1. A preparation method of a low-temperature co-fired ceramic substrate is characterized by comprising the following steps:

(1) mixing 40-60 wt% of ceramic powder, 30-50 wt% of solvent, 5-15 wt% of binder and 0.2-2 wt% of dispersant to obtain ceramic tape-casting slurry, wherein the binder is polymethacrylate;

(2) carrying out casting molding on the obtained ceramic casting slurry to obtain a ceramic casting green tape;

(3) placing the obtained ceramic tape-cast green ceramic tape in an air atmosphere or an oxygen-free atmosphere, carrying out degumming at 380-450 ℃, and then sintering to obtain the ceramic substrate; or printing at least one of a Cu electrode and a Ni electrode on a ceramic tape casting green ceramic tape, placing the ceramic tape casting green ceramic tape in an oxygen-free atmosphere, performing binder removal at 380-450 ℃, and sintering to obtain the low-temperature co-fired ceramic substrate.

2. A producing method according to claim 1, characterized in that said ceramic casting slurry further comprises a plasticizer in an amount of not more than 2 wt%; the plasticizer is at least one of butyl benzyl phthalate, dioctyl phthalate, glycerol and polyethylene glycol.

3. The production method according to claim 1 or 2, characterized in that the solvent is at least one of butanone, ethanol, and isopropanol; the dispersant is at least one of tributyl phosphate, artificial fish oil and polyoxyalkylene polymer MALIALIIM series.

4. The production method according to any one of claims 1 to 3, wherein the ceramic powder is selected from the group consisting of Ca-B-Si-O system ceramic powder, AlN ceramic powder ceramic + sintering aid system, BaTiO₃At least one of capacitor dielectric ceramic powder and SiC powder; the average grain diameter of the ceramic powder is 700-1000 nm.

5. A production method according to any one of claims 1 to 4, characterized in that the production method of the ceramic casting slurry comprises:

(1) mixing ceramic powder, a solvent and a dispersing agent, and then carrying out primary ball milling for 4-12 hours, wherein the mass ratio of the raw materials to the grinding body is 1: (3-4);

(2) adding a binder and a plasticizer into the slurry subjected to the primary ball milling, and carrying out secondary ball milling for 12-24 hours;

(3) and removing bubbles in the slurry subjected to secondary ball milling in vacuum to obtain the ceramic tape-casting slurry.

6. The method of any one of claims 1-5, wherein the ceramic cast green tape has a thickness of 50 to 120 micrometers.

7. The production method according to claim 6, wherein the tensile strength of the ceramic tape is 1.5 to 3.0 MPa.

8. The production method according to any one of claims 1 to 7, wherein the Cu electrode comprises copper powder, glass powder, a solvent, and a binder; the Ni electrode comprises nickel powder, glass powder, a solvent and a binder.

9. The production method according to any one of claims 1 to 8, wherein the oxygen-free atmosphere is a neutral atmosphere or a reducing atmosphere; the neutral atmosphere is nitrogen atmosphere; the reducing atmosphere is a hydrogen atmosphere or a carbon monoxide atmosphere.

10. A low-temperature co-fired ceramic substrate produced by the production method according to any one of claims 1 to 9.

Background

In recent years, with the increasing demands for the diversity of devices and the reliability of systems in the fields of wireless communication, aerospace, automobiles, and the like, the development of electronic components toward miniaturization, high frequency, multi-functionalization, and integration is an inevitable trend. As package sizes become smaller and circuit pack densities and system stability requirements continue to increase, these have led to an inevitable trend and choice for modularity and high integration of multiple chips, circuits and components. If part of the passive elements can be integrated into the substrate, it is advantageous not only to miniaturize the system and increase the packaging density of the circuit, but also to improve the reliability of the system. The low temperature co-fired ceramic (LTCC) technology is a multilayer circuit made by laminating unsintered tape-cast ceramic materials, and embedding printed interconnection conductors, passive elements and functional devices (such as low-capacitance capacitors, resistors, filters, couplers and the like) into a multilayer ceramic substrate, then laminating the multilayer ceramic substrate and the printed interconnection conductors, the passive elements and the functional devices together, and co-firing the multilayer ceramic substrate and metal electrodes of gold, silver, copper and the like at 850-900 ℃ to form an integrated ceramic multilayer material. LTCC technology fully exhibits its superior performance in terms of high frequency characteristics, sealing properties, heat dissipation, etc., and thus is the first choice for packaging technology in the fields of radio communication, automotive electronics, military, and aerospace, etc.

