JPH11312850A - Heat-dissipating wiring substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent problems such as crackings of a substrate, etc., caused by thermal stresses due to the difference in thermal expansion between a substrate and a low-resistance wiring conductor formed on a heat-dissipating wiring substrate. SOLUTION: A substrate 1 is formed of ceramics, of a thickness 30 mm or less, comprising aluminum nitride sintered body or silicon nitride sintered body in which at least one kind selected from among yttrium oxide, erbium oxide, and ytterbium oxide is the main sintering assistant. The area ratio in occupancy of a low-resistance wiring conductor 4 with respect to the main surface of substrate 1 is at least 1%, with the porosity of the low-resistance wiring conductor 4 being set at 3-40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric car, a hybrid car, a bullet train, a subway, a commuter train, an elevator,
IGBT (Insulated Gate Bipolar Transformer) which is a power device mounted on robots, cranes, air conditioners, etc.
Large current can flow through istors), packages for housing semiconductor devices that house semiconductor devices, and hybrid integrated circuit devices that mount various electronic components such as capacitors and resistors in addition to semiconductor devices. The present invention relates to a heat dissipation wiring substrate having a low-resistance wiring conductor.

[0002]

2. Description of the Related Art Power devices are the oldest semiconductor elements. However, in recent years, high breakdown voltage, large current, high speed and high frequency, and high performance have been remarkably advanced, and IGBT, GTO (Ga
te Turn Off thyrister), IPM (Intelligent Powe)
r Module), high-speed MOS-based power devices such as power MOSFETs. These power devices are widely used in automobiles, inverter trains, strobes, microwave ovens, golf carts, and the like. However, in recent years, hybrid vehicles and electric vehicles are becoming popular due to environmental problems, and these power devices, particularly IGBTs, are required to have higher withstand voltage, smaller size, thinner, and lighter weight.

As a heat dissipation wiring board used in this power device, Japanese Patent Application Laid-Open No. 7-162157 discloses that a power element is arranged on a multilayer substrate composed of a plurality of insulating layers, Shown is a multilayer substrate filled with a heat transfer medium for the power element.

That is, as shown in FIG.
Substrate 11 composed of multilayer alumina composed of 1a to 11c
A low-resistance wiring conductor 14 is proposed in which a power element 17 is disposed thereon, and a recess 13 provided in a lower region of the power element 17 of the insulating layer 11a is filled with a heat transfer conductor. The low-resistance wiring conductor 14 is connected to an internal wiring 15 built in the substrate 11, and a wiring 16 formed between the wiring portion formed on the substrate 11 and the power element 17 is bonded with a wire 16.

On the other hand, Japanese Patent Application Laid-Open No. 63-120448 proposes, as a heat dissipation substrate, a heat dissipation substrate obtained by impregnating a base material made of a fiber of a low thermal expansion metal material with a metal material having good heat dissipation properties. ing.

When these substrates are applied to, for example, a package for accommodating a semiconductor element, the semiconductor element is bonded and fixed to the bottom surface of the concave portion of the insulating base via an adhesive such as glass, resin or brazing material. Each electrode of the element is electrically connected to a wiring conductor located around the concave portion via wire bonding, and a cover made of metal, ceramics, or the like is interposed via a sealing agent similar to the adhesive so as to cover the concave portion. And a semiconductor device as a final product is housed in such a manner that the semiconductor element is confidentially accommodated in the concave portion of the insulating base.

[0007]

However, in the conventional heat dissipation wiring board, the electric resistance of W or Mo forming the low resistance wiring conductor 14 or the via hole conductor is 4 to 8 × 10 ^-6.
Since the resistance is extremely high at Ω · cm, it has been difficult to reduce the electric resistance between the wirings and flow a large current of, for example, 100 A or more. In addition, wiring boards used in a cold environment of -40 ° C to 150 ° C, such as hybrid vehicles, electric vehicles, and various control devices used in the next Shinkansen, which have been forced to appear due to environmental issues. And other applications.

