JP2001185825A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly reliably wiring board in which no crack occurs on the insulating substrate or solder layer even when the thickness of a wiring conductor is increased in accordance with reduction in resistance, and which can be connected electrically to electronic parts and can transfer heat in good states. SOLUTION: The wiring board is formed by bonding a wiring conductor 2 to the surface of the ceramic insulating substrate 1 composed of a ceramic containing at least one kind selected out of Al2O3, AlN, and Si3N4 as the main ingredient and the electronic parts 3 are mounted on the conductor 2. The conductor 2 is formed in a laminated body by respectively laminating low thermal expansion conductor layers 2b having thicknesses which are >=1/40 of the thickness of a Cu conductor layer 2a, which is composed of Cu or a Cu-alloy and has a thickness of >=0.3 mm, and a coefficient of linear thermal expansion of <=11×10-6/ deg.C at 25-100 deg.C upon the electronic parts mounting-side surface and insulting substrate bonding-side surface of the conductor layer 2a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a package for housing a semiconductor element in which electronic parts such as a semiconductor element are hermetically mounted on the surface, and various electronic parts such as a capacitor and a resistor in addition to the semiconductor element. The present invention relates to a wiring board having wiring conductors on the surface of a ceramic integrated board such as a hybrid integrated wiring board or a power module board.

[0002]

2. Description of the Related Art Conventionally, a multilayer wiring board used for a package for housing a semiconductor element, a hybrid integrated wiring board, and the like generally uses an insulating substrate made of an electrically insulating ceramic sintered body such as an alumina sintered body. Tungsten (W), molybdenum (Mo), manganese (M)
n) and a plurality of wiring conductors made of a high melting point metal are arranged, and each wiring conductor is connected to a via hole conductor made of the same high melting point metal provided in the insulating substrate.

Further, when it is necessary to lower the resistance of the wiring conductor, a Cu plate or an Al plate is formed on a wiring conductor made of a high melting point metal formed on the surface of the insulating substrate by using an Ag brazing system, an Al brazing system, or the like. Bonding with a brazing material to form wiring.

When the firing temperature of a glass ceramic or the like is about 1000 ° C., both the inner wiring and the surface wiring inside the insulating substrate are provided by Cu paste and formed by simultaneous firing. Things are going on.

A power module substrate or the like that requires high thermal conductivity uses an AlN ceramic as an insulating substrate, and uses a silver brazing alloy,
A wiring conductor is also formed by joining with a brazing material such as a brazing material.

[0006] A conductive layer of Ni, Au or the like having excellent solder wettability is formed on the surface of these wiring conductors by plating or the like, and various electronic components are soldered and mounted on the surface by soldering or the like.

[0007]

However, when a wiring conductor is formed of Cu in a wiring board in which the resistance of the wiring conductor needs to be reduced, the thermal expansion coefficient of Cu is about 18 × 10 ⁻⁶ / ° C. Since the thermal expansion coefficient is larger than that of general ceramics (3 to 8 × 10 ⁻⁶ / ° C.), when a thermal cycle is applied to the wiring board, the thermal expansion coefficient differs from that of the ceramic insulating substrate. Stress occurs, cracks occur in the board near the joint to the insulating substrate, cracks occur in the solder layer of the brazing part with the electronic components,
There was a problem that the wiring conductor was peeled off from the substrate, and the joint reliability could not be ensured.

When the wiring conductor is made of Al, the Young's modulus and the yield stress are low as compared with Cu, so that peeling off at the joint surface with the insulating substrate hardly occurs, but the thermal expansion coefficient is 23 × 10 ^−. As large as ⁶ / ° C., resulting in a significant change in shape, there is a possibility that the function as a wiring conductor may be impaired. Furthermore, since Al has a higher electric resistance and lower thermal conductivity than Cu, increasing the thickness of the Al wiring conductor deteriorates the thermal resistance of the wiring conductor. I had to raise it. Therefore, there was a problem that it was not possible to meet the demands for thinning (miniaturization) and cost reduction of the module.

[0009] Accordingly, the present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a low-resistance,
It is an object of the present invention to provide a highly reliable wiring board having good electrical connection and thermal conductivity without generating a crack or peeling of a wiring conductor in an insulating substrate or a solder layer.