The green tape is a basic form for LTCC ceramic powder application, and high solid content, tensile strength and low surface roughness are ideal green tapes which are required to be obtained by the technical personnel in the field. The green porcelain tape is prepared by carrying out casting molding on slurry obtained by mixing ceramic powder, a solvent and a functional auxiliary agent, so that the properties of the casting slurry directly determine the properties of the green porcelain tape. The casting slurry is often required to have a viscosity within a suitable range so that the green tape after casting has the above-described characteristics. However, the commonly used polyvinyl butyral (PVB) binder tends to result in a slurry with a relatively high viscosity, a low green tape strength, a high green tape surface roughness, a high residual thermally decomposed carbon, and is only suitable for sintering in an oxygen atmosphere, and is not suitable for applying to ceramic powder sintered in a reducing atmosphere. In particular, LTCC ceramic powders generally contain borosilicate glass, which is sensitive to the aldehyde groups of PVB and can cause slurry flocculation. In addition, compared with noble metal electrodes such as Ag and Au, base metal electrodes such as Cu and Ni can greatly reduce the cost. However, when the green tape is co-fired with electrodes such as Cu and Ni which are very easily oxidized, sintering in a reducing atmosphere is required.

Disclosure of Invention

Aiming at the problems, the invention provides the low-temperature co-fired ceramic substrate which has strong slurry compatibility and environmental friendliness, can perform adhesive discharging and sintering in an air atmosphere or a reducing atmosphere and has less organic residue and the preparation method thereof.

In one aspect, the invention provides a method for preparing a low-temperature co-fired ceramic substrate, comprising the following steps:

(1) mixing 40-60 wt% of ceramic powder, 30-50 wt% of solvent, 5-15 wt% of binder and 0.2-2 wt% of dispersant to obtain ceramic tape-casting slurry, wherein the binder is polymethacrylate;

(2) carrying out casting molding on the obtained ceramic casting slurry to obtain a ceramic casting green tape;

(3) placing the obtained ceramic tape-cast green ceramic tape in an air atmosphere or an oxygen-free atmosphere, carrying out degumming at 380-450 ℃, and then sintering to obtain the ceramic substrate; or printing at least one of a Cu electrode and a Ni electrode on a ceramic tape casting green ceramic tape, placing the ceramic tape casting green ceramic tape in an oxygen-free atmosphere, performing binder removal at 380-450 ℃, and sintering to obtain the low-temperature co-fired ceramic substrate.

In the invention, the polymethacrylate is firstly used for preparing the ceramic tape-casting slurry and the low-temperature co-fired ceramic substrate. The polymethacrylate is decomposed into methacrylic acid monomers at high temperature, can be removed cleanly under neutral or reducing atmosphere, and has the characteristics of little ash residue. For example, ceramic powders such as silicon carbide and aluminum nitride are suitable for sintering in a reducing atmosphere. Meanwhile, the polymethacrylate has strong compatibility with borosilicate glass in LTCC ceramic powder, the slurry viscosity is low, and flocculation is not caused. And, the decomposition product of the methacrylic acid ester at high temperature is only H₂O and CO₂The method conforms to the environment-friendly principle, the content of decomposed residual carbon is less than 0.04 percent and far less than the content of carbon residue (0.34 percent) of PVB (polyvinyl butyral), the influence of the decomposed residual organic matter on the dielectric property of the component is greatly reduced, and the method has important significance on the preparation of high-performance electronic components.

Preferably, the ceramic casting slurry also comprises a plasticizer with the weight percent not more than 2 percent; the plasticizer is at least one of butyl benzyl phthalate, dioctyl phthalate, glycerol and polyethylene glycol.

