JPH0727995B2 - Ceramic wiring board - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic wiring board excellent in heat dissipation using a silicon nitride polycrystal having a high thermal conductivity.

[0002]

2. Description of the Related Art The amount of heat generated is increasing with the increasing integration and speed of semiconductor chips. This tendency is particularly remarkable for chips having bipolar circuits, and in recent years, a ceramic wiring board using a material having excellent heat dissipation, that is, having good thermal conductivity has been required as a board for mounting these chips. Became.

For example, conventionally, a ceramic wiring board made of alumina ceramic has been widely used for such a chip because it has higher reliability and better heat dissipation than a board using resin. . However, the alumina substrate was inferior in practical strength to the resin substrate, and the heat dissipation property was insufficient.

Recently, in order to improve heat dissipation, aluminum nitride ceramics having higher thermal conductivity and silicon carbide ceramics to which a small amount of BeO is added have begun to be used as substrate materials.

[0005]

However, aluminum nitride ceramic has poor environmental resistance such as water resistance and alkali resistance, and is an electric metal terminal because of stress caused by the difference in thermal expansion coefficient from metal. There is a problem that the bonding portion between the pin and the lead is easily broken.

Further, since silicon carbide ceramics to which a small amount of BeO is added have an insulating property only in the grain boundaries of the ceramics, there are problems in electrical characteristics such as poor withstand voltage and a large dielectric constant of about 40. However, there is a problem that the process cost becomes high because it is not densified unless it is hot-press fired.

The object of the present invention is to solve the above problems,
It is an object of the present invention to provide a ceramic wiring board having a heat dissipation property higher than that of an alumina substrate and having excellent environmental resistance, mechanical strength and electrical characteristics.

[0008]

In the ceramic wiring substrate of the present invention, the ceramic used as the substrate is a silicon nitride polycrystal, and the crystal grains of the polycrystal have a linear distance of 10 μm.
It is characterized by containing 20 or less in m.

[0009]

In the present invention, a silicon nitride polycrystal is used as a substrate material. As is well known, silicon nitride has very high strength and excellent environmental resistance. In addition, the coefficient of thermal expansion matches the coefficient of thermal expansion of silicon as compared with that of alumina, so that reliability when mounting a semiconductor chip is also high. However, most of ordinary silicon nitrides have a composition that pursues mechanical strength at room temperature and high temperature, and their thermal conductivity is small, which is equivalent to that of alumina ceramics.
Therefore, it was not possible to obtain a substrate having a good heat dissipation property.

In the present invention, 20 or less polycrystal grains are contained in a linear distance of 10 μm, and the insulating layer is preferably composed of a silicon nitride polycrystal containing 0.3% by weight or less of aluminum in terms of alumina. , The conductor is made of metal such as tungsten, molybdenum or zirconium which is co-fired with the ceramic inside or on the surface of the substrate, or nitride or boride of various metals such as zirconium, tantalum or vanadium which are also co-fired. To be done. Also, it is formed by a post process after firing the ceramic.
It may be composed of a thick film conductor of Ag, Au or Cu system, a thin film conductor using sputtering, vapor deposition, plating method, so-called Moriman conductor using metallic molybdenum and metallic manganese, or the like.

When a conductor is obtained by co-firing a substrate material using tungsten or molybdenum metal, if the firing temperature is high such as over 1800 ° C., tungsten or molybdenum partially reacts with silicon nitride. It may become a sirisite. In particular, the reaction tends to occur at the interface between the conductor and the substrate material, but there is no problem because the resistance of silicite is lower than that of tungsten or molybdenum metal.

Since the silicon nitride substrate according to the present invention has a thermal conductivity of silicon nitride of 40 W / mk or more, typically 100 W / mk, which is sufficiently higher than about 20 W / mk of alumina, it has a good heat dissipation property. The strength is very strong, the environment resistance is excellent, the coefficient of thermal expansion matches the coefficient of thermal expansion of silicon, and the electric insulation is excellent, and the dielectric constant is 6-8 and that of alumina is 9-10.
Since it has good electrical characteristics such as smaller size, a ceramic wiring board with extremely excellent characteristics can be obtained by combining with a conductor.

