JP7438743B2 - Aluminum nitride wiring board and its manufacturing method - Google Patents

Description

Embodiments of the present invention generally relate to an aluminum nitride wiring board formed by co-firing (cofire) a conductor layer with an aluminum nitride base material, and a method for manufacturing the same.

In recent years, with the development of semiconductor elements that require large currents such as power electronics and next-generation power semiconductors, the demand for ceramic substrates has been increasing year by year. In particular, aluminum nitride (AlN) substrates have characteristics such as high thermal conductivity and excellent heat dissipation, and are therefore used as substrates that can cope with the increasing amount of heat dissipated from semiconductor devices.

Since the aluminum nitride substrate is an insulator, when it is used as a semiconductor package or a circuit board, for example, when the upper and lower surfaces are electrically connected, conductor circuits are formed on the upper and lower surfaces and electrical conduction is achieved using vias or through holes. When the substrate has conductive circuits such as vias and through holes, it is common to fabricate the aluminum nitride substrate and the wiring conductor layer by simultaneous firing.

By the way, in the firing process of the aluminum nitride co-fired substrate as described above, there is a difference between the sintering temperature of aluminum nitride and the densification temperature of a high melting point metal such as tungsten (W), and the densification behavior also differs. Because of the difference, there was a problem in that there was a difference in shrinkage rate after simultaneous firing. Therefore, it has conventionally been possible to add an aluminum nitride component or its sintering aid component to the printing composition used to form the wiring metal layer to match the sintering shrinkage rates of the aluminum nitride sintered body and the wiring metal. It has been done. For this type of aluminum nitride wiring board, for example, JP-A-9-036521 (Patent Document 1) discloses that tungsten powder or molybdenum (Mo) powder and aluminum nitride powder with an average particle size of less than 0.1 μm as a filler are used. There is an aluminum nitride circuit board characterized in that a conductive paste layer is formed by applying a conductive paste containing aluminum in a pattern. Further, some conventional aluminum nitride substrates are characterized by adding aluminum nitride and a sintering aid component to molybdenum or tungsten (see, for example, Patent Document 2).

However, when a fixed amount of aluminum nitride or its sintering aid is added to a high-melting point metal such as tungsten, there is a difference in shrinkage between circuits on the board surface and circuits inside the board (vias). There was a phenomenon that occurred. When this difference in shrinkage becomes large, there is a problem that voids (pores) are likely to occur in the via and the bonding strength of the metal layer is likely to decrease.

Japanese Patent Application Publication No. 9-036521 Japanese Patent Application Publication No. 2002-261445

As electronic components have become smaller and more sophisticated in recent years, it has become necessary for ceramic circuit boards to respond to miniaturization and miniaturization.
The embodiment solves such problems, and describes an aluminum nitride wiring board formed by co-firing a wiring layer with an aluminum nitride base material and a method for manufacturing the same. An object of the present invention is to provide a highly productive aluminum nitride wiring board that suppresses the shrinkage difference with a base material.

The aluminum nitride wiring board according to the embodiment is a paste prepared by mixing high-melting point metal powder with pulverized sheet powder after removing the organic solvent and organic binder by degreasing an aluminum nitride green sheet. A paste for forming circuits on the surface of a board with a powder addition ratio of 1 to 10 wt% and a paste for forming vias inside the board in which a crushed sheet powder addition ratio of 10 to 30 wt% are printed on an aluminum nitride green sheet. It is characterized by simultaneous firing.

FIG. 1 is a diagram showing a cross section of an aluminum nitride wiring board according to an embodiment. FIG. 1 is a diagram showing a surface (plane) of an aluminum nitride wiring board according to an embodiment. FIG. 1 is a diagram showing a cross section of an aluminum nitride multilayer wiring board according to an embodiment.

