JP2002111211A - Ceramic wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic wiring board in which a metallic sheet and a ceramic insulating substrate are stably joined to each other with a brazing material and the metallic sheet has a high joining strength. SOLUTION: In the ceramic wiring board A, wiring or a heat sink is formed by joining the metallic sheet 2 composed mainly of Al or Cu to the surface of the ceramic insulating substrate 1 composed of Al2O3, AlN, Si3N4, etc., with the brazing material 4. The center-line average height (Ra) of the surface of the joint between the insulating substrate 1 and metallic sheet 2 is adjusted to 0.05-10 μm and, at the same time, a metallic layer 3 composed of Al, Ni, etc., and having superior wettability to the brazing material 4 is formed on the surface of the substrate 1 to a thickness of 1-10 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic insulating substrate such as a hybrid integrated circuit substrate on which various electronic components such as capacitors and resistors are mounted in addition to a semiconductor element on a surface of a ceramic insulating substrate, and a ceramic insulating substrate such as a power module substrate. And a ceramic wiring board having a wiring and a heat sink formed on the surface of the ceramic wiring board.

[0002]

2. Description of the Related Art Conventionally, as a wiring board used for a package for housing a semiconductor element, a hybrid integrated circuit board, or the like, a ceramic insulating substrate made of an electrically insulating ceramic sintered body such as an alumina sintered body is generally used. And tungsten (W), molybdenum (Mo), manganese (M
n) and a plurality of wiring layers made of a high melting point metal are arranged, and each wiring layer is connected by a via hole conductor made of the high melting point metal provided in an insulating substrate. For circuits requiring low-resistance wiring, a Cu paste is printed on the surface layer of the ceramic insulating substrate and fired at a temperature lower than the melting point to form a Cu thick film wiring. Further, when a heat sink is required to dissipate heat, such as a wiring for a large current that cannot be handled by a Cu thick film wiring or a power element, the Al or C
A metal plate made of u is joined to the surface of the ceramic insulating substrate with a brazing material such as a silver brazing alloy or an Al brazing alloy, solder, or the like.

[0003] Power module substrates and the like that require high thermal conductivity include AlN substrates and Si ₃ substrates having excellent thermal conductivity.
A metal plate made of Al or Cu is joined to the N ₄ substrate by the same joining method as described above to form a wiring or a heat sink. Then, a metal layer having excellent solder wettability is formed on the surface of these wiring layers by plating or the like, and various electronic components are solder-mounted to form a circuit.

[0004]

However, in a ceramic insulating substrate in which a metal plate such as Al or Cu is bonded, a thickness variation of a bonding layer such as a brazing material, a void in the bonding layer, or bonding to a metal plate. If the bonding state between the metal plate and the ceramic insulating substrate is poor due to the presence of voids at the interface between the layers, there has been a problem that the bonding reliability is deteriorated, and the electrical connection and thermal conductivity of electronic components and the like are deteriorated.

[0005] In particular, in the case of a ceramic insulating substrate, there is a problem that the wettability with a brazing material changes depending on the surface state, and the bonding strength when a metal plate is brazed is reduced.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has as its object the object of joining a metal plate and a ceramic insulating substrate with excellent joining stability with a brazing material and a high joining strength of the metal plate. An object of the present invention is to provide a ceramic wiring board.

[0007]

SUMMARY OF THE INVENTION The present invention provides a ceramic insulating substrate having a center line average roughness (Ra) of 0.05 to 10 .mu.m and a surface roughness of the ceramic insulating substrate. By forming a metal layer having a thickness of 1 to 10 μm on the ceramic surface so as to improve the wettability of the brazing material, and forming a joint structure of a ceramic insulating substrate, a metal layer, a brazing material, and a metal member, the ceramic insulating material is formed. The wettability of the brazing material to the substrate is always stable, and the joining strength of the metal plate can be increased.

That is, according to the ceramic wiring board of the present invention, by setting the surface roughness (Ra) of the surface of the ceramic insulating substrate to be bonded to the metal plate to 0.05 to 10 μm, the physical bonding by the anchor effect is stabilized. Therefore, the bonding reliability between the metal plate and the ceramic insulating substrate via the brazing material is improved. Further, by setting the thickness of the metal layer existing between the brazing material and the ceramic insulating substrate to 1 to 10 μm, the wettability with the brazing material is improved, so that the metal plate can be firmly joined. Thereby, the electrical connection reliability and the heat dissipation by the metal plate functioning as the wiring layer and the heat sink can be improved.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a ceramic wiring board according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a perspective view showing one embodiment of the ceramic wiring board of the present invention, and FIG.
FIG. 2 is a cross-sectional view of the ceramic wiring board of FIG.

