JP4166360B2 - Dielectric paste and multilayer substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dielectric paste suitable for firing in a non-oxidizing atmosphere such as a nitrogen atmosphere and a multilayer substrate using the dielectric paste.
[0002]
[Prior art]
Conventionally, for example, as shown in FIG. 1, a ceramic circuit board used in a semiconductor device has a wiring layer 12 made of a conductive material as a multilayer of two or more layers, and a dielectric layer 13 as an insulating material for insulating the wiring layers. There are multilayer thick film substrates used. This multilayer thick film substrate is obtained by repeating the process of forming the wiring layer 12 by printing and baking a conductor paste, and then forming the dielectric layer 13 by printing and baking the dielectric paste.
[0003]
Such a multilayer thick film substrate has a structure in which a wiring layer 12 is disposed on the substrate 1 and a wiring layer 14 is further disposed thereon via a dielectric layer 13. As a conductor material for forming these wiring layers 12 and 14, a Cu-based conductor is rarely used, but an Ag-based conductor is generally used in many cases.
[0004]
Here, since the Cu-based conductor has a low wiring resistance, it is possible to reduce the wiring width, and as a result, there is an advantage that the downsizing of the ceramic substrate can be achieved. Furthermore, Cu-based conductors are very excellent in environmental resistance such as body sulfur resistance and solder resistance such as migration resistance.
[0005]
[Problems to be solved by the invention]
However, despite the fact that the Cu-based conductor has excellent characteristics as a conductive material, an Ag-based conductor is exclusively used as the conductive material for forming the wiring layer of the multilayer thick film substrate. It is rarely used. The reason is because of the following problems.
[0006]
When a Cu-based conductor is used as a conductor material for forming a wiring layer in a multilayer thick film substrate, the Cu-based conductor needs to be fired in, for example, a nitrogen atmosphere in order to avoid oxidation of the Cu-based conductor. Furthermore, in order to prevent oxidation of the first Cu wiring layer 12 formed by printing and baking a Cu-based conductor paste, the dielectric layer 13 must also be formed in a nitrogen atmosphere.
[0007]
The dielectric layer 13 is formed by printing and drying a dielectric paste in which glass powder, an inorganic insulating material, and an organic resin are dispersed in an organic solvent, followed by firing. When this dielectric paste is baked, the organic components usually decompose and disappear, the glass powder melts and becomes a dense film together with the inorganic insulating material, and the first layer Cu wiring layer 12 and the second layer Cu wiring An interlayer insulating film between the layers 14 is formed.
[0008]
The organic resin is added in order to satisfactorily print the dielectric paste, and usually ethyl cellulose is used.
[0009]
However, since ethyl cellulose requires oxygen to decompose, when a dielectric paste containing ethyl cellulose is baked in a nitrogen atmosphere, most of it decomposes and disappears at 300 to 600 ° C., but some does not decompose and glass It remains in the dielectric film up to a temperature range of 700 to 900 ° C. where the powder melts. For this reason, carbon remains in the dielectric film even after firing, or reacts with oxygen in the molten glass powder to gasify to generate pores in the dielectric film. As a result, the insulating property of the dielectric film as the interlayer insulating film is significantly deteriorated. This is the reason why Cu-based conductors are hardly used as a conductor material for forming a wiring layer of a multilayer thick film substrate.
[0010]
Note that since the Ag-based conductor has a property of being hardly oxidized even when fired in an oxygen atmosphere, the wiring film using the Ag-based conductor and the dielectric film that insulates the wiring layers can be formed in the oxygen atmosphere. Therefore, the problem that ethyl cellulose remains in the dielectric film does not occur, and it is widely used as a conductor material for forming a wiring film.
[0011]
In response to the above problems, for example, Japanese Patent Application Laid-Open No. 4-208598 discloses a nitrogen atmosphere in a relatively low temperature region in order to reduce the occurrence of residual carbon and pores due to the firing of the dielectric paste in the nitrogen atmosphere. It is shown that oxygen is mixed in. That is, by supplying oxygen in a relatively low temperature range, the decomposition of ethyl cellulose is promoted before the dielectric film is fired and sintered.
[0012]
However, this method has a drawback that the first layer Cu wiring layer 12 is oxidized by the mixed oxygen, and the solder wettability of the Cu wiring layer 12 is impaired.