[0010]

According to the present invention, there is provided a wiring board in which a wiring conductor is joined to a surface of a ceramic insulating substrate, and an electronic component is mounted on the wiring conductor. A Cu conductor layer having a thickness of 0.3 mm or more;
The linear thermal expansion coefficient at 25 ° C. to 100 ° C. is 11 × 1 on the electronic component mounting surface side of the u conductor layer and the bonding surface side to the insulating substrate.
It has been found that the above object can be achieved by forming a laminate of a low thermal expansion conductor layer made of a metal of 0 ⁻⁶ / ° C. or less and having a thickness of 1/20 or more of the thickness of the Cu conductor layer. The present invention has been reached.

The thickness of the low thermal expansion conductor layer is desirably not more than 1/3 of the thickness of the Cu conductor layer in order to sufficiently exhibit the above-mentioned effect by forming the low thermal expansion conductor layer.

It is preferable that the Cu conductor layer and the low thermal expansion conductor layer are diffusion-bonded. In this case, low thermal expansion on the electronic component mounting surface side and the bonding surface side to the insulating substrate is preferable. It is desirable that the difference between the thicknesses of the conductor layers is 0.1 mm or less.

The low thermal expansion conductor layer may be made of W or M
It is preferable to contain o in order to lower the thermal expansion and lower the resistance.

According to the wiring board of the present invention, the wiring conductor to be bonded to the insulating substrate is placed on both sides of the electronic component mounting surface of the Cu conductor layer mainly composed of Cu and the bonding surface to the insulating substrate at 25 ° C.
The low thermal expansion conductor layer suppresses the thermal expansion of the Cu conductor layer by forming a low thermal expansion conductor layer made of a metal having a coefficient of linear thermal expansion of 11 × 10 ⁻⁶ / ° C. or less at 100 ° C. or less. As a result, since the overall thermal expansion coefficient of the laminate can be made smaller than the original thermal expansion coefficient of Cu, the thermal expansion difference between the insulating substrate and the wiring conductor can be reduced,
Thermal stress generated due to the difference in thermal expansion between the two can be reduced. Thereby, it is possible to effectively prevent the occurrence of cracks at the joint portion with the insulating substrate and the solder mounting portion with the electronic component, the separation of the wiring conductor from the insulating substrate, and the like.

[0015] By including a metal having high rigidity such as Mo or W in the low thermal expansion conductor layer, the thermal expansion of the Cu conductor layer can be effectively suppressed, and
Since the current effectively flows through the low thermal expansion conductor layer, the Cu conductor layer does not hinder lowering of the resistance of the entire wiring conductor, and the Cu conductor layer does not need to be unnecessarily thickened.

Furthermore, by forming the low thermal expansion conductor layer with substantially the same thickness on both sides of the Cu conductor layer, the balance of the stress of the laminate when diffusion bonding between the Cu conductor layer and the low thermal expansion conductor layer is maintained, Deformation of the laminate can be prevented.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a wiring board according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view of a multilayer wiring board showing one embodiment of the wiring board of the present invention.
FIG. 3 is an enlarged view of a main part of a mounting portion of the wiring conductor and the electronic component.

According to the wiring board shown in FIGS. 1 and 2, the insulating substrate 1 is constituted by a laminate in which a plurality of insulating layers 1a to 1d are laminated, and the surface of the insulating substrate 1 has
The wiring conductor 2 is joined by a brazing material. Further, according to this multilayer wiring board, metallized wiring layers 3 and 4 are formed on the front surface, inside or back surface of insulating substrate 1, and are connected to internal metallized wiring layer 4 by via hole conductor 5. On the surface of the wiring conductor 2, an electronic component 6 such as a power transistor or a semiconductor element is mounted by soldering with a solder layer 7.

According to the present invention, in the above-mentioned wiring board, the wiring conductor 2 is composed of the Cu conductor layer 2a and the Cu conductor layer 2a.
The linear thermal expansion coefficient at 25 ° C. to 100 ° C. is 11 × 10 ⁻⁶ /
The low thermal expansion conductor layers 2b, 2b made of a metal having a temperature of not more than 0 ° C. are formed by a laminate.

In the present invention, the Cu conductor layer 2a forming a part of the wiring conductor 2 is preferably made of a simple substance of Cu having a purity of 99% or more from the viewpoints of reducing the resistance of the wiring conductor, increasing the thermal conductivity, and reducing costs. Advantageously, other metals may be included as long as they do not impair the excellent properties of Cu.

