JP4867399B2 - Conductor paste and ceramic multilayer substrate manufacturing method - Google Patents

Description

  The present invention relates to a method for producing a ceramic multilayer substrate by a low temperature co-fired ceramics (LTCC) technique and a conductor paste.

The LTCC technology is widely used as a technology for incorporating high-frequency passive components. Recently, application to antennas and various filters for wireless LAN, bluetooth, or ultra wide band (UWB) is expected.
FIG. 1 is a conceptual diagram of a cross section of a typical antenna for UWB, which is a kind of ceramic multilayer substrate. The antenna 10 electrically joins a laminated body of glass ceramic layers (ceramic layers) 11 which is a main body thereof, an inner layer conductor 2 wired inside thereof, and a vertical pattern necessary for being multilayered. And a surface layer conductor 1 used for power feeding to the antenna and soldering to the substrate to be joined thereto.

The ceramic layer 11 is formed by firing a glass ceramic composition made of a ceramic green sheet (hereinafter sometimes simply referred to as a green sheet). As such a glass ceramic composition, for example, a composition comprising SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —RO (alkaline earth metal oxide) —ZnO glass powder and alumina powder is known ( Patent Document 1).

  The green sheets are laminated to form a green sheet laminate, and the conductor paste layer that is fired to become the surface layer conductor 1 is on the green sheet laminate surface, and the conductor paste layer that is fired to become the inner conductor 2 is between the green sheet layers. Conductive paste filling holes that are baked to become via conductors 3 are formed in the green sheets.

  Silver is often used for the conductor of such a ceramic multilayer substrate, but it is known that this silver diffuses into the ceramic layer and causes migration during firing. In particular, since the inner conductor is in strong surface contact with the ceramic layers on both sides, this diffusion tends to be significant.

  The diffusion of silver into the ceramic layer reduces the volume of the electrode, and the line width of the electrode is reduced or the electrode film thickness is reduced. Become. In particular, when the thickness of the ceramic layer is thin, problems such as a short circuit is likely to occur and the insulation resistance is significantly deteriorated.

  In order to suppress such migration during firing, it has been proposed to improve the conductor material and process.

As a method for solving the problem by improving the conductor material, a method has been proposed in which a metal such as platinum or palladium is mixed with a silver paste which is an electrode material (conductor material) (see Patent Document 2).
However, this method has problems such as an expensive electrode material and a high specific resistance.

As a method for solving the problem by improving the process, a method has been proposed in which the oxidation of silver is prevented and the diffusion into the ceramic layer is suppressed by firing in an atmosphere in which oxygen is controlled (see Patent Document 3).
However, in this method, not only the manufacturing apparatus becomes expensive, but also, as described in Patent Document 4, if the oxygen partial pressure is not accurately controlled, the dielectric may be reduced and performance may be deteriorated. There are problems such as.

In addition, a method of suppressing the migration by shortening the heating time by firing by microwave heating has been proposed (see Patent Document 5).
However, this method not only makes the manufacturing apparatus expensive, but also causes problems such as an increase in residual carbon in the ceramic multilayer substrate due to a rapid temperature rise, and bubbles remaining without leaving the substrate.

JP 2005-126250 A JP 2001-35739 A JP-A-9-55332 JP 2002-80274 A JP 2002-15943 A

  An object of the present invention is to provide a conductor paste and a method for producing a ceramic multilayer substrate that can solve such problems.

The present invention, silver contact and silver - one or more metal powders selected from the group consisting of palladium alloy, a conductive paste containing glass powder and Si powder, average particle diameter of the Si powder is 0.5 A conductor paste that is 1.5 μm is provided.
A ceramic green sheet laminate in which a plurality of ceramic green sheets are laminated and a conductive paste layer that is fired to form an inner conductor is formed between at least one pair of adjacent ceramic green sheets is fired, and the inner layer is fired. A method for producing a ceramic multilayer substrate having a conductor, wherein the conductor paste layer comprises the conductor paste.

In order to suppress or prevent silver diffusion into the ceramic layer as described above, the present inventor changed the particle size of the metal powder in the conductor paste or removed the fine powder contained in the metal powder. Add metal oxide with high heat resistance to the surface of the metal powder, or add platinum, rhodium, palladium, etc. that are commonly used for the purpose of increasing the heat resistance of the sintered conductor paste (conductor) and suppressing diffusion However, it has been difficult to reduce the diffusion of silver into the ceramic layer (dielectric) without significantly increasing the specific resistance of the conductor.
However, the inventors have found that by adding silicon (Si) powder having a small particle size, the diffusion of silver into the dielectric can be reduced without significantly increasing the specific resistance of the conductor, and the present invention has been achieved.

