Low-temperature high-reliability pressureless sintering silver paste and preparation method thereof

Abstract

The invention discloses low-temperature high-reliability pressureless sintered silver paste and a preparation method thereof. The low-temperature high-reliability pressureless sintered silver paste comprises 75-85 parts of nano silver powder, 5-10 parts of micron silver powder, 5-10 parts of micron silver powder and 8-15 parts of an organic carrier. Through the mode, according to the low-temperature high-reliability pressureless sintering silver paste and the preparation method thereof, through the synergistic effect of high surface activity of the nano silver powder and the sintering aid, pressureless sintering at 180-200 DEG C is achieved, the pressure requirement for equipment is reduced, damage to a base material is avoided, high heat conductivity, high mechanical property and long-term reliability of the silver paste can be improved, and the low-temperature high-reliability pressureless sintering silver paste and the preparation method thereof can be used for preparing the low-temperature high-reliability pressureless sintering silver paste. And the process cost can be further reduced, which is a key for solving the packaging bottleneck of the high-temperature power device.

Description

Technical Field

[0001] This invention relates to the field of electronic packaging materials technology, and in particular to a low-temperature, high-reliability, pressureless sintering silver paste suitable for high-temperature and high-power scenarios such as power semiconductor devices and 5G RF modules, and its preparation method. Background Technology

[0002] In fields such as new energy vehicles and photovoltaic inverters, as the requirements for power density and temperature resistance of power devices continue to increase, traditional solders (such as tin-based alloys) are no longer sufficient to meet the demands due to their low melting point (<250℃) and limited thermal conductivity (<60 W / (m•K)). Sintered silver paste, as an alternative material, has become the core interconnect material for high-temperature packaging due to its high thermal conductivity (>200 W / (m•K)), high melting point (>961℃), and excellent electrical properties.

[0003] However, existing sintered silver paste technology has the following limitations: (1) Harsh sintering conditions: Traditional silver paste needs to be sintered at high temperature and high pressure, which not only consumes a lot of energy, but may also cause chip / substrate warping and cracking (especially for brittle ceramic substrates). (2) Insufficient reliability: Low-temperature sintering (<200℃) silver paste often reduces the sintering temperature by introducing low-melting-point additives (such as organic silver salts), but carbonaceous impurities are easily left behind, causing interface cracking and resistance drift of the solder joint during high and low temperature cycles. (3) Poor process adaptability: Some silver pastes have poor thixotropy and cannot meet the precision requirements of mass production processes such as screen printing and dispensing, which can easily lead to excessively high void ratios after sintering. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A low-temperature, high-reliability, pressureless sintering silver paste is provided, comprising the following raw material components by mass parts: Nano silver powder: 75-85 parts, wherein the average particle size of the nano silver powder is 200-300 nm and the specific surface area is 10-15 m² / g; Micron-sized silver powder: 5-10 parts, wherein the average particle size of the micron-sized silver powder is 2-5 μm; Nano copper powder: 1-5 parts; Organic carrier: 8-15 parts, including the following raw material components by mass: 5-8 parts binder, 80-85 parts solvent, 7-10 parts dispersant, and 2-5 parts thixotropic agent.

[0005] In a preferred embodiment of the present invention, the shape of the nano-silver powder is spherical or near-spherical.

[0006] In a preferred embodiment of the present invention, the micron-sized silver powder is spherical or near-spherical in shape, accounting for 5-15 parts by mass of the total silver powder.

[0007] In a preferred embodiment of the present invention, the average particle size of the nano-copper powder is 300 nm, and its shape is spherical or near-spherical, accounting for 1 part of the total mass of the solid content (nano-silver powder, micron-sized silver powder, nano-copper powder and organic carrier).

[0008] In a preferred embodiment of the present invention, a sintering aid is further included, which includes silver octoate, silver acetylacetone, or zinc stearate, and the mass of the sintering aid accounts for 0.5-0.8% of the total mass of the silver paste.

[0009] A method for preparing a low-temperature, high-reliability, pressureless sintering silver paste, comprising the following steps: (1) Silver powder pretreatment: Nano silver powder, micron silver powder and nano copper powder are dried in a vacuum drying oven at 60°C for 2 hours to remove surface adsorbed water; (2) Preparation of organic carrier: The binder, solvent and dispersant are stirred at 120±5℃ until completely dissolved, the thixotropic agent is added, and stirring is continued for 30 minutes, then cooled to room temperature; (3) Silver paste mixing: Add nano silver powder, micron silver powder, nano copper powder and sintering aid to the organic carrier in proportion, then premix the mixture and then grind it to obtain a uniformly dispersed silver paste. (4) Pressureless sintering: Print silver paste onto silver-plated or copper-clad ceramic substrates, place the chips, heat to 180-200°C in air or nitrogen at 5°C / min, hold for 40-60 minutes, and then cool naturally to room temperature.

[0010] In a preferred embodiment of the present invention, in step (3), the mixture is stirred and mixed in a planetary mixer at 30 rpm.

[0011] In a preferred embodiment of the present invention, in step (3), the mixture after stirring and mixing is ground three times at 300 rpm in a three-roll mill for 5 minutes each time.

[0012] The beneficial effects of this invention are: through the synergistic effect of the high surface activity of nano silver powder and sintering aid, pressureless sintering at 180-200℃ is achieved, reducing the pressure requirements on the equipment, avoiding damage to the substrate, and improving the high thermal conductivity, high mechanical properties and long-term reliability of silver paste. It can also further reduce the process cost, becoming a key to solving the bottleneck of high-temperature power device packaging. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein: Figure 1 This is a SEM image of the cross-section of the sintered body in Example 1 of this invention; Figure 2 This is a SEM image of the sintered body cross-section in Example 2 of this invention; Figure 3 This is a SEM image of the sintered body cross-section in Example 3 of this invention; Figure 4 This is a SEM image of the sintered body cross-section of Example 4 in this invention; Figure 5 This is a SEM image of the sintered body cross-section of Example 5 in this invention; Figure 6 This is a SEM image of the sintered body cross-section of Example 6 in this invention. Detailed Implementation

[0014] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0015] Please see Figure 1-6 The embodiments of the present invention include: A low-temperature, high-reliability, pressureless sintering silver paste enables low-temperature, pressureless interconnection between chips and substrates, exhibiting excellent thermal and electrical conductivity and mechanical reliability. It comprises the following raw material components by weight: Nano silver powder: 75-85 parts. The average particle size of the nano silver powder is 200-300nm. The shape is spherical or near-spherical. The specific surface area is 10-15 m² / g. Its high surface energy can reduce the sintering activation energy and achieve low-temperature sintering.

[0016] Micron-sized silver powder: 5-10 parts. The average particle size of the micron-sized silver powder is 2-5μm, and the shape is spherical or near-spherical. It accounts for about 5-10% of the total mass of silver powder. It serves as a sintering attachment core to reduce the porosity of the sintered body and improve the sintering performance.

[0017] Nano copper powder: 1-5 parts. The average particle size of the nano copper powder is 300nm. Its shape is spherical or near-spherical. It accounts for 1 part of the total solid content by mass. Without reducing the solder joint performance, the silver powder content can be reduced and the cost can be controlled.

[0018] Sintering aids include silver octoate, silver acetylacetone, or zinc stearate, and the mass of sintering aids accounts for 0.5-0.8% of the total solid content.

[0019] Organic carrier: 8-15 parts, including the following raw material components by mass: 5-8 parts binder, 80-85 parts solvent, 7-10 parts dispersant, and 2-5 parts thixotropic agent.

[0020] The silver paste of this application can be widely used in: (1) Packaging and interconnection of IGBT modules and SiC MOSFET chips for new energy vehicles; (2) Thermal packaging of 5G base station radio frequency power amplifier (PA); (3) High-reliability connection of high-temperature electronic devices for aerospace.

[0021] A method for preparing a low-temperature, high-reliability, pressureless sintering silver paste, comprising the following steps: (1) Silver powder pretreatment: Nano silver powder, micron silver powder and nano copper powder are dried in a vacuum drying oven at 60°C for 2 hours to remove surface adsorbed water; (2) Preparation of organic carrier: The binder and solvent are stirred at 120±5℃ until completely dissolved, the thixotropic agent is added, and stirring is continued for 30 minutes. The mixture is then cooled to room temperature. (3) Silver paste mixing: Add nano silver powder, micron silver powder, nano copper powder and sintering aid to the organic carrier in proportion. First, premix in a planetary mixer at 30 rpm for 15 minutes, then transfer to a three-roll mill and grind at 300 rpm 3 times (5 minutes each time) to obtain a uniformly dispersed silver paste. (4) Pressureless sintering: Print silver paste onto silver-plated or copper-clad ceramic substrates, place the chips, heat to 180-200°C at 5°C / min in air or nitrogen, hold for 40-60 minutes, and cool naturally to room temperature. The sintering atmosphere can be nitrogen or air.

