JPH04212441A - Ceramic wiring board - Google Patents

Abstract

PURPOSE:To obtain a ceramic wiring board excellent in environmental resistance, mechanical characteristics, and electric characteristics, whose heat dissipation is larger than an alumina board, by using, as a board, a silicon nitride sintered body wherein the density of crystal grains of polycrystal is restrained to be a specified value, and a specified amount of aluminum is contained. CONSTITUTION:Ceramic used as a board is silicon nitride polycrystal, and crystal grains of the polycrystal are contained less than 20 in a linear distance of 10mum. An insulative layer 1 is constituted of the silicon nitride polycrystal wherein aluminum less than or equal to 0.3wt.% is preferably contained by alumina reduction. Conductor 2 is constituted of metal like tungsten, molybdenum and zirconium which are baked in the substrate or on the surface at the same time as the ceramic, or constituted of nitride or boride of metal like zirconium, tantalum and vanadium which are similarly baked at the same time.

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 with excellent heat dissipation properties using polycrystalline silicon nitride having high thermal conductivity.

0002

2. Description of the Related Art As semiconductor chips become more highly integrated and operate faster, the amount of heat generated is increasing. This tendency is particularly noticeable for chips with bipolar circuits, and in recent years, ceramic wiring boards using materials with excellent heat dissipation, that is, good thermal conductivity, have been required as substrates on which these chips are mounted. Became.

[0003] For example, conventionally, ceramic wiring boards made of alumina ceramic have been widely used for such chips because they are more reliable and have better heat dissipation than boards made of resin. . However, the practical strength of the alumina substrate is inferior to that of the resin substrate, and the heat dissipation property is also insufficient.

In order to improve heat dissipation, aluminum nitride ceramics and BeO
Silicon carbide ceramics to which small amounts of are added are beginning to be used as substrate materials.

[0005]

[Problems to be Solved by the Invention] However, aluminum nitride ceramic has poor environmental resistance such as water resistance and alkali resistance, and is difficult to use as an electrical metal terminal due to stress caused by the difference in thermal expansion coefficient with metal. There were problems such as the bonding part between the pin and the lead being easily broken.

[0006] Furthermore, silicon carbide ceramics to which a small amount of BeO 2 has been added have problems with electrical properties, such as poor voltage resistance because only the grain boundaries of the ceramic are insulating, and the dielectric constant is as high as about 40. However, since it cannot be densified unless it is hot press fired, there is a problem that the process cost increases.

[0007] The purpose of the present invention is to solve the above-mentioned problems,
The present invention aims to provide a ceramic wiring board that has greater heat dissipation than an alumina substrate, and has excellent environmental resistance, mechanical strength, and electrical properties.

[0008]

Means for Solving the Problems In the ceramic wiring board of the present invention, the ceramic used as the substrate is a polycrystalline silicon nitride, and the crystal grains of the polycrystalline are separated by a straight line distance of 10
It is characterized by containing 20 or less particles per μm.

[0009]

[Operation] In the present invention, polycrystalline silicon nitride is used as the substrate material. As is well known, silicon nitride has extremely high strength and excellent environmental resistance. In addition, the coefficient of thermal expansion is more consistent with that of silicon than that of alumina, so it is highly reliable when mounted with semiconductor chips. However, many ordinary silicon nitrides have compositions that pursue mechanical strength at room and high temperatures, and their thermal conductivity is low and comparable to that of alumina ceramics. Therefore, it was not possible to obtain a substrate with good heat dissipation properties.

In the present invention, the insulating layer is made of polycrystalline silicon nitride, which contains 20 or less polycrystalline crystal particles within a linear distance of 10 μm, and preferably contains 0.3% by weight or less of aluminum in terms of alumina. The conductor is made of metals such as tungsten, molybdenum, and zirconium that are co-fired with the ceramic inside or on the surface of the substrate, or nitrides and borides of various metals such as zirconium, tantalum, and vanadium that are also co-fired. Consisted of. In addition, Ag, Au, and Cu-based thick film conductors formed in post-processes after ceramic firing, sputtering,
It may be constructed of a thin film conductor using a vapor deposition or plating method, a so-called Moriman conductor using metal molybdenum and metal manganese, or the like.

[0011] When obtaining a conductor by co-firing tungsten or molybdenum metal with the substrate material, if the firing temperature is high enough to exceed 1800°C, some of the tungsten or molybdenum may react with silicon nitride. You may end up with Sirisite. This reaction tends to occur particularly at the interface between the conductor and the substrate material, but this is not a problem because the resistance of silicite is lower than that of tungsten or molybdenum metals.