[0013]
The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a dielectric paste that can be fired in a non-oxidizing atmosphere and has excellent insulating properties after firing, and a multilayer substrate using the same. And
[0014]
[Means for Solving the Problems]
The dielectric paste according to claim 1 includes a glass powder, and the inorganic insulating material, and a resin dispersed in an organic solvent, a derivative collector paste was added both of ethylcellulose and acrylic as the resin, The addition amount of the ethyl cellulose is 0.3 to 0.8 wt%, the addition amount of the acrylic is 0.2 to 0.8 wt%, and the glass powder has a softening point of 800 to 860 ° C, B ₂ O ₃ —SiO ₂ —PbO—Al ₂ O ₃ glass powder having a thermal expansion coefficient of 60 to 70 × 10 ⁻⁷ / ° C., and the content in the paste is 45 to 49% by weight, The inorganic insulating material is composed of aluminum oxide having a content of 27 to 29.5% by weight in the paste and calcium zirconate having a content of 18 to 19.5% by weight in the paste. Yes.
[0015]
Ethyl cellulose improves the printability of the dielectric paste. For this reason, when printing the dielectric paste, pinholes are prevented from being generated in the dielectric paste. However, when ethyl cellulose is used alone, it is not completely decomposed as described above when firing the dielectric paste, and remains as carbon in the dielectric film or generates pores.
[0016]
An acrylic resin is a resin that does not require oxygen for decomposition and can be completely decomposed even in, for example, nitrogen. However, the acrylic resin has poor printability compared to ethyl cellulose, and if used alone, pinholes are likely to occur in the film when the dielectric film is printed. Such pinholes remain even after the dielectric paste is dried and baked, which causes a deterioration in the insulating characteristics of the formed dielectric film.
[0017]
In the present invention, by adding both ethyl cellulose and acrylic, the thermal decomposability of the added resin is promoted even in an oxygen-free atmosphere while ensuring sufficient printability to suppress the generation of pinholes. In this way, an insulating layer (dielectric layer) having good insulating properties can be formed.
[0018]
Furthermore, the addition amount of ethyl cellulose was 0.3 to 0.8% by weight, and the addition amount of acrylic was 0.2 to 0.8% by weight . The reason is as follows. If the resin is ethyl cellulose alone and the amount added is 1.0% by weight or less, the printability cannot be ensured, pinholes are likely to occur, and the insulating properties may be impaired. On the other hand, if the added amount exceeds 1.0% by weight, it is not completely pyrolyzed and remains as carbon in the fired dielectric film or generates pores, thereby impairing the insulating properties. . Therefore, the amount of ethyl cellulose added is 0.3 to 0.8% by weight so that it does not deteriorate the insulating properties after remaining in the dielectric film after firing, and the printability is reduced due to the reduced amount of ethyl cellulose. order to compensate for, at the you added acrylic resin 0.2 to 0.8 wt%.
[0019]
The glass powder is made of borosilicate lead glass, inorganic insulating material shall be the at least one of aluminum oxide and calcium zirconate. More specifically, glass powder has a softening point of from 800 to 860 ° C., the thermal expansion coefficient of _{^{60~70 × 10 -7 / ℃ B 2}} O 3 -SiO 2 -PbO-Al 2 O 3 based glass powder In the paste, the content in the paste is 45 to 49% by weight, and the inorganic insulating material is aluminum oxide in which the content in the paste is 27 to 29.5% by weight, and the content in the paste is 18 to 19%. .5 that make up and a weight% of calcium zirconate. By using such glass powder and an inorganic insulating material, a dense dielectric film excellent in electrical insulation can be formed.
[0020]
According to a third aspect of the present invention , a wiring layer made of a conductive material containing copper, which is formed in multiple layers on a ceramic substrate, is formed between the wiring layers in order to ensure electrical insulation between these wiring layers. In a multi-layer substrate comprising a dielectric layer, a dielectric paste in which a dielectric layer is dispersed in an organic solvent, glass powder, an inorganic insulating material, ethyl cellulose resin and acrylic resin is baked in a non-oxidizing atmosphere. The addition amount of the ethyl cellulose in the paste is 0.3 to 0.8% by weight, the addition amount of the acrylic is 0.2 to 0.8% by weight, and the glass powder is a softening point of eight hundred to eight hundred and sixty ° C., a coefficient of thermal expansion a 60~70 × 10 ^-7 / ℃ of _{B 2 O 3 -SiO 2 -PbO-} Al 2 O 3 based glass powder, the paste The content is 45 to 49% by weight, and the inorganic insulating material includes 27 to 29.5% by weight of aluminum oxide in the paste and 18 to 19.5% by weight in the paste. By being made of this calcium zirconate, it is possible to obtain a multilayer substrate having a dielectric layer that is excellent in printability during dielectric paste printing and excellent in electrical insulation after firing.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0022]
FIG. 1 shows a configuration of a multilayer thick film substrate as an embodiment of the present invention. As shown in FIG. 1, a first wiring layer 12 made of a Cu-based conductor is disposed on the ceramic substrate 1. On the 1st wiring layer 12, the 2nd wiring layer 14 formed from the Cu-type conductor is further arrange | positioned through the dielectric material layer 13 as an insulating layer. In this way, a plurality of Cu wiring layers 12 and 14 are laminated via the dielectric layer 13 to constitute a multilayer thick film substrate.
