JP2001185838A - Ceramic wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ceramic wiring board which is improved in adhesion with the wiring conductor of a metal plated layer and eliminates bulging or the like of the metal plated layer, when an electronic component or the like is mounted on the surface of the wiring conductor formed with the metal plated layer by soldering. SOLUTION: A wiring conductor 2 with Cu or Al as the main conductor is attached and formed on the surface of a ceramic insulated substrate 1, the surface of the wiring conductor 2 is coated and formed with a metal plated layer 3 composed of a metal such as Ni improved in solder wetting, and an electronic component 7 is mounted on this metal plated layer 3 with solder 6. Concerning such a wiring board, the average centerline roughness (Ra) of the wiring conductor 2 coated and formed with the metal plated layer 3 is 1 to 3 μm and the thickness of the metal plated layer 3 is 1 to 4 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device housing package in which a semiconductor device is housed and mounted, a hybrid integrated circuit board on which electronic components such as a capacitor and a resistor are mounted in addition to the semiconductor device on the surface. The present invention relates to a wiring substrate having a wiring conductor on a surface of a ceramic insulating substrate used as a power module substrate or the like.

[0002]

2. Description of the Related Art Conventionally, a multilayer wiring board used for a package for housing a semiconductor element, a hybrid integrated circuit board or the like generally uses an insulating board made of an electrically insulating ceramic sintered body such as an alumina sintered body. Tungsten (W), molybdenum (Mo), manganese (M) are formed from the periphery of the concave portion provided in the approximate center of the upper surface to the lower surface, or inside and on the surface.
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. For circuits requiring low-resistance wiring, print a Cu paste on the surface layer and bake at a temperature lower than the melting point.
A wiring conductor made of u is formed.

If the ceramic insulating substrate is made of glass ceramic or the like and the firing temperature is around 1000 ° C., a wiring pattern is printed and formed on the surface of the unsintered sheet compact with Cu paste for both the inner wiring and the surface wiring. It is performed by simultaneous firing.

On the other hand, in the case of a power module substrate or the like that requires high thermal conductivity, a high thermal conductive conductor plate such as a Cu plate or an Al plate is formed on the surface of an insulating substrate by using a brazing material such as a silver brazing alloy or an Al brazing alloy. It is also performed to form a wiring conductor by bonding.

In the case where various electronic components are mounted on the surface of the wiring conductor in the above various ceramic wiring boards, a metal layer having excellent wettability with solder is formed on the surface of the wiring conductor by plating or the like. After that, various electronic components are mounted on the plating layer by soldering.

[0006]

However, if only a metal layer having excellent solder wettability is formed on a wiring conductor by plating, the bonding between the plating layer and the wiring conductor may be caused when heat treatment such as electronic component mounting is performed. Since the strength is weakened and plating swelling occurs, which adversely affects the bonding strength and solder wettability, there has been a problem that electrical connection and thermal conductivity of electronic components and the like are deteriorated. In particular, when the thickness of the plating layer was set to 1 μm or more in order to improve the wettability with the solder and to suppress the occurrence of voids and the like in the solder and the like, it was particularly remarkable.

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a method for wiring a plating layer when an electronic component or the like is solder-mounted on a surface of a wiring conductor on which the plating layer is formed. An object of the present invention is to provide a ceramic wiring board which has excellent adhesion to a conductor, has no swelling of a plating layer, and has good electrical connection and thermal conductivity.

[0008]

According to the present invention, a wiring conductor having Cu or Al as a main conductor is formed on the surface of a ceramic insulating substrate, and the surface of the wiring conductor has excellent solder wettability. It is formed by coating a metal plating layer,
In a ceramic wiring board on which an electronic component is mounted and mounted on the plating layer by soldering, the center line average roughness (Ra) of the wiring conductor that covers and forms the plating layer is 1 to 3.
It has been found that by setting the thickness of the plating layer to 1 to 4 μm, the adhesion of the plating layer to the wiring conductor is increased, and the above object is achieved.

[0009] Incidentally, in such a wiring board, as an excellent metal to the solder wettability, it is desirable to use Ni, further, as a ceramic insulating substrate, Al ₂
At least one selected from the group consisting of O ₃ , AlN, and Si ₃ N ₄
It is desirable that it be composed of seed-based ceramics.

