JP2001185826A - Wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a highly reliable 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 wiring conductor 2 is formed by respectively laminating Al conductor layers 2b having thicknesses which are >=1/10 of the thickness of a Cu conductor layer 2a having a thickness of >=0.3 mm upon the electronic parts mounting-side surface and insulating 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 approximately 18 ppm / ° C. Since the thermal expansion coefficient is larger than that of ceramics (3 to 8 ppm / ° C.), when a thermal cycle is applied to the wiring board, a thermal stress is generated due to a difference in thermal expansion coefficient with the ceramic insulating substrate, and the insulating substrate is subjected to thermal stress. Cracks occur at the interface between the insulating substrate or the wiring conductor and the insulating substrate near the joints of the parts, cracks occur in the solder layer of the brazing part with the electronic components, the electronic components come off from the wiring conductors, There has been a problem that a problem such as peeling of the conductor from the insulating substrate has occurred, and the bonding reliability cannot 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 does not easily occur, but the coefficient of thermal expansion is 23 ppm / ° C. Since it is large, as a result, a remarkable shape change is caused, and 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, in 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, the wiring conductor is made of a Cu conductor. It has been found that the above object can be achieved by forming a layer and a laminate in which an Al conductor layer is laminated on the electronic component mounting surface side of the Cu conductor layer and the bonding surface side to the insulating substrate, and the present invention has been accomplished.

In the above metal conductor, the thickness of the Cu conductor layer is 0.3 mm or more, and the thickness of the Al conductor layer is 1/10 or more and 1/2 or less of the thickness of the Cu wiring conductor. desirable.

It is preferable that the Cu conductor layer and the Al conductor layer are diffusion bonded to each other by hot rolling after lamination.

Further, the ceramic insulating substrate includes:
Ceramics containing at least one of Al ₂ O ₃ , AlN, and Si ₃ N ₄ as a main component are exemplified.

According to the wiring board of the present invention, Cu or Cu
By forming an Al conductor layer on both sides of the electronic component mounting surface of the wiring conductor having as a main component and the bonding surface side to the insulating substrate, a difference in thermal expansion coefficient between the ceramic insulating substrate and Cu is caused. Even if a thermal stress is generated, the thermal stress is favorably absorbed by the conductor layer having a small Young's modulus, so that the thermal stress applied to the insulating substrate or the solder layer can be reduced. It is possible to prevent cracks and peeling of the solder layer and the wiring conductor.

Further, by forming the Al conductor layer on both surfaces of the Cu conductor layer with substantially the same thickness and by diffusion bonding, the wiring conductor is prevented from warping and deforming when a wiring conductor made of a laminate is produced. In addition to this, even when thermal stress is applied, deformation and warpage can be prevented because the balance of stress is maintained.

In addition, since the current effectively flows through the conductor layer, it is not necessary to unnecessarily increase the thickness of the wiring conductor even when the resistance of the wiring conductor is reduced, and the thickness of the entire wiring board is reduced. be able to.

[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, and an electronic component 3 such as a power transistor or a semiconductor element is mounted on the surface of the wiring conductor 2 by soldering with a solder layer 4.

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.
Is formed by a laminated body in which Al conductor layers 2b, 2b are laminated on the electronic component 3 mounting surface side and the bonding surface side to the insulating substrate 1.

In other words, the Cu conductor layer 2a is joined to the insulating substrate 1 via the Al conductor layer 2b.
The electronic component 3 is mounted on the surface of the u conductor layer 2a via the Al conductor layer 2b.

According to this multilayer wiring board, a similar wiring conductor 5 may be formed on the back surface of the insulating substrate 1, and in this case, the wiring conductor 2 formed on the front surface may be formed.
The wiring conductor 5 formed on the back surface can be connected to each other by a via-hole conductor 6 or an internal wiring conductor 7 formed inside the insulating substrate 1.

