KR960007378B1 - Method for metallizing of aluminium nitride base - Google Patents

Abstract

The aluminum nitride substrate is metallized by (A) printing and drying a molybdenum based metallizing paste on a sintered aluminum nitride, (B) forming a metallizing layer by sintering under weak reduction atmosphere, and (C) forming a metallic plated layer on the metallized layer. The sintered aluminum nitride is made of primary aluminum nitride, less than 2wt% calcium oxide and less than 8wt% yttrium oxide. And the metallizing paste is composed of 70-97wt% molybdenum, 1-10wt% manganese compound, 1-10 wt% titanium oxide, 1-10wt% silicon oxide, and 25-50wt% the organic additive mixture such as ethyl cellulose, which contains organic binder such as n-butyl carbitol actate, organic solvent, plasticizer and dispering agent, to the total amount of the solid components.

Description

Metalizing Method of Aluminum Nitride (AIN) Substrate

1 is a metallization process diagram of the method of the present invention.

2 is a SEM photograph of the cross section of the metallized layer produced by the method of the present invention.

3 is a schematic diagram showing a mechanism for forming a metallizing layer by the method of the present invention.

The present invention relates to a method for forming a metal layer on the surface of an aluminum nitride (AIN) sintered body.

Conventionally, alumina porcelain has been mainly used for insulating substrate materials such as semiconductor substrates and IC substrates. However, the high integration density and high speed used in devices such as high-definition television (HDTV) and supercomputers, which have emerged recently due to the development of electronic technology. In the case of the LSI mounting substrate which operates, since a high heat density is generated by the high density of the circuit, a ceramic substrate having a higher thermal conductivity than the conventional alumina ceramic is required.

As a result of using a conventional alumina porcelain substrate as an LSI mounting substrate, a newly developed insulating material, which has a high thermal conductivity of about 8 to 10 times higher than that of alumina, has a thermal conductivity close to Si. Aluminum (AIN) sintered bodies have emerged, and aluminum nitride has attracted attention as a next-generation insulating material due to the excellent properties described above.

On the other hand, in order to use the ceramic sintering agent as a semiconductor substrate or an IC substrate, it is required to metallize a portion of the surface of the sintered body, and the method of metallizing the alumina (Al ₂ O ₃ ), which is a conventional insulating material Although a number of technically superior methods have been developed and applied, a satisfactory technology has not been developed to date regarding the metallizing method of non-oxide-based ceramics.

In particular, the aluminum nitride sintered body belonging to the non-oxide-based ceramics has poor wettability and hardly contains impurities that promote metallization reaction such as SiO ₂ . For this reason, it is known that formation of a rigid metallizing layer on the aluminum nitride sintered body is difficult.

On the other hand, as a typical method for forming an insulating substrate by forming a metallization layer on a conventional alumina self-sintered body,

1) a method of forming a Cu film on the surface of an aluminum nitride using a CuO process reaction layer known as alumina "DBC method" (Direct Bonded Copper),

2) Metal powders such as Ag / Pd, Ag / Pt, Au, Cu, etc. are mixed with glass frit, glass binder, etc., and then paste-pasted into a substrate and sintered at 800 ~ 1000 ℃. Thick film printing method for promoting a liquid phase transfer reaction of a to form a bonding layer,

3) A method of forming a bonding layer by printing and applying a paste containing a high melting point metal such as Mo or Mn as a main component on a substrate and firing at 1300 to 1800 ° C. in a wet reducing atmosphere.

As a method for forming a metallization layer on an aluminum nitride sintered body, it is considered to apply a metallization method to the three alumina substrates listed above. However, when applied to an aluminum nitride substrate, these methods are nitrided due to the following problems. It cannot be applied to an aluminum substrate as it is.

First, the DBC method has a limitation in forming a microcircuit, and since it is necessary to form an Al ₂ O ₂ film on the surface of aluminum nitride, there is a high possibility of inhibiting high thermal conductivity, which is the maximum characteristic of aluminum nitride, and further, aluminum nitride and Cu There is a problem in thermal shock resistance because the difference in thermal expansion coefficient of.

In addition to the above problems, it is difficult to control the temperature and the atmosphere at the time of joining, so there is a problem in that the variation in the bonding strength is increased and the reliability of the product is lowered.