If the conventional heat-radiating wiring board is used for the above purpose, thermal stress is generated between the low-resistance wiring conductor 14 and the substrate 11 due to the difference in thermal expansion between them, and particularly, the low-resistance wiring Stress concentrates on the substrate 11 in the vicinity of the conductor 14, resulting in a large residual stress. As a result, when a thermal cycle or an external force is applied to the heat-dissipating wiring board, it becomes extremely large in combination with the residual stress, which may cause cracks in the board 11 or the cracks may develop to break other wiring conductors. .

[0009]

Means for Solving the Problems Accordingly, the present inventors have:
A ceramic substrate having a thickness of 30 mm or less made of an aluminum nitride-based sintered body or a silicon nitride-based sintered body containing at least one selected from yttrium oxide, erbium oxide, and ytterbium oxide as a main sintering aid; Copper (Cu) and silver (A) having a thickness of 50 μm or more
g), a heat-radiating wiring board is formed from a low-resistance wiring conductor containing at least one or more selected from aluminum (Al) as a main component, and the area ratio of the low-resistance wiring conductor to the area of the main surface of the substrate is set to 1% or more. In addition, it has been found that the above problem can be solved by making the low-resistance wiring conductor have a porosity of 3 to 40%.

Further, Ni, Cu,
When at least one type of metal plating selected from Au, Zn, and Sn is applied, solder wettability is improved, and work efficiency is improved.

Further, when at least one metal layer of W, Mo, V, Ti is interposed between the low-resistance wiring conductor and the ceramic substrate, the compatibility with the ceramic substrate is good, and the low-resistance wiring conductor and the ceramic substrate are provided. Bonding became easier.

Further, the low-resistance wiring conductor and W, Mo, V, T
Ag, Ti, M between at least one metal layer of i
By applying at least one type of metal plating selected from o, V, Ni, Cu, Au, Zn, and Sn, the bonding strength between the low-resistance wiring conductor and the ceramic substrate could be further increased.

According to the present invention, by setting the porosity of the low-resistance wiring conductor to 3 to 40%, generation of thermal stress between the low-resistance wiring conductor and the substrate due to a difference in thermal expansion between the two. Can be prevented, the occurrence of cracks in the substrate and the propagation of the cracks can be prevented, and disconnection of the wiring conductor can be prevented. Therefore, a highly reliable heat-dissipating wiring board which does not cause any trouble even when repeatedly used in a cold environment of -40 ° C to 150 ° C can be obtained.

Further, the low-resistance wiring conductor does not peel off from the wiring space or groove of the substrate, and therefore does not break other wiring conductors connected to the low-resistance wiring conductor.
The resistance of the wiring conductor is reduced, and a large current of 100 A or more can flow.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows an example of a heat dissipation wiring board of the present invention. A substrate 1 is formed by laminating a plurality of insulating layers 1a, 1b, 1c made of an aluminum nitride sintered body or a silicon nitride sintered body.
Is formed, and a porosity of 3-4 is formed in the concave portion 2 provided in the insulating layer 1a.
A low-resistance wiring conductor 4 having a built-in pore so as to be 0%,
4 'is provided. Then, a semiconductor element 3 of Si or the like is arranged on one of the low-resistance wiring conductors 4, and the semiconductor element 3 and the other low-resistance wiring conductor 4 ′ are bonded by wires 5.

Therefore, the semiconductor element 3 can input and output signals through the low-resistance wiring conductors 4 and 4 ′, and heat generated in the semiconductor element 3 is radiated through the low-resistance wiring conductor 4 and the substrate 1. can do. In addition, since the low-resistance wiring conductors 4 and 4 ′ have built-in porosity so as to have a porosity of 3 to 40%, even if they are used in an application where a cooling / heating cycle is applied, a difference in thermal expansion from the substrate 1 may occur. The generation of stress can be prevented, and the generation of cracks and the like can be prevented.

The substrate 1 is formed of an aluminum nitride sintered body or a silicon nitride sintered body in which the main sintering aid is at least one selected from yttrium oxide, erbium oxide, and ytterbium oxide. This is because the highest fracture toughness is obtained when yttrium oxide, erbium oxide or ytterbium oxide is used as a main sintering aid among aluminum nitride-based sintered bodies and silicon nitride-based sintered bodies. The characteristic of high toughness is -40
This is because this is a main reason for providing a highly reliable heat-dissipating wiring board that does not cause any trouble even when repeatedly used in a cold environment of 150C to 150C.