According to the ceramic wiring board A of FIG. 1, a wiring layer 2 is formed by joining a metal plate 2 to the surface of a ceramic insulating substrate 1 formed by laminating a plurality of insulating layers 1a to 1c. The electronic component 7 is mounted on the surface of the wiring layer 2 on the substrate A or on a predetermined portion of the ceramic insulating substrate 1. Wiring layer 2 formed on surface of ceramic insulating substrate 1
Is a ceramic insulating substrate 1 as shown in the sectional view of FIG.
Via the via-hole conductor 5 or the internal wiring layer 6 formed inside the insulating substrate 1.

According to the present invention, as shown in the enlarged sectional view of FIG. 3, the metal plate 2 on which the wiring layer 2 is formed is formed of a metal having excellent wettability with a brazing material on the surface of the ceramic insulating substrate 1. A layer 3 is formed, and the metal plate 2 is bonded to the metal layer 3 via a bonding layer 4 made of a brazing material.

According to the present invention, in such a bonding structure, the center line average roughness (Ra) of the surface of the ceramic insulating substrate 1 to which the metal plate 2 forming the wiring layer 2 is bonded is 0.05.
It is important that the thickness be 10 μm to 10 μm. The reason for limiting this surface roughness is that Ra is smaller than 0.05 μm.
If Ra is less than 10 μm, the metal layer 3 is not formed uniformly, the wettability with the brazing material is deteriorated, voids are generated inside the bonding layer 4, 2, the bonding strength with the second metal is reduced. Particularly, the surface roughness (Ra) is optimally 1.5 to 5 μm. Such surface roughness can usually be easily adjusted by blasting or polishing the surface of the ceramic sintered body. However, the baked surface depends on the particle size of the ceramic raw material powder to be used, the molding method, and the firing conditions. Can be controlled to the above-mentioned surface roughness.

The metal layer 3 is not particularly limited as long as it has excellent wettability with the brazing material constituting the bonding layer 4, but it depends on the type of the brazing material, and may be Au, Ni, Cu, Ag. It is desirable to select from the group as appropriate and form. For example,
When an AlSi brazing material is used as a brazing material when joining an Al plate, Al or Ni is preferable. Also,
When joining a Cu plate, when AgCu is used as the brazing material, Cu or Ni is preferable.

The metal layer 3 can be easily formed by vapor deposition or plating of Al or Cu, and easily formed of Ni by plating or the like.

According to the present invention, it is important that the thickness of the metal layer 3 is 1 to 10 μm. This is because if the thickness of the metal layer is less than 1 μm, the metal layer 3 cannot be formed uniformly on the surface of the ceramic insulating substrate 1 so that the wettability of the brazing material deteriorates. Swelling and peeling of the metal layer 3 due to the difference in thermal expansion of the metal layer 3 and further increase the cost. The optimal thickness of the metal layer 3 is 1.5 to 5 μm.

The brazing material forming the bonding layer 4 may be any material that melts at a temperature lower than the melting point of Al or Cu constituting the metal plate 2 and provides good connection. When joining plates, an Al-Si brazing material is preferably used. When joining Cu plates, an Al-Si brazing material or an Ag-Cu brazing material is preferably used.
When joining l-plates, an Al-Si brazing material to which Cu or Sn is added in order to lower the melting point of the brazing material may be corroded and deteriorated in a severe environment. Al-Si-based brazing filler metal containing 1% by weight or less of Sn is preferable.

The metal plate 2 to be joined is made of Cu or Al. If low resistance is required, a metal containing Cu as a main component is used. It is desirable to constitute from the metal which has as a main component.

The insulating substrate 1 is generally made of alumina (Al ₂ O ₃ ), mullite (3Al ₂ O ₃ .2SiO ₂ ), aluminum nitride (Al
N), silicon nitride (Si ₃ N ₄ ), silicon carbide (SiC) and the like can be applied to any ceramic sintered body as a main component, and may be appropriately used according to the required characteristics. For example, for a power module substrate requiring high thermal conductivity, a ceramic sintered body containing AlN as a main component is preferable from the viewpoint of thermal conductivity. When strength is required,
A ceramic sintered body containing Si ₃ N ₄ as a main component is preferably used. In the case of inexpensive formation, a ceramic sintered body mainly containing Al ₂ O ₃ is preferably used. For multilayering, a ceramic sintered body containing Al ₂ O ₃ or AlN as a main component is preferable.

