Silver paste for high-strength low-temperature co-fired ceramic and preparation method thereof

Abstract

The invention discloses silver paste for high-strength low-temperature co-fired ceramic and a preparation method of the silver paste. The silver paste is formed by rolling silver powder, inorganic glass powder, an additive and an organic carrier. Wherein the inorganic glass powder is prepared from the following components: CaO, B2O3, SiO2, MgO, AlF3 and ZrO2; the additive is selected from at least one of Cu, Cu2O, CuO or any compound capable of generating Cu2O or CuO during sintering. In the substrate sintering process, the inorganic glass powder drives the silver powder to shrink along with the rising of the sintering temperature, the shrinkage rate and the shrinkage speed of the silver paste are controlled to be matched with the high-strength LTCC material, and the substrate high in flatness and small in warping degree is prepared. The additive generates copper oxide or cuprous oxide during sintering, so that the binding force between the silver paste and the ceramic is increased, the adhesive force of the film layer is improved, and meanwhile, the weldability of the sintered silver film layer is improved due to the existence of the additive.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic materials, and in particular relates to a silver paste for high-strength low-temperature co-fired ceramics and a preparation method thereof. Background Art

[0002] Low temperature co-fired ceramic (LTCC) technology is a ceramic packaging technology used to integrate high-frequency and high-speed digital circuits, passive devices and chips. It can achieve miniaturization, lightweight and multifunctionality of electronic components and is widely used in aerospace, new energy vehicles, 5G communications, smart terminals and the Internet of Things. As silver electrode slurry has excellent electrical and thermal conductivity, can be sintered in air, and has relatively low cost, it is used as a key raw material in the processing and production of LTCC substrates and LTCC chip components (antennas, filters, duplexers, baluns, etc.), promoting the rapid development of LTCC technology.

[0003] At present, silver paste is used for metallization of LTCC substrates. Generally, attention should be paid to the matching of silver paste and substrate, the adhesion of sintered film layer and the solderability of silver film layer. For silver paste used in high-strength LTCC material system, the mismatch between silver paste and high-strength LTCC green ceramic sintering causes substrate warping, low adhesion of silver film layer and poor solderability. Therefore, it is urgent to develop a new type of silver paste to be used with high-strength LTCC green ceramic to solve the problems of substrate warping, low adhesion and poor solderability. Summary of the invention

[0004] In view of this, it is necessary for the present invention to provide a silver paste for high-strength, low-temperature co-fired ceramics. The scheme adopts inorganic glass powder and additives to jointly control the matching between the silver paste and the high-strength LTCC material system. The prepared LTCC substrate has good flatness, strong bonding between the sintered silver film layer and the ceramic, and excellent solderability of the silver film layer.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention provides a silver paste for high-strength low-temperature co-fired ceramics, which is rolled from 70-85wt% silver powder, 0.1-5% inorganic glass powder, 0.1-3% additives and the balance organic carrier;

[0007] Wherein, the inorganic glass powder is composed of CaO, B 2 O 3 、SiO 2 、MgO、AlF 3 and ZrO 2 The components are as follows: CaO is 20-40%, B2 O 3 15~35%, SiO 2 25-40%, MgO 3-10%, AlF 3 0.1~5%, ZrO 2 It is 0.1~5%.

[0008] Preferably, the inorganic glass powder has a D50 of 1.5 to 3.5 μm and a softening point of 420 to 650° C.

[0009] The additive is selected from Cu, Cu 2 O, CuO and Cu can be generated during sintering 2 At least one of any compound of O or CuO.

[0010] In a further embodiment, the silver powder is a mixture of one or more of spherical silver powder, flaky silver powder, linear silver powder, and irregular silver powder.

[0011] Preferably, the silver powder is selected from spherical silver powder, the D50 of the spherical silver powder is 0.5-3.5 μm, and the tap density is 4.5-6.8 g / cm 3 The greater the tap density of the silver powder, the smaller the sintering shrinkage, and it is easier to form a tight conductive network.

[0012] In a further embodiment, the organic carrier comprises, by mass percentage, 5-25% of thickener, 60-90% of solvent, and 3-20% of organic additive.

[0013] In a further embodiment, the thickener is selected from at least one of ethyl cellulose, nitrocellulose, polyvinyl butyral, acrylic resin, and epoxy resin.

[0014] In a further embodiment, the solvent is selected from at least one of diethylene glycol butyl ether, diethylene glycol butyl ether acetate, DBE, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and terpineol.

[0015] In a further embodiment, the organic auxiliary agent is selected from at least one of a dispersant, a leveling agent, a plasticizer, a thixotropic agent, and a defoaming agent.