The aluminum nitride wiring board according to the embodiment is produced by adding a sintering aid to the aluminum nitride powder used in manufacturing the aluminum nitride board, mixing an organic solvent and an organic binder, and molding the green sheet into a green sheet in a reducing atmosphere such as nitrogen. For a paste made by mixing pulverized sheet powder with high melting point metal powder after removing the organic solvent and organic binder by degreasing at 600 to 800°C, the addition ratio of the pulverized sheet powder is 1 to 10 wt%. The paste for forming a conductor circuit and the paste for forming internal vias in which the additive rate of crushed sheet powder is 10 to 30 wt% are printed on an aluminum nitride green sheet and fired at the same time. .
FIG. 1 shows an example of a cross-sectional view of an aluminum nitride wiring board. 1 is an aluminum nitride wiring board (cross-sectional view), 2 is an aluminum nitride substrate, 3 is an internal conductor layer (via) , 4 is a surface conductor layer , 5
is the back conductor layer. FIG. 2 shows a surface view (plan view) of an aluminum nitride wiring board. The embodiment is not limited to such a shape, and other wiring circuits and via shapes may be used. Further, multilayer wiring and cavity portions may be formed. FIG. 3 shows an example of a cross-sectional view of an aluminum nitride multilayer wiring board.

The aluminum nitride substrate is made by mixing aluminum nitride powder with a sintering aid and sintering the mixture.
The aluminum nitride powder has an average primary particle size of 0.03 to 3.5 μm, more preferably an average primary particle size of 0.1 to 1.5 μm, and an impurity oxygen content of 0.2 to 3 μm for sinterability. It is desirable to use powder having an impurity oxygen content of 0.5 wt%, more preferably 0.3 to 3 wt%. If the average primary particle size of the aluminum nitride powder is less than 0.03 μm, it becomes very difficult to form a sheet, and the amount of impurity oxygen increases in the final insulating layer mainly composed of aluminum nitride, resulting in high There is a possibility that thermal conductivity cannot be obtained. Furthermore, since the sheet density during molding decreases, the shrinkage rate during sintering increases, making it difficult to control the position of the conductor layer on the sheet surface. Furthermore, it becomes difficult to match the shrinkage rate with the conductor layer, leading to problems such as the formation of voids between the conductor layer and the insulating layer whose main component is aluminum nitride. On the other hand, if the average particle size of the aluminum nitride powder exceeds 3.5 μm, the sinterability will be significantly reduced, making it difficult to form an insulating layer made of a sufficiently dense sintered body. Furthermore, if the amount of impurity oxygen is less than 0.2 wt%, the sinterability will be reduced, and there is a possibility that it will not be possible to form a sufficiently dense insulating layer mainly composed of aluminum nitride.

The sintering aids include rare earth compounds (oxides, halides, etc.), alkaline earth compounds (oxides, halides, etc.) that are generally effective for sintering aluminum nitride, or rare earth compounds used in the sintering process. , at least one kind of substances that become alkaline earth compounds can be used. Examples of compounds that become oxides in the sintering process include carbonates, oxalates, nitrates, and alkoxides. Examples of rare earth compounds include yttrium oxide (Y2O3), lanthanum oxide (La2O3), dysprosium oxide (Dy2O3), and the like. Examples of alkaline earth compounds include calcium oxide (CaO) and magnesium oxide (MgO). Further, the amount of the sintering aid added is preferably 1 to 10 wt% in total of all the sintering aids based on the aluminum nitride powder. A more preferable amount of the sintering aid added is 2 to 5 wt%. If the amount of the sintering aid added is less than 1 wt%, there is a risk that it will not effectively sinter aluminum nitride, and it will be difficult to form an insulating layer mainly composed of aluminum nitride, which has high thermal conductivity. Become. On the other hand, if the amount of the sintering aid added exceeds 10 wt %, it becomes difficult to form an insulating layer containing aluminum nitride as a main component and having similarly high thermal conductivity.

For the purpose of improving sinterability, some of the sintering aids may be aluminum compounds such as alumina (aluminum oxide: Al2O3), aluminum fluoride (AlF3), boron compounds such as boron oxide (B2O3), and rare earth borides. , phosphorus compounds to improve surface cleanliness, and manganese compounds such as silicon oxide (SiO2), silicon nitride (Si3N4), and manganese oxide (MnO2) effective to increase mechanical strength. . Furthermore, for coloring and high strength, transition metals such as titanium (Ti), tungsten, molybdenum, tantalum (Ta), niobium (Nb), and manganese (Mn) or their compounds (oxides and carbides) are used. , fluoride, carbonate, oxalate, nitrate, etc.) may be contained in the mixed powder in a range of 0.1 to 1 wt% in terms of transition metal.

