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

Abstract

The application discloses a low-temperature pressureless sintering high-thermal-conductivity silver paste and a preparation method thereof. The low-temperature pressureless sintering high-thermal-conductivity silver paste comprises the following components in percentage by mass: nanosheet silver powder 10-100%, microsheet silver powder 0-70%, copper / silver plated diamond 0-50%, solvent 20-10%, and dispersant 0-5%. The preparation method comprises the following key steps: powder premixing, organic system preparation and three-roll grinding. The high-thermal-conductivity silver paste produced by the application has a shear force not less than 20 MPa and a thermal conductivity not less than 100 W / (m*K) after sintering.

Description

Technical Field

[0001] This invention belongs to the field of packaging and assembly materials, specifically relating to a low-temperature pressureless sintering high thermal conductivity silver paste and its preparation method. Background Technology

[0002] With the expansion of the operating temperature range of third-generation semiconductors, theoretically reaching over 300℃, traditional gold-tin alloy solders and conductive adhesives, which require operating temperatures below 280℃, can no longer meet the heat dissipation and high-temperature service requirements of next-generation high-power semiconductor devices. For example, Banu et al. studied the long-term operating stability of SiC SBDs at temperatures ranging from -170 to 280℃; Godignon et al. reported 300 V / 5 A SiC Schottky diodes with both high and low temperature resistance, which can operate stably from -170 to 300℃, exceeding the service temperature of ordinary gold-tin alloy solders and conductive adhesives. The limitations of lead-free solders and conductive adhesives severely restrict their application in high-density packaging of high-power devices. Therefore, low-temperature sintering interconnect technology based on nano-silver has emerged. One of the main characteristics of low-temperature pressureless sintering high thermal conductivity silver paste based on nano-silver is low-temperature sintering and high-temperature service. Its sintering temperature can be as low as 150℃, or even room temperature, and its remelting temperature can theoretically reach 960℃. This characteristic offers significant advantages for the integration of high-power chips and complex microsystems. It can reduce thermal damage during semiconductor device packaging, minimize thermal mismatch during sintering, reduce residual stress, and improve device reliability, especially in multi-stage assembly where it is no longer affected by temperature gradients. It can be said to have epoch-making significance for the development of microsystem integration processes. However, traditional nano-silver paste requires the application of pressure when used for semiconductor chip sintering interconnects. Applying pressure to the surface undoubtedly poses a major challenge to chip reliability. It places high demands on substrate flatness and chip thickness, severely reducing yield and hindering chip miniaturization and integration. This deficiency significantly reduces the applicability of nano-silver low-temperature interconnect technology.

[0003] Currently, there are low-temperature pressureless sintering silver pastes made with silver powder particles smaller than 100nm. However, due to insufficient dispersion and filling of the nano-silver particles, they are irregularly arranged and have problems such as large secondary gaps, high porosity, low bonding strength, and edge cracking.

[0004] To solve the above problems and achieve high thermal conductivity, it is necessary to develop a silver paste that can achieve high bonding strength and good thermal conductivity by sintering under no-pressure conditions. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned technical problems by providing a high thermal conductivity silver paste for low-temperature pressureless sintering and its preparation method. The silver paste uses nano-silver flakes that can be oriented to fill pores, and micron-sized silver flakes that have good lubricity and support properties, allowing the silver paste to maintain good fluidity even with a high silver powder filling ratio and preventing cracking after sintering. Copper / silver diamond plating improves thermal conductivity while maintaining the stability of the sintered silver paste, preventing overburning and voids when subjected to high-temperature impact.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A high thermal conductivity silver paste for low-temperature pressureless sintering comprises the following components by weight percentage: nano-flake silver powder: 10~95%, micron-flake silver powder: 0~70%, copper-plated / silver diamond: 0~50%, solvent: 5~20%, and dispersant: 0~5%; wherein, after sintering, the high thermal conductivity silver paste has the characteristics of shear force not less than 20MPa and thermal conductivity not less than 100W / (m·K).

[0007] According to the above-mentioned high thermal conductivity silver paste, the nanosheet silver powder has a thickness of 10~100nm, a sheet diameter of 0.2~1.5μm, a surface coating agent thickness of less than 3nm, and an absolute value of zeta potential of less than 30mV.