[0012] In the silicon nitride substrate according to the present invention, the thermal conductivity of silicon nitride is 40 W/mk or more, typically 100 W/mk or more.
It has good heat dissipation as it is sufficiently larger than the 20W/mk of mk and alumina, and is also very strong and has excellent environmental resistance, and its coefficient of thermal expansion matches that of silicon. Furthermore, it has excellent electrical insulation properties and a dielectric constant of 6 to 8.
It also has good electrical properties, with a value smaller than 9 to 10 of alumina, so in combination with a conductor, a ceramic wiring board with extremely excellent properties can be obtained.

[0013] Furthermore, by combining it with other wiring board materials, it is possible to obtain a wiring board with a composite structure that has even better overall characteristics.

For example, in order to make the wiring more suitable for high-speed signal propagation, it is possible to form the wiring in that part in a wiring board material different from the silicon nitride substrate, and to create a composite structure with the silicon nitride wiring board. desirable.

In other words, use a substrate material that has a dielectric constant lower than silicon nitride and allows high-speed signal propagation, or use a substrate material that allows the use of low-resistance conductors such as Ag or Cu, which are suitable for high-speed propagation, as the conductor material. and combined with a silicon nitride wiring board. Then, a portion of the silicon nitride wiring board is used as a power supply circuit.

[0016] In this way, depending on the application, the crystal grains of the polycrystalline body can be combined with other substrate materials with a straight line distance of 1.
By combining the excellent heat dissipation properties of a silicon nitride wiring board, which contains 20 or less pieces per 0 μm and preferably contains 0.3% by weight or less of aluminum in terms of alumina, with the excellent properties of other board materials. Therefore, the effects of the present invention can be made even more effective.

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

[High heat dissipation] The ceramic used contains 20 or less polycrystalline crystal particles in a linear distance of 10 μm, and preferably contains 0.3% by weight or less of aluminum in terms of alumina, as described above. A silicon nitride polycrystalline body containing nitride is used. A component that forms a liquid phase during firing is usually added to the polycrystalline silicon nitride as a sintering aid. Typically, rare earth oxides, alkaline earth metal oxides, and other metal oxides are considered. Further, as additives specific to semiconductor package materials, metal molybdenum, tungsten, and their oxides and compounds may be added for coloring.

In the present invention, the number of crystal particles is below a limited amount,
Basically, it can be applied to silicon nitride multi-sintered bodies of any composition as long as the amount of aluminum is preferably below the above-mentioned limit. This is because the thermal conductivity of the silicon nitride multi-sintered body is most influenced by the amount of aluminum, and if the amount is below the above limit, a silicon nitride multi-sintered body with a performance of 40w/mk or more can be obtained, and alumina A substrate having comparatively excellent heat dissipation properties can be obtained. If silicon nitride is used in which more than 20 crystal grains are present within a linear distance of 10 μm, the thermal conductivity of the ceramic will deteriorate, resulting in a ceramic wiring board with poor heat dissipation.

[High Strength] Another important feature of the substrate made of polycrystalline silicon nitride of the present invention is that it has high strength. Conventional alumina substrates have a mechanical strength of about 30 kg/mm2, but due to the brittleness characteristic of ceramics, their practical strength was considered to be inferior to that of resin substrates. However, the silicon nitride ceramic substrate of the present invention has a fracture strength of 30 kg/mm2 or more and a high fracture toughness value of 5 MPam1/2, so the brittleness is greatly improved compared to the alumina substrate.

[0021]Also, aluminum nitride substrates have problems such as the bonding parts with pins and leads, which are electrical metal terminals, being easily broken due to stress caused by the difference in thermal expansion coefficient with metal. In the present invention, such a problem does not occur because the silicon nitride ceramic substrate used has a high fracture toughness value.

[High Reliability] Good environmental resistance is also an important feature. In other words, a major feature of ceramic substrates is that they have superior environmental resistance such as water resistance compared to resin substrates, resulting in high reliability.For example, alumina substrates have been evaluated as having sufficiently high reliability. I was getting it. However, aluminum nitride substrates, which are ceramic substrates with excellent heat dissipation properties, have poor environmental resistance such as water resistance and alkali resistance, so there has been a problem with reliability, which is a major feature of ceramic substrates. On the other hand, the silicon nitride substrate material of the present invention has excellent environmental resistance and does not have the problems that occur with aluminum nitride.