According to the present invention, it is possible to prevent the phenomenon that the line width of the electrode becomes thin or the film thickness of the electrode becomes thin without causing the improvement of the conductive material or the process as described above. .
In addition, even when the ceramic layer is thin, short-circuiting is less likely to occur or insulation resistance is less likely to deteriorate.

The method for producing a ceramic multilayer substrate of the present invention is characterized in that the conductor paste layer of the green sheet laminate that is fired to become the inner layer conductor is used as the conductor paste of the present invention, and the other portions are not limited.
The method for producing a ceramic multilayer substrate of the present invention is generally performed using LTCC technology, and firing is usually performed at 850 to 910 ° C.

The conductive paste layer is usually formed as follows. That is, the conductive paste of the present invention is applied to one surface of the green sheet by screen printing.
The inner layer conductor is usually formed as a wiring pattern and is typically a conductive line. Taking a conductive line as an example, when the conductor paste layer corresponding to the conductive line is formed by a screen printing method, the cross-sectional shape thereof is a mountain shape, and the thickness of the mountain bottom portion is smaller than the thickness of the central portion.

When a conductive line is formed using a conventional silver paste, the amount of silver that ionizes and diffuses into the ceramic layer and melts increases, and the silver content at the bottom of the conductor paste layer decreases significantly, resulting in a conductive line width. However, there was a problem that it was significantly reduced.
On the other hand, when the conductive line is formed using the conductive paste of the present invention in which the metal powder is silver powder, the amount of silver that is ionized and diffused into the ceramic layer is reduced, so that the conductive line width is significantly reduced. It can be suppressed.

  The Si powder in the conductor paste of the present invention has an average particle size smaller than that of commercially available Si powder, and therefore acts as a strong reducing agent, so that the oxidation / ionization of the silver can be suppressed and diffusion can be reduced. Conceivable. A reagent is often used as a commercially available Si powder, but the average particle diameter of the reagent is 20 to 100 μm, typically 50 to 80 μm.

The conductor paste of the present invention is suitable for forming an inner layer conductor of a ceramic multilayer substrate.
The metal powder of the conductor paste of the present invention is typically silver powder. Hereinafter, this typical case will be mainly described as an example.

  The Si powder in the present invention is produced, for example, as follows. That is, commercially available Si powder is pulverized by a tungsten ball mill to reduce its average particle size. As a specific example, a commercially available Si powder having an average particle diameter of 75 μm is placed in a tungsten 100 cc container together with five tungsten balls having a diameter of 10 mm, and rotated for 8 minutes at a speed of 3 rotations per second for 8 minutes. The diameter is 1.0 μm. Note that large crushed powder having a particle diameter of 20 μm or more is removed by a stainless steel sieve.

The average particle size of the Si powder is usually measured by a laser diffraction / scattering method using a commercially available measuring device such as a laser diffraction particle size distribution measuring device SALD-2100 manufactured by Shimadzu Corporation.
When the average particle size is less than 0.5 μm, the Si powder tends to aggregate in the conductor paste, and the silver diffusion suppressing effect is reduced. Typically, it is 0.8 μm or more. If it exceeds 1.5 μm, the specific surface area of the Si powder becomes small and the silver diffusion suppressing effect becomes small. Typically, it is 1.2 μm or less.

  The glass powder in the present invention should be appropriately selected according to the use of the conductor paste, but if it is for forming an inner layer conductor, the softening point is preferably 700 to 850 ° C. If the temperature is lower than 700 ° C., the softening flow during firing becomes too significant, and the reaction with the ceramic layer becomes large, which may change the characteristics of the ceramic layer. If it exceeds 850 ° C., the softening flow becomes insufficient, and cracks or voids may occur at the interface with the ceramic layer. It is typically 700 to 750 ° C.

As a glass powder having such a softening point, from SiO ₂ 40 to 50%, Al ₂ O ₃ 6 to 10%, ZnO 7 to 11%, MgO 33 to 41% in terms of mol% based on the following oxides What becomes essentially is illustrated. The essential components of the glass powder are the above-mentioned four components, but other components may be contained within a range not impairing the object of the present invention. In that case, the total content of such components is preferably 5% or less.

Essential powder components in the conductor paste of the present invention, silver contact and silver - (. The following, the powder may be referred to the metal powder) at least one metal powder selected from the group consisting of palladium alloy, glass powder and Although it is Si powder whose average particle diameter is 0.5-1.5 micrometers, you may contain other powders, for example, an alumina powder, a zirconia powder, etc. as a filler in the range which does not impair the objective of this invention besides.
The total content of the metal powder and the glass powder is 100 parts by mass, and the content ratio of the other powders is preferably 2 parts by mass or less.