In addition, in the case of thick film printing, aluminum nitride has a disadvantage in that high adhesion strength cannot be expected because sintering of aluminum nitride is difficult to cause a liquid transfer reaction of glass frit.

Next, the high melting point metallizing method is the most commonly used method for alumina ceramics, but when the method is applied to aluminum nitride, the wettability with the glass phase is poor because aluminum nitride is a non-oxide, and also aluminum nitride is used. Due to the property of high purity substrate material, there is a problem that high metallizing strength cannot be expected because it does not have an impurity component (SiO ₂ ) which becomes glassy.

As described above, in view of the various problems of applying the metallizing method of the existing alumina ceramics to aluminum nitride as it is, the present inventors of the three metallizing methods, in particular, the high melting point metal metallizing method is applied to other methods. Compared with the following advantages, the study aimed to develop a technology that can effectively perform metallizing of aluminum nitride substrates by improving the high melting point metal metallizing method.

The high melting point metal metallizing method,

1) Because metallizing firing is carried out in a reducing atmosphere, oxidation of aluminum nitride can be avoided, and high thermal conductivity, which is the most characteristic of aluminum nitride, is less likely to decrease even during metallizing firing.

2) Compared to the other two methods described above, in principle, the bonding strength is very high and the airtightness is a metallizing method.

3) It is economical because the production equipment used for metallizing existing alumina ceramics can be used as it is.

Accordingly, an object of the present invention is to provide a metallizing method of aluminum nitride, which enables the formation of a metallizing layer having a high metallizing strength by improving the conventional high melting point metal metallizing method to be suitable for metallizing of aluminum nitride ceramics. There is this.

Prior to the detailed description of the method of the present invention look at the metallizing mechanism of the alumina by the high melting point metal metallization method to be improved in the present invention as follows.

Mo and Mn, the main constituents of the paste coated on the surface of alumina, are oxidized by moisture in the atmosphere during the temperature raising process, and the surface-oxidized Mn diffuses into the alumina as a preparation during metallization firing.

At this time, some of the Mn diffused to the alumina side forms an intermediate layer of MnO ₂ -Al ₂ O _{3 on} the surface of the alumina, and part of the Mn is in contact with the glass phase (SiO ₂ ) contained as a sintering aid in the alumina to improve the viscosity of the glass phase. Lowers the flowability of the glass phase. On the other hand, the glass phase, in which the fluidity is further increased in contact with MnO ₂ , moves to the alumina surface to enclose the Mo particles.

After cooling, the glass phase forms a eutectic point such as MnO ₂ -SiO ₂ or MnO ₂ -SiO ₂ -Al ₂ O ₃ to form a strong bond between the alumina and the Mo layer, thereby completing the bonding of the Mo metal layer on the alumina porcelain.

The critical reason why the high melting point metallization method of the metallizing mechanism is not directly applied to aluminum nitride is that the wettability of the glass is much worse than that of oxide ceramics such as alumina, and the aluminum nitride substrate contains almost no impurity component that becomes glassy. Because it is not.

In order to solve this problem, the present inventors have attempted to oxidize aluminum nitride to modify the surface of aluminum nitride with an oxide, and as a result, it is not preferable because of the troublesome process and lowering of thermal conductivity of aluminum nitride. Reached.

Therefore, the present invention promotes the formation of the glass phase by adding TiO ₂ to the paste as a means for improving the wettability of the glass phase, and adding SiO ₂ to the paste for the replenishment of the glass phase, and the atmosphere during the metallizing reaction. There is a technical feature of forming a metallizing layer having a high bonding strength on an aluminum nitride substrate by changing it to prevent a lowering of the thermal conductivity of aluminum oxide.

Hereinafter, the technical features of the present invention will be described in more detail.

First, in the present invention, TiO ₂ , which easily releases oxygen at high temperature, is added to the metallizing paste to improve the wettability of the glass. When TiO ₂ is added to the paste, it is oxidized in the reducing atmosphere of the surface of aluminum nitride. Since the alumina layer is formed, the wettability of the glass phase is improved by the same process as the metallization method used in the existing alumina.

Incidentally, the present invention is low in variation in the joint strength by promoting the formation of a glass phase in addition to the SiO _υ paste in order to make up the glass phase that requires a metallizing reaction is made possible the manufacture of the tensile strength is stable practical paste.