After a sintering aid is added to the aluminum nitride powder and thoroughly mixed, a binder is added to the mixed powder and kneaded and dispersed in a predetermined solvent to adjust to a predetermined viscosity. Subsequently, the obtained suspension is formed into a sheet by, for example, a doctor blade method, and dried at, for example, a temperature of about 200° C. to form a green sheet. Subsequently, a plurality of via holes for interlayer connection are formed in predetermined positions of the green sheet. As the binder added to the mixed powder, for example, an acrylic binder, a PVB binder, or the like can be used. As the solvent for dispersing the mixed powder and the binder, alcohols such as n-butanol, methyl isobutyl, toluene, xylene, etc. can be used. As a method for forming the via hole, for example, a mechanical method using a punch, a die, a punching machine, etc., a laser processing method, etc. can be adopted.

A necessary amount of the green sheet formed above is degreased to produce a pulverized sheet powder to be added to the paste. The degreasing conditions may be the same as those used in the degreasing step described below, but the temperature rise during degreasing may be increased to achieve more efficient formation. Further, in order to improve removal of the remaining binder, it is also possible to perform the treatment at a higher temperature or for a longer period of time. The degreased sheet is made into a powder using a grinder or the like.

The paste for conductor circuits and internal vias is a mixture of tungsten powder or molybdenum powder and the above-mentioned pulverized sheet powder.

The tungsten powder preferably has an average particle size of 0.2 to 2.0 μm, and the molybdenum powder preferably has an average particle size of 0.2 to 5.0 μm. If the average particle size of such conductive metal powder is less than the lower limit of the above range, it will not be easy to handle, and it will be difficult to form it into a paste, which may make it impossible to print the resulting conductive paste on the grease sheet. Furthermore, when the conductive paste containing the conductive metal powder is co-sintered with the molded body, its shrinkage rate becomes extremely large, so that the formed conductor layer cannot match the shrinkage rate with the aluminum nitride insulating layer. The conductor layer peels off, creating a gap between the conductor layer and the insulating layer.
On the other hand, if the average particle size of the conductive metal powder exceeds the upper limit of the range, the formed conductor layer may not be sufficiently densified and the resistance may become high. Furthermore, if the conductive paste containing the conductive metal powder is co-sintered with the molded body, its shrinkage rate will be excessively small, making it impossible to match the shrinkage rate with the aluminum nitride insulating layer, resulting in the final product being There is a risk that cracks, bulges, etc. may occur in the ceramic circuit board.

Since the shrinkage of the paste for conductive circuits progresses in accordance with the shrinkage of the substrate, it is preferable that the pulverized sheet powder is blended in an amount of 1 to 10 wt% with respect to the conductive metal powder. A more preferable blending amount of the pulverized sheet powder is 2 to 8 wt%. If the blending amount of the pulverized sheet powder is less than 1 wt%, the blending effect will not be sufficiently achieved, and it will be difficult to prevent disconnection of the conductor layer. On the other hand, if the blending amount of the pulverized sheet powder exceeds 10 wt%, the resistivity of the conductor layer increases, which may cause signal delay.

Since the shrinkage of the internal via paste is larger than the shrinkage of the substrate, it is preferable that the pulverized sheet powder is blended in an amount of 10 to 30 wt% with respect to the conductive metal powder. The blending amount of the pulverized sheet powder is more preferably 15 to 25 wt%. If the blending amount of the pulverized sheet powder is less than 10 wt%, the shrinkage of the conductor portion becomes large, resulting in defects inside the conductor or between the conductor and aluminum nitride. On the other hand, if the blending amount of the sheet powder exceeds 30 wt%, the resistivity of the conductor layer increases, which may cause signal delay.
By blending the sheet powder in such an amount, it becomes possible to better match the shrinkage rate of the aluminum nitride sheet and the shrinkage rate of the conductor layer.