[Electrical Properties] The electrical insulation properties are very excellent, and there is no problem of low withstand voltage as with silicon carbide substrates. Further, the dielectric constant of the silicon nitride substrate material used in the present invention is 6 to 8, which is smaller than 9 to 10 for an alumina substrate, 8 to 9 for an aluminum nitride substrate, and 40 for a silicon carbide substrate. For this reason, high-speed signals,
The propagation delay time, which is a problem when propagating high-frequency signals, is reduced, making it suitable for high-speed signal propagation.

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

[0025]

EXAMPLES The method of the present invention will be explained in detail below. Figure 1~
FIG. 2 is a cross-sectional view of a wiring board obtained by the present invention. In the embodiment shown in FIGS. 1 to 3, a silicon nitride insulating layer 1 made of a green sheet and a metal conductor 2 made of tungsten form an internal wiring circuit. As an external terminal, a metal pin 3 is connected to a conductor portion on the surface of the substrate by an Ag solder 4.

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 further, in the example shown in FIG. , a Cr/Cu sputtered layer 9 is provided as a surface conductor,
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 metal conductor wiring is provided inside the silicon nitride insulating layer 21, and a large number of metal pins 2 are provided for connection terminals between the mounted semiconductor chip 22 and an external circuit.
3 is arranged in a pin grid array type ceramic package.

FIGS. 5 and 6 are cross-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 3 for a low-temperature firing board is placed on a wiring board consisting of a silicon nitride insulator layer 1 and a metal conductor 2 made of tungsten provided therein.
This figure shows an example in which a wiring board with a metal conductor 32 made of copper arranged inside the wiring board 1 is provided to constitute a wiring board with a composite structure. Further, the semiconductor chip 7 is connected to a metal conductor 32 via a bonding wire 8, is protected by a cap 33, and is further connected to an external element by a metal lead 34.

In the example shown in FIG. 6, similar to the example shown in FIG. 5, a metal layer made of a gold thin film conductor is placed on a wiring board made of a silicon nitride insulating layer 1 and a metal conductor 2 in a substrate 41 made of a polyimide resin. A wiring board having a conductor 42 arranged thereon is provided to constitute a wiring board with a composite structure.

The manufacturing method will be described below. Example 1 A mixed powder consisting of predetermined amounts of silicon nitride powder, yttrium oxide powder, and 0.2 wt% alumina, an acrylic organic binder, a plasticizer, toluene, and an alcohol solvent were mixed in a resin pot and a silicon nitride ball. The mixture was mixed to form a slurry. Furthermore, a green tape with a thickness of 0.1 mm to 1.0 mm was produced by a doctor blade method.

Tungsten powder, an acrylic organic binder, and a terpineol organic solvent were thoroughly kneaded using three rollers to form a conductive paste for printing. These pastes were used to print conductor wiring patterns and ground layers on green tape. After stacking the green tapes printed with these conductor patterns in a predetermined order,
They were laminated and integrated under the conditions of 100°C and 100 kg/cm2. Connections between each conductor layer were realized by filling conductor paste into through holes formed in the green tape by punching or the like.

[0031] Nitrogen atmosphere 9.5 atmospheres at 1850°C
It was held for a while and fired. Thereafter, the surface conductor was plated with nickel, and a metal pin was further bonded using Ag solder. Finally, the surface conductor and metal pins were plated with gold. As a result, a wiring board as shown in FIG. 1 was realized.

Example 2 A fired substrate was obtained in the same manner as in Example 1. however,
No conductor pattern was formed on the surface except for the connection portion with the metal terminal. Nickel plating is applied to the surface conductor. Furthermore, metal pins were bonded using Ag solder. After that, the surface opposite to the surface with the metal pin was polished. A Cr/Cu thin film was formed on this polished surface by sputtering and formed into a pattern by photolithography. 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 to a predetermined thickness. A ceramic substrate was obtained by firing in the same manner. After both surfaces were polished, patterns were printed using Ag-based, Au-based, and Cu-based thick-film conductor pastes using a conventional 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 A 120-pin pin grid array (PGA) type package shown in FIG. 4 was produced in the same manner as in Example 1. The sintering aid and firing conditions are as shown in Table 1. The atmosphere was a nitrogen atmosphere at 9.5 atmospheres. The number of silicon nitride particles in the created package is determined by the linear distance 1
It was determined from the number of silicon nitride particles present around 0 μm. The number of particles was measured as follows. First, a photograph of the microstructure in an arbitrary cross section of the silicon nitride body was taken using a scanning electron microscope at a magnification that allowed individual Si3N4 particles to be identified. Next, a straight line was drawn on the photograph and the number of particles crossed by the straight line was counted. Change the field of view and draw a straight line until the number of particles exceeds 1000, and from the total distance L (μm) of the straight line required to measure 1000 particles, (1000/L)
)×10 to calculate the number of particles per 10 μm. For example, to measure 1000 particles, a straight line of 500
If μm is required, the number of pieces per 10μm is 20
become individual. Silicon nitride is No. Except for No. 6, there was only β phase. No. 6, some α phase was detected. Al2
The amount of O3 was measured by fluorescent X-ray analysis. These measured values are shown in Table 1. Table 1 also shows the results of measuring thermal conductivity using a laser flash method for silicon nitride polycrystals sintered under the same conditions. Further, the coefficient of thermal expansion was 3 to 4 ppm/°C in all the sintered bodies. A semiconductor wrap was actually mounted on this package to generate heat and then cooled at a wind speed of 4 m/s to measure the thermal resistance, and the package thermal resistance shown in Table 1 was obtained.