The Cu conductor layer 2a of the wiring conductor 2 is made of C
u as a main conductor and having a purity of 99% or more.
That is, it is possible to flow a large current by reducing the resistance and increasing the thermal conductivity of the wiring conductor, and it is also advantageous in terms of cost.

It is desirable that the Al conductor layer 2b also has a small deformation stress of Al having a purity of 99% or more. The Al conductor layer 2b is easily plastically deformed, and the Cu conductor layer 2a
Even if the thickness is increased, the thermal stress generated due to the difference in the thermal expansion coefficient between the insulating substrate 1 and the solder layer 4 is favorably absorbed and alleviated. Since metals other than Al have large deformation resistance, thermal stress cannot be sufficiently absorbed and alleviated, and it is difficult to prevent cracks and peeling.

The thickness of the Cu conductor layer 2a is 0.3 m
m or more, especially 0.5 mm or more is necessary from the viewpoint of applying a large current and obtaining high reliability.

On the other hand, it is important that the thickness of the Al conductor layer 2b is 1/10 or more, especially 1/5 or more of the thickness of the Cu conductor layer 2a in order to sufficiently exhibit the effect of absorbing and relaxing thermal stress. If the thickness is smaller than 1/10, even if the Al conductor layer 2b is formed, thermal stress cannot be sufficiently absorbed and alleviated, and it becomes difficult to prevent cracking and peeling. On the other hand, the thickness of the Al conductor layer is desirably not more than の 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.

The above-mentioned wiring conductor is made of a Cu conductor layer 2a.
It is necessary to arrange the Al conductor layers on both sides thereof. This is because the Cu conductor layer 2a and the Al conductor layer 2
This is for keeping the balance of the thermal stress caused by the difference in thermal expansion from b and suppressing the deformation of the Cu conductor layer 2a itself.
In particular, in keeping the stress balance, the two Al conductor layers 2
The difference in the thickness of b is preferably 0.1 mm or less, particularly preferably 0.05 mm or less.

The Cu conductor layer 2a and the Al conductor layer 2
It is desirable that b is diffusion-bonded. this is,
When both are laminated with an adhesive such as brazing material, the thermal resistance and electric resistance of the brazing material layer are high, and the thermal and electrical
While electrical characteristics are deteriorated, diffusion bonding is excellent in that the bonding strength is strong, the reaction layer is extremely thin, and the electrical and thermal characteristics are not deteriorated. It is.

The insulating substrate 1 may be 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. Any of them can be applied, but AlN ceramics is suitable for a power module substrate requiring high thermal conductivity, and alumina ceramics is suitable for a multilayered wiring substrate.

For example, an insulating substrate made of alumina ceramic is prepared by adding alumina (Al ₂ O ₃ ) powder to silica (Si).
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,
It is obtained by filling the conductive paste or screen-printing the conductive paste on the surface of the green sheet, laminating a plurality of them, and firing at a temperature of about 1500 to 1700 ° C.

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, a via hole conductor and a wiring pattern are appropriately formed, and the green sheet is fired 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
1600 ~ 1950 ℃
It is obtained by firing.

The conductor to be filled in the via-hole conductor in the above manufacturing process is at least one kind of high melting point selected from the group consisting of tungsten (W), molybdenum (Mo), rhenium (Re), and cobalt (Co). A material containing a metal as a main component is exemplified, and W and Mo are particularly preferable from the viewpoint of matching of thermal expansion coefficient with an insulating substrate and cost. Also,
The via-hole conductor is a power MO mounted on the surface of the board.
An effect of transferring heat generated from a heat-generating electronic component such as an SFET to the back surface of the substrate can also be obtained.

On the other hand, when the internal wiring conductor is formed by firing simultaneously with the ceramic insulating substrate, the same high melting point metal as that of the through-hole conductor can be used.