[0008] According to the above-mentioned high thermal conductivity silver paste, the thickness of the nanosheet silver powder is 10~50nm and the sheet diameter is 0.4~1μm.

[0009] According to the above-mentioned high thermal conductivity silver paste, the micron-sized flake silver powder has a D50 of less than 15 μm, a tap density of greater than 3.0 g / cm³, and an absolute value of zeta potential of less than 50 mV.

[0010] According to the above-mentioned high thermal conductivity silver paste, the tap density of the micron-sized flake silver powder is greater than 5.0 g / cm³.

[0011] According to the above-mentioned high thermal conductivity silver paste, the particle size of the copper / silver diamond is 50nm~10μm, and the absolute value of the zeta potential is less than 50mV.

[0012] According to the above-mentioned high thermal conductivity silver paste, the solvent is an alcohol, ether, or ester substance with a boiling point between 180℃ and 300℃ and a LogP value between 2 and 3.

[0013] According to the above-mentioned high thermal conductivity silver paste, the solvent is selected from terpineol, γ-butyrolactone, N,N-dimethylformamide, diethylene glycol butyl ether, hydroxyphenylethanol, or amyl benzoate.

[0014] According to the above-mentioned high thermal conductivity silver paste, the dispersant is selected from polyethylene glycol, Triton X-100, nitrocellulose or PVB.

[0015] A method for producing the above-mentioned high thermal conductivity silver paste includes the following steps: (a) Mixing nano-flake silver powder, micron-flake silver powder and copper / silver-plated diamond in a specific weight percentage; (b) Select appropriate amounts of solvent and dispersant, and mix them to obtain an organic system; (c) Add the organic system to the mixed powder obtained in step (a) and premix it; (d) The premixed material is rolled through a three-roll mill; (e) The rolled silver paste is degassed using a vacuum homogenizer; (f) The degassed silver paste is sintered at 180~300℃ to obtain a high thermal conductivity silver paste with a thermal conductivity of not less than 100W / (m·K).

[0016] According to the preparation method described above, the rolling process in step (d) is performed 3 to 5 times.

[0017] Technical effects of the present invention: The low-temperature pressureless sintering high thermal conductivity silver paste of the present invention achieves the technical effect of sintering to form high thermal conductivity without external pressure through special component design and preparation method, which significantly improves the thermal management capability and packaging reliability of semiconductor devices. Detailed Implementation

[0018] This invention discloses a method for preparing a high thermal conductivity silver paste by low-temperature pressureless sintering. The silver paste comprises nano-flake silver powder, micron-flake silver powder, copper-plated / silver diamond, solvent, and dispersant. The components are mixed in the following weight percentages: 10-95% nano-flake silver powder, 0-70% micron-flake silver powder, 0-50% copper-plated / silver diamond, 5-20% solvent, and 0-5% dispersant. After sintering, the silver paste prepared by this formulation exhibits a shear strength of at least 20 MPa and a thermal conductivity of at least 100 W / (m·K), significantly surpassing the performance of traditional solders and conductive adhesives.

[0019] Preferably, the nanosheet silver powder has a thickness of 10~100nm, a sheet diameter of 0.2~1.5μm, a surface coating agent thickness of less than 3nm, and an absolute value of zeta potential of less than 30mV.

[0020] Preferably, the thickness of the nanosheet silver powder is 10~50nm and the sheet diameter is 0.4~1μm.

[0021] Preferably, the micron-sized flake silver powder has a D50 of less than 15 μm, a tap density of greater than 3.0 g / cm³, and an absolute value of zeta potential of less than 50 mV. More preferably, the micron-sized flake silver powder has a tap density of greater than 5.0 g / cm³.

[0022] Preferably, the copper / silver-plated diamond has a particle size of 50 nm to 10 μm and an absolute value of zeta potential of less than 50 mV.

[0023] Preferably, the solvent is an alcohol, ether, or ester with a boiling point between 180°C and 300°C and a LogP value between 2 and 3. Solvents can be selected from terpineol, γ-butyrolactone, N,N-dimethylformamide, diethylene glycol butyl ether, hydroxyphenylethanol, or amyl benzoate. The dispersant can be selected from polyethylene glycol, Triton X-100, nitrocellulose, or PVB.