This phenomenon can be easily estimated from the following equation, which is generally recognized for fracture toughness. As the fracture toughness increases, the fracture stress can be increased. σf = K _1C / Ya ^1/2 where σf: fracture stress K _1C : fracture toughness Y: shape factor a: crack length.

When at least one selected from the group consisting of yttrium oxide, erbium oxide and ytterbium oxide is used as the main sintering aid in the aluminum nitride-based sintered body or silicon nitride-based sintered body, The reason why higher fracture toughness is obtained compared to other sintering aids is thought to be that the crystallization of the grain boundary phase is more likely to occur, and it is easier to improve fracture toughness by crack deflection. I don't know the details.

Further, by using the above sintering aid,
The thermal conductivity of the sintered body can be improved. For example,
As shown in FIG. 3, by adding yttrium oxide to aluminum nitride, a grain boundary layer that inhibits heat conduction gathers at the triple point of a crystal grain boundary, and the number of contacts between crystals having good heat conductivity increases, so that heat conduction increases. Can be improved. By improving the thermal conductivity of the substrate 1, the heat dissipation of the semiconductor element 3 can be improved.

Further, the thickness of the substrate 1 is set to 30 mm or less, because if it exceeds 30 mm, thermal conductivity deteriorates.

Next, the low-resistance wiring conductor 4 is made of copper (Cu),
Formed from a type of silver (Ag), aluminum (Al),
The porosity is set to 3 to 40%. The reason for having such a porosity is that the elastic modulus (Young's modulus) of the low-resistance wiring conductor 4 is deliberately reduced and easily deformed by an external force. This is to prevent the generation of residual stress based on the above.

For example, when the Young's modulus of dense copper (Cu) is 1
By providing 3 to 40% of the pores in comparison with 30 GPa, it can be reduced to about 50 to 110 GPa. As a result, when the substrate 1 and the low-resistance wiring conductor 4 are integrated by firing or when a thermal cycle is applied during use, even if a thermal stress is generated between the two due to a difference in the coefficient of thermal expansion, The thermal stress is reduced by the deformation of the low-resistance wiring conductor 4, and almost no residual stress is generated in the substrate 1 and the low-resistance wiring conductor 4.

The reason for setting the porosity in the range of 3 to 40% is that if the porosity is higher than 40%, the resistance becomes too high, and the porosity does not function as the low-resistance wiring conductor 4, and the porosity does not function as a wiring board. There is a fundamental problem of not being able to use it. If the porosity is 3% or less, the Young's modulus of the low-resistance wiring conductor 4 cannot be sufficiently reduced. further,
The porosity of the low-resistance wiring conductor 4 is preferably 5 to 30%,
More preferably, the range is 10 to 20%.

In order to give the low-resistance wiring conductor 4 a porosity of 3 to 40%, the sintering temperature is generally adjusted. However, in order to accurately obtain a desired porosity, the sintering is performed in advance. There is a method in which an appropriate amount of plastic beads having a desired shape and a desired size are mixed in the low-resistance wiring conductor 4 before the sintering, and the plastic beads are burned off during firing to obtain pores.

Here, a method of measuring the porosity of the low-resistance wiring conductor 4 in the heat dissipation wiring board will be described. Since the low-resistance wiring conductor 4 has a very small thickness of about 50 μm, it is difficult to measure the porosity by an ordinary method. Therefore, in the present invention, the porosity was measured using a porosimeter in accordance with JIS-C2141.

In this measurement method, the substrate 1 provided with the low-resistance wiring conductor 4 is placed in a glass container (dilatometer), and after the mercury (Hg) is filled in the glass container, a pressure is applied to the mercury from outside, and the mercury is applied. The porosity is calculated from the volume of mercury penetrating into the low-resistance wiring conductor 4 at this time. Due to the surface tension of mercury,
Mercury does not penetrate into the pores of the low-resistance wiring conductor 4 as it is, but when pressure is applied from the outside, mercury penetrates into the pores according to the following equation, and the amount of permeation is measured to measure the pore volume K. it can. In the present invention, the external pressure is set to 100
The pressure was raised to the atmospheric pressure, and the porosity was measured.