[0016] The present invention further discloses a method for preparing the silver paste as described above, comprising the following steps:

[0017] The silver powder, inorganic glass powder, additives and organic carrier are fully mixed according to the proportion to obtain a slurry;

[0018] The slurry is rolled for multiple times until the slurry fineness reaches the requirement of screen printing to obtain silver slurry.

[0019] In a further embodiment, the preparation process of the inorganic glass powder is: after the components in the inorganic glass powder are evenly mixed, the mixture is subjected to high-temperature melting, water quenching, ball milling, drying, and sifting through a 300-mesh sieve for later use; and / or, the preparation process of the organic carrier is: after the components in the organic carrier are evenly mixed, the mixture is heated and stirred at 50-100° C. until a uniform paste is formed, and then cooled to room temperature for later use.

[0020] The present invention has the following beneficial effects:

[0021] The present invention adopts the method of the inorganic glass powder and the additive acting together. During the sintering of the substrate, as the sintering temperature increases, the inorganic glass powder drives the silver powder to shrink, and the shrinkage rate and shrinkage speed of the silver paste are controlled to match the high-strength LTCC material to prepare a substrate with high flatness and small warpage. The additive generates cupric oxide or cuprous oxide during sintering, which increases the bonding force between the silver paste and the ceramic and improves the adhesion of the film layer. At the same time, the presence of the additive improves the solderability of the silver film layer after sintering. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a printing effect diagram of the silver paste prepared in Example 1. DETAILED DESCRIPTION

[0023] In order to describe the embodiments of the present invention in detail below, the embodiments described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0025] The present invention provides a silver paste for high-strength low-temperature co-fired ceramics, which is rolled from 70-85wt% silver powder, 0.1-5% inorganic glass powder, 0.1-3% additives and the balance organic carrier;

[0026] Wherein, the inorganic glass powder is composed of CaO, B 2 O 3 、SiO 2 、MgO、AlF 3 and ZrO 2 The components are as follows: CaO is 20-40%, B 2 O 3 15~35%, SiO 2 25-40%, MgO 3-10%, AlF 3 0.1~5%, ZrO2 The high strength low temperature co-fired ceramic material is composed of CaO, B 2 O 3 、SiO 2 、MgO、AlF 3 、ZrO 2 Composition of inorganic glass powder and Al 2 O 3 The raw ceramic material is formed by tape casting with powders in different proportions. In order to match the high-strength and low-temperature co-fired ceramic material, the composition of the inorganic glass powder in the silver paste needs to be similar to that in the high-strength and low-temperature co-fired ceramic material to reduce the occurrence of adverse chemical reactions and increase the sintering matching between the silver paste and the ceramic material.

[0027] Preferably, the D50 of the inorganic glass powder is 1.5-3.5 μm, and the softening point is 420-650° C. On the one hand, the D50 of the inorganic glass powder is related to the dispersibility of the slurry. If the D50 of the inorganic glass powder is less than 1.5 μm, the powder particle size is small, easy to agglomerate, and the dispersibility is poor; if the D50 of the inorganic glass powder is greater than 3.5 μm, the powder particle size is large, and when the silver slurry is sintered, the inorganic glass powder cannot be evenly dispersed between the silver powder particles, and the effect of evenly wetting the silver powder cannot be achieved. On the other hand, to select suitable glass powder to adjust the sintering behavior of the slurry, it is necessary to control the softening point temperature of the inorganic glass powder. Too low or too high softening point temperature is not conducive to the sintering of the silver paste. If the glass softening point temperature is too low, it means that the glass powder can start to flow at a lower temperature. When the slurry is sintered, there is a risk of the inorganic glass powder floating, affecting the welding performance of the silver paste. If the glass powder softening point temperature is too high, it cannot soften and melt in time during the heating process, and cannot fully fill the gaps between the silver powder particles.

[0028] The additive is selected from Cu, Cu 2 O, CuO and Cu can be generated during sintering 2 At least one of any compounds of O or CuO. The addition of the additive improves the sintering effect between the silver powder and the inorganic glass powder, strengthens the bonding force between the silver film layer and the LTCC substrate, inhibits the floating of the inorganic glass powder, and improves the solderability of the silver film layer.

[0029] In a further embodiment, the silver powder is a mixture of one or more of spherical silver powder, flaky silver powder, linear silver powder, and irregular silver powder.

[0030] Preferably, the silver powder is selected from quasi-spherical silver powder, the D50 of the quasi-spherical silver powder is 0.5-3.5 μm, and the tap density is 4.5-6.8 g / cm 3 .

[0031] In a further embodiment, the organic carrier comprises, by mass percentage, 5-25% of thickener, 60-90% of organic solvent, and 3-20% of organic additive.

[0032] In a further embodiment, the thickener is selected from at least one of ethyl cellulose, nitrocellulose, polyvinyl butyral, acrylic resin, and epoxy resin.