On the other hand, the low thermal expansion conductor layer 2b is
The coefficient of linear thermal expansion at 00 ° C is 11 × 10 ^-6Is the metal below / ℃
It is important that the coefficient of linear thermal expansion is 11 ×
10 ^-6If it is higher than / ° C, the composite with the Cu conductor layer 2a is formed.
It is difficult to achieve low thermal expansion due to
You. Moreover, the thermal expansion of the Cu conductor layer 2a is suppressed by the compounding.
High rigidity, especially Young's modulus of 200 GPa or more
Of molybdenum (5 ×
10^-6/ ° C) and tungsten (6 × 10^-6/ ℃)
Body or a complex with other metals such as Cu
Is desirable. The composite controls the content ratio of each metal.
It can be adjusted to an arbitrary coefficient of thermal expansion.

The thickness of the Cu conductor layer 2a is 0.2 m
m or more, especially 0.3 mm or more is necessary to allow a large current to flow and obtain high reliability.

On the other hand, the thickness of the low thermal expansion conductor layer 2b is Cu
In order to effectively exert the effect of suppressing the thermal expansion of the conductor layer 2a, it is important that the thickness is 1/20 or more of the thickness of the Cu conductor layer 2a. When the thickness is smaller than 1/20,
Even if the low thermal expansion conductor layer 2b is formed, the thermal expansion of the Cu conductor layer 2a cannot be suppressed, the thermal expansion of the entire laminate cannot be brought close to the insulating substrate, and cracks and peeling can be prevented. It will be difficult. On the other hand, the thickness of the low thermal expansion conductor layer is desirably not more than 1/3 of the thickness of the Cu conductor layer 2a in order not to hinder the low resistance and high thermal conductivity of Cu as the characteristics of the entire wiring conductor 2.

It is desirable that the Cu conductor layer 2a and the low thermal expansion conductor layer 2b are firmly joined by diffusion joining. This is because, when both are laminated by an adhesive such as a brazing material, the thermal resistance of the brazing material layer is high and the electrical resistance is high, thereby deteriorating the thermal and electrical characteristics of the wiring conductor. This is because diffusion bonding is excellent in that the bonding is strong, the reaction layer is extremely thin, and there is almost no deterioration in electrical and thermal characteristics.

The above-mentioned wiring conductor is made of a Cu conductor layer 2a.
And the low thermal expansion conductor layers 2b are formed on both sides thereof, and the difference in thickness between the two low thermal expansion conductor layers 2b is desirably 0.1 mm or less, particularly 0.05 mm or less. This is to maintain the balance of stress in the wiring conductor at the time of diffusion bonding or bonding of the wiring conductor, and to prevent deformation of the wiring conductor. (Insulating Substrate) The insulating substrate 1 is made of a ceramic mainly composed of alumina (Al ₂ O ₃ ), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ) or the like generally applied to a ceramic wiring substrate. As long as it is applicable to any of them, AlN ceramics are suitable for a power module substrate requiring high thermal conductivity, and alumina ceramics are suitable for a multilayered wiring substrate. (Manufacturing method) For example, an insulating substrate made of alumina ceramic is obtained by adding silica (Si) to alumina (Al ₂ O ₃ ) powder.
O _2), magnesia (MgO), calcia (CaO) raw material powder to a known organic binder and an organic solvent such as, plasticizers, a slip prepared by adding and mixing dispersant, a well-known doctor blade method or calendar A ceramic green sheet is prepared by a sheet forming method such as a roll method. Then, as appropriate, after forming a via hole in this green sheet,
After filling the conductor paste or screen-printing the conductor paste on the surface of the green sheet on a metallized wiring pattern, a plurality of them are laminated, and about 1500 to 1700 ° C.
By sintering at a temperature of

When AlN ceramics is used as the insulating substrate, a sintering aid such as an oxide of Group 3a of the periodic table such as Y ₂ O ₃ or an alkaline earth metal oxide such as CaO is added to the AlN powder. Then, a green sheet is prepared using the slurry prepared in the same manner as described above, and a via-hole conductor or a metallized wiring pattern is appropriately formed, followed by firing at 1600 to 1850 ° C.