Weight ratio of metal powder is 98.5 parts by mass or more, the weight ratio of the Si powder is Ru 0.1 to 1.8 parts by der.
When the mass ratio of the metal powder is less than 98.5 parts by mass, for example, silver easily diffuses into the ceramic layer or the specific resistance of the conductor increases with the softening flow of the glass powder during firing. The mass ratio is preferably 99.5 parts by mass or less. If it exceeds 99.5 parts by mass, the mass ratio of the glass powder becomes small, the adhesion between the conductor and the ceramic layer becomes weak, and the conductor may peel off during firing.

  If the mass proportion of the Si powder is less than 0.1 parts by mass, the Si powder is not dispersed throughout the conductor paste, and the suppression of silver diffusion may be insufficient. Typically 0.3 parts by mass or more. If it exceeds 1.8 parts by mass, the specific resistance of the conductor obtained by firing the conductor paste becomes large. Typically, it is 1 part by mass or less.

In addition to these powder components, the conductor paste contains organic varnish by mass percentage, typically 3 to 20%.
If the content of the organic varnish is less than 3%, the coating strength before firing becomes insufficient, or the paste viscosity becomes high and the printability may be lowered. If it exceeds 20%, voids will increase in the conductor and the specific resistance will increase, or the paste viscosity will become too low, and the printability may be lowered. Typically 10% or less.
The organic varnish is usually obtained by dissolving a resin such as acrylic or cellulose with a high boiling point solvent such as α-terpineol or butyl carbitol acetate. Typically, about 10 to 30% by mass of the resin component is contained, and the remainder is a solvent.

  The specific resistance of the conductor obtained by firing the conductor paste of the present invention is preferably 3 μΩ · cm or less. If it exceeds 3 μΩ · cm, it may be difficult to use it for high-frequency passive components.

A ceramic green sheet was prepared as follows.
First, mol% _{composition, SiO 2 30.5%, B 2} O 3 22.0%, Al 2 O 3 6.6%, 18.2% ZnO, CaO 7.8%, BaO 14.9% A glass powder A was prepared. In addition, this glass powder was a flake shape manufactured by pouring and cooling molten glass obtained by melting raw materials and then pulverizing, and the average particle size was 1 μm.

Moreover, the barium titanate powder was produced as follows. That is, 88 g of BaCO ₃ powder (barium carbonate BW-KT manufactured by Sakai Chemical Industry Co., Ltd.) and 130 g of TiO ₂ powder (HT0210 manufactured by Toho Titanium Co., Ltd.) were mixed in a ball mill using water as a solvent, and kept at 1150 ° C. for 2 hours after drying. . Thereafter, it was pulverized for 60 hours by a ball mill to obtain a powder having an average particle size of 1 μm.

  Next, the glass ceramic composition GC-A was prepared by mixing the glass powder A and the barium titanate powder at a mass ratio of 50:50.

Regarding the glass ceramic composition GC-A, 70 parts by mass of an organic solvent containing toluene, xylene, isopropyl alcohol, and 2-butyl alcohol in a mass ratio of 4: 2: 2: 1 in 100 parts by mass of the glass ceramic composition. Part, 5 parts by weight of dioctyl phthalate, 0.3 parts by weight of a dispersant (BYK180 manufactured by BYK Japan) and 10 parts by weight of polyvinyl butyral were added and stirred to obtain a smooth slurry.
This slurry was applied onto a PET film by a doctor blade method and dried to obtain a ceramic green sheet GS-A having a thickness of 200 μm.

On the other hand, Si powders Si-1 to 5 were prepared. Si-1, Si-2, Si-3, Si-4, the average particle diameter _{D 50} of the Si-5, respectively, 0.3μm, 0.5μm, 1.0μm, 1.5μm , is 1.8 .mu.m, , _{D 50} to transfer liquid by Shimadzu laser diffraction particle size distribution measuring apparatus SALD-2100 was measured water, the refractive index as 3.5.
In addition, silver powder AgF-5 (average particle size: 5 μm) manufactured by Tokuru Chemical Laboratory Co., Ltd. was prepared as a metal powder.

Further, as the glass powder for a conductive paste, mol% _{composition, SiO 2 45.5%, Al 2} O 3 7.9%, ZnO 9.1%, was prepared glass powder G is 37.5% MgO . The glass powder is a flake produced by pouring and cooling molten glass obtained by melting the raw material, and then pulverizing it. The average particle size measured by the particle size distribution analyzer SALD-2100 The diameter was 1 μm.

The glass had a softening point Ts of 730 ° C. and a crystallization temperature Tc of 860 ° C.
Ts and Tc were measured by differential thermal analysis as follows. That is, using DTA-50 manufactured by Shimadzu Corporation, 30 mg of glass powder was filled in the platinum container, and the temperature was raised to 900 ° C. at a speed of 10 ° C. per minute. The temperature at the bottom of the second endothermic part and the temperature at which the heat generation becomes maximum were read from the heat generation / absorption curve at that time, and were respectively set as Ts and Tc.