[0010]

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 schematic cross-sectional view of a multilayer wiring board as an example of the ceramic wiring board of the present invention, and FIG. 2 is an enlarged cross-sectional view of a main part when an electronic component is mounted on a wiring conductor surface on the board surface.

The multilayer wiring board shown in FIG. 1 has a structure in which a plurality of ceramic insulating layers 1a to 1d are laminated on a surface of an insulating substrate 1.
A wiring conductor 2 having u or Al as a main conductor is provided, and a plating layer 3 made of a metal having excellent solder wettability is formed on a portion of the wiring conductor 2 where electronic components are mounted. The wiring conductor 2 is formed via the via-hole conductor 4 or the internal wiring conductor 5 formed inside the insulating substrate 1.
It is led to the other surface of the insulating substrate 1. Then, a semiconductor element,
Electronic components 7 such as a capacitor element, a resistance element, and a power element such as a power MOSFET are mounted.

According to the present invention, in such a wiring board, the surface of the wiring conductor 2 on which the plating layer 3 is formed has a center line average roughness (Ra) (hereinafter sometimes simply referred to as surface roughness). By roughening the surface to 1 to 3 μm, the bonding area between the plating layer 3 and the wiring conductor 2 can be increased. As a result, the metal of the plating layer 3 is physically bonded to the surface of the wiring conductor 2 by an anchor effect. The joining strength can be increased without deteriorating the electrical characteristics of the chemical bond due to a reaction or the like.

The reason why the center line average roughness (Ra) is limited to the above range is that if the Ra is less than 1 μm, the effect of improving the bonding strength is not sufficient, and if the Ra is more than 3 μm, the wiring conductor 2 The plating layer 3 cannot be formed uniformly on the surface, and the solder wettability of the plating layer 3 deteriorates. When the electronic component 7 is mounted on the surface of the plating layer 3 by soldering, a void is formed inside the solder 6. This causes the reliability of solder mounting to decrease. Further, in order to form the plating layer uniformly, it is desirable that Rmax is 8 to 30 μm.
If x is less than 8 μm, the adhesion is insufficient, and 30
If it exceeds μm, it becomes difficult to form a plating layer uniformly.

The center line surface roughness (Ra) of the surface of the wiring conductor 2 on which the plating layer 3 is formed is determined by observing the cross section of the plating layer 3 and the wiring conductor 2.
Can be determined from the unevenness of the interface line.

According to the present invention, it is important that the thickness of the plating layer 3 is 1 to 4 μm, especially 2 to 3 μm. By setting the thickness to 1 μm or more, the solder wettability is excellent and the bonding strength is improved. When the thickness is 4 μm or less, plating swelling can be reduced.

The metal having excellent solder wettability formed as the plating layer 3 on the wiring conductor 2 includes Cu, N
At least one selected from the group consisting of i and Sn is used, but Ni is most preferable because of easiness of the plating process.

The insulating substrate is a ceramic sintered body mainly composed of alumina (Al ₂ O ₃ ), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), etc., which is generally used for a multilayer wiring board. Can be applied to any of them. However, in a power module substrate requiring high thermal conductivity, AlN
Is desirable. In the case of a multilayer wiring board, it is particularly desirable to use a board made of an alumina sintered body.

For example, an alumina ceramic is used as an insulating substrate.
The wiring substrate is made of alumina (Al _TwoO_Three) To powder,
Mosquito (SiO_Two), Magnesia (MgO), calcia (C
aO) and other raw material powders with known organic binders and organic solvents
Agent, plasticizer, slurry prepared by adding and mixing a dispersant, etc.,
Well-known systems such as the doctor blade method and calendar roll method
Making ceramic green sheets by sheet molding
You. And, if necessary, add a via hole to this green sheet.
After forming, fill with conductive paste or use green sheet
Conductor paste on the surface to metallized wiring pattern
After printing, a plurality of them are laminated, and
It is obtained by firing at a temperature of 700 ° C.

In a wiring board using AlN ceramics as an 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 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.

In addition, a wiring board using silicon nitride ceramics as an insulating substrate is made by adding Si ₃ N ₄ powder to a Group 3a oxide of the periodic table such as Y ₂ O ₃ , an alkaline earth metal oxide such as MgO, Al _A sintering aid such as ₂ O ₃ or SiO ₂ is added, and the mixture is press-molded, or a green sheet is prepared using a slurry prepared in the same manner as described above, and a via-hole conductor or a metallized wiring pattern is formed as appropriate. , 1600-
It is obtained by firing at 1950 ° C.