In addition to the crushed sheet powder, a sintering aid of aluminum nitride may be added to the conductor paste in order to improve sinterability. These sintering aids include rare earth compounds (oxides, halides, etc.), alkaline earth compounds (oxides, halides, etc.) that are generally effective in sintering aluminum nitride, or rare earth compounds used in the sintering process. , at least one kind of substances that become alkaline earth compounds can be used. Examples of compounds that become oxides in the sintering process include carbonates, oxalates, nitrates, and alkoxides. Further, the amount of the sintering aid added is preferably 0.1 to 1 wt% in total of all the sintering aids based on the pulverized sheet powder. Furthermore, for the purpose of improving sintering properties, some of the sintering aids may be alumina, aluminum compounds such as aluminum fluoride, boron compounds such as boron oxide or rare earth borides, or phosphorus to improve surface cleanliness. It is permissible to substitute with manganese compounds such as silicon oxide, silicon nitride, manganese oxide, etc., which are effective for increasing mechanical strength.

In the aluminum nitride wiring board according to this embodiment, a conductive circuit paste is printed on a green sheet. Even when the wiring is multilayered, conductive circuit paste is printed on green sheets and laminated. When forming via holes or through holes to establish continuity between the front and back surfaces of a wiring board, between the front surface and internal wiring, or between internal wiring, use paste for internal vias in the via holes and paste for conductive circuits in the through holes. use.

An example of a method for simultaneously firing a green sheet printed with paste is to degrease it at 600 to 800°C in a non-oxidizing atmosphere such as nitrogen gas, and then sintering it at 1,700 to 1,950°C in a non-oxidizing atmosphere. . If the degreasing temperature is lower than 600° C., a sufficient degreasing effect may not be obtained and sintering may become insufficient. Furthermore, if the temperature exceeds 800°C, the degreasing progresses too much, and the green sheet may become brittle and difficult to handle. If the firing temperature is less than 1700°C, the firing will be insufficient and the high melting point metal may not be sintered. On the other hand, if the temperature exceeds 1950° C., grain growth of aluminum nitride may cause a decrease in thermal conductivity and waviness of the sheet.
By plating the conductor surface of the co-fired aluminum nitride substrate, it can be joined to other parts by brazing or soldering.

By crushing the produced green sheet after degreasing and adding it to the paste, it is possible to equalize the difference in shrinkage between the green sheet and the paste in the subsequent process. Furthermore, by dividing the amount of degreased green sheet added to the paste into the circuit part and the via part, it is possible to adjust the subtle difference in shrinkage between the circuit part and the via part during sintering.
According to the above method for manufacturing an aluminum nitride circuit board, the yield can be significantly improved by improving the quality of the aluminum nitride and the conductor circuit.

(Examples 1 to 11, Comparative Examples 1 to 6)
A raw material powder was prepared by adding the sintering aid shown in Table 1 to aluminum nitride powder having an average particle size of 1.0 μm, and crushed and mixed in a ball mill. An organic binder and an organic solvent (ethanol) were added to this raw material powder, and then mixed to form a slurry. This slurry was formed into a sheet by a doctor blade method to produce a green sheet measuring 50 mm long x 50 mm wide x 0.4 mm thick. Holes for vias of Φ0.2 mm were formed in the green sheet at 10 mm intervals as shown in FIGS. 1 and 2. Further, a part of the green sheet was degreased in a nitrogen atmosphere at 700° C. for 3 hours and then crushed to obtain a crushed sheet powder for use in adding paste.
Next, as shown in Table 1, crushed sheet powder is added to tungsten powder with an average particle size of 1.0 μm or molybdenum powder with an average particle size of 1.5 μm, and a resin binder and a dispersant are mixed. I made a paste. After injecting via paste into the green sheet via portions, surface circuit paste was printed on both sides of the green sheet.
The aluminum nitride substrate printed with the above paste was subjected to degreasing treatment at 700° C. for 3 hours in a nitrogen atmosphere.
A degreased aluminum nitride substrate was placed on an aluminum nitride setter (sintered plate), and co-fired at 1750°C for 4 hours under a pressure of 0.8 MPa in a nitrogen atmosphere to obtain an aluminum nitride co-fired substrate. . The obtained aluminum nitride co-fired substrate was plated with 2 μm of nickel to obtain an aluminum nitride wiring board.

For each aluminum nitride wiring board of the above-mentioned Examples and Comparative Examples, the aluminum nitride portion was processed and the density was measured using the Archimedes method. Further, a high temperature storage test was conducted at 400° C. for 30 minutes in a reducing atmosphere, and the appearance was observed using a microscope. The joint strength was measured by soldering a nail head pin to the surface plating part and pulling it in the vertical direction. Additionally, the resistivity of the wiring conductor layer was measured. A scanning electron micrograph of a cross section of the internal wiring layer was processed by image analysis, and the amount of voids remaining in the cross section of the internal wiring layer (residual void ratio) was measured. The measurement results are shown in Table 2.