Preferably, the solvent is at least one of butanone, ethanol and isopropanol; the dispersant is at least one of tributyl phosphate, artificial fish oil and polyoxyalkylene polymer (MALIALIIM) series.

Preferably, the ceramic powder is selected from Ca-B-Si-O system ceramic powder, AlN ceramic powder ceramic and sintering aid system, BaTiO₃At least one of capacitor dielectric ceramic powder and SiC powder; the average grain diameter of the ceramic powder is 700-1000 nm.

Preferably, the preparation method of the ceramic casting slurry comprises the following steps:

(1) mixing ceramic powder, a solvent and a dispersing agent, and then carrying out primary ball milling for 4-12 hours, wherein the mass ratio of the raw materials to the grinding body is 1: (3-4);

(2) adding a binder and a plasticizer into the slurry subjected to the primary ball milling, and carrying out secondary ball milling for 12-24 hours;

(3) and removing bubbles in the slurry subjected to secondary ball milling in vacuum to obtain the ceramic tape-casting slurry.

In the invention, the polymethacrylate binder has strong compatibility and can greatly reduce the viscosity of the slurry. The ceramic tape-casting slurry prepared by the method can be used for tape-casting a raw ceramic tape with the thickness of dozens of micrometers to hundreds of micrometers on a full-automatic tape-casting machine, and the raw ceramic tape and a PET carrier film are well wetted and have good strength and flexibility. In addition, the green ceramic tape prepared by casting molding has high tensile strength and low surface roughness, and the subsequent processes of punching, laminating and the like are convenient and simple, so that the green ceramic tape is suitable for preparing various components and functional substrates.

Preferably, the time of the primary ball milling is 6 to 10 hours.

Preferably, the time of the secondary ball milling is 16 to 20 hours.

Preferably, the thickness of the ceramic tape casting green tape is 20-200 microns, preferably 50-120 microns. The thickness of the ceramic tape casting green tape can be adjusted according to the tape casting process.

Preferably, the ceramic cast green tape has a solids content of not less than 70 wt%, preferably not less than 75 wt%.

Preferably, the tensile strength of the ceramic tape casting green tape is 1.5-3.0 MPa.

Preferably, the Cu electrode comprises copper powder, glass powder, a solvent and a binder; the Ni electrode comprises nickel powder, glass powder, a solvent and a binder. In a preferable example, the raw material components of the Cu electrode comprise 50-60 wt% of copper powder, 5-15 wt% of glass powder, 20-40 wt% of solvent and 2-4 wt% of binder, and the sum of the mass percentages of the components is 100 wt%. In a preferred example, the raw material components of the Ni electrode comprise 40-50 wt% of nickel powder, 2-10 wt% of glass powder, 40-60 wt% of solvent and 2-6 wt% of binder, and the sum of the mass percentages of the components is 100 wt%.

Preferably, the oxygen-free atmosphere is a neutral atmosphere or a reducing atmosphere; the neutral atmosphere is nitrogen atmosphere; the reducing atmosphere is hydrogen atmosphere or carbon monoxide atmosphere.

On the other hand, the invention also provides a low-temperature co-fired ceramic substrate prepared by the preparation method.

Has the advantages that:

the invention selects the polymethacrylate as the binder, has strong compatibility and environmental protection, realizes the binder removal under the conditions of low temperature (380-450 ℃) and reduction, and has excellent application prospect;

the green porcelain strip prepared by the method has the advantages of smooth and flat surface, high strength, simple preparation process and strong processing adaptability, and is suitable for batch production;

the low-temperature co-fired ceramic substrate prepared by the invention has the advantages of simple process flow, good repeatability and high controllability, and is suitable for mass production;

in addition, the low-cost base metal electrodes such as Cu and Ni which need to be sintered in a reducing atmosphere are also the application advantage of the polymethacrylate binder.