[0022] The present invention will be further illustrated by specific embodiments below, but is not limited to these embodiments. The content of each raw material is in parts by mass.

[0023]

[0024] The test performance of specific embodiments is shown in the table below:

[0025] Therefore, the silver paste sintering method of this application can achieve the following objectives: sintering temperature ≤200℃, no external pressure required (pressureless conditions); solder joint void ratio ≤3% after sintering, and volume resistivity ≤5.0×10⁻⁶. -6Ω•cm, thermal conductivity ≥220W / (m•K); room temperature shear strength ≥20 MPa.

[0026] The beneficial effects of the low-temperature, high-reliability, pressureless sintering silver paste and its preparation method of the present invention are as follows: (1) Low-temperature pressureless sintering: Through the high surface activity of nano silver powder and the synergistic effect of sintering aids, pressureless sintering at 180-200℃ is achieved, reducing the pressure requirements of the equipment and avoiding damage to the substrate; (2) High reliability: The silver powder gradation (nano + micro) combined with the filling effect of the additives makes the sintered body density ≥95% and void ratio ≤3%; thermal conductivity ≥220 W / (m•K) and volume resistivity ≤3.0×10 -6 Ω•cm, superior to traditional solder (<60W / (m•K), >10×10 -6 (Ω•cm); high strength retention after thermal cycling, meeting the long-term use requirements of automotive-grade components (-55℃~150℃); (3) Strong process adaptability: The organic carrier formula optimizes the thixotropic properties of the silver paste (viscosity is adjustable in the range of 10-100 Pa•s), which is suitable for screen printing with line width of 0.1-0.5 mm and has good consistency in mass production; (4) Reduced production costs: Adding a certain amount of nano-Cu powder to silver powder can further reduce process costs while ensuring solder joint performance.

[0027] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A low-temperature, high-reliability, pressureless sintering silver paste, characterized in that, The raw material components are included in parts by weight: Nano silver powder: 75-85 parts, wherein the average particle size of the nano silver powder is 200-300 nm and the specific surface area is 10-15 m² / g; Micron-sized silver powder: 5-10 parts, wherein the average particle size of the micron-sized silver powder is 2-5 μm; Nano copper powder: 1-5 parts; Organic carrier: 8-15 parts; The organic carrier comprises the following raw material components by mass: 5-8 parts binder, 80-85 parts solvent, 7-10 parts dispersant, and 2-5 parts thixotropic agent.

2. The low-temperature, high-reliability, pressureless sintering silver paste according to claim 1, characterized in that, The shape of the nano-silver powder is spherical or near-spherical.

3. The low-temperature, high-reliability, pressureless sintering silver paste according to claim 1, characterized in that, The micron-sized silver powder is spherical or near-spherical in shape.

4. The low-temperature, high-reliability, pressureless sintering silver paste according to claim 1, characterized in that, The average particle size of the nano-copper powder is 300 nm, and its shape is spherical or near-spherical.

5. The low-temperature, high-reliability, pressureless sintering silver paste according to claim 1, characterized in that, It also includes sintering aids, which include silver octoate, silver acetylacetone, or zinc stearate, and the mass of the sintering aids accounts for 0.5-0.8% of the total mass of the silver paste.

6. A method for preparing a low-temperature, high-reliability, pressureless sintering silver paste, characterized in that the steps include... include: (1) Silver powder pretreatment: Nano silver powder, micron silver powder and nano copper powder are dried in a vacuum drying oven at 60°C for 2 hours to remove surface adsorbed water; (2) Preparation of organic carrier: The binder, solvent and dispersant are stirred at 120±5℃ until completely dissolved, the thixotropic agent is added, and stirring is continued for 30 minutes, then cooled to room temperature; (3) Silver paste mixing: Add nano silver powder, micron silver powder, nano copper powder and sintering aid to the organic carrier in proportion, then premix the mixture and then grind it to obtain a uniformly dispersed silver paste. (4) Pressureless sintering: Print silver paste onto silver-plated or copper-clad ceramic substrates, place the chips, heat to 180-200°C in air or nitrogen at 5°C / min, hold for 40-60 minutes, and then cool naturally to room temperature.

7. The low-temperature, high-reliability, pressureless sintering silver paste and its preparation method according to claim 1, characterized in that, In step (3), the mixture is stirred and mixed in a planetary mixer at 30 rpm.

8. The low-temperature, high-reliability, pressureless sintering silver paste and its preparation method according to claim 1, characterized in that, In step (3), the mixture after stirring is ground three times at 300 rpm in a three-roll mill for 5 minutes each time.

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