A low-temperature silver-based active paste for AMB ceramic substrates and its preparation method

Abstract

This invention relates to the field of electronic packaging materials technology, providing a low-temperature silver-based active paste for AMB ceramic substrates and its preparation method. The paste comprises: 40%-70% nano-silver alloy powder, 25%-55% low-temperature decomposition solvent, 2%-5% dispersant, and 0.5%-2% thixotropic agent. The invention utilizes a microreactor continuous reaction preparation technology to synthesize the paste, uniformly coating nano-silver particles onto the surface of the nano-active powder to form nano-silver alloy powder. A small-molecule organic dispersant is used to ensure complete decomposition at a soldering temperature of 200℃. The synthesized nano-silver dispersion is a stable material system that can be directly used as solder paste or slurry. This invention lowers the traditional medium-to-high temperature active brazing temperature to below 200℃, and the soldering interface formed by sintering or soldering the nano-silver active paste has a silver alloy structure, capable of withstanding temperature cycles >900℃, exhibiting high reliability. This represents a significant breakthrough and innovation for industry applications.

Description

Technical Field

[0001] This invention belongs to the field of electronic packaging materials technology, and particularly relates to a low-temperature silver-based active paste for AMB ceramic substrates and its preparation method. Background Technology

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

[0003] Existing AMB ceramic substrates mostly use Ag-Cu-Ti based active solders, which require soldering at high temperatures of 700-900℃. This leads to thermal stress damage to the ceramic substrate, high energy consumption, and makes it unsuitable for thin-walled devices or temperature-sensitive components. Although low-temperature nano-silver paste exists (sintering temperature 200-300℃), it lacks active elements, has poor interfacial adhesion, insufficient high-temperature reliability, and is prone to failure during thermal cycling. Summary of the Invention

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

[0005] This invention is achieved by providing a low-temperature silver-based active paste for AMB ceramic substrates, comprising:

[0006] Nano-silver alloy powder: 40-70% (composed of nano-active cores and a silver coating layer; the active core is one or a mixture of Ti, Zr, TiH2, and 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℃);

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

[0009] Thixotropic agent: 0.5-2% (a mixture of hydrogenated castor oil and nano silica).

[0010] The present invention provides a low-temperature silver-based active paste for AMB ceramic substrates and its preparation method, which has the following beneficial effects:

[0011] This invention reduces the traditional high-temperature active brazing temperature from 700-900℃ to below 200℃, solving many problems in ceramic electronic packaging. Furthermore, the nano-silver active paste, after sintering or welding at 150-200℃, forms a silver alloy structure at the weld interface, capable of withstanding temperature cycles exceeding 900℃, exhibiting high reliability. This represents a significant breakthrough and innovation for industry applications. It can be used in ceramic substrates, carbon material brazing, thin-walled product brazing, chip packaging, and other fields, significantly contributing to cost reduction and improved product stability across the supply chain. Attached Figure Description

[0012] Figure 1 This is a rendering of Example 1;

[0013] Figure 2 This is a rendering of Example 2;

[0014] Figure 3 This is a rendering of Example 3. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0016] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

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

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

[0019] Low-temperature decomposition solvent: 25-55% (decane / dodecane mixed solvent, boiling point 180-220℃);

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

[0021] Thixotropic agent: 0.5-2% (a mixture of hydrogenated castor oil and nano silica).

[0022] A method for preparing a low-temperature silver-based active paste for AMB ceramic substrates, specifically including the following steps.

[0023] Step 1: In a microreactor, silver nitrate solution (0.1-0.5 mol / L) and active nanoparticle suspension (Ti / Zr based, 0.05-0.2 mol / L) are continuously mixed at a 1:1 volume ratio. Ascorbic acid (C5H8O6) and sodium borohydride (NaBH4) are used in combination, with a molar ratio controlled at 1:0.5~1:2. The total amount added is 1.2~2 times the molar amount of silver nitrate (AgNO3). Ascorbic acid acts as a mild reducing agent to control the nucleation rate, while sodium borohydride accelerates the reduction of silver ions. Together, they achieve uniform silver coating. The addition of the reducing agent can be divided into two stages. The first stage involves mixing ascorbic acid solution and silver nitrate solution at a 1:1 volume ratio at the inlet of the microreactor to trigger the initial reduction reaction. The second stage involves injecting sodium borohydride solution into the middle of the reaction channel at a flow rate of 20%–50% of that of the ascorbic acid solution for secondary reduction and particle size control. The reaction temperature is controlled at 50–80℃, and the residence time at 30–120 s, to generate silver-coated active core alloy powder through in-situ reduction.