[0033] In a further embodiment, the organic solvent is selected from at least one of diethylene glycol butyl ether, diethylene glycol butyl ether acetate, DBE, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and terpineol; and the organic additive is selected from at least one of a dispersant, a leveling agent, a plasticizer, a thixotropic agent, and a defoaming agent. It is understood that the selection of solvents and organic additives is not limited to the above examples, and any conventionally used in the art can be used.

[0034] The second aspect of the present invention provides a method for preparing the silver paste as described in the first aspect of the present invention, comprising the following steps:

[0035] Silver powder, inorganic glass powder, additives and organic carrier are fully mixed according to the ratio to obtain slurry; the mixing method is not particularly limited, such as high-speed stirring. In some typical embodiments of the present invention, stirring is performed at a speed of 600 to 2000 rpm for 2 to 20 minutes.

[0036] The slurry is rolled for multiple times until the slurry fineness meets the requirements of screen printing to obtain silver slurry. It is understood that the slurry can be rolled using a three-roller mill, and the specific number of times is not particularly limited, as long as the slurry fineness meets the requirements.

[0037] Among them, the preparation of inorganic glass powder and organic carrier can be carried out according to the process well known to those skilled in the art. In some typical embodiments of the present invention, the preparation process of the inorganic glass powder is: after the components in the inorganic glass powder are evenly mixed, high-temperature melting, water quenching, ball milling, drying, and passing through a 300-mesh sieve for use; and / or, the preparation process of the organic carrier is: after the components in the organic carrier are evenly mixed, heating and stirring at 50-100°C until a uniform paste is formed, and then cooling to room temperature for use.

[0038] The present invention is described below by means of specific examples. It should be noted that the following specific examples are only for illustrative purposes and do not limit the scope of the present invention in any way. In addition, unless otherwise specified, methods without specific conditions or steps are conventional methods, and the reagents and materials used can be obtained from commercial channels.

[0039] Example 1

[0040] This embodiment discloses a silver paste for high-strength low-temperature co-fired ceramics. The silver paste comprises the following components by mass percentage: 74% silver powder, D50 of 1.7 μm, and a tap density of 5.1 g / cm 3 , inorganic glass powder 5%, D50 is 2.9μm, softening point temperature is 620℃, additives are 1%, organic carrier is 20%. Among them, the components of inorganic glass powder are as follows: CaO is 30%, B 2 O 3 29%, SiO 2 30%, MgO 5%, AlF 3 is 3%, ZrO 2 The organic carrier is 3%; the additive is 1% copper powder. The organic carrier is calculated by mass percentage of the total raw materials, and the thickener is 2.8% ethyl cellulose, 1.2% acrylic resin, the organic solvent is 7% pine alcohol, 7% diethylene glycol butyl ether, and the organic additive is 1% fish oil and 1% lecithin.

[0041] The preparation method of the silver paste comprises the following specific steps:

[0042] Preparation of inorganic glass powder: Inorganic oxides are weighed in proportion and stirred and mixed, and then melted at high temperature, quenched with water, ball milled, dried, and passed through a 300-mesh sieve for later use;

[0043] Preparation of organic carrier: weigh thickener, organic solvent and organic additive according to proportion, add into double-layer glass reactor, first add organic solvent and organic additive and stir evenly, set heating temperature to 70°C, stirring speed to 240r / min, then slowly add thickener while stirring until a uniform paste is formed, cool to room temperature for use;

[0044] Preparation of silver paste: weigh organic carrier, inorganic glass powder, additives and silver powder into a mixing tank according to the ratio, put the mixing tank into a homogenizer, and stir at high speed to make them evenly mixed, wherein the stirring speed is 1000r / min, and the stirring time is 10 minutes; the mixed slurry is rolled into a paste slurry with a three-roll machine until the slurry fineness meets the requirements of screen printing to obtain the required silver paste.

[0045] Figure 1 This is a printing effect diagram of the silver paste prepared in Example 1, and it can be seen that the silver paste has excellent printing performance.

[0046] Example 2

[0047] The proportions of the components of the inorganic glass powder and the preparation method of the silver paste in this embodiment are the same as those in Example 1, except that the types and proportions of the silver paste components are different, as shown in Table 1.

[0048] Example 3

[0049] The proportions of the components of the inorganic glass powder and the preparation method of the silver paste in this embodiment are the same as those in Example 1, except that the types and proportions of the silver paste components are different, as shown in Table 1.

[0050] Example 4

[0051] The composition, proportion and preparation method of the silver paste in this embodiment are the same as those in embodiment 1, except that the components of the inorganic glass powder are respectively as follows: CaO is 38%, B 2 O 3 15%, SiO 2 38%, MgO 3%, AlF 3 is 5%, ZrO 2 It is 1%, as shown in Table 1 for details.

