阅读说明：本技术 一种氮化铝用环保型银导体浆料 (Environment-friendly silver conductor paste for aluminum nitride ) 是由 赵科良 党丽萍 孙社稷 王顺顺 高辉 张建益 张亚鹏 刘琪瑾 于 2021-09-06 设计创作，主要内容包括：本发明公开了一种氮化铝用环保型银导体浆料,其由以下重量百分比的成分组成：70%～82%银粉、1%～5%玻璃粉、硼酰化钴1%～3%、锂冰晶石1%～3%、10%～20%有机载体。本发明导体浆料安全环保,不含铅和铋,其借助锂冰晶石在高温下可与氮化铝基体强结合而作为附着力粘合剂,采用微量的硼酰化钴作为烧结表面浸润剂,可有效的提高导体浆料与氮化铝基体的浸润性,使浆料和基板的结合更充分,具有附着力好、导电性能好的特点,同时对基体也不会造成污染,可满足丝网印刷的工艺要求。(The invention discloses an environment-friendly silver conductor paste for aluminum nitride, which comprises the following components in percentage by weight: 70-82% of silver powder, 1-5% of glass powder, 1-3% of cobalt boroacylate, 1-3% of lithium cryolite and 10-20% of organic carrier. The conductor paste is safe and environment-friendly, does not contain lead and bismuth, can be strongly combined with an aluminum nitride matrix at high temperature by means of lithium cryolite to serve as an adhesive force adhesive, adopts trace cobalt boroacylate as a sintering surface impregnating compound, can effectively improve the wettability of the conductor paste and the aluminum nitride matrix, enables the combination of the paste and a substrate to be more sufficient, has the characteristics of good adhesive force and good conductivity, does not cause pollution to the matrix, and can meet the process requirement of screen printing.)

1. The environment-friendly silver conductor paste for aluminum nitride is characterized by comprising the following components in percentage by weight:

70-82% of silver powder, 1-5% of glass powder, 1-3% of cobalt boroacylate, 1-3% of lithium cryolite and 10-20% of organic carrier;

the glass powder is composed of B₂O₃、SiO₂、Al₂O₃、ZnO、BaO。

2. The environmentally friendly silver conductor paste for aluminum nitride according to claim 1, wherein: the silver powder is spherical silver powder, the average particle diameter of the silver powder is 1.0-2.5 mu m, and the tap density of the silver powder is 4.5-5.5 g/cm³。

3. The environmentally friendly silver conductor paste for aluminum nitride according to claim 1, wherein: the average particle size of the cobalt boroacylate is 1.0-2.5 mu m, and the average particle size of the lithium cryolite is 0.5-3.0 mu m.

4. The environment-friendly silver conductor paste for aluminum nitride according to claim 1, wherein the glass powder has an average particle size of 1.0 to 1.8 μm, and comprises, in weight percent: 1% -5% of B₂O₃、30%～47%SiO₂、7%～22%Al₂O₃、6%～20%ZnO、15%～28%BaO。

5. The environmentally friendly silver conductor paste for aluminum nitride according to claim 1, wherein: the organic carrier is composed of the following raw materials in percentage by weight: 5-15% of resin, 1-5% of organic additive and 80-93% of organic solvent.

6. The environmentally friendly silver conductor paste for aluminum nitride according to claim 5, wherein: the resin is one or more of rosin resin, maleic acid resin, polyvinyl butyral and ethyl cellulose.

7. The environmentally friendly silver conductor paste for aluminum nitride according to claim 5, wherein: the organic additive is one or a mixture of hydrogenated castor oil and polyethylene wax.

8. The environmentally friendly silver conductor paste for aluminum nitride according to claim 5, wherein: the organic solvent is any one or a mixture of more than two of terpineol, diethylene glycol dibutyl ether and butyl carbitol acetate.

Technical Field

The invention belongs to the technical field of silver conductor paste, and particularly relates to environment-friendly silver conductor paste for aluminum nitride.

Background

In recent years, along with the improvement of the integration level of a high-power module circuit, higher requirements are correspondingly put forward on an insulating substrate, and mature ceramic materials with high thermal conductivity at the present stage comprise beryllium oxide, aluminum nitride and silicon carbide, wherein the beryllium oxide is toxic and not beneficial to environmental protection, the silicon carbide has a high dielectric constant and is not suitable for a thick-film ceramic substrate, and the aluminum nitride ceramic material has high thermal conductivity and good electrical performance, so that the aluminum nitride ceramic material is widely applied to various high-power products and becomes an ideal heat dissipation substrate and packaging material of an integrated circuit.

