Low-temperature silver-based active slurry for AMB ceramic substrate and preparation method of low-temperature silver-based active slurry

Abstract

The invention is applicable to the technical field of electronic packaging materials, and provides low-temperature silver-based active paste for an AMB ceramic substrate and a preparation method of the low-temperature silver-based active paste, and the paste comprises 40%-70% of nano-silver alloy powder, 25%-55% of a low-temperature decomposition solvent, 2%-5% of a dispersing agent and 0.5%-2% of a thixotropic agent. The nano-silver alloy powder is synthesized by using a micro-reactor continuous reaction preparation technology, and nano-silver particles are uniformly coated on the coating surface of the nano-active powder to form the nano-silver alloy powder. The used dispersing agent is a micromolecular organic dispersing agent and can be completely decomposed at the welding temperature of 200 DEG C; the synthesized nano-silver dispersoid is a stable substance system and can be directly used as soldering paste or slurry. The temperature of traditional medium-high temperature active brazing is reduced to be within 200 DEG C, a welding interface formed after sintering or welding of the nano-silver active slurry is of a silver alloy structure, temperature circulation of more than 900 DEG C can be borne, high reliability is achieved, and great breakthrough and innovation are achieved for industrial application.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic packaging materials, and particularly relates to a low-temperature silver-based active paste for AMB ceramic substrates and a preparation method thereof. Background Art

[0002] In the field of electronic packaging, AMB (active metal brazing) ceramic substrates are widely used in high-power device packaging due to their excellent thermal conductivity, insulation, and mechanical strength.

[0003] Existing AMB ceramic substrates mostly use Ag-Cu-Ti-based active solders, which need to be welded at a high temperature of 700 - 900°C, resulting in thermal stress damage to the ceramic substrates, high energy consumption, and inability to be applied to thin-walled devices or temperature-sensitive components. Although there are low-temperature nano-silver pastes (sintering temperature 200 - 300°C), they lack active elements, have poor interfacial bonding force, insufficient high-temperature reliability, and are prone to failure during thermal cycling. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-temperature silver-based active paste for AMB ceramic substrates, aiming to solve the problems existing in the background art.

[0005] The present invention is implemented as follows. A low-temperature silver-based active paste for AMB ceramic substrates includes:

[0006] Nano silver alloy powder: 40 - 70% (composed of a nano active core and a coated silver layer, the active core is one or a mixture of Ti, Zr, TiH2, ZrH2, with a particle size of 50 - 200 nm; the silver layer thickness is 5 - 20 nm);

[0007] Low-temperature decomposition solvent: 25 - 55% (decane / dodecane mixed solvent, boiling point 180 - 220°C);

[0008] Dispersant: 2 - 5% (PVP-K30 or sodium dodecyl sulfate);

[0009] Thixotropic agent: 0.5 - 2% (hydrogenated castor oil).

[0010] The low-temperature silver-based active paste for AMB ceramic substrates and the preparation method provided by the present invention have the following beneficial effects:

[0011] The present invention directly reduces the traditional medium and high temperature active brazing temperature from 700 - 900 °C to within 200 °C, solving many problems in ceramic electronic packaging. Moreover, after the nano-silver active paste is sintered or welded at 150 - 200 °C, the formed welding interface is a silver alloy structure, which can withstand a temperature cycle of > 900 °C and has high reliability, representing a major breakthrough and innovation in industrial applications. It can be used in fields such as ceramic substrates, brazing of carbon materials, brazing of thin-walled products, and chip packaging, and is of great significance for cost reduction in the industrial chain and improvement of product stability. Description of the Drawings

[0012] Figure 1 It is the effect diagram of Example 1;

[0013] Figure 2 It is the effect diagram of Example 2;

[0014] Figure 3 It is the effect diagram of Example 3. Detailed Description of the Invention

[0015] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0016] The following describes the specific implementation of the present invention in detail in conjunction with specific embodiments.

[0017] A low-temperature silver-based active paste for AMB ceramic substrates, comprising:

[0018] Nano-silver alloy powder: 40 - 70% (composed of a nano-active core and a coated silver layer, the active core is one or a mixture of Ti, Zr, TiH2, ZrH2, with a particle size of 50 - 200 nm; the silver layer thickness is 5 - 20 nm);

[0019] Low-temperature decomposition solvent: 25 - 55% (a mixture of decane / dodecane solvents, with a boiling point of 180 - 220 °C);

[0020] Dispersant: 2 - 5% (PVP-K30 or sodium dodecyl sulfate);

[0021] Thixotropic agent: 0.5 - 2% (hydrogenated castor oil).