As a specific method for producing a ceramic wiring board having a multilayer structure, for example, a ceramic sintered body mainly containing Al ₂ O ₃ will be described. First, alumina (Al ₂ O ₃ ) A slurry prepared by adding a known organic binder, an organic solvent, a plasticizer, a dispersant, and the like to a raw material powder such as silica (SiO ₂ ), magnesia (MgO), and calcia (CaO) is mixed with a known doctor blade method. It is obtained by subjecting a ceramic green sheet formed by a sheet forming method such as a calendering method to a predetermined punching process, laminating a plurality of the sheets, and firing at a temperature of 1550 to 1800 ° C.

The via-hole conductor 5 is mainly composed of a high melting point metal such as tungsten (W), molybdenum (Mo), rhenium (Re), and cobalt (Co). W and Mo are preferred from the viewpoint of the matching of the coefficient of thermal expansion and the cost.

On the other hand, for the internal wiring layer 6 formed by firing simultaneously with the ceramic insulating substrate 1, the same high melting point metal as that of the through-hole conductor can be used. Further, when thermal conductivity or low-resistance wiring is required on the surface of the ceramic insulating substrate 1, copper (Cu), silver (Ag), nickel (Ni), aluminum (Al) is formed by a post-fire method or a plating method. It can be formed of at least one member selected from the group.

The ceramic insulating substrate is made of Al ₂ O ₃ , AlN,
In the case of Si ₃ N _{4, in} the case of the simultaneous firing, W is preferable from the relationship between the firing temperature and the melting point.

A metal layer 3 having a thickness of 1 to 10 μm is formed on the multilayered ceramic wiring board thus formed by a vapor deposition method or a plating method, and then a predetermined brazing material is applied thereto to form a metal plate. After stacking two, A in a reflow furnace
1, when joining a Cu plate with an AlSi brazing material, 50
When joining a Cu plate with an AgCu brazing material at 0 to 610 ° C, the metal plate 2 can be joined to the surface of the ceramic insulating substrate 1 by heating at 800 to 900 ° C.

[0024]

EXAMPLE 1 Next, the wiring board of the present invention was evaluated as follows.
In the evaluation, an insulating substrate made of an Al ₂ O ₃ sintered body was used as the insulating substrate. First, Al ₂ O ₃ powder, Si
A slurry is prepared by adding and mixing an acrylic organic binder, a plasticizer, a solvent and a dispersant to an Al ₂ O ₃ composition containing a total of 5% by weight of O ₂ , CaO and MgO powders. Was formed into a sheet having a thickness of about 300 μm by a doctor blade method. After laminating a plurality of these ceramic green sheets, they were fired at 1750 ° C. to produce a ceramic insulating substrate having a thickness of 1 mm.

Next, the surface of the ceramic insulating substrate to which the metal plate is bonded is blasted and polished to obtain a surface roughness (R).
a) A plurality of substrates having a thickness of 0.03 to 12.0 μm were prepared.

After that, a metal layer made of Al having a thickness of 0.5 to 7.0 μm was formed by a vapor deposition method at the metal plate joining portion of each of the ceramic insulating substrates having different surface roughness. Then, an Al plate having a thickness of 0.3 mm and a thickness of 10 mm □ was heat-treated at 600 ° C. in a vacuum atmosphere via an AlSi braze on the Al metal layer and joined.

The following evaluation was performed on the ceramic wiring board to which the Al plate manufactured by the above method was joined. First, the void ratio under the Al plate (bonding area 5 m
The void area ratio per m □ was evaluated. Next, the Al plate was pulled vertically, and the bonding strength until the Al plate was peeled from the substrate was evaluated.

FIG. 4 shows the relationship between the surface roughness (Ra) of the ceramic insulating substrate and the bonding strength of the Al plate, and also evaluates the change due to the thickness of the metal layer made of Al.