[0024] To prepare this high thermal conductivity silver paste, nano-flake silver powder, micron-flake silver powder, and copper-plated / silver diamond are first mixed in a defined ratio. Then, appropriate amounts of solvent and dispersant are added to form a homogeneous organic system. The organic system is added to the mixed powder and pre-mixed to obtain a premixed material. Next, the mixture is rolled multiple times using a three-roll mill to ensure highly uniform and fine mixing. The uniformly rolled silver paste is then placed in a homogenizer for vacuum degassing. Finally, the degassed silver paste is sintered at 180–300°C. At this temperature, some of the coating agent volatilizes, forming sintering necks between adjacent nano-silver particles, nano-silver particles and micron-silver particles, or nano-silver particles and copper-plated / silver diamond. These necks become high thermal conductivity and high shear strength interfacial bonding materials for pure silver interconnection, forming the final high thermal conductivity silver paste product. The preparation method of this invention enables low-temperature sintering of high thermal conductivity silver paste without applying pressure, while ensuring high thermal conductivity and high shear strength, thus meeting the application requirements of high-power semiconductor devices under extreme temperature conditions. Example 1

[0025] 50% nano-flake silver powder with a zeta potential of -3mV, 10% micron-flake silver powder with a zeta potential of -0.2mV, and 20% silver-plated diamond with a zeta potential of +0.2mV were mixed in a mortar. 18% solvent (terpineol, γ-butyrolactone, N,N-dimethylformamide) and 2% polyethylene glycol 200 were mixed and labeled as organic system 1. Organic system 1 was poured into the mixed powder and premixed in a mortar. Then, it was transferred to a three-roll mill and rolled 5 times. The uniformly rolled silver paste was then placed in a homogenizer for vacuum degassing. Finally, it was sintered at 180℃ to obtain a high thermal conductivity silver paste with a thermal conductivity of 100W / (m·K). Example 2

[0026] 70% nano-flake silver powder with a zeta potential of -20mV and 20% silver-plated diamond with a zeta potential of +3mV were mixed in a mortar. 8% solvent (terpineol) and 2% PVB were mixed and labeled as organic system 2. Organic system 2 was poured into the mixed powder and premixed in a mortar. Then, it was transferred to a three-roll mill and rolled 5 times. The uniformly rolled silver paste was then placed in a homogenizer for vacuum degassing. Finally, it was sintered at 250℃ to obtain a high thermal conductivity silver paste with a thermal conductivity of 210W / (m·K). Example 3

[0027] Mix 50% nano-flake silver powder with a zeta potential of +3mV and 40% micron-flake silver powder with a zeta potential of -0.5mV. Mix 9% solvent (diethylene glycol butyl ether, hydroxyphenylethanol, and amyl benzoate) with 1% nitrocellulose and label this as organic system 3. Pour organic system 3 into the mixed powder and premix it in a mortar. Then, transfer it to a three-roll mill and roll it 5 times. Then, put the uniformly rolled silver paste into a homogenizer for vacuum degassing. Finally, after sintering at 200℃, the thermal conductivity is 180W / (m·K). Example 4

[0028] 10% of nano-flake silver powder (zeta potential -30mV, thickness 10nm, flake diameter 0.2μm), 70% of micron-flake silver powder (zeta potential -50mV, D50 less than 15μm, tap density 5.0g / cm³), and 20% of copper-plated diamond (zeta potential +50mV, particle size 10μm) were mechanically stirred and mixed. The mixture was then mixed with 20% solvent (terpineol) and 2% polyethylene glycol 200, and labeled as organic system 4. Organic system 4 was added to the mixed powder and premixed. The mixture was then transferred to a three-roll mill for three rolling passes. The uniformly rolled silver paste was then placed in a homogenizer for vacuum degassing and finally sintered at 300℃ to obtain a high thermal conductivity silver paste with a thermal conductivity of 260W / (m·K). Example 5

[0029] 95% of nano-flake silver powder (zeta potential -10mV, thickness 100nm, flake diameter 1.5μm), 0% of micron-sized flake silver powder, and 0% of silver-plated diamond were uniformly mixed in a mortar. Subsequently, 5% of a solvent (amyl benzoate, boiling point approximately 300℃, LogP value approximately 3) was mixed with 0% of a dispersant to form organic system 5. Organic system 5 was poured into the previously mixed powder and pre-mixed using a mortar. The material was then transferred to a three-roll mill and rolled three times. The uniformly rolled silver paste was then placed in a homogenizer for vacuum degassing and sintering at 180℃. The sintered silver paste exhibited a thermal conductivity of 160 W / (m·K), exceeding the minimum standard specified in the claims. Example 6