Although aluminum nitride has many excellent properties, it has some limitations in practical application, and besides the process for preparing the aluminum nitride substrate itself is not mature enough, there is a lack of electronic paste which is fully applied to aluminum nitride or aluminum nitride-containing substrates, and the commercialized aluminum oxide electronic paste cannot be fully applied to aluminum nitride substrates.

Silver conductor pastes for aluminum nitride are required to exhibit high stability and excellent adhesion to aluminum nitride substrates, especially after aging.

In the known technical invention applied to the conductor paste of the aluminum nitride matrix, a low-melting-point glass powder of a bismuth borosilicate system (for example, Chinese patent CN 104715805A) and a conventional boron-containing compound (for example, Chinese patent ZL96110998.X and ZL 02819782.8) are adopted as the conductor paste of the aluminum nitride matrix. Because the bismuth-containing glass can react with the aluminum nitride ceramic matrix violently in the sintering process, a large amount of gas is generated to enable the conductor sintering film to form bubbles, and the use of the aluminum nitride matrix cannot be met due to poor process control. Conventional boron-containing compounds do provide good adhesion to aluminum nitride silver pastes because of the good bond strength produced by the reaction of borides with the ceramic matrix of the filter. However, the boride has high hardness, is not easy to roll in the slurry production process, cannot be uniformly dispersed in the whole slurry system, and is easy to burn and cause poor weldability of silver slurry after sintering, so that the conductor slurry has uneven tension and the product tension fails.

Disclosure of Invention

The invention aims to provide the environment-friendly silver conductor paste for the aluminum nitride, which improves the adhesive force and effectively reduces the reliability loss after aging, and the silver paste does not contain lead and is safe and environment-friendly.

The invention relates to an environment-friendly silver conductor paste for aluminum nitride, which comprises the following raw materials in percentage by weight:

70-82% of silver powder, 1-5% of glass powder, 1-3% of cobalt boroacylate, 1-3% of lithium cryolite and 10-20% of organic carrier.

The silver powder is spherical silver powder, and has an average particle diameter of 1.0 to 2.5 μm and a tap density of 4.5 to 5.5g/cm³。

The cobalt boroacylate has an average particle diameter of 1.0 to 2.5 μm and the lithium cryolite has an average particle diameter of 0.5 to 3.0. mu.m.

The composition of the glass powder is B₂O₃、SiO₂、Al₂O₃ZnO and BaO, the average particle diameter of which is 1.0 to 1.8 μm. The concrete weight percentage composition is as follows: 1% -5% of B₂O₃、30%～47%SiO₂、7%～22%Al₂O₃、6%～20%ZnO、15%～28%BaO。

The organic carrier consists of the following raw materials in percentage by weight: 5-15% of resin, 1-5% of organic additive and 80-93% of organic solvent. The resin is one or more of rosin resin, maleic resin, polyvinyl butyral and ethyl cellulose, the organic additive is one or a mixture of hydrogenated castor oil and polyethylene wax, and the organic solvent is one or a mixture of more than two of terpineol, diethylene glycol dibutyl ether and butyl carbitol acetate.

The invention has the following beneficial effects:

1. the conductor paste does not adopt bismuth-containing glass powder and bismuth-containing compounds, so that the conductor paste is prevented from losing efficacy due to the bubbling phenomenon caused by the violent reaction of bismuth oxide and an aluminum nitride matrix in the sintering process.

2. According to the invention, the lithium cryolite is introduced as an adhesive force adhesive, so that the conductor slurry is more fully combined with the aluminum nitride matrix, and the adhesion force is obviously improved after sintering. The chemical formula of lithium cryolite is LiNa₃Al₂F₁₂Usually, it is a monoclinic system and is converted into a tetragonal system at 565 to 600 ℃. Generally, the conductive paste is a compact and granular structure, and the conductive paste starts to melt and infiltrate into an aluminum nitride matrix at 650 ℃ to form stronger bonding strength with the aluminum nitride matrix, so that the effect of improving the adhesive force of the conductive paste is achieved.

3. According to the invention, a certain amount of cobalt boroacylate is added as a sintering surface impregnating compound, so that the wettability of the conductor slurry and the aluminum nitride matrix can be effectively improved, the combination is more sufficient, and the tensile force after sintering is obviously improved.

4. According to the invention, the conductor slurry is simultaneously added with the lithium cryolite serving as an adhesive force adhesive and the cobalt boroacylate serving as a sintering impregnating compound, and the wetting property of the conductor slurry and an aluminum nitride matrix can be improved by matching the lithium cryolite and the cobalt boroacylate, so that the slurry and the substrate are combined more sufficiently and form stronger combination with the aluminum nitride matrix, and meanwhile, the influence of component pollution on the matrix material is avoided. The slurry has the advantages of simple preparation process, no lead, environmental protection, little pollution and good adhesive force, is mainly applied to the manufacture of integrated circuits to form a conductive network, has strong adhesive force and good conductivity of electrodes, and can be directly welded for use.