[0022] A preparation method of a low-temperature silver-based active paste for AMB ceramic substrates specifically includes the following steps

[0023] Step 1: Continuously mix silver nitrate solution (0.1 - 0.5 mol / L) and active nano - powder suspension (Ti / Zr - based, 0.05 - 0.2 mol / L) in a micro - reactor at a volume ratio of 1:1. Use a combination of ascorbic acid (C5H8O6) and sodium borohydride (NaBH4), with the molar ratio controlled at 1:0.5 - 1:2, and the total addition amount being 1.2 - 2 times the molar amount of silver nitrate (AgNO3). Ascorbic acid, as a mild reducing agent, controls the nucleation rate, and sodium borohydride accelerates the reduction of silver ions. The two work together to achieve uniform silver layer coating. The addition of the above reducing agents can be divided into two stages. The first stage: Mix the ascorbic acid solution and silver nitrate solution at a volume ratio of 1:1 at the inlet of the micro - reactor to trigger the initial reduction reaction. The second stage: Inject the sodium borohydride solution in the middle section of the reaction channel at a flow rate of 20% - 50% of the ascorbic acid solution for secondary reduction and particle size regulation. Control the reaction temperature at 50 - 80 °C and the residence time at 30 - 120 s to in - situ reduce and generate alloy powder with silver - coated active nuclei;

[0024] Step 2: Mix the alloy powder, solvent, and dispersant in a planetary mixer (rotation speed 800 - 1500 rpm, time 2 h). After adding a thixotropic agent, grind it with a three - roll mill until the particle size ≤ 1 μm;

[0025] Step 3: After vacuum degassing (-0.095 MPa, 30 min), encapsulate to obtain a paste - like slurry with a thixotropic index of 1.5 - 2.5.

[0026] Technical effects:

[0027] Low - temperature welding: The solvent completely decomposes at 200 °C, and silver particles form a dense connection through surface diffusion at 150 - 200 °C;

[0028] High - temperature durability: Active core elements migrate to the interface to form an Ag - Ti / Zr alloy layer. It is confirmed by XRD that its melting point > 960 °C, and the shear strength remains ≥ 25 MPa after 100 thermal cycles at 900 °C;

[0029] Application advantages: Compared with the traditional process, the welding thermal stress is reduced by 60%, and the qualified rate of ceramic substrate encapsulation is increased to over 98%.

[0030] Example 1 (core solution)

[0031] Raw materials and process parameters:

[0032] Active core: Nano - TiH2 powder (purity ≥ 99.9%, D50 = 100 nm)

[0033] Silver nitrate solution: 0.3 mol / L, pH = 7.5 (adjusted with ammonia water)

[0034] Reducing agent:

[0035] Ascorbic acid solution: 0.2 mol / L (molar ratio to AgNO3 is 1:1)

[0036] Sodium borohydride solution: 0.1 mol / L (molar ratio to AgNO3 is 0.5:1)

[0037] Total reducing agent / AgNO3 molar ratio = 1.5:1

[0038] Reaction control: Microreactor temperature gradient 50°C → 80°C, residence time 60 s

[0039] Slurry preparation:

[0040] Input silver nitrate solution and TiH2 suspension (0.1 mol / L) into the microreactor at a volume ratio of 1:1;

[0041] Inject ascorbic acid solution (flow rate 10 mL / min) at the entrance of the reaction channel and sodium borohydride solution (flow rate 4 mL / min) in the middle section;

[0042] Collect the product, centrifuge and wash to obtain Ag-TiH2 alloy powder (silver layer thickness 12 ± 2 nm);

[0043] Mix according to the formula: 60% alloy powder, 40% dodecane, 3% PVP-K30, 1% hydrogenated castor oil;

[0044] Grind with a three-roll mill until D90 ≤ 1 μm, degas under vacuum and then encapsulate.

[0045] Performance test:

[0046] Sintering conditions: 200°C / 10 min (N2 atmosphere);

[0047] As Figure 1 shown, Welding interface analysis: Brazing rate of the welding interface is greater than 99%;

[0048] Reliability: -55°C 900°C thermal cycle 100 times, shear strength retention rate 92% (initial value 28 MPa → 25.8 MPa).

[0049] Example 2 (Optimization of reducing agent ratio)

[0050] Active nucleus: Nano-TiH2 powder (purity ≥ 99.9%, D50 = 100 nm)

[0051] Silver nitrate solution: 0.3 mol / L, pH = 7.5 (adjusted with ammonia water)

[0052] Reducing agent:

[0053] Ascorbic acid solution: 0.2 mol / L (molar ratio to AgNO3 is 1:1)

[0054] Sodium borohydride solution: 0.2 mol / L (molar ratio to AgNO3 is 1:1)

[0055] Total reducing agent / AgNO3 molar ratio = 2:1

[0056] Reaction control: Microreactor temperature gradient 50°C → 80°C, residence time 60 s

[0057] Slurry preparation:

[0058] Inject silver nitrate solution and TiH2 suspension (0.1 mol / L) into the microreactor at a volume ratio of 1:1;

[0059] Inject ascorbic acid solution (flow rate 10 mL / min) at the inlet of the reaction channel and sodium borohydride solution (flow rate 6 mL / min) in the middle section;

[0060] Collect the product, centrifuge and wash to obtain Ag-TiH2 alloy powder (silver layer thickness 18 ± 2 nm);

[0061] Mix according to the formula: alloy powder 60%, dodecane 40%, PVP-K30 3%, hydrogenated castor oil 1%;

[0062] Grind with a three-roll mill until D90 ≤ 1 μm, degas under vacuum and then encapsulate.