In addition, the present invention changes the atmosphere of the metallizing reaction from a humid atmosphere which is a metallizing condition of the oxide ceramics to a dry atmosphere (N ₂ 85-95 vol%, H ₂ 5-15 vol%), if the metalizing in the humid atmosphere The oxidation proceeds to the inside of the aluminum nitride generated during the reaction, thereby preventing the risk of cracking due to a decrease in thermal conductivity and a difference in thermal expansion coefficient.

As described above, in the method of the present invention, the metallization of the non-oxide-based aluminum nitride is effectively performed by changing the composition and firing conditions (atmosphere, temperature, time) of the metallizing paste in a specific range.

In the metallizing method of the present invention, as shown in the manufacturing process diagram of FIG. 1, a small amount of TiO ₂ and SiO ₂ are added to a high melting point metal whose Mo is the main component of the aluminum nitride sintered compact, and an organic binder is added thereto. After printing and coating with a paste in which a small amount of an organic solvent, a plasticizer and a dispersant are added, and then baking in a mildly reducing atmosphere to form a metallizing layer, a plating layer is formed on the metallizing layer.

When explaining the metallizing process of the present invention in detail step by step as follows.

[Manufacture of Aluminum Nitride Sintered Body]

The aluminum nitride sintered body is composed of aluminum nitride powder containing CaO: 2wt% or less, or Y ₂ O ₃ : 8wt% or less, and sintering aid is used.The sintering condition is 1900 ℃ -8 hours in nitrogen atmosphere. The aluminum nitride sintered body having a density of 99.9% of the theoretical density (3.262 g / cm 3) and a thermal conductivity of 200 to 250 w / mk is prepared.

[Production of Metallizing Paste]

Metallizing paste is mainly composed of Mo as a main component, inorganic solids containing a small amount of TiO ₂ , SiO ₂ and Mn compounds, organic solvents including organic binders, and organic additives including plasticizers and dispersants. The compounding ratio is as follows.

Inorganic solids: Mo metal powder 70 ~ 97wt%

Mn compound 1 ~ 10wt%

Tio ₂ 1 ~ 10wt%

Sio ₂ 1 ~ 10wt%

With respect to the inorganic solid content 100 of the composition, an organic additive of the following composition is added and mixed in the range of 25 to 50 to obtain a printable paste.

Organic additives: organic binder 5 ~ 12wt%

58 ~ 90wt% organic solvent

Plasticizer 5 ~ 25wt%

Dispersant 0.5 ~ 5wt%

When explaining the role of each component and the reason for numerical limitation in the metallizing paste composition of the present invention as described above in detail.

TiO ₂ serves to improve the wettability with the glass phase by oxidizing the surface of aluminum nitride to form an Al ₂ O ₃ layer.

2AIN + 2TiO ₂ → Al ₂ O ₃ + 2TiN + (O)

It is indicated by and the reaction occurs easily at a temperature of 1100 ℃ or more.

Next, SiO ₂ is added to supplement the glass phase because aluminum nitride is high purity and contains no glass phase, and SiO ₂ is Al ₂ O ₃ formed by oxidation of the aluminum nitride surface by oxygen released from TiO ₂ . React with to form a glass phase.

This glass phase plays an important role in bonding the Mo thick film layer to the aluminum nitride substrate by the liquid phase transfer reaction.

In addition, the Mn compound is any one of Mn metal, MnO, Mn (OH) ₂ or MnO ₂ , which is activated at high temperature to react with Al ₂ O ₃ and SiO ₂ to form a glass phase. Do it.

When the addition amount of the TiO ₂ , SiO ₂ and Mn compounds, which are the additives of the inorganic solids, is less than 1 wt%, respectively, the effect of the addition is not sufficient. On the contrary, when the addition amount exceeds 15 wt%, the addition of the inorganic solids will adversely affect the performance of subsequent processes. It is preferable to maintain the range at 1-15 wt%, respectively.

Next, the organic additive solution plays a big role in obtaining a thick film having good uniformity and reproducibility by controlling the fluidity of the paste during printing. Specific components and properties of each component constituting the organic binder are as follows.

First of all, the organic binder plays a role of imparting a viscosity suitable for printing a paste, and ethyl cellulose, nitro cellulose, and the like, which have strong bonding power and good thermal decomposition property, are suitable.

If the added amount of the organic binder is less than 5wt%, the viscosity becomes low and printing is impossible.If the organic binder is more than 12wt%, the viscosity increases, conversely, there is a high possibility of defects during printing. Therefore, the range of addition of the organic binder is maintained at 5 ~ 12wt%. It is preferable.