[0024] Step 2: Mix the alloy powder with solvent and dispersant in a planetary mixer (800-1500 rpm, 2 hours), add thixotropic agent, and then grind the mixture with a three-roll mill until the particle size is ≤1μm;

[0025] Step 3: Vacuum degassing (-0.095MPa, 30min) followed by encapsulation 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℃, and silver particles form a dense bond at 150-200℃ through surface diffusion;

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

[0029] Application advantages: Compared with traditional processes, welding thermal stress is reduced by 60%, and the ceramic substrate packaging qualification rate 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=100nm)

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

[0034] reducing agent:

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

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

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

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

[0039] Slurry preparation:

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

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

[0042] The product was collected, centrifuged and washed to obtain Ag-TiH2 alloy powder (silver layer thickness 12±2nm).

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

[0044] Three-roll milling to D90≤1μm, followed by vacuum degassing and encapsulation.

[0045] Performance testing:

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

[0047] like Figure 1 As shown, the weld interface analysis shows that the brazing rate at the weld interface is greater than 99%.

[0048] Reliability: -55℃ After 100 thermal cycles at 900℃, the shear strength retention rate is 92% (initial value 28MPa→25.8MPa).

[0049] Example 2 (Optimization of Reducing Agent Ratio)

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

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

[0052] reducing agent:

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

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

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

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

[0057] Slurry preparation:

[0058] Silver nitrate solution and TiH2 suspension (0.1 mol / L) were introduced 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] The product was collected, centrifuged and washed to obtain Ag-TiH2 alloy powder (silver layer thickness 18±2nm).

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

[0062] Three-roll milling to D90≤1μm, followed by vacuum degassing and encapsulation.

[0063] Performance testing:

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

[0065] like Figure 2 As shown, the weld interface analysis shows that the brazing rate at the weld interface is greater than 98%.

[0066] Conclusion: Excessive sodium borohydride leads to coarsening of silver particles. Although the soldering adhesion rate meets the requirements, it is lower than that of Example 1. The total reducing agent / AgNO3 ratio needs to be controlled to ≤1.8:1.

[0067] Example 3 (Active Core Composite Scheme)

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

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

[0070] reducing agent:

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

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

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

[0074] Reaction control: Microreactor temperature gradient 60℃→90℃, residence time 80s

[0075] Slurry preparation:

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

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

[0078] The product was collected, centrifuged and washed to obtain Ag-TiH2 alloy powder (silver layer thickness 15±2nm).

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

[0080] Three-roll milling to D90≤1μm, followed by vacuum degassing and encapsulation.

[0081] Performance testing:

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

[0083] like Figure 3 As shown, the weld interface analysis shows that the brazing rate at the weld interface is greater than 97%.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low temperature silver-based active paste for AMB ceramic substrates, characterized by, The low-temperature silver-based active paste for the AMB ceramic substrate comprises: Nano-silver alloy powder 40%-70%, which has a core-shell structure composed of an active core and a silver coating layer, the active core being selected from at least one of Ti, Zr, TiH2 and ZrH2, the silver layer having a thickness of 5-20 nm, and the mass ratio of the active core to the silver layer being 1:3-1:8; Low-temperature decomposition solvent 25%-55%, which is a C10-C12 linear alkane having a residual amount of ≤0.5wt% at 200℃; Dispersant 2%-5%, which is a complex system containing PVP-K30 and sodium dodecyl sulfate, the complex ratio being 3:1-5:1; Thixotropic agent 0.5%-2%, which is a mixture of hydrogenated castor oil and nano-silicon dioxide, the mass ratio being 2:1-5:

1.

2. The low temperature silver-based active paste for AMB ceramic substrate according to claim 1, characterized in that, 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 substrate according to claim 1, characterized in that, 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, characterized in that, The particle size of the active core of the nano-silver alloy powder is 50-200 nm.

5. A process for the preparation of a low temperature silver-based active paste for AMB ceramic substrates according to any one of claims 1 to 4, characterized by, The preparation method comprises: S1. In a microreactor, continuously mix silver nitrate solution and active core suspension, use ascorbic acid and sodium borohydride double reduction system, inject in two stages, control the reaction temperature at 50-80℃, the residence time at 30-120 seconds, generate nano-silver alloy powder, wherein: ascorbic acid and sodium borohydride are combined, the molar ratio is 1:0.5~1:2, and the total addition amount is 1.2~2 times the molar amount of silver nitrate; S2. After mixing the alloy powder with solvent, dispersant and thixotropic agent, grind to a particle size of ≤1μm; S3. Vacuum degassing treatment to obtain paste-like paste with a thixotropic index of 1.5-2.

5.

6. The process for the preparation of low temperature silver based active paste for AMB ceramic substrate as claimed in claim 5 wherein, The molar ratio of ascorbic acid to sodium borohydride in the double reduction system is 1:0.5-1:2, and the molar ratio of total reducing agent to silver nitrate is 1.2:1-2:

1.

7. The process for the preparation of low temperature silver based active paste for AMB ceramic substrate as claimed in claim 5 wherein, The microreactor is provided with multiple vortex mixing units, the mixing efficiency is improved by 40%-60%, and the particle size distribution PDI is ≤0.

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

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