[0063] Performance testing:

[0064] Sintering conditions: 200°C / 10 min (N2 atmosphere);

[0065] As Figure 2 shown, Welding interface analysis: Welding interface brazing rate is greater than 98%;

[0066] Conclusion: Excessive sodium borohydride leads to coarsening of silver particles. Although the welding brazing rate meets the requirements, it is inferior to Example 1. It is necessary to control the total reducing agent / AgNO3 ≤ 1.8:1.

[0067] Example 3 (Active nucleus composite scheme)

[0068] Active nucleus: Nano ZrH2 powder = 3:1 (mixed particle size 80 - 150 nm)

[0069] Silver nitrate solution: 0.4 mol / L, pH = 7.5 (adjusted with ammonia water)

[0070] Reducing agent:

[0071] Ascorbic acid solution: 0.2 mol / L (molar ratio with AgNO3 is 1:1)

[0072] Sodium borohydride solution: 0.2 mol / L (molar ratio with AgNO3 is 0.6:1)

[0073] Total reducing agent / AgNO3 molar ratio = 1.6:1

[0074] Reaction control: The temperature gradient of the microreactor is 60°C → 90°C, and the residence time is 80 s

[0075] Slurry preparation:

[0076] Input the silver nitrate solution and the ZrH2 suspension (0.1 mol / L) into the microreactor at a volume ratio of 1:1;

[0077] Inject the ascorbic acid solution (flow rate 10 mL / min) at the inlet of the reaction channel, and inject the sodium borohydride solution (flow rate 5 mL / min) in the middle section;

[0078] Collect the product, centrifuge and wash to obtain Ag-TiH2 alloy powder (silver layer thickness 15 ± 2 nm);

[0079] Mix according to the formula: 60% alloy powder, 40% dodecane, 3% PVP-K30, 1% hydrogenated castor oil;

[0080] Grind with a three-roll mill until D90 ≤ 1 μm, and encapsulate after vacuum degassing.

[0081] Performance testing:

[0082] Sintering conditions: 200°C / 10 min (N2 atmosphere);

[0083] As Figure 3 shown, Welding interface analysis: The brazing rate of the welding interface is greater than 97%;

[0084] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. A low-temperature silver-based active paste for AMB ceramic substrates, characterized in that, The low-temperature silver-based active paste for AMB ceramic substrates comprises: 40%-70% of nano silver alloy powder, wherein the nano silver alloy powder has a core-shell structure composed of an active core and a silver coating layer, the active core is selected from at least one of Ti, Zr, TiH2, and ZrH2, the thickness of the silver layer is 5-20 nm, and the mass ratio of the active core to the silver layer is 1:3-1:8; 25%-55% of a low-temperature decomposition solvent, which is a C10-C12 straight-chain alkane with a residue content ≤ 0.5 wt% at 200 °C; 2%-5% of a dispersant, comprising a compound system of PVP-K30 and sodium dodecyl sulfate, with a compounding ratio of 3:1-5:1; 0.5%-2% of a thixotropic agent, which is a mixture of hydrogenated castor oil and nano-silica with a mass ratio of 2:1-5:

1.

2. The low-temperature silver-based active paste for AMB ceramic substrates according to claim 1, wherein The matching degree of the HLB value of the low-temperature decomposition solvent and the dispersant is ±1.

5.

3. The low-temperature silver-based active paste for AMB ceramic substrates according to claim 1, wherein, The thixotropic index of the thixotropic agent is 1.5-2.

5.

4. The low-temperature silver-based active paste for AMB ceramic substrates according to claim 1, wherein The particle size of the active core of the nano silver alloy powder is 50-200 nm.

5. A preparation method of a low-temperature silver-based active paste for an AMB ceramic substrate according to any one of claims 1-4, characterized in that, The preparation method comprises: S1. In a microreactor, continuously mix a silver nitrate solution and an active core suspension, adopt a double reduction system of ascorbic acid and sodium borohydride, inject in two stages, control the reaction temperature at 50-80 °C and the residence time at 30-120 seconds to generate nano silver alloy powder; S2. Mix the alloy powder with a solvent, a dispersant, and a thixotropic agent, and then grind to a particle size ≤ 1 μm; S3. Perform vacuum degassing treatment to obtain a paste-like slurry with a thixotropic index of 1.5-2.

5.

6. The preparation method of the low-temperature silver-based active paste for AMB ceramic substrates according to claim 5, characterized in that, In the double reduction system, the molar ratio of ascorbic acid to sodium borohydride is 1:0.5-1:2, and the molar ratio of the total reducing agent to silver nitrate is 1.2:1-2:

1.

7. The preparation method of the low-temperature silver-based active paste for AMB ceramic substrates according to claim 5, characterized in that, A multi-stage vortex mixing unit is arranged in the microreactor, the mixing efficiency is increased by 40%-60%, and the particle size distribution PDI ≤ 0.

2.

8. The preparation method of the low-temperature silver-based active paste for AMB ceramic substrates according to claim 5, wherein, The vacuum degree of the vacuum degassing is -0.095 MPa, and the treatment time ≥ 30 minutes.

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