As can be seen from Table 2, both the Examples and Comparative Examples had good densities of 3.26 Mg/m3 or higher. Although the appearance of the aluminum nitride wiring board according to the example was good, in Comparative Examples 1 and 3, dents of a size that could lead to problems when mounting components were observed in the portions of the plating surface where there were vias. This is due to the large shrinkage of the paste in the via area. On the other hand, in Comparative Examples 4 and 6, blistering was observed on the plating surface. This is because unplated areas occurred due to the addition of the paste deposited on the metallized surface. Regarding the resistance value, the aluminum nitride wiring board according to the example had a good resistance value of 11×10 −6 Ω·cm or less. Comparative Examples 1 and 3 to 6 showed large values of 30×10 −6 Ω·cm or more. This is thought to be due to the addition of an excessive amount of pulverized sheet powder and voids generated within the vias. Regarding the bonding strength, all of the aluminum nitride wiring boards according to the examples had a good bonding strength of 50 N/mm 2 or more, but Comparative Examples 1 and 2 showed a low value of less than 30 N/mm 2 . This is because the amount of pulverized sheet powder added was small, so the bondability with the green sheet was reduced. Note that in Comparative Examples 4 and 6, the tensile strength was not measured because plating blisters occurred. Regarding the internal wiring void ratio, the aluminum nitride wiring boards according to the examples were all 1.5% or less, which was good, but Comparative Examples 1 and 3 showed a large value of 20% or more. This is because the amount of pulverized sheet powder added was too small and the shrinkage of the paste inside the via became too large.

As is clear from the results shown above, there is a paste for forming conductor circuits in which the addition ratio of pulverized sheet powder is 1 to 10 wt%, and a paste for forming internal vias in which the addition ratio of pulverized sheet powder is 10 to 30 wt%. According to the aluminum nitride wiring board according to each example using the aluminum nitride wiring board, it is possible to obtain a good appearance and resistance value without deteriorating the bonding strength or the internal wiring void rate.

Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, changes, etc. can be made without departing from the gist of the invention. These embodiments and their modifications are included within the scope and gist of the invention, as well as within the scope of the invention described in the claims and its equivalents. Further, each of the embodiments described above can be implemented in combination with each other.

1...Aluminum nitride wiring board (cross-sectional view)
2...Aluminum nitride substrate 3... Inner conductor layer (via)
4... Surface conductor layer
5... Back wiring layer 6... Aluminum nitride wiring board (top view)
7...Aluminum nitride multilayer wiring board (cross-sectional view)
8...Internal wiring layer

Claims (4)

A process of adding an organic solvent and an organic binder to aluminum nitride powder and a sintering aid to create a molded body, a process of degreasing and pulverizing the molded body in a non-oxidizing atmosphere to create a paste additive, and a process of creating a paste additive by adding tungsten or A step of forming a conductor paste layer on at least one surface of the molded body using a conductor paste containing 1 to 10 wt% of the paste additive in a high melting point metal powder made of molybdenum, and adding the paste additive to a high melting point metal made of tungsten or molybdenum. A step of forming a via portion in the thickness direction of the molded body using a conductive paste containing 10 to 30 wt% of a conductive agent, and a step of forming a conductive circuit portion by firing the molded body having the conductive paste in a non-oxidizing atmosphere. A method for manufacturing an aluminum nitride wiring board, comprising: 2. The method of manufacturing an aluminum nitride wiring board according to claim 1 , wherein the sintering aid is a rare earth element or an alkaline earth element. The above method for manufacturing an aluminum nitride wiring board, wherein the average grain size of the tungsten is 0. ．． 2 to 2.0 μm or the average particle size of the molybdenum powder is 0.2 to 5.0 μm. The aluminum nitride according to claim 1 or 2, which is a melting point metal powder. A method of manufacturing a wiring board. The above method for manufacturing an aluminum nitride wiring board, wherein the degreasing temperature is 600 to 800°C. ℃, and the firing temperature is 1700 to 1950℃. The method for manufacturing an aluminum nitride wiring board according to claim 2.

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