Next, the organic solvent dissolves the organic binder well, and is less volatile n-butyl acetate (glycerol), n-butyl alcohol (n-buthyl alcohol), Terpineol ( -terpineol) and the like, these organic solvents are adjusted in the range of 58 ~ 90wt% according to the viscosity when printing.

In addition, plasticizers are indispensable ingredients for controlling fluidity of the paste, and suitable are DOP (Dioctyl phthalate), BBP (n-Buthyl benzyl phthalate), DBP (Di-n-buthyl phthalate), and DOA (Dioctyl adipic acid). .

The amount of plasticizer added is less effective at less than 5wt% and the fluidity is lowered if it exceeds 25wt%, so the amount of plasticizer should be maintained in the range of 5-25wt%.

Finally, dispersants are needed to uniformly disperse the inorganic solids in the organic binder solution, including sorbitan mono oleate, 12-hydroxy stearic acid and aluminum stearate. If the addition amount is not added at all or 0.5wt% or less, the inorganic solids are not uniformly dispersed in the organic binder solution during paste production, so that sufficient adhesion strength of the metallizing layer cannot be obtained. If it exceeds 5wt%, the dispersant may excessively cover the inorganic solid surface, so it should be limited to 0.5wt% or more and 5wt% or less.

[Screen printing process]

A printing process is a process of printing a metallizing paste on the aluminum nitride sintered compact by the screen printing method, and evaporating and drying the solvent contained in a paste in an infrared dryer.

As for the thickness of the printed layer by the screen printing method, about 5-20 micrometers with sufficient adhesive strength is practical.

[Metalizing firing process]

The firing process is a process of baking an aluminum nitride sintered body on which the metallization paste is printed and dried at a temperature of 1100 to 1500 ° C. for about 1 hour and bonding a metal layer to the ceramic surface. A TiO ₂ , SiO ₂ , Mn compound added as a preparation to the paste It is an important process of forming a glass phase on the surface of this aluminum nitride sintered compact and realizing metal bonding by a liquid-phase transfer reaction.

A particularly important factor in metallizing firing is the control of the minor component atmosphere. Even when pastes of the same composition are used, the metallizing strength is greatly changed due to the difference in litigation atmosphere. Atmospheric conditions necessary for metallizing the aluminum nitride sintered body are preferably fired in a mixed gas atmosphere containing 85 to 95 vol% of nitrogen and 5 to 15 vol% of hydrogen in a dry atmosphere containing no water vapor. As the hydrogen mixing ratio of the atmospheric gas, it is necessary to set it as a weak reducing atmosphere in which at least 5 vol% of hydrogen is mixed in order to prevent oxidation of aluminum nitride and Mo. When the mixing exceeds 15 vol%, the added TiO ₂ is reduced and oxygen is reduced. Since the effect of release becomes low, 15 volume% or less is preferable.

In addition, if the atmospheric gas contains water vapor, the surface of the aluminum nitride sintered body is oxidized to Al ₂ O ₃ in the form of deodorizing oxygen from H ₂ O in the reducing atmosphere, so that there is a problem of deterioration of thermal conductivity and occurrence of cracks. It needs to be done in a dry atmosphere.

[Plating Process]

A plating layer of Ni-P, Ni-B, Cu, Au, or the like is formed on the Mo metallizing layer by electroless plating or barrel plating. As for plating layer thickness, 2-5 micrometers is practical.

Specific manufacturing method and technical features and effects of the present invention will be more clearly understood through the following examples.

Example 1

1.0 wt% of CaO-based sintering aid was ground to sinter the aluminum nitride substrate, and the surface roughness Ra was adjusted to 0.8 mu m. In addition, the metallizing paste is mixed in a ratio of Mo: Mn: SiO ₂ : TiO ₂ = 80: 8: 7: 5, and Nitrocellulose: Glycerine: n-Butyl Acetate: Dioctyl Ar is used for 70 g of the mixed powder. 30 g of an organic additive mixed in a ratio of diacid: aluminum stearate = 7: 20: 56: 15: 2 was added and dispersed and mixed in a ball mill to prepare a paste. The paste was screen printed on a surface of the polished aluminum nitride substrate with a thickness of 20 µm, dried, and calcined at 1300 ° C for 1 hour in an 87 vol% N2 + 13 vol% H2 atmosphere to form a 10 µm thick metallized layer on the aluminum nitride substrate. Subsequently, plating was performed for the metallization layer to form a plating layer having a thickness of Ni-P 4-6 μm. As a result of the strength test, the contact strength (peel strength) was 4.0 kg / 4 mm 2 and it was confirmed that the contact strength was sufficiently high in practical use.