The via-hole conductor is mainly composed of at least one refractory metal selected from the group consisting of 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 with the insulating substrate and the cost. The via-hole conductor has a heat sink effect by connecting heat generated from a heat-generating electronic component from a surface-mounted power MOSFET or the like to the wiring conductor 2 formed on the opposite surface by heat conduction. You can also.

Further, when a power MOSFET or the like requiring a large current is surface-mounted on the multilayer wiring board of the present invention, a wiring conductor for a large current is also formed on the power MOSFET wiring, and as described above. It is desirable to provide a large number of via-hole conductors that also serve as thermal vias in the portion where the power MOSFET is surface-mounted, and to improve the heat dissipation property in combination with the heat sink function of the wiring conductor.

On the other hand, for a wiring conductor having Cu or Al as a main conductor, a paste containing Cu or Al is printed and applied to form a C
For u, 900-1000 ° C., for Al, 550-
It can be formed by baking at 600 ° C.

Further, when a large current of 10 A or more is passed, for example, a Cu plate or an Al plate having a thickness of 0.1 mm or more, or a press forming method of Cu or Al powder into a predetermined wiring conductor shape by powder metallurgy. Heat treatment (950 to 1000 ° C. for Cu, 5 for Al)
(50 to 600 ° C.), the metal sintered body can be formed by bonding with a brazing material containing an active metal such as AgCuTi in the case of Cu, or with an AlSi brazing material in the case of Al. .

The internal wiring conductors 5 and via-hole conductors 4 formed inside the insulating substrate 1 are formed by simultaneous firing with the insulating substrate 1, and the surface wiring conductors formed by simultaneous firing are formed on the surface of the insulating substrate. May be formed.

According to the present invention, the center line average surface roughness (Ra) of the surface of the wiring conductor 2 formed as described above needs to be 1 to 3 μm. In order to form such a surface, when the wiring conductor 2 having Cu or Al as a main conductor is formed by applying a conductive paste and then sintering, the particle size of the metal powder of Cu or Al in the conductive paste is reduced. As the size is increased, the surface roughness of the fired wiring conductor can be increased.

Also, in a method in which the metal powder is formed into a predetermined shape by powder metallurgy and then fired, the surface roughness of the baked metal can be arbitrarily controlled by controlling the particle size of the metal powder used.

As still another method, it is possible to roughen the surface by applying an acid or alkali to a Cu plate or an Al plate and etching it.

On the surface of the wiring conductor formed as described above, a plating layer made of at least one metal selected from the group consisting of Cu, Ni and Sn is formed with a thickness of 1 to 4 μm. The plating layer may be a single layer or a multi-layer formed by a combination of the above-mentioned groups. Even in such a case, the total thickness is desirably 1 to 4 μm.

[0030]

Next, the ceramic wiring board of the present invention was evaluated as follows. Note that AlN ceramics was used as the insulating substrate. First, CaO0.
A slurry is prepared by adding and mixing an acrylic organic binder, a plasticizer, and a solvent to the AlN composition containing 5% by weight and 5% by weight of Y ₂ O ₃ , and the slurry is about 300 μm thick by a doctor blade method. Into a sheet. Next, a predetermined wiring pattern having a thickness of 20 μm was printed on a wiring forming portion on the surface of the ceramic green sheet using a printing paste containing W as a main component, and the predetermined paste was filled in the through holes. After laminating a plurality of these ceramic green sheets, they are fired at 1750 ° C. to have a thickness of 2 mm.
Was manufactured.

The surface of the Cu plate having a thickness of 0.5 mm was etched to be processed into various surface roughnesses. This is bonded to a predetermined portion of the insulating substrate surface with an AgCuTi brazing material,
An m □ wiring conductor was formed. Thereafter, the Ni plating layer was formed to a thickness of 0.5 to 5 μm by an electroless plating method.