[0030] 30% of nano-flake silver powder (zeta potential -25mV, thickness 50nm, flake diameter 1μm), 50% of micron-flake silver powder (zeta potential -45mV, D50 less than 15μm, tap density greater than 3.0g / cm³), and 20% of copper-plated diamond (zeta potential +45mV, particle size 50nm) were mixed using mechanical stirring. Next, 18% solvent (γ-butyrolactone, N,N-dimethylformamide) and 2% dispersant (Traraton X-100) were mixed to form organic system 6. Organic system 6 was added to the mixed powder, pre-mixed in a mortar, then rolled five times on a three-roll mill. The uniformly rolled silver paste was then placed in a homogenizer for vacuum degassing, and finally sintered at 230℃ to obtain a high thermal conductivity silver paste with a thermal conductivity of 260W / (m·K).

Claims

1. A high thermal conductivity silver paste sintered at low temperature without pressure, characterized in that, It contains the following components by weight percentage: Nano-flake silver powder: 10%–95%, micron-flake silver powder: 0%–70%, copper-plated diamond or silver-plated diamond: 0%–50%, solvent: 5%–20%, and dispersant: 0%–5%; The nanosheet silver powder has a thickness of 10~100nm, a sheet diameter of 0.2~1.5μm, and a surface coating agent. The thickness of the surface coating agent is less than 3nm, and the absolute value of the zeta potential of the nanosheet silver powder is less than 30mV. The micron-sized flake silver powder has a D50 of less than 15 μm, a tap density of greater than 3.0 g / cm³, and an absolute value of zeta potential of less than 50 mV. The copper-plated diamond or silver-plated diamond has a particle size of 50 nm to 10 μm and an absolute value of zeta potential of less than 50 mV. The high thermal conductivity silver paste is sintered at 180~300℃ without pressure to form a pure silver interconnect interface bonding material. The shear strength of the interface bonding material is not less than 20MPa and the thermal conductivity is not less than 100W / (m·K).

2. The high thermal conductivity silver paste according to claim 1, characterized in that, The thickness of the nanosheet silver powder is 10~50nm, and the sheet diameter is 0.4~1μm.

3. The high thermal conductivity silver paste according to claim 1, characterized in that, The tap density of the micron-sized flake silver powder is greater than 5.0 g / cm³.

4. The high thermal conductivity silver paste according to claim 1, characterized in that, The solvent is an alcohol, ether, or ester with a boiling point between 180°C and 300°C and a LogP value between 2 and 3.

5. The high thermal conductivity silver paste according to claim 4, characterized in that, The solvent is selected from terpineol, γ-butyrolactone, N,N-dimethylformamide, diethylene glycol butyl ether, hydroxyphenylethanol, or amyl benzoate.

6. The high thermal conductivity silver paste according to claim 1, characterized in that, The dispersant is selected from polyethylene glycol, Triton X-100, nitrocellulose, or PVB.

7. A method for preparing the high thermal conductivity silver paste according to any one of claims 1-6, characterized in that, Includes the following steps: (a) Mixing nano-flake silver powder, micron-flake silver powder and copper-plated diamond or silver-plated diamond in a specific weight percentage; (b) Select appropriate amounts of solvent and dispersant, and mix them to obtain an organic system; (c) Add the organic system to the mixed powder obtained in step (a) and premix it; (d) The premixed material is rolled through a three-roll mill; (e) The rolled material is degassed using a vacuum homogenizer to obtain the high thermal conductivity silver paste; (f) The high thermal conductivity silver paste obtained in step (e) is sintered at 180~300℃ under pressureless conditions to form a pure silver interconnect interface bonding material, wherein the shear strength of the interface bonding material is not less than 20MPa and the thermal conductivity is not less than 100W / (m·K).

8. The method for preparing high thermal conductivity silver paste according to claim 7, characterized in that, In step (d), the rolling process is repeated 3 to 5 times.