Drawings

FIG. 1 is a rheological profile of the casting slurry of example 1;

FIG. 2 is a tensile curve of the cast green tape of example 1;

FIG. 3 is a low temperature co-fired ceramic substrate prepared from the cast green tape of example 1;

FIG. 4 is a co-fired substrate of cast green tape and copper electrode of example 1;

FIG. 5 is an SEM image of a co-fired mating interface of a cast green tape and a copper electrode of example 1;

fig. 6 is a tensile curve of the cast green tape of example 3.

Detailed Description

The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.

In the disclosure, polymethacrylate is selected as a binder for the first time, and by utilizing the characteristic that polymethacrylate decomposes into volatile methacrylate monomers at high temperature (220-380 ℃), the polymethacrylate can realize the effects of removing completely and having little ash residue under neutral or reducing atmosphere, and is suitable for low-temperature co-fired ceramic substrates sintered under oxygen-free atmosphere (such as reducing atmosphere).

The following exemplarily illustrates a method for manufacturing a low temperature co-fired ceramic substrate provided by the present invention.

Preparation of ceramic casting slurries based on polymethacrylate binders. And mixing the ceramic powder, a dispersing agent, a solvent, a binder and a plasticizer to obtain the ceramic tape-casting slurry. The ceramic powder used is not particularly limited, and ceramic powders commonly used in the art may be used, and examples thereof include Ca-B-Si-O system ceramic powders, AlN ceramic powder ceramics + sintering aid system, and BaTiO₃Capacitor dielectric ceramic powder, SiC powder, and the like. The average particle size of the ceramic powder can be 700-1000 nm.

The solvent can be butanone, ethanol or isopropanol. The weight percentage of the ceramic tape-casting slurry can be 30-50%. Butanone with relatively low toxicity is used as a solvent, so that the cost is low and the environmental compatibility is good. In addition, the invention has relatively less solvent consumption and is especially suitable for preparing thick film ceramic material by a tape casting method.

The binder used may be a polymethacrylate. The weight percentage of the ceramic tape-casting slurry can be 5-15%, and the preferable weight percentage is 8-12.5%. When the weight percentage of the polymethacrylate binder is less than 5%, the raw porcelain tape is low in strength and fragile, and cannot be completely uncovered, and when the weight percentage of the polymethacrylate binder is more than 15%, the organic content in the raw porcelain tape is too high, so that the raw porcelain tape is extremely easy to deform. The polymethacrylate has a molecular weight of 17 to 37 ten thousand. Moreover, the ceramic tape casting slurry provided by the invention can effectively reduce the viscosity of the slurry, improve the tensile strength of the raw ceramic tape, and reduce the influence of residual impurities on the dielectric property of the raw ceramic tape, and the decomposition product is environment-friendly.

The dispersant can be tributyl phosphate, artificial fish oil, polyoxyalkylene polymer (MALIALIM series), etc. The weight percentage of the ceramic tape-casting slurry can be 0.2-2%, and preferably 0.5-1.5%.

The plasticizer can be one or more of Butyl Benzyl Phthalate (BBP), dioctyl phthalate (DOP), glycerol GL, polyethylene glycol (PEG), etc. The weight percentage of the ceramic tape-casting slurry can be 0-2%.

As a detailed example of the preparation of the ceramic casting slurry, it includes: (1) mixing the raw materials containing ceramic powder, solvent and dispersant, and then carrying out primary ball milling. The mass ratio of the mixture of the ceramic powder, the solvent and the dispersing agent to the grinding body can be 1: (3-4). The rotation speed of the primary ball milling can be 50-90 r/min, and the time can be 4-12 hours. (2) And adding a binder and a plasticizer into the slurry subjected to the primary ball milling, and carrying out secondary ball milling. Wherein the rotation speed of the secondary ball milling can be 60-120 r/min, and the time can be 12-24 hours. (3) And removing bubbles in the slurry subjected to secondary ball milling in vacuum to obtain the ceramic tape-casting slurry. Wherein, the parameter of vacuum bubble removal can be-30 to-42 kPa.