The following evaluation was performed on the wiring board manufactured by the above method. (Plating swelling amount) The blister area per 10 mm square of the plating area of the plating layer after the wiring substrate was heat-treated at 400 ° C in a reducing atmosphere was evaluated. (Joint strength) A copper wire having a diameter of 0.6 mm
After bonding with n60Pb 40% solder, the copper wire was pulled vertically, and the strength when the plating layer was peeled was evaluated as the bonding strength. (Void amount) In addition, the other wiring conductor of the wiring board for which the bonding strength was evaluated was coated with 7 mm square Si with 40% Sn60Pb solder.
The chip was mounted, and the void ratio under the chip (void area per 7 mm square of solder mounting area) was evaluated by an X-ray transmission apparatus. In each evaluation result, the number of samples (number of wiring conductors)
The average of the ten values was plotted on a graph.

FIG. 3 shows the relationship between bonding strength, surface roughness Ra and plating thickness. As shown in FIG. 3, the surface roughness of the wiring conductor was 1 μm for both plating thicknesses of 0.5 to 5 μm.
m, the joining strength is 4 kgf / 5 mm.
□ or more, and at 1 μm or more, little change in bonding strength was observed.

FIG. 4 shows the relationship between the plating thickness, the void ratio and the surface roughness Ra. FIG. 4 shows that when the surface roughness Ra is 4 μm, the void ratio is high even when the plating thickness is changed, and the lowest value is 10% when the plating thickness is 3 μm.
Met. When the plating thickness was 0.5 μm, the void ratio was 10% or more regardless of the surface roughness. Under the conditions of a surface roughness Ra of 1 to 3 μm and a plating thickness of 1 to 4 μm, the void ratio was reduced to about 5%.

FIG. 5 shows the relationship between the plating swollen amount, the plating thickness and the surface roughness Ra. FIG. 5 shows that the plating thickness is 0.5 to 2 irrespective of the surface roughness of the wiring conductor.
There is no plating swelling at μm, but plating thickness 3-4μ
m, and when the plating thickness became 5 μm, the plating swelling sharply increased to 10% or more. This tendency coincides with the tendency of the void ratio shown in FIG. 4, and it can be seen that the plating swelling affects the void ratio.

From these results, the surface roughness R of the wiring conductor was obtained.
It was confirmed that a was 1 to 3 μm and the plating thickness was preferably 1 to 4 μm.

A wiring board was prepared in the same manner as described above except that a sintered metal of Al was used as the wiring conductor, and the same evaluation was performed. As a result, almost the same results as in FIGS. 3 to 5 were obtained. I got

[0038]

According to the wiring board of the present invention, the surface roughness of the wiring conductor with which the plating layer comes into contact is reduced by the center line average roughness (R
a) 1 to 3 μm, maximum height (Rmax) 8 to 30 μm
m, and the plating thickness is 1 to 4 μm, so that the bonding strength between the plating layer and the wiring conductor can be strengthened. Further, plating swelling is small and solder wettability is excellent. And a wiring board which can be solder-mounted with good thermal conductivity can be obtained. 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 schematic sectional view of a multilayer wiring board showing one embodiment of a ceramic wiring board of the present invention.

FIG. 2 is an enlarged sectional view of a main part when an electronic component is mounted on the surface of a wiring conductor.

FIG. 3 is a graph showing a relationship between bonding strength between a wiring conductor and a plating layer, surface roughness of the wiring conductor, and plating thickness.

FIG. 4 is a graph showing a relationship among a void ratio, a surface roughness of a wiring conductor, and a plating thickness.

FIG. 5 is a graph showing a relationship between a plating swelling amount, a surface roughness of a wiring conductor, and a plating thickness.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating board 2 Wiring conductor 3 Plating layer 4 Via hole conductor 5 Internal wiring conductor 6 Solder 7 Electronic component

Claims (3)

[Claims] A wiring conductor having Cu or Al as a main conductor is formed on a surface of a ceramic insulating substrate, and a plating layer made of a metal having excellent solder wettability is formed on the surface of the wiring conductor. In a wiring board on which an electronic component is mounted and mounted on the plating layer by soldering, the center line average roughness (Ra) of the wiring conductor covering the plating layer is formed.
Is 1 to 3 μm, and the thickness of the plating layer is 1 to 4 μm
Ceramic wiring board characterized by the following: 2. The ceramic wiring board according to claim 1, wherein the metal having excellent solder wettability is made of Ni. 3. The ceramic insulating substrate according to claim 1, wherein said substrate is made of Al ₂ O ₃ , A
l N, claim 1, characterized by comprising a ceramic mainly containing at least one selected from the group the Si ₃ N ₄
The ceramic wiring board as described.