Low-stress conductive silver adhesive and preparation method thereof

Abstract

The invention discloses a low-stress conductive silver adhesive and a preparation method thereