiment of the circuit board of the present invention. According to FIG. 1, according to the circuit board of the present invention, the electronic component 2 such as an IC element is mounted on one surface of the insulating substrate 1. The electronic component 2 is mounted via the metal conductor layer 3 formed on the surface of the insulating substrate 1. The electronic component 2 is electrically connected to a wiring layer (not shown) formed on the surface of the insulating substrate 1.

The insulating substrate 1 is made of a well-known ceramic insulating material having an electrically high electric resistance, but alumina, AlN, and Si ₃ are used in order to maintain excellent durability under harsh conditions such as vehicle mounting. Ceramics such as N ₄ are desirable. In some cases, an internal wiring layer (not shown) connected to the electronic component 2 and the surface wiring layer may be formed inside the insulating substrate 1.

On the other hand, since the metal conductor layer 3 itself is in direct contact with the electronic component, the metal conductor layer 3 serves to efficiently transfer the heat generated from the electronic component 2. Therefore, it is desirable that the metal conductor layer 3 be made of a metal with high thermal conductivity such as copper or silver. This metal conductor layer is 5
It is suitable that a thickness of ˜15 μm is formed, and when the insulating substrate is made of ceramics, a paste containing a metal such as copper is applied to the surface of the ceramics,
It is formed by baking at an appropriate temperature of 1100 ° C.

In FIG. 1, a radiator 4 is integrally formed on the back surface of the insulating substrate 1 with the insulating substrate 1. The heat radiator itself is made of a material having high thermal conductivity, and is made of, for example, copper-tungsten or Kova.
r), aluminum and the like. This radiator 4
Are integrally attached to the insulating substrate 1 by a method such as brazing or soldering.

Further, the circuit board of the present invention has a heat transfer via-hole conductor (hereinafter also referred to as a thermal via) 5 inside the insulating substrate 1. The thermal via 5 is formed so as to penetrate the inside of the insulating substrate 1 so as to thermally connect the metal conductor layer 3 and the radiator 4. The thermal via 5 is composed of a cylindrical body made of metal.

According to the present invention, the thermal via 5 described above is used.
Has three or more, and the maximum diameter d is 0.1
.About.0.4 mm, especially 0.15 to 0.3 mm. This is because if the maximum diameter is larger than 0.4 mm, cracks or warpage of the substrate occurs due to the difference in thermal expansion from the ceramic insulating substrate, and if it is smaller than 0.1 mm, the heat transfer function of the thermal via becomes low. Is.

Further, according to the present invention, as shown in the layout diagram of FIG. 2, three or more thermal vias have an interval c between adjacent thermal vias of all 1.5d to 4.0d, particularly 1.d. It is arranged so as to have an interval of 5d to 3.0d. As a result, an equilateral triangle is formed by the line segment connecting the centers of adjacent via-hole conductors, and the thermal vias are arranged in a triangular lattice pattern.

As described above, in the present invention, by setting the interval c between the thermal vias as described above, efficient heat transfer is performed, and even in the case of simultaneous firing with the ceramic insulating substrate, the periphery of the thermal vias. It is possible to suppress the occurrence of cracks between the thermal vias,
If this distance c is smaller than 1.5d, the thermal via 5
There is a problem that cracks are likely to occur when the thermal vias 5 are formed by co-firing because the thickness of the ceramics of the insulating substrate existing between them is thin. Further, if the distance c is larger than 4.0d, the heat dissipation performance per unit area is significantly reduced, and the heat dissipation efficiency is reduced.

Further, if the thermal vias are formed in a square lattice shape, the number of thermal vias formed per unit area is reduced and the heat dissipation is deteriorated, and the distance between the thermal vias around one thermal via is a square lattice shape. As a result of different distances depending on the thermal vias located on the diagonal of the
The stress distribution around the thermal vias becomes non-uniform, and cracks easily occur in the ceramics between the thermal vias.

In the present invention, in order to form the thermal vias 5 in the ceramic insulating substrate 1, for example, a mixed powder mainly containing alumina is slurried and then formed into a green sheet by a sheet forming method such as a doctor blade method. A hole having a predetermined diameter is formed in the green sheet by a microdrill or the like, and then the hole is filled with a conductor paste containing a refractory metal such as tungsten or molybdenum. And this is 1500-
It is formed by heating in a non-oxidizing atmosphere at 1800 ° C. and simultaneously firing the green sheet and the thermal via.