Further, the silicon nitride ceramic is used as an insulating substrate.
If you do_ThreeN_FourY to powder _TwoO_ThreePeriodic table such as
Oxidation of alkaline earth metals such as Group 3a oxide and MgO
Object, Al_TwoO_Three, SiO_TwoAdd a sintering aid such as
Press the mixture or prepare it as described above.
Make green sheets using the sludge
Metal conductors and metallized wiring patterns.
It is obtained by firing at 1950 ° C.

The conductors to be filled in the metallized wiring layers and via-hole conductors in the above manufacturing process include tungsten (W), molybdenum (Mo), rhenium (Re),
Examples include those containing at least one high melting point metal selected from the group of cobalt (Co) as a main component. In particular, W and Mo are preferable from the viewpoints of matching of thermal expansion coefficient with an insulating substrate and cost. . The via-hole conductor can also have an effect of transmitting heat generated from a heat-generating electronic component such as a power MOSFET mounted on the front surface of the substrate to the rear surface of the substrate.

In particular, for the purpose of heat transfer, a thermal via is also used for a portion on which a heat-generating electronic component is mounted by a method similar to the above-described method of forming a via-hole conductor for the purpose of dissipating heat inside an insulating substrate. It is also possible to provide a large number of via-hole conductors. The wiring conductor on the substrate surface in the present invention is, for example, a copper jig sandwiched between two Cu plates of a predetermined thickness sandwiched between two low thermal expansion conductor plates of a predetermined thickness, at a temperature of about 1100 ℃ By melting Cu, the Cu plate and the low thermal expansion conductor plate can be diffusion bonded. Further, as another method, a low-thermal-expansion conductor powder is filled into a press mold so as to have a predetermined thickness,
Next, a Cu powder or a Cu plate is filled thereon so as to be stacked thereon, and then a similar low thermal expansion conductor powder is further filled thereon, and then pressed at 100 MPa or more, and fired in a reducing atmosphere at about 1050 ° C. Can be produced.

The laminate thus produced is joined to the surface of the ceramic insulating substrate directly or on the metallized wiring layer with a brazing material having an active metal such as Ti to form a wiring conductor on the surface of the insulating substrate. can do.

When an electronic component such as a power MOSFET is mounted on the surface of the surface wiring conductor 2, it is mounted by soldering. In order to improve the wettability with the solder, the surface of the wiring conductor is made of Ni or Cu. It is desirable to apply a plating process to the metal layer having a thickness of 1 to 3 μm.

[0032]

Next, the wiring board of the present invention was evaluated as follows. In the evaluation, A was used as the insulating substrate.
It was produced using 1N ceramics.

First, an AlN powder composition containing 0.5% by weight of CaO and 5% by weight of Y ₂ O ₃ was added to an AlN powder, and an acrylic organic binder, a plasticizer and a solvent were added and mixed to prepare a slurry. The slurry was formed into a sheet having a thickness of about 300 μm by a doctor blade method. After laminating a plurality of the ceramic green sheets, firing at 1750 ° C.
An insulating substrate having a width of 20 mm, a length of 60 mm and a thickness of 1 mm was produced.

Next, a wiring conductor was manufactured. Of a given thickness
A copper conductor plate and two low-conducting plates made of various metals shown in Tables 1 and 2
Laminated sandwiched between thermal expansion conductor plates, 1100 ° C, 1.0kg /
cm ^TwoPressure, diffusion bonding, Cu conductor layer, low heat
Laminates for wiring conductors whose expansion conductor layers have thicknesses of Table 1
Was prepared.

When the low thermal expansion conductor layer is made of Cu / W or Cu / Mo, a mixed powder of Cu and W or Mo having a predetermined composition and a Cu powder are used to form a mold in a mold press. Laminated and filled to form a three-layer structure of a predetermined thickness.
After molding at ton / cm ² , heat treatment was performed at 1100 ° C.

After processing this three-layer laminated wiring conductor to a width of 15 mm and a length of 50 mm, the above-described Al
The wiring substrate having the wiring conductor was formed by heating and bonding at 850 ° C. to the surface of the N substrate.

Thereafter, a thickness of 3 to 4 is applied to the surface of the wiring conductor.
The composition Pb 60%-
Using a 40% Sn solder ribbon, a 10 mm square Si chip was mounted on the wiring conductor.