Si powder Si-1 to 5, silver powder AgF-5, glass powder G, organic varnish, ratios shown in parts by mass in the columns of Si powder amount, silver powder amount, glass powder amount, and varnish amount in Tables 1 and 2, respectively. After mixing, the mixture was kneaded in a porcelain mortar for 1 hour and further dispersed three times with three rolls to prepare 10 types of conductor pastes. In addition, as an organic varnish, what melt | dissolved the ethyl cellulose resin of the polymerization degree 7 in (alpha) -terpineol so that a density | concentration might be 20 mass% was used, and each column of the amount of Si powder of this table, silver powder amount, and glass powder amount In parentheses, the mass ratio of each powder when the total of the silver powder mass and the glass powder mass is 100 parts by mass is shown.
The conductor pastes of Examples 2 to 4 and 6 to 9 are examples, the conductor pastes of Examples 1 and 5 are comparative examples, and the conductor paste of Example 10 is a reference example .

Six ceramic green sheets GS-A having a size of 40 mm × 40 mm were prepared, and a linear pattern shown in FIG. These ceramic green sheets were laminated so that the pattern was located on the third and fourth green sheets, and were heated to 80 ° C. and integrated by applying a pressure of 80 MPa to obtain a ceramic green sheet laminate.
The ceramic green sheet laminate was fired by raising the temperature from room temperature to 550 ° C. for 5 hours, from 550 ° C. to 875 ° C. in 30 minutes, and holding at 875 ° C. for 1 hour and 30 minutes to obtain a ceramic multilayer substrate. .

  The obtained ceramic multilayer substrate was cut so that a cross section in the width direction of the linear pattern was obtained, the cut surface was mirror-polished using a 0.3 μm diamond paste, and each line width was measured with a microscope for the mirror cross section. Measured with a vessel. When the line width before firing is W1, the line width after firing is W2, and the shrinkage rate when the ceramic green sheet laminate is fired is SR (unit:%), the line width reduction rate (unit:%) is (( W1-W2) * 100 / W1) -SR. The respective line width reduction rates of 80 μm, 100 μm, 200 μm, and 300 μm shown in FIG. 2 are preferably 6% or less.

Moreover, the same thing as the said ceramic green sheet laminated body was produced, and the specific resistance measurement pattern as shown in FIG. 3 was formed on the surface using the conductor paste. Thereafter, firing was performed to obtain a ceramic multilayer substrate having a conductive pattern for measuring specific resistance formed on the surface.
The electrical resistance R of this conductor pattern was measured with a digital multimeter manufactured by Advantest Corporation, and the conductor cross-sectional area S was determined by scanning electron microscope observation of the conductor wire cross-section.
R × S ÷ L was calculated using R, S and the length L of the conductor wire, and this was defined as the specific resistance. The results are shown in Tables 1 and 2 (unit: μΩ · cm), but the specific resistance is preferably 3 μΩ · cm or less.
Similarly, the line width reduction rate and the specific resistance were measured for the conductor pastes of Examples 2 to 10.

  It can be used as a conductor paste for interior conductors of high-frequency passive components.

The conceptual diagram of the cross section of a ceramic multilayer substrate. The figure which shows the filament pattern on a ceramic green sheet. The figure which shows the conductor pattern for specific resistance measurement on a ceramic multilayer substrate.

Explanation of symbols

1: Surface conductor 2: Inner layer conductor 3: Via conductor 10: Ceramic multilayer substrate 11: Glass ceramic layer

Claims (5)

Silver, Contact and silver - one or more metal powders selected from the group consisting of palladium alloy, a conductive paste containing glass powder and Si powder, average particle diameter of the Si powder is 0.5~1.5μm der is,
The total of the mass of the metal powder and the mass of the glass powder is 100 parts by mass, the mass ratio of the metal powder is 98.5 parts by mass or more, and the mass ratio of the Si powder is 0.1 to 1.8 parts by mass. Conductor paste. The conductive paste according to claim 1, wherein the softening point of the glass powder is 700 to 850 ° C. The conductor paste according to claim 1 or 2 , wherein the conductor obtained by firing has a specific resistance of 3 µΩ · cm or less. A ceramic green sheet laminate in which a plurality of ceramic green sheets are laminated and a conductive paste layer that is fired to form an inner conductor is formed between at least one pair of adjacent ceramic green sheets is fired, and the inner conductor is A method for producing a ceramic multilayer substrate having a conductor paste layer comprising the conductor paste according to any one of claims 1 to 3 . 5. The method for producing a ceramic multilayer substrate according to claim 4 , wherein the conductor paste is applied to one surface of the adjacent ceramic green sheets by a screen printing method to form a conductor paste layer.

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