[0018]

Example A green sheet having a thickness of 300 μm was prepared by a doctor blade method after making a mixed powder mainly containing alumina into a slurry. Then, after stacking 6 layers of this green sheet, a via hole was formed in a region of 10 mm square by using a microdrill so that the diameter and pitch after firing were as shown in Table 1. Then, the hole was filled with a conductor paste in which alumina was added to tungsten and mixed. Then, this was co-fired in a reducing atmosphere at 1600 ° C. to produce a circuit board.

After firing, copper paste was applied to one surface of the substrate where the end surface of the thermal via was exposed and baked at 900 ° C. to form a metal conductor layer having a thickness of 10 μm. Further, a radiator made of aluminum was attached to the other surface of the substrate at a position where it was connected to the thermal via, using a Si-based adhesive. In addition, as a comparative example of arrangement, an arrangement in which thermal vias are arranged in a square lattice shape was produced in the same manner as above.

As for the finished state of each of the obtained circuit boards, the occurrence of cracks between the thermal vias and the occurrence of warpage of the boards were visually observed with a stereoscopic microscope. In addition, a heater chip is attached to the circuit board on the metal conductor layer,
The temperature of the aluminum radiator was measured when heat was generated by applying a constant output in an atmosphere of ° C. The measurement results are shown in Table 1.
It was shown to.

[0021]

[Table 1]

As is clear from the results shown in Table 1, the thermal via diameter d is 0.1 to 0.4 mm and c / d is 1.5 to.
In the case of 4.0, it was found that there was no crack or warpage, the temperature of the heat sink was as high as 130 ° C. or higher, and the heat transfer due to the thermal via was excellent.

On the other hand, the thermal via diameter d is 0.4.
When it exceeds mm, a large number of cracks are observed around the thermal via. Also, many cracks were confirmed even when c / d was less than 1.5. If it is more than 4.0, the heat transfer property is lowered.

Sample No. 12 arranged in a square lattice pattern
When compared with Sample No. 9 in which the same diameter and the same pitch are arranged in a triangular lattice pattern, the triangular lattice pattern is superior in heat transfer property, and in the case of a square lattice pattern, a slight crack is observed. Was given.

[0025]

As described above in detail, in the circuit board of the present invention, when the thermal vias are used in the ceramic insulating substrate by co-firing by adjusting the diameter, the distance between the vias and the arrangement of the thermal vias. In addition, the heat dissipation efficiency can be improved without the occurrence of warpage or cracks. As a result, the heat generated from the electronic component such as the IC can be efficiently transmitted to the radiator, and a highly reliable circuit board without malfunction of the IC can be provided.

[Brief description of drawings]

FIG. 1 is a schematic sectional view for explaining an embodiment of a circuit board of the present invention.

FIG. 2 is a schematic diagram for explaining the arrangement of thermal vias in the present invention.

FIG. 3 is a schematic cross-sectional view for explaining a conventional circuit board.

[Explanation of symbols]

1 Insulation board 2 electronic components 3 Metal conductor layer 4 radiator 5 thermal vias

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Claims (2)

(57) [Claims] 1. A ceramic insulating substrate having a first surface and a second surface, an electronic component mounted on the first surface via a metal conductor layer, and an integral part of the second surface. A circuit board comprising: a heat dissipation member formed on the heat dissipation member; and three or more heat transfer via hole conductors for thermally connecting the metal conductor layer and the heat dissipation member, the heat transfer via hole conductor being provided. Is composed of a columnar body having a maximum diameter d of 0.1 to 0.4 mm, and the distance between the via-hole conductors is 1.5d to 4.
A circuit board in which line segments connecting the centers of adjacent via-hole conductors are arranged at regular intervals of 0d so as to form an equilateral triangle. 2. The insulating substrate is made of an alumina sintered body, and the heat transfer via-hole conductor is W (tungsten).
The circuit board according to claim 1, which is made of a refractory metal such as Mo (molybdenum).