[0023]
Next, a method for manufacturing this multilayer thick film substrate will be described.
[0024]
As Cu-based conductor paste for forming the first and second wiring layers 12, 14, Cu powder, glass powder and inorganic oxide powder for ensuring the bonding strength between the ceramic substrate 1, and printability An organic resin (for example, ethyl cellulose) for imparting water is dispersed in an organic solvent. This Cu-based conductor paste is applied on the ceramic substrate 1 by screen printing. Then, after drying and forming a predetermined pattern, the Cu wiring layer 12 is obtained by baking for about 1 hour in a belt furnace having a peak temperature of about 900 ° C. in a nitrogen atmosphere.
[0025]
Subsequently, as a dielectric paste for forming the dielectric layer 13, a finely pulverized glass powder, an inorganic insulating material, and ethyl cellulose and acrylic as organic resin components dispersed in an organic solvent to prepare a paste To do.
[0026]
More specifically, 0.3 to 0.8% by weight of ethyl cellulose is added and 0.2 to 0.8% by weight of acrylic is added. The reason for this is that the added amount of 0.3 to 0.8% by weight so that the ethyl cellulose remains in the dielectric film after firing and does not impair the insulation properties, and the printability associated with the reduced amount of added ethyl cellulose. In order to compensate for the decrease, 0.2 to 0.8% by weight of an acrylic resin is added.
[0027]
The glass powder is a lead borosilicate glass powder having a softening point of 800 to 860 ° C. and a thermal expansion coefficient of 60 to 70 × 10 ⁻⁷ / ° C., and the content in the paste is 45 to 49% by weight. As the inorganic insulating material, a material containing at least one of aluminum oxide powder and calcium zirconate powder is used. More specifically, it can be composed of aluminum oxide having a content of 25 to 35% by weight in the paste and calcium zirconate having a content of 15 to 25% by weight in the paste. By using such glass powder and an inorganic insulating material, a dense dielectric film excellent in electrical insulation can be formed. Further, terpineol is used as the organic solvent.
[0028]
Furthermore, the optimum composition, the softening point as the glass powder is eight hundred to eight hundred sixty ° C., the thermal expansion coefficient of 60~70 × 10 ^-7 / ℃ with _{B 2 O 3 -SiO 2 -PbO-} Al 2 O 3 based glass powder And the content rate in a paste is 45 to 49 weight%, As an inorganic insulating substance, the content rate in a paste is 27-29.5 weight%, and the content rate in a paste is 18-19. What contains 5 weight% of calcium zirconate is good.
[0029]
As shown in FIG. 1, this dielectric paste is applied by screen printing so that at least a part thereof covers the Cu wiring layer 12. Then, after drying and forming a predetermined pattern, the dielectric layer 13 is obtained by baking for about 1 hour in a belt furnace having a peak temperature of about 900 ° C. in a nitrogen atmosphere.
[0030]
In this printing process, since both ethylcellulose and acrylic are added, good printability is maintained and the generation of pinholes is suppressed. In addition, in the firing process of the dielectric paste, since the amount of ethyl cellulose, which is inferior in thermal decomposability, is minimized, the remaining carbon in the dielectric film and the generation of pores are suppressed, and the insulation characteristics are good. A dielectric layer can be formed.
[0031]
Subsequently, the Cu-based conductor paste is applied by screen printing so that at least a part thereof covers the dielectric layer 13. Then, after drying and forming a predetermined pattern, the second Cu wiring layer 14 is obtained by baking for about 1 hour in a belt furnace having a peak temperature of about 900 ° C. in a nitrogen atmosphere. Through such steps, the multilayer Cu thick film substrate shown in FIG. 1 can be manufactured.
[0032]
As shown in FIG. 2, as a resin to be added to the paste, a dielectric paste is prepared by changing the amount of acrylic added to 0.7% by weight of ethyl cellulose, and the dielectric layer formed by printing and firing the dielectric paste. Indicates the voltage characteristics (insulation characteristics) and the number of pinholes generated during dielectric paste printing.
[0033]
From the graph shown in FIG. 2, it can be seen that the addition of acrylic reduces the number of printed pinholes and improves the withstand voltage characteristics. As the addition amount of acrylic, the effect starts to appear from 0.2% by weight, but in the present example, the range of 0.4% by weight to 0.8% by weight was optimal.
[0034]
As a comparative example, FIG. 3 shows the evaluation results regarding the withstand voltage characteristics and the number of pinholes generated when only ethyl cellulose is used as the resin material.