According to FIG. 4, the thickness of the Al metal layer is 0.5 to
10 μm is good, and it can be seen that the bonding strength sharply increases from the surface roughness (Ra) of the ceramic insulating substrate surface of 0.05 μm, and that the bonding strength does not change much when Ra is 1 μm or more. However, the thickness of the Al metal layer is 12 μm
, The bonding strength was reduced, and particularly when the surface roughness of the ceramic insulating substrate was smaller than Ra 6 μm, a remarkable reduction in strength was observed.

FIG. 5 shows the relationship between the void ratio in the joining layer made of a brazing material and the thickness of the Al metal layer, and also evaluates the change due to the surface roughness of the ceramic insulating substrate. According to FIG. 5, when the surface roughness Ra of the insulating substrate is 12.0 μm, the void ratio cannot be effectively reduced even when the thickness of the metal layer is changed, and even when the thickness of the Al metal layer is set to 5 μm. It had a void ratio of 19%.

When the thickness of the Al metal layer was 0.5 μm, the void ratio was 20% or more regardless of the surface roughness. That is, the void ratio could be reduced to 17% or less under the conditions of a surface roughness Ra of 0.05 to 10 μm and an Al deposition thickness of 1 to 10 μm.

Example 2 A ceramic insulating substrate was manufactured in the same manner as in Example 1.
Then, the surface of the ceramic insulating substrate to which the metal plate was bonded was blasted and polished to produce a substrate having a surface roughness (Ra) of 3.0 μm.

Thereafter, a metal layer made of Cu having a thickness of 2.0 μm was formed by plating at the joint of the ceramic insulating substrate with the metal plate. Then, on this Cu metal layer, a thickness of 0.3 mm and a thickness of 10 mm
Was heat-treated at 850 ° C. in a vacuum atmosphere and joined.

The evaluation was performed in the same manner as in Example 1 for the ceramic wiring board to which the Cu plate manufactured by the above method was joined. As a result, the void ratio was 10%, and the bonding strength was 3%.
5 (N / 5 mm □), indicating a high strength.

On the other hand, when the Cu plates were joined by the AgCu brazing material without forming the Cu metal layer, the joining strength was as low as 9 (N / 5 mm □).

[0036]

As described in detail above, according to the ceramic insulating substrate of the present invention, the surface roughness of the surface of the ceramic insulating substrate joined to the metal plate and the thickness of the metal layer excellent in wettability with the brazing material are controlled. By doing so, the wettability of the brazing material is excellent, voids in the bonding layer are reduced, and the metal plate can be bonded firmly. As a result, it is possible to join a metal plate and a ceramic insulating substrate having good electrical connection and thermal conductivity. Therefore, it is possible to operate without failure even in a severe environment such as an in-vehicle environment, which is excellent in reliability that can be adapted to a large current.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a ceramic wiring board of the present invention.

FIG. 2 is a sectional view showing one embodiment of the ceramic wiring board of the present invention.

FIG. 3 is an enlarged sectional view showing a joint portion of a metal plate in the ceramic wiring board of the present invention.

FIG. 4 is a graph showing the relationship between the bonding strength of a metal plate, the surface roughness of a ceramic insulating substrate, and the thickness of a metal layer.

FIG. 5 is a graph showing a relationship among a void ratio, a surface roughness of a ceramic insulating substrate, and a metal layer thickness.

[Explanation of symbols]

 A ceramic wiring board 1 ceramic insulating substrate 2 wiring layer (metal plate) 3 metal layer 4 bonding layer (brazing material) 5 via hole conductor 6 internal wiring layer 7 electronic component

Claims (3)

[Claims] An Al or C on a surface of a ceramic insulating substrate.
u is a ceramic wiring board on which a wiring layer or a heat sink is formed by bonding a metal plate containing any one of the main components via a bonding layer made of a brazing material. A center line average roughness (Ra) of the joint surface is 0.05 to 10 μm, and a metal layer having excellent wettability with a brazing material is formed on the surface of the ceramic wiring board in a thickness of 1 to 10 μm. A ceramic wiring substrate, characterized in that: 2. The method according to claim 1, wherein said ceramic insulating substrate is made of Al ₂ O ₃ , A
2. The ceramic wiring board according to claim 1, comprising at least one selected from the group consisting of 1N and Si ₃ N ₄ . 3. The metal layer having excellent wettability with the brazing material,
3. The ceramic wiring board according to claim 1, comprising at least one selected from the group consisting of Al, Ni, and Cu.