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

[0036]

[Table 1]

From Table 1, it can be seen that the silicon nitride heat dissipation substrate has superior heat dissipation characteristics compared to alumina. Also, in silicon nitride, the number of silicon nitride particles present per 10 μm of straight line distance is 20 or less, and preferably the contained A
It can be seen that it is even better if the l2O3 amount is 0.3 wt% or less. The reason for this is thought to be that when the number of silicon nitride particles existing per 10 μm of linear distance is 20 or more, the scattering of heat at the grain boundaries increases and the thermal conductivity decreases. This is considered to be because if the amount is .3 wt % or more, it may form a solid solution within the silicon nitride particles and reduce the thermal conductivity of the silicon nitride particles.

Example 5 A mixed powder with a ceramic composition for a low-temperature firing substrate consisting of 90% by weight of cordierite-based glass powder and 10% by weight of alumina powder, an acrylic binder, a plasticizer, toluene, and an alcohol-based solvent were placed in an alumina pot. The mixture was mixed well with an alumina ball to form a slurry. moreover,
A green tape with a thickness of 0.3 mm was produced by the doctor plate method.

Next, Cu-based powder, acrylic-based organic binder, and terpineol-based organic solvent were thoroughly kneaded using three rollers to form a conductive paste for printing. Using this paste, a conductor wiring pattern was printed on the green tape. The green tapes with these conductor patterns printed on them were stacked in a predetermined order and then placed on a silicon nitride wiring board prepared in the same manner as in Example 1.
They were laminated and integrated by applying pressure at 100 kg/cm2 at 100°C. Connections between each conductor layer were realized by filling conductor paste into through holes formed in the green tape by punching or the like. After that, the whole was heated in a nitrogen atmosphere at 950°C.
It was fired in

As a result, as shown in FIG. 5, it was possible to obtain a package with a composite structure in which a low temperature fired wiring board was bonded to a silicon nitride substrate. Note that the metal lead is Au-S.
n Joined using alloy solder.

Example 6 Via holes for connecting conductor patterns and interlayer conductor patterns were formed by photolithography on a silicon nitride wiring board obtained in the same manner as in Example 2 using a photosensitive polyimide resin and an Au sputtered thin film. A multilayer wiring circuit was obtained.

As a result, as shown in FIG. 6, it was possible to obtain a package with a composite structure in which a substrate made of polyimide was bonded to a silicon nitride substrate.

[0043]

As is clear from the above description, according to the present invention, the number of polycrystalline crystal grains is set to 20 or less within a linear distance of 10 μm, and the amount of aluminum contained in silicon nitride used as a substrate is preferably reduced. 0. in terms of alumina.
By setting the content to 3 wt% or less, it is possible to obtain an excellent ceramic wiring board that has high heat dissipation, good environmental resistance, excellent reliability, and has high strength and toughness.

[Brief explanation of the drawing]

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

FIG. 2 is a 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 a wiring board obtained by the present invention.

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

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

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

[Explanation of symbols]

1 Silicon nitride insulator 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 sputtered layer 10 Thick film conductor 11 Resistor 21 Silicon nitride insulator layer 22 Semiconductor chip 23 External terminal pin 31 Cordierite ceramic 32 Metal conductor 33 Cap 34 Metal lead 41 Substrate 42 made of polyimide resin Metal conductor

Claims (3)

[Claims] 1. A ceramic wiring board, wherein the ceramic used as the substrate is a polycrystalline silicon nitride, and 20 or less crystal grains of the polycrystalline material are included 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. The ceramic wiring board according to claim 1, wherein the substrate made of polycrystalline silicon nitride has a composite structure further including a wiring board made of a material different from the polycrystalline silicon nitride.