Further, by combining with other wiring board materials, it is possible to obtain a wiring board having a composite structure having more excellent overall characteristics.

For example, in order to make the wiring more suitable for high-speed signal propagation, the wiring at that portion may be formed in a wiring board material different from that of the silicon nitride substrate to form a composite structure with the silicon nitride wiring board. desirable.

That is, a substrate material having a dielectric constant smaller than that of silicon nitride and capable of high-speed signal propagation is used, or a substrate material capable of using a low resistance conductor such as Ag or Cu suitable for high-speed propagation is used as a conductor material. And combined with a silicon nitride wiring board. Then, the portion of the silicon nitride wiring board is used as a power supply circuit.

As described above, the combination of the substrate material with other substrate materials is such that the crystal grains of the polycrystalline body have a linear distance of 10 mm.
20m or less contained in μm, preferably 0.3% by weight or less of aluminum in terms of alumina, which combines the excellent heat dissipation of the silicon nitride wiring board with the excellent characteristics of other board materials. The effect of the present invention can be made more effective.

The excellent features of the substrate of the present invention will be described in more detail below.

[High Heat Dissipation] In the ceramic used, the crystal grains of the polycrystalline body have a linear distance.
A silicon nitride polycrystal containing 20 or less in 10 μm, and preferably 0.3% by weight or less of aluminum in terms of alumina is used as described above. The silicon nitride polycrystal is
Usually, a component that forms a liquid phase during firing is added as a sintering aid. Typically, rare earth oxides, alkaline earth metal oxides, and other metal oxides are considered. In addition, metallic molybdenum, tungsten, and oxides or compounds thereof may be added for coloring as additives peculiar to semiconductor package materials.

According to the present invention, the number of crystal particles is not more than a limited amount,
As long as the amount of aluminum is preferably not more than the above-mentioned limited amount, basically, any composition-based silicon nitride multi-sintered body can be applied. This is because the thermal conductivity of the silicon nitride multi-sintered body is most affected by the amount of aluminum, and if the amount is less than the above-mentioned limited amount, a silicon nitride multi-sintered body of 40 w / mk or more can be obtained and By comparison, a substrate having excellent heat dissipation is obtained. The use of silicon nitride, which has more than 20 crystal grains in a linear distance of 10 μm, deteriorates the thermal conductivity of the ceramic and results in a ceramic wiring board with poor heat dissipation.

[High Strength] The substrate made of the silicon nitride polycrystal of the present invention is also important in that it has high strength. The conventional alumina substrate has a bending strength of about 30 kg / mm ² , but it is said that the practical strength is inferior to the resin substrate due to the brittleness peculiar to ceramics. However, since the silicon nitride ceramic substrate of the present invention has a folding strength of 30 kg / mm ² or more and a fracture toughness value of 5 MPam ^{1/2, which} is large, its brittleness is greatly improved as compared with the alumina substrate.

Further, in the aluminum nitride substrate, there is a problem that the bonding portion between the pin which is an electrical metal terminal and the lead is easily broken due to the stress caused by the difference in thermal expansion coefficient with the metal. In the present invention, such a problem does not occur because the silicon nitride ceramic substrate used has a large fracture toughness value.

[High reliability] Good environmental resistance is also an important feature. In other words, a major characteristic of ceramic substrates is that they are highly reliable as a result of their environmental resistance such as water resistance being superior to that of resin substrates. For example, alumina substrates are evaluated to have sufficiently high reliability. I was getting. However, since an aluminum nitride substrate which is a ceramic substrate having excellent heat dissipation has poor environmental resistance such as water resistance and alkali resistance, there is a problem in reliability, which is a major feature of the ceramic substrate. On the other hand, the silicon nitride substrate material of the present invention has excellent environmental resistance and does not have the problem that aluminum nitride has.