FIG. 2 is an SEM photograph of the metallized substrate obtained by the above metallizing process, and FIG. 3 is a schematic diagram for explaining the process of forming the metallization layer shown in FIG. As can be seen in FIG. 2, the cross-sectional structure is formed from the upper layer in order of Ni plating layer, Mo layer, reaction layer, and aluminum nitride substrate. Since the reaction layer is thick and dense with a thickness of 4 to 6 μm, the bonding is very good. It can be confirmed.

Example 2

The aluminum nitride substrate sintered by adding 4.0 wt% of yttrium oxide (Y ₂ O ₃ ) sintering aid was polished to adjust the surface roughness Ra to 0.8 μm. In addition, the metallizing paste was prepared in a ratio of Mo: Mn (OH) ₂ : SiO ₂ : TiO ₂ = 82: 3: 7: 8 and ethyl cellulose: α-terpineol: n-butyl to 65 g of the mixed powder. Alcohol: n-butyl carbitol acetate: di-n-butyl phthalate: 12 hydroxy stearic acid = 10: 30: 10: 31: 18: 1 Add a 35 g mixed organic additive solution, disperse and mix in a ball mill paste Was prepared. The paste was screen printed on a polished aluminum nitride substrate to a thickness of 20 μm, dried, and then fired at 1400 ° C. for 1 hour in an 85 vol% N ₂ +15 vol% H ₂ atmosphere to form a 10 μm thick metallized layer on the aluminum nitride substrate. Thereafter, a Ni-B plated layer having a thickness of 4 to 6 µm was formed by an electroless plating method thereon.

As a result of the strength test, the adhesion strength (peel strength) of this metallizing layer was 5.5 kg / 4 mm 2, and it was confirmed that the adhesion strength was sufficiently high in practical use.

Claims (6)

Print and dry a metalizing paste containing Mo metal as a main component on the surface of the sintered aluminum nitride (AIN), and then fire in a mild reducing atmosphere to form a metallization layer, and a metal plating layer is formed on the metallization layer. Metallizing method of an aluminum nitride substrate, characterized in that. 2. The method of claim 1, wherein the aluminum nitride sintered body comprises aluminum nitride as a main component and contains 2 wt% or less of CaO or 8 wt% or less of Y ₂ O ₂ . 2. The metallizing paste of claim 1, wherein the metallizing paste is composed of an organic binder and an organic component in a solid component consisting of Mo metal: 70 to 97 wt%, Mn compound: 1 to 10 wt%, TiO ₂ : 1 to 10 wt%, and SiO ₂ : 1 to 10 wt%. An organic additive comprising a solvent, a plasticizer, and a dispersant is added to the solid component 100 in a range of 25 to 50, wherein the metal nitride method of the aluminum nitride substrate. The organic additive of claim 3, wherein the organic additive is selected from ethyl cellulose and nitro cellulose in an amount of 5 to 12 wt%, n-butyl carbitol acetate, n-butyl acetate 58-90 wt% of organic solvents selected from (n-buthyl acetate), glycerin (glycerine), n-butyl alcohol (n-buthyl alcohol) and α-terpineol, and dioctyl phthalate , 5-25 wt% of a plasticizer selected from n-butyl thyl benzyle phthalate, di-n-butyl phthalate, dioctyl adipic acid, and sorbitan Metallizing of an aluminum nitride substrate, comprising 0.5 to 5 wt% of a dispersant selected from monovitamin monooleate, 12-hydroxy stearic acid, and aluminum stearate Way. The metallizing method of an aluminum nitride substrate as claimed in claim 1, wherein the atmosphere upon firing is a dry atmosphere containing no water vapor and composed of 85 to 95 vol% nitrogen and 5 to 15 vol% hydrogen. 2. The metallizing of an aluminum nitride substrate according to claim 1, wherein a metal layer of Ni-P, Ni-B, Cu, or Au is formed in a thickness of 2 to 5 탆 on the metallizing layer by electroless plating or a baling method. Way.