And carrying out casting molding on the ceramic casting slurry to obtain the ceramic casting green tape. The thickness of the ceramic tape casting green tape obtained by the invention can be 20-200 micrometers, and preferably 50-120 micrometers. The tensile strength of the ceramic tape casting green tape is 1.5-3.0 MPa according to the national standard GB/T1040.3-2006.

And (3) slicing the ceramic tape casting green porcelain tape, and stacking the ceramic tape casting green porcelain tape to a certain thickness by using a laminating machine to obtain a flaky biscuit. At the same time, at least one of a Cu electrode and a Ni electrode can be printed on a ceramic casting green ceramic tape, and the ceramic biscuit can be obtained after 15-35 MPa isostatic pressing.

And (3) finishing glue discharging of the ceramic tape or the sheet biscuit at low temperature (380-450 ℃) in air atmosphere or under reducing conditions. Wherein the temperature of the rubber discharge can be 0.5-2 hours. For example, the flaky biscuit is heated to 380-450 ℃ at a rate of 0.5-2 ℃/min and is kept for 60-120 minutes to remove organic matters.

Sintering the sheet biscuit or the ceramic tape casting green tape after the binder removal to obtain the low-temperature co-fired ceramic substrate. The parameters of sintering may be: heating to 850-900 ℃ at a rate of 2-5 ℃/min and keeping the temperature for 20-50 minutes.

When the sheet biscuit and the ceramic casting green ceramic band are selected without a Cu electrode or/and a Ni electrode, the glue discharging and sintering atmosphere is an air atmosphere or an oxygen-free atmosphere. When the sheet biscuit and the ceramic casting green ceramic band are selected to be provided with the Cu electrode or/and the Ni electrode, the glue discharging and sintering atmosphere is only an oxygen-free atmosphere so as to avoid the oxidation of the electrodes.

The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.

Example 1

The embodiment provides a processing method of electronic ceramic casting slurry, which comprises the following steps:

(1) according to a predetermined proportion, a Ca-B-Si-O system (42 percent of CaO-26 percent of B)₂O₃-32％SiO₂) And carrying out primary ball milling on the ceramic powder, the solvent and the dispersing agent for 6 hours. The mass ratio of the raw materials to the grinding body is 1: 3. the used solvent is butanone/ethanol, and the addition amount of the solvent in the casting slurry is 80 percent of the mass of the ceramic powder. The dispersant is MALIALIIM (AKM0531, Japan), and the addition amount is 1% of the mass of the ceramic powder;

(2) and adding a binder into the ball milling tank, carrying out secondary ball milling for 16 hours to obtain the ceramic tape casting slurry. The binder used was polymethacrylate (M6003, japan), and the amount added was 12.5% by mass of the ceramic powder. The plasticizer is Butyl Benzyl Phthalate (BBP), and the addition amount of the plasticizer is 2.5% of the mass of the ceramic powder.

The ceramic tape-casting slurry prepared by the method is used for tape-casting a ceramic green tape with the thickness of 120 microns on a full-automatic tape-casting machine. Wherein the ceramic green ceramic tape and the PET carrier film are well wetted, the solid phase amount of the green ceramic tape reaches 86 percent, and the density of the green ceramic tape is about 1.33g/cm³And has good tensile strength and flexibility.

The slurry of example 1 was tested for rheological properties using a rheometer and exhibited shear thinning and a pseudoplastic fluid type.

The tensile property of the green porcelain tape is detected by using a universal material testing machine, the tensile strength of the green porcelain tape prepared by casting the slurry described in the embodiment 1 is 2.5MPa, and the fracture deformation is less than 10%, so that the later punching and cutting are facilitated.

The green tape obtained by casting the slurry described in example 1 was taken off from the carrier tape, laminated to a certain thickness by a lamination machine, subjected to isostatic pressing, cut into square green bodies, and placed in a high-temperature sintering furnace for binder removal and sintering in an air atmosphere. The glue discharging temperature is 450 ℃, the heating rate is 2 ℃/min, and the temperature is kept for 120 minutes. After the glue is discharged, the temperature is raised to 890 ℃ at the heating rate of 5 ℃/min, and the temperature is kept for 30 minutes to obtain the flat and smooth ceramic substrate.