[Electrical Characteristics] The electrical insulating property is very excellent, and there is no problem of low withstand voltage as in a silicon carbide substrate. Further, the dielectric constant of the silicon nitride substrate material used in the present invention is 6 to 8, which is smaller than that of the alumina substrate of 9 to 10, the aluminum nitride substrate of 8 to 9 and the silicon carbide substrate of 40. Therefore, the propagation delay time, which is a problem when propagating a high-speed signal or a high-frequency signal, becomes small, which is suitable for high-speed signal propagation.

As described above, the wiring board obtained by the present invention has excellent characteristics not only in the conventional alumina substrate but also in the aluminum nitride and silicon carbide substrates.

[0025]

EXAMPLES The method of the present invention will be specifically described below. Figure 1
FIG. 2 is a sectional view of a wiring board obtained by the present invention. In the embodiment shown in FIGS. 1 to 3, the silicon nitride insulator layer 1 formed of a green sheet and the metal conductor 2 made of tungsten form an internal wiring circuit. As an external terminal, the metal pin 3 is Ag solder 4 on the conductor part on the substrate surface.
Connected by.

Further, in the example shown in FIG. 1, the other surface conductors are plated with Ni 5 and Au 6, and the die bond and wire bond of the semiconductor chip 7 are bonded by the bonding wire 8, and in the example shown in FIG. A Cr / Cu sputter layer 9 is provided as a surface conductor, and in the example shown in FIG. 3, an Ag-based, Au-based or Cu-based thick film conductor 10 and a resistor 11 are provided as a thick film circuit board. . Furthermore,
In the example shown in FIG. 4, a silicon nitride insulator layer 21 has metal conductor wiring inside, and a large number of metal pins 23 are arranged for connecting terminals of the mounted semiconductor chip 22 and an external circuit. Forming a ceramic package.

5 and 6 are sectional views showing an example of a composite type wiring board among the wiring boards of the present invention.
In the example shown in FIG. 5, a cordierite ceramic 31 for a low temperature firing substrate is formed on a wiring substrate composed of a silicon nitride insulator layer 1 and a metal conductor 2 made of tungsten provided therein.
An example is shown in which a wiring board having a metal conductor 32 made of copper arranged therein is provided to form a wiring board having a composite structure. The semiconductor chip 7 is connected to the metal conductor 32 via the bonding wire 8, the cap 33 protects the semiconductor chip 7, and the metal lead 34 connects to the external element.

In the example shown in FIG. 6, similar to the example shown in FIG. 5, on the wiring substrate composed of the silicon nitride insulator layer 1 and the metal conductor 2, the metal composed of the gold thin film conductor is formed in the substrate 41 composed of the polyimide resin. A wiring board having conductors 42 is provided to form a wiring board having a composite structure.

The manufacturing method will be described below. Example 1 In addition to a predetermined amount of silicon nitride powder and yttrium oxide powder, a mixed powder of 0.2 wt% alumina, an acrylic organic binder, a plasticizer, toluene and an alcohol solvent are well mixed in a resin pot and a silicon nitride ball. Made into a slurry. Furthermore, 0.1mm by doctor blade method
A green tape having a thickness of 1.0 mm was prepared.

Tungsten powder, an acrylic organic binder, and a terpineol-based organic solvent were well kneaded with a three-roller to obtain a conductor paste for printing. Using these pastes, a conductor wiring pattern and a ground layer were printed on the green tape. After stacking the green tapes on which these conductor patterns are printed in a predetermined order,
The layers were integrated under the conditions of 100 ° C and 100 kg / cm ² . The connection of each conductor layer was realized by filling a through hole formed in a green tape by punching or the like with a conductor paste.