[0035]
First, when the addition amount of ethyl cellulose is 1.0% by weight or less, printability cannot be ensured and a large number of pinholes are generated. As a result, the withstand voltage characteristics after firing are reduced. If the added amount of ethyl cellulose exceeds 1.0% by weight, the number of pinholes can be reduced, but in a nitrogen atmosphere, it is not completely pyrolyzed and remains as carbon in the dielectric film after firing, As a result, pores are generated and the withstand voltage characteristic is also lowered.
[0036]
Furthermore, as a comparative example, FIG. 4 shows the evaluation results regarding the withstand voltage characteristics and the number of pinholes generated when only acrylic is used as the resin material.
[0037]
Acrylic is inferior to ethyl cellulose in terms of printability, and the number of pinholes cannot be reduced even if the amount added is increased. Therefore, the withstand voltage characteristics after firing of the dielectric paste cannot be sufficiently improved in spite of excellent decomposition characteristics upon firing in a nitrogen atmosphere.
[0038]
In this embodiment, ethyl cellulose, which is excellent in printability but poor in thermal decomposability in a nitrogen atmosphere, and an acrylic resin that is poor in printability but excellent in thermal decomposability in a nitrogen atmosphere are both added to the dielectric paste. Then, by adjusting the amount of addition to the optimum range, it is possible to form a dielectric film having excellent printability during paste printing and excellent insulating properties after firing.
[0039]
By applying this dielectric film as an insulating film between Cu wiring layers formed in multiple layers on a ceramic substrate, a multilayer Cu wiring layer substrate having excellent insulating characteristics can be obtained.
[0040]
FIG. 5 is a table showing compositions and physical properties of various acrylic resins A to D. All the acrylic resins A to D described in this table were added together with ethyl cellulose to prepare a dielectric paste. As a result, all the dielectric pastes exhibited good printability, and the thermal decomposability upon firing was sufficiently satisfactory. Among them, the acrylic resin A having the smallest weight average molecular weight is a particularly preferable material because good printability can be obtained (the viscosity of the dielectric paste can be lowered) even if the amount of the organic solvent is reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a multilayer thick film substrate in an embodiment of the present invention.
FIG. 2 is a graph showing the printability of a dielectric paste and the withstand voltage characteristics of a dielectric film formed by firing when both ethyl cellulose and acrylic are mixed as a resin added to the dielectric paste.
FIG. 3 is a graph showing the printability of the dielectric paste and the withstand voltage characteristics of the dielectric film formed by firing when only ethyl cellulose is used as the resin added to the dielectric paste.
FIG. 4 is a graph showing the dielectric paste printability and the withstand voltage characteristics of a dielectric film formed by firing when only acrylic is used as the resin added to the dielectric paste.
FIG. 5 is a table showing compositions and physical properties of various acrylic resins.

Claims (4)

Glass powder, and the inorganic insulating material, and a resin dispersed in an organic solvent, a derivative collector paste was added both of ethylcellulose and acrylic as the resin,
The addition amount of the ethyl cellulose is 0.3 to 0.8% by weight, the addition amount of the acrylic is 0.2 to 0.8% by weight,
The glass powder has a softening point of 800-860 ° C., a coefficient of thermal expansion a 60~70 × 10 ^-7 / ℃ of _{B 2 O 3 -SiO 2 -PbO-} Al 2 O 3 based glass powder, the paste The content in the paste is 45 to 49% by weight, and the inorganic insulating material includes aluminum oxide in which the content in the paste is 27 to 29.5% by weight, and the content in the paste is 18 to 19.5. A dielectric paste comprising weight percent calcium zirconate. The dielectric paste according to claim 1 Symbol placement of the dielectric paste, characterized in that it is intended to be fired in a nitrogen atmosphere. A multilayer substrate comprising a wiring layer made of a conductor material containing copper and formed in multiple layers on a ceramic substrate, and a dielectric layer formed between the wiring layers in order to ensure electrical insulation between the wiring layers. There,
The dielectric layer is formed by baking a dielectric paste in which glass powder, an inorganic insulating material, ethyl cellulose resin and acrylic resin are dispersed in an organic solvent in a non-oxidizing atmosphere ,
The addition amount of the ethyl cellulose in the paste is 0.3 to 0.8% by weight, the addition amount of the acrylic is 0.2 to 0.8% by weight,
The glass powder has a softening point of 800-860 ° C., a coefficient of thermal expansion a 60~70 × 10 ^-7 / ℃ of _{B 2 O 3 -SiO 2 -PbO-} Al 2 O 3 based glass powder, the paste The content in the paste is 45 to 49% by weight, and the inorganic insulating material includes aluminum oxide in which the content in the paste is 27 to 29.5% by weight, and the content in the paste is 18 to 19.5. A multilayer substrate comprising weight percent calcium zirconate. The multilayer substrate according to claim 3 , wherein the dielectric paste is fired in a nitrogen atmosphere .

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