In particular, for the purpose of heat transfer, a thermal via is also used in a portion for mounting a heat-generating electronic component by the same method as 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 formed, for example, by stacking a Cu plate having a predetermined thickness on a carbon jig so as to be sandwiched between two Al plates having a predetermined thickness, and then forming Cu at a temperature of about 1100 ° C. By melting, the Cu plate and the Al plate can be diffusion bonded. Further, as another method, Al powder is filled into a press mold so as to have a predetermined thickness, and then Cu powder or a Cu plate is filled so as to be stacked thereon, and further Al powder is further placed thereon. After filling, it can be produced by press-molding at 1 ton / cm ³ or more and firing in a reducing atmosphere at about 1050 ° C.

When electronic components are mounted on the surface of the surface wiring conductor 2, they are mounted by soldering. In order to improve the wettability with the solder, Ni or Cu is applied to the surface of the wiring conductor.
It is desirable to apply a plating process to a metal layer having a thickness of 1 to 3 μm.

[0036]

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. A Cu plate having a predetermined thickness is sandwiched and laminated between two Al plates having a predetermined thickness.
Hot rolling was performed at 00 ° C. and diffusion bonding was performed to produce a wiring conductor having a Cu conductor layer and an Al conductor layer each having a thickness shown in Table 1. After processing this three-layer laminated wiring conductor into a width of 15 mm and a length of 50 mm, it was heated and joined to the surface of the AlN substrate at 500 ° C. using an Al solder to form a wiring substrate having a wiring conductor.

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). Table 1 shows the results.

[0041]

[Table 1]

Sample No. in which the wiring conductor was formed of a single Cu conductor layer. In Sample No. 1, even when the Al conductor layer was formed, the thickness of Sample No. 1 was smaller than 1/10 of the thickness of the Cu conductor layer.
In No. 9, 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.

Incidentally, an Al plate was laminated on only one side to produce a laminate in the same manner as described above. However, the laminate was greatly deformed and could not be used as a wiring conductor.

In the temperature cycle test, an Al conductor layer was not formed even at the solder joint (sample No.
1) and 30 with a thin Al conductor layer (Sample No. 10)
At 0 cycles or less, cracks were observed in the solder layer near the junction with the chip.

On the other hand, in the sample of the present invention, peeling and cracking were not observed up to 400 cycles in the joint between the wiring conductor and the insulating substrate, and 400 cycles in the solder joint.
It was confirmed that the wiring board had high reliability.

[0046]

As described above in detail, according to the wiring board of the present invention, the Al conductor layer is provided on the electronic component mounting surface of the Cu conductor layer having a thickness of 0.3 mm or more and the bonding surface to the insulating substrate. The thickness of the Al conductor layer absorbs and relaxes the thermal stress generated due to the difference in the coefficient of thermal expansion due to the Al conductor layer, suppresses the occurrence of cracks and peeling, and has a low resistance and good thermal conductivity. A reliable wiring board can be obtained.

[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, 5 Wiring conductor 2a Cu conductor layer 2b Al conductor layer 3 Electronic component 4 Solder layer 6 Via hole conductor 7 Internal wiring conductor

Continued on the front page F term (reference) 4E067 AA05 AA07 BA00 EB00 4E351 AA07 AA08 AA09 BB01 BB23 BB24 BB29 BB35 CC18 DD04 DD10 DD54 GG03 GG04 GG06

Claims (5)

[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 0.3 mm or more. From a laminate obtained by laminating an Al conductor layer having a thickness of 1/10 or more of the thickness of the Cu conductor layer on the electronic component mounting surface side of the Cu conductor layer and the bonding surface side to the insulating substrate of the Cu conductor layer. A wiring substrate, comprising: 2. The wiring board according to claim 1, wherein the thickness of the Al conductor layer is not more than の of the thickness of the Cu conductor layer. 3. The wiring board according to claim 1, wherein the difference between the thickness of the Al conductor layer on the electronic component mounting surface side and the thickness of the Al conductor layer on the bonding surface side to the insulating substrate is 0.1 mm or less. 4. The wiring board according to claim 1, wherein said Cu conductor layer and said Al conductor layer are diffusion bonded. 5. The method according to claim 1, wherein said ceramic insulating substrate is made of Al ₂ O ₃ ,
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 .