With respect to the wiring board on which the Si chip is mounted, immediately after joining the wiring conductor to the insulating substrate, and
At every 100 cycles up to 500 cycles of the temperature cycle test of 0 to 125 ° C., the peeling of the wiring conductor and the occurrence of cracks at the joint between the insulating substrate and the wiring conductor and the solder joint of the Si chip were measured with a microscope (25 to 200
Times). The results are shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

Sample No. 1 in which the wiring conductor was formed of a single Cu conductor layer. Sample No. 1 and the low thermal expansion conductor layer were formed, but their thickness was smaller than 1/20 of the thickness of the Cu conductor layer. 1
In the case of No. 0, after brazing, peeling from the joint surface between the conductor layer and the substrate and cracks occurred in the insulating substrate near the end of the wiring conductor.

A laminated body was produced in the same manner as described above by laminating a low thermal expansion conductor layer on only one of the layers. However, the laminated body was greatly deformed and could not be used as a wiring conductor.

In the solder joints, those having no conductor layer outside the scope of the present invention (Sample No. 1) and those having a thin conductor layer (Sample Nos. 2, 6, 10, 11, 1 and 2) were also used.
4, 18, 22, 23, 26, 30, 34, 35) is 4
Cracks were confirmed near the joint between the insulating substrate and the wiring conductor by 00 cycles, and 500
Peeling was observed on the cycle.

Further, the low thermal expansion conductor layer has a thermal expansion coefficient of 11
More than × 10 ^-6 / ° C (Sample Nos. 38 to 4)
In 9), when the thickness of the Cu conductor layer was increased, thermal expansion of the Cu conductor layer could not be suppressed, and cracks and peeling were confirmed in the insulating substrate and the solder portion by 500 cycles.

On the other hand, in the sample of the present invention, no peeling or cracking was observed at the junction between the wiring conductor and the insulating substrate or at the solder junction even after 500 cycles, and it was a highly reliable wiring substrate. confirmed.

[0046]

As described in detail above, according to the wiring board of the present invention, the bonding between the electronic component mounting surface side of Cu or a wiring conductor having a thickness of 0.2 mm or more containing Cu as a main component and the insulating substrate is performed. By forming a predetermined low thermal expansion conductor layer on the surface side, the thermal expansion coefficient of the wiring conductor can be reduced by the low thermal expansion conductor layer, and the difference in thermal expansion between the insulating substrate and the entire wiring conductor can be reduced. As a result, it is possible to absorb and alleviate the thermal stress generated due to the difference in thermal expansion coefficient, suppress the occurrence of cracks and peeling, and obtain a highly reliable wiring board with low resistance and good thermal conductivity. it can.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a multilayer wiring board showing one embodiment of a wiring board of the present invention.

FIG. 2 is an enlarged view of a main part of a mounting portion of the wiring conductor and the electronic component of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating board 2 Wiring conductor 2a Cu conductor layer 2b Low thermal expansion conductor layer 3, 4 Metallized wiring layer 5 Via hole conductor 6 Electronic component 7 Solder layer

Claims (6)

[Claims] 1. A wiring board in which a wiring conductor is joined to a surface of a ceramic insulating substrate, and an electronic component is mounted on the wiring conductor, wherein the wiring conductor is a Cu conductor having a thickness of 0.2 mm or more. A layer and a metal having a linear thermal expansion coefficient of 11 × 10 ⁻⁶ / ° C. or less at 25 ° C. to 100 ° C. on the electronic component mounting surface side and the bonding surface side of the Cu conductor layer on the insulating substrate; A wiring board comprising a laminate in which a low thermal expansion conductor layer having a thickness of 1/20 or more of the thickness of the Cu conductor layer is laminated. 2. The method according to claim 1, wherein the thickness of the low thermal expansion conductor layer is one third or less of the thickness of the Cu conductor layer.
The wiring board as described. 3. The wiring board according to claim 1, wherein the Cu conductor layer and the low thermal expansion conductor layer are diffusion-bonded. 4. The thickness difference between the low thermal expansion conductor layer on the electronic component mounting surface side and the thickness of the low thermal expansion conductor layer on the bonding surface side to the insulating substrate is 0.1 mm.
The wiring board according to claim 4, wherein: 5. The wiring board according to claim 1, wherein said low thermal expansion conductor layer contains Mo or W. 6. A method according to claim 1, wherein said ceramic insulating substrate is made of Al ₂ O ₃ , A
2. The wiring board according to claim 1, wherein the wiring board is made of a ceramic mainly containing at least one of 1N and Si ₃ N ₄ .