Fig. 1 is a rheological curve of the casting slurry of example 1. It can be seen from the figure that the slurry exhibits good shear-thinning properties, and the viscosity rapidly decreases as the slurry passes the doctor blade, which is more advantageous for the slurry casting process. FIG. 2 is a tensile curve of the cast green tape of example 1, where sample 1 and sample 2 are repeatability test data; FIG. 3 is a ceramic substrate prepared from the cast green tape of example 1.

The green tape obtained by casting the slurry described in example 1 was taken off from the carrier tape, stacked to a certain thickness by a lamination machine, subjected to isostatic pressing, cut into square green bodies, and placed in a high-temperature sintering furnace for binder removal and sintering in a reducing atmosphere (hydrogen atmosphere). And, prior to the discharge of the paste, green ceramic tapes printed with copper electrodes (C-4178 conductive paste manufactured by SHOEI CHEMICAL INC, japan) were laminated in a square biscuit. The glue discharging temperature is 450 ℃, the heating rate is 2 ℃/min, and the temperature is kept for 120 minutes. After the glue is removed, the temperature is raised to 890 ℃ at the heating rate of 5 ℃/min, and the temperature is kept for 30 minutes to obtain a flat and smooth ceramic substrate sintered with a Cu electrode, which is shown in figure 4. FIG. 5 is an SEM image of the co-fired mating interface of the cast green tape and the copper electrode of example 1, showing that the co-fired mating is good and there is no diffusion reaction.

Comparative example 1

The procedure for preparing the electroceramic casting slurry in this comparative example 1 is as in example 1, except that: the adhesive is polyvinyl butyral (PVB). The experiment shows that: when LTCC ceramic powder consisting of borosilicate glass is used as a raw material, a slurry system is easy to flocculate and cannot be stably cast into a ceramic green tape in batches; if toluene or xylene is used as a solvent, the casting forming can be carried out, but the slurry has high viscosity, is not friendly to the environment and personnel, has large odor of the raw porcelain tape, and is not beneficial to batch preparation and production.

Example 2

The procedure for the preparation of the electroceramic casting slurry in this example 2 is as in example 1, except that: the content of polymethacrylate was 5 wt%. The ceramic tape prepared by the ceramic tape casting slurry prepared in the embodiment is cast on a full-automatic tape casting machine to form a ceramic green tape with the thickness of 120 microns. The ceramic green porcelain has partial cracks, cannot be completely peeled from the PET carrier film, and has poor tensile strength and flexibility.

Example 3

The procedure for the preparation of the electroceramic casting slurry in this example 3 is as in example 1, except that: the polymethacrylate content was 15 wt%. The ceramic tape prepared by the ceramic tape casting slurry prepared in the embodiment is cast on a full-automatic tape casting machine to form a ceramic green tape with the thickness of 120 microns. The ceramic green tape and the PET carrier film are well wetted, but due to the increase of the content of the binder, the solid phase amount of the green tape is reduced, the flexibility is higher, the tensile strength is lower (0.45MPa), the green tape is easy to deform (the fracture deformation is 72%), and the later processing is not facilitated, as shown in FIG. 6.

FIG. 6 is a tensile curve of the cast green tape of example 3, showing that the cast green tape of example 3 has a lower tensile strength and a higher elastic deformation.

Example 4

The procedure for the preparation of the electroceramic casting slurry in this example 4 is as in example 1, except that: the polymethacrylate content was 8 wt%. The ceramic tape prepared by the ceramic tape casting slurry prepared in the embodiment is cast on a full-automatic tape casting machine to form a ceramic green tape with the thickness of 120 microns. Wherein, the ceramic green porcelain tape and the PET carrier film have good wetting performance and no cracks and other defects. The tensile properties of the green tape were tested by a universal material testing machine, and it was determined that the green tape produced by casting the slurry described in example 4 had a tensile strength of 1.5MPa and a fracture set of 5%.