Firing was carried out by holding at 1850 ° C. for 4 hours in a nitrogen atmosphere of 9.5 atm. After that, the surface conductor was plated with nickel, and the metal pins were adhered using Ag solder. Finally, the surface conductor and the metal pin were plated with gold. As a result, a wiring board as shown in FIG. 1 was realized.

Example 2 A fired substrate was obtained by the same method as in Example 1. However,
The conductor pattern on the surface was not formed except for the connection portion with the metal terminal. Nickel plating is applied to the surface conductor. In addition, Ag brazing was used to bond the metal pins. Then, the surface opposite to the surface having the metal pin was polished. A Cr / Cu thin film was formed on this polished surface by sputtering, and a pattern was formed by a photolithography technique. The pins and thin film pattern were plated with Ni and gold. As a result, a wiring board as shown in FIG. 2 was realized.

Example 3 The same green tape as in Example 1 was used and laminated so as to have a predetermined thickness. It was similarly fired to obtain a ceramic substrate. After polishing both surfaces, a thick film conductor paste of Ag series, Au series, or Cu series was pattern-printed by a usual screen printing method. Firing was performed in each firing atmosphere and firing temperature.
As a result, a wiring board as shown in FIG. 3 was realized.

Example 4 In the same manner as in Example 1, a 120-pin pin grid array (PGA) type package shown in FIG. 4 was prepared. The sintering aid and firing conditions are as shown in Table 1. The atmosphere is a nitrogen atmosphere of 9.5 atm. The number of silicon nitride particles in the formed package was calculated from the number of silicon nitride particles present per linear distance of 10 μm. The number of particles was measured as follows. First, with a scanning electron microscope,
The microstructure of an arbitrary cross section of the silicon nitride body was photographed at a magnification that allows individual identification of the Si ₃ N ₄ particles. Next, a straight line was drawn on the photograph, and the number of particles crossing the straight line was counted. Change the field of view until the number of particles exceeds 1000 and draw a straight line. From the total distance L (μm) of the straight line required to measure 1000 particles
It was converted to the number per 10 μm by (1000 / L) × 10.
For example, if a straight line of 500 μm was required to measure 1000 particles, the number of particles per 10 μm would be 20. Except for No. 6, silicon nitride was only β phase. In No. 6, some α phase was detected. The amount of Al ₂ O ₃ was measured by a fluorescent X-ray analysis method. Table 1 shows these measured values. Table 1 also shows the results of measuring the thermal conductivity of the silicon nitride polycrystals sintered under the same conditions by the laser flash method. Moreover, the coefficient of thermal expansion is 3 to 3 for any sintered body.
It was 4 ppm / ° C. A semiconductor wrap was actually mounted on this package to generate heat and cooled at a wind speed of 4 m / s, and the thermal resistance was measured to obtain the package thermal resistance shown in Table 1.

For comparison, the thermal resistance measured by the same method using alumina as a heat dissipation substrate was 22 ° C./w.

[0036]

[Table 1]

From Table 1, it can be seen that the heat dissipation substrate made of silicon nitride is superior in heat dissipation characteristics to alumina. Further, in the case of silicon nitride as well, it is understood that the number of silicon nitride particles present per linear distance of 10 μm is 20 or less, and preferably the amount of Al ₂ O ₃ contained is 0.3 wt% or less, which is further excellent. The reason is that when the number of silicon nitride particles present per linear distance 10μm is 20 or more, the thermal conductivity increases the heat scattering at the grain boundaries is considered to be due to lower, Al ₂ O ₃ Quantity
It is considered that when it is 0.3 wt% or more, it may be solid-dissolved in the silicon nitride particles to reduce the thermal conductivity of the silicon nitride particles.

Example 5 A ceramic composition mixed powder for a low temperature fired substrate consisting of 90% by weight of glass powder having a cordierite composition and 10% by weight of alumina powder, an acrylic binder, a plasticizer, toluene and an alcohol solvent were added to an alumina pot. And well mixed with alumina balls to make a slurry. Further, a green tape having a thickness of 0.3 mm was prepared by the doctor blade method.