Drawings

Fig. 1 is a graph of a printing screen made by conducting paste performance testing. Wherein region 1 is used for adhesion and film thickness testing, region 2 is used for resistance testing, and region 3 is used for solderability testing.

FIG. 2 is a 2000-fold surface SEM image of sintered conductive pastes of example 5, comparative example 1 and commercial boron-containing compound.

Detailed Description

The invention will be further described in detail with reference to the following figures and examples, but the scope of the invention is not limited to these examples.

Examples

According to the weight percentage composition of the table 1, the tap density of the average grain diameter of 1.0 to 2.5 mu m is 4.5 to 5.5g/cm³The silver paste is prepared by rolling and grinding spherical silver powder, glass powder with the average particle size of 1.0-1.8 mu m, cobalt boroacylate with the average particle size of 1.0-2.5 mu m, lithium cryolite with the average particle size of 0.5-3.0 mu m and an organic carrier to prepare a paste mixture, and then filtering the paste mixture by using a 325-mesh filter screen cloth to obtain 100g of silver conductor paste with the fineness of less than or equal to 10 mu m. Wherein, the preparation of the glass powder comprises the following steps: 3.5g B₂O₃、43g SiO₂、16g Al₂O₃Uniformly mixing 15.5g of ZnO and 22g of BaO, drying in an oven at 150 ℃ for 2 hours, then smelting at 1250 ℃ for 2 hours, water-quenching the uniformly molten glass to obtain coarse glass particles, adding the coarse glass particles into a polyurethane tank, ball-milling for 12 hours, and drying at 125 ℃ to obtain glass powder with the average particle size of 1.0-1.8 mu m; the preparation method of the organic carrier comprises the following steps: heating 85g of terpineol to 70 ℃, slowly adding 3g of rosin resin, 10g of ethyl cellulose and 2g of hydrogenated castor oil under the condition of stirring, fully and uniformly stirring, and continuously stirring for 30 minutes to obtain the organic carrier.

TABLE 1

Meanwhile, 100g of silver conductor paste is prepared by the method according to the weight percentage composition of comparative examples 1-3 in the table 1, and a control experiment is carried out.

The silver conductor paste prepared in the above examples 1 to 6 and comparative examples 1 to 3 was printed on an aluminum nitride substrate by a screen printing process, respectively, after natural leveling for 10min, dried at 150 ℃ for 10min, the sample was sintered in a belt sintering furnace at 850 ± 5 ℃ for 80min for a sintering period and 12min for peak heat preservation, and the following performance tests were performed after a test sample was prepared.

1. And (3) sintering surface appearance: the surface state of the sintered film of the obtained sample was observed by SEM magnification of 2000 times, see fig. 2;

2. initial adhesion: and welding the wire plane with the diameter of 0.8mm on a pattern of a position 1 of a sample as shown in figure 1, and performing an initial adhesion test by using a tensile machine after the wire is bent by 90 degrees.

3. Aging adhesion: and placing the welded sample in a drying oven at 150 +/-5 ℃ for 96 hours, taking out the sample, bending the lead at 90 degrees, and carrying out aging adhesion test by using a tensile machine.

4. Weldability: a standard solder block having a diameter of 4mm and a thickness of 2.85mm was placed at the position 3 in FIG. 1, and the diffusion area was measured after placing the solder block at 220. + -. 3 ℃ under 62Sn/36Pb/2Ag for 5 seconds.

5. Square resistance value: and (3) overlapping two ends of the digital multimeter at two ends of a line segment at the position 2 in the figure 1, testing the resistance value of the sample, and calculating the square resistance value under the corresponding film thickness.

The test results are shown in table 2. And the conductor paste of example 5 was compared to a commercial boron-containing conductor paste (dupont ALN 11).

TABLE 2

As can be seen from Table 2, the silver conductor paste prepared in the embodiments 1-6 of the invention has good initial adhesion, good tensile force after aging, and high product reliability; comparing examples 1-6 with comparative examples 1-3, it is obvious that the adhesion of the conductor paste is obviously better than that of the conductor paste without adding lithium cryolite and cobalt boroacylate, and the aging adhesion is reduced by a small amount, which shows that the adhesion of the conductor paste is significantly improved by adding lithium cryolite and cobalt boroacylate, and the sintering promotion effect of cobalt boroacylate on lithium cryolite is shown by comparing example 5 with comparative example 2. Comparing the conductor paste of example 5 with the commercial boron-based conductor paste DuPont ALN11, the sintered surface of the commercial boron-based conductor paste was significantly less infusible (see FIG. 2) and less solderable than that of example 5.