Mercury intrusion pore diameter (μm) = 15 / pressure applied to mercury (atm) The thickness t of the low-resistance wiring conductor 4 is measured using a surface roughness meter or an optical interference thickness meter, and the width h is And the length L are measured with a measure scope, and the volume V of the low-resistance wiring conductor 4 is calculated and calculated according to V = t × h × L, and the porosity A is represented by porosity A (%) = K / V × 100.

Here, since the silicon nitride or aluminum nitride sintered body forming the substrate 1 is dense, the porosity of the sintered body was neglected. May prepare the same dummy as the measurement test piece, and subtract the dummy porosity to obtain the porosity of the low-resistance wiring conductor 4.

The material of the low-resistance wiring conductor 4 is copper (C
u), silver (Ag), and aluminum (Al) as the main components. These three types are important as the low-resistance wiring conductor 4, 0.2%
This is because the two requirements of low proof stress and high thermal conductivity are satisfied.

Further, in the present invention, the area ratio occupied by the low-resistance wiring conductor 4 to the area of the main surface of the substrate 1 is set to 1% or more. This is because the area ratio is less than 1%. This is because the low-resistance wiring conductor 4 was extremely heated, and a disconnection was likely to occur.

The thickness of the low-resistance wiring conductor 4 is 50 μm.
The reason for this is that when the thickness is less than 50 μm, the amount of heat generated becomes too large when a large current flows.

Next, another embodiment of the present invention will be described.

In the heat dissipation wiring board shown in FIG. 2, a metal layer 6 of W or the like which is simultaneously fired is formed on a substrate 1 made of a silicon nitride or aluminum nitride sintered body, and a metal plating layer 7 of Ni or the like is formed thereon. Further, a low-resistance wiring conductor 4 having pores therein is formed thereon, and a metal plating 8 of Ni or the like is formed on the low-resistance wiring conductor 4. Are joined.

Thus, Ni, Ni on the low-resistance wiring conductor 4
By applying at least one kind of metal plating 8 selected from Cu, Au, Zn, and Sn, the wettability of the solder 9 is improved, and the production when the semiconductor element 3 such as Si is mounted thereon is efficiently advanced. be able to.

By interposing a metal layer 6 made of at least one of W, Mo, V and Ti between the low-resistance wiring conductor 4 and the substrate, the low-resistance wiring conductor 4 and the ceramic substrate 1 Can be easily joined and the joining strength can be improved.

Further, between the low resistance wiring conductor 4 and the metal layer 6, Ag, Ti, Mo, V, Ni, Cu, Au, Z
By applying at least one type of metal plating 7 selected from n and Sn, the bonding strength between the low-resistance wiring conductor 4 and the substrate 1 can be further increased.

[0039]

EXAMPLE As a working example of the present invention, a heat dissipation wiring board shown in FIG. 2 was manufactured.

A 0.7 mm thick green sheet of silicon nitride or aluminum nitride containing erbium oxide as a main sintering aid is tape-formed by a doctor blade method.
A tungsten ink forming the metal layer 6 was printed thereon. After that, several green sheets were laminated and then subjected to a degreasing process to densify silicon nitride or aluminum nitride at 1850 ° C. for 3 hours.

After densification, Ni metal plating 7 was applied on the tungsten metal layer 6. On top of this, a particle size of 1 to 50
A powder obtained by mixing 3 to 40% by volume of spherical plastic beads having a particle size of 20 μm into 3 to 40% by volume of Cu, Al, or Ag powder is pasted, applied by printing or dispenser, and then baked at 600 to 900 ° C. Thus, a low-resistance wiring conductor 4 was formed. Ni metal plating 8 was newly applied on the low-resistance wiring conductor 4 after baking, and solder 9 was flowed over the metal plating 8 to mount the semiconductor element 3 of Si.

As described above, a heat dissipation wiring board having the size of the substrate 1 of B6 size was obtained.