Next, Cu-based powder, acrylic organic binder, and terpineol-based organic solvent were well kneaded by a three-roller to obtain a conductive paste for printing. Using this paste, a conductor wiring pattern was printed on the green tape. The green tapes on which these conductor patterns were printed were superposed in a predetermined order and then placed on a silicon nitride wiring board manufactured by the same method as in Example 1, and the temperature was kept at 100 ° C. for 10 minutes.
Pressure was applied under the condition of 0 kg / cm ² to laminate and integrate. The connection of each conductor layer was realized by filling a through hole formed in a green tape by punching or the like with a conductor paste. Then, the whole was baked at 950 ° C. in a nitrogen atmosphere.

As a result, as shown in FIG. 5, it was possible to obtain a package having a composite structure in which a low temperature firing wiring substrate was bonded onto a silicon nitride substrate. The metal leads were joined with Au-Sn alloy solder.

Example 6 A via hole for connecting a conductor pattern and an interlayer conductor pattern was formed by photolithography using a photosensitive polyimide resin and an Au sputtered thin film on a silicon nitride wiring substrate obtained by the same method as in Example 2. A multi-layered wiring circuit was obtained.

As a result, as shown in FIG. 6, a package having a composite structure in which a substrate made of polyimide was bonded onto a silicon nitride substrate could be obtained.

[0043]

As is apparent from the above description, according to the present invention, the crystal grains of the polycrystal are formed in a linear distance of 10 μm in an amount of 20
The number of aluminum is less than or equal to, preferably 0.3 wt% or less of aluminum contained in silicon nitride used as the substrate in terms of alumina, so that the heat dissipation is high and the environment resistance is good, so the reliability is excellent and the strength is high. Thus, it is possible to obtain an excellent ceramic wiring board having high toughness, which has never been obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an example of a wiring board obtained by the present invention.

FIG. 2 is a cross-sectional view of another example of a wiring board obtained by the present invention.

FIG. 3 is a cross-sectional view of still another example of the wiring board obtained by the present invention.

FIG. 4 is a cross-sectional view of still another example of the wiring board obtained by the present invention.

FIG. 5 is a cross-sectional view of still another example of the wiring board obtained by the present invention.

FIG. 6 is a cross-sectional view of still another example of the wiring board obtained by the present invention.

[Explanation of symbols]

 1 Silicon Nitride Insulation Layer 2 Metal Conductor 3 Metal Pin 4 Ag Solder 5 Ni Plating 6 Au Plating 7 Semiconductor Chip 8 Bonding Wire 9 Cr / Cu Sputtering Layer 10 Thick Film Conductor 11 Resistor 21 Silicon Nitride Insulating Layer 22 Semiconductor Chip 23 External terminal pin 31 Cordierite ceramic 32 Metal conductor 33 Cap 34 Metal lead 41 Substrate made of polyimide resin 42 Metal conductor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C04B 35/58 102 B (72) Inventor Takao Soma 36 Yoshira, Fukutani, Yoshiyoshi, Nishikamo-gun, Aichi Prefecture Address 1 (56) Reference JP-A-4-125952 (JP, A) JP-A-60-161641 (JP, A) JP-A-62-73800 (JP, A)

Claims (3)

[Claims] 1. A ceramic wiring substrate, wherein the ceramic used as the substrate is a silicon nitride polycrystal, and 20 or less crystal grains of the polycrystal are contained in a linear distance of 10 μm. 2. The ceramic wiring board according to claim 1, wherein the ceramic wiring board contains 0.3% by weight or less of aluminum in terms of alumina. 3. A substrate made of the silicon nitride polycrystal,
The ceramic wiring board according to claim 1 or 2, further comprising a composite structure having a wiring board made of a material different from that of the silicon nitride polycrystal.