[0052] Example 5

[0053] The composition, proportion and preparation method of the silver paste in this embodiment are the same as those in embodiment 1, except that: the components of the inorganic glass powder are respectively as follows: CaO is 20%, B 2 O 3 35%, SiO 2 35%, MgO 5%, AlF 3 is 4%, ZrO 2 It is 1%, as shown in Table 1 for details.

[0054] Comparative Example 1

[0055] The proportions of the inorganic glass powder components and the preparation method of the silver paste in this comparative example are the same as those in Example 1, except that the types and proportions of the silver paste components are different, as shown in Table 1.

[0056] Comparative Example 2

[0057] The proportions of the inorganic glass powder components and the preparation method of the silver paste in this comparative example are the same as those in Example 1, except that the types and proportions of the silver paste components are different, as shown in Table 1.

[0058] Comparative Example 3

[0059] The proportions of the inorganic glass powder components and the preparation method of the silver paste in this comparative example are the same as those in Example 1, except that the types and proportions of the silver paste components are different, as shown in Table 1.

[0060] Comparative Example 4

[0061] The composition, proportion and preparation method of the silver paste in this comparative example are the same as those in Example 1, except that the components of the inorganic glass powder are respectively as follows: CaO is 30%, B 2 O 3 29%, SiO2 30%, MgO 5%, Al 2 O 3 is 3%, ZrO 2 It is 3%, as shown in Table 1 for details.

[0062] Table 1 Composition and ratio of silver paste

[0063]

[0064]

[0065] The above Examples 1 to 3 and Comparative Examples 1 to 3 were tested for performance, and the results are shown in Table 2:

[0066] Table 2 Performance test of silver paste

[0067]

[0068] It can be seen from the results in Table 2 that, compared with Comparative Examples 1 to 4, the inorganic glass powder in Examples 1 to 5 provides a stronger bonding force between the silver paste and the LTCC substrate, and the inorganic glass powder and the additives work together to inhibit the floating of the inorganic glass powder, thereby avoiding the problem of reduced solderability of the silver film layer caused by the floating of the inorganic glass powder.

[0069] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0070] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A silver paste for high-strength low-temperature co-fired ceramics, characterized in that: It is rolled from 70-85wt% silver powder, 0.1-5% inorganic glass powder, 0.1-3% additives and the balance organic carrier; The inorganic glass powder comprises the following components by mass percentage: 20-40% CaO, 15-35% B2O3, 25-40% SiO2, 3-10% MgO, 0.1-5% AlF3, and 0.1-5% ZrO2; The additive is selected from at least one of Cu, Cu2O, CuO or any compound capable of generating Cu2O or CuO during sintering.

2. The silver paste for high-strength low-temperature co-fired ceramics according to claim 1, characterized in that: The inorganic glass powder has a D50 of 1.5 to 3.5 μm and a softening point of 420 to 650° C.

3. The silver paste for high-strength low-temperature co-fired ceramics according to claim 1, characterized in that: The silver powder is selected from spherical silver powder, the D50 of the spherical silver powder is 0.5-3.5 μm, and the tap density is 4.5-6.8 g / cm3.

4. The silver paste for high-strength low-temperature co-fired ceramics according to claim 1, characterized in that: The organic carrier comprises the following components by mass percentage: 5-25% of a thickener, 60-90% of an organic solvent and 3-20% of an organic auxiliary agent.

5. The silver paste for high-strength low-temperature co-fired ceramics according to claim 4, characterized in that: The thickener is selected from at least one of ethyl cellulose, nitrocellulose, polyvinyl butyral, acrylic resin and epoxy resin.

6. The silver paste for high-strength low-temperature co-fired ceramics according to claim 4, characterized in that: The organic solvent is selected from at least one of diethylene glycol butyl ether, diethylene glycol butyl ether acetate, DBE, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate, and terpineol.

7. The silver paste for high-strength low-temperature co-fired ceramics according to claim 4, characterized in that: The organic auxiliary agent is selected from at least one of a dispersant, a leveling agent, a plasticizer, a thixotropic agent, and a defoaming agent.

8. The method for preparing the silver paste according to any one of claims 1 to 7, characterized in that: The following steps are involved: The silver powder, inorganic glass powder, additives and organic carrier are fully mixed according to the proportion to obtain a slurry; The slurry is rolled for multiple times until the slurry fineness reaches the requirement of screen printing to obtain silver slurry.

9. The preparation method according to claim 8, characterized in that: The preparation process of the inorganic glass powder is as follows: after the components of the inorganic glass powder are uniformly mixed, the mixture is melted, water quenched, ball milled, dried, and sieved for later use; And / or, the preparation process of the organic carrier is: after uniformly mixing the components in the organic carrier, heating and stirring at 50-100° C. until a uniform paste is formed, cooling to room temperature for use.

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