The porosity of the low-resistance wiring conductor 4 was measured for the obtained heat-dissipating wiring board by the above-described method, and the area ratio of the low-resistance wiring conductor 4 to the main surface of the substrate 1 was determined. Was.

The heat / cold test means that two types of liquid tanks at -40 ° C. and 150 ° C. are prepared, and the heat radiating wiring board is left in each liquid tank for 30 minutes. And the change in resistance value were measured.

The results are shown in Table 1. As shown in Table 1, the main sintering aid of the ceramics constituting the substrate 1 is out of the range of the present invention (Nos. 6, 15), and the porosity of the low-resistance wiring conductor 4 is lower. 3
% (No. 7, 17), cracks occurred in less than 1000 cycles. In the case of the low-resistance wiring conductor 4 having a porosity exceeding 40% (Nos. 8, 16), the electric resistance was too high. Further, when the area ratio of the low-resistance wiring conductor 4 was less than 1% (Nos. 9 and 18), disconnection occurred.

On the other hand, those (N
o. Nos. 1 to 5, 10 to 14) showed no cracks even after the test of 1000 cycles, and no influence on the resistance value was observed.

[0047]

[Table 1]

[0048]

According to the present invention, the thickness of an aluminum nitride-based sintered body or a silicon nitride-based sintered body containing at least one selected from yttrium oxide, erbium oxide and ytterbium oxide as a main sintering aid is provided. A ceramic substrate having a thickness of 30 mm or less and a low-resistance wiring conductor having at least one selected from copper (Cu), silver (Ag), and aluminum (Al) having a thickness of 50 μm or more integrated with the ceramic substrate. A low-resistance wiring conductor having an area ratio of 1% or more to the main surface of the ceramic substrate and a porosity of the low-resistance wiring conductor of 3% to 40%, thereby adding a thermal cycle. However, it is possible to prevent the occurrence of the cracks in the substrate and the progress of the cracks, and to prevent the disconnection of the wiring conductor.

Further, the low-resistance wiring conductor does not peel off from the wiring space or the groove of the substrate, and therefore does not break other wiring conductors connected to the low-resistance wiring conductor.
Highly reliable heat-dissipation wiring that realizes a low resistance of the wiring conductor, allows a large current of 100 A or more to flow, and does not cause any trouble even if it is repeatedly used in a cold environment of -40 ° C to 150 ° C. A substrate can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a heat dissipation wiring board of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the heat dissipation wiring board of the present invention.

FIG. 3 is a schematic view of a mechanism showing that heat conduction is improved by adding yttrium oxide to aluminum nitride.

FIG. 4 is a sectional view showing a conventional heat dissipation wiring board.

[Explanation of symbols]

 1: substrate 1a to 1c: insulating layer 2: concave portion 3: semiconductor element 4: low-resistance wiring conductor 5: wire 6: metal layer 7, 8: metal plating 9: solder

Claims (4)

[Claims] 1. A ceramic substrate having a thickness of 30 mm or less made of an aluminum nitride sintered body or a silicon nitride based sintered body containing at least one selected from yttrium oxide, erbium oxide and ytterbium oxide as a main sintering aid. , A copper (C) having a thickness of 50 μm or more integrated with the substrate
u), a low-resistance wiring conductor containing at least one or more selected from silver (Ag) and aluminum (Al) as a main component, and the area ratio occupied by the low-resistance wiring conductor to the area of the main surface of the ceramic substrate is A heat dissipation wiring board, wherein the low-resistance wiring conductor has a porosity of 3 to 40% or more. 2. The method according to claim 2, wherein the low-resistance wiring conductor includes Ni, Cu, Au,
2. The heat dissipation wiring board according to claim 1, wherein at least one kind of metal plating selected from Zn and Sn is applied, and a semiconductor element is mounted thereon. 3. The heat dissipation wiring board according to claim 1, wherein at least one metal layer of W, Mo, V, and Ti is interposed between the low-resistance wiring conductor and the ceramic substrate. 4. A method according to claim 1, further comprising the step of:
4. The heat dissipation wiring board according to claim 3, wherein at least one metal plating selected from the group consisting of g, Ti, Mo, V, Ni, Cu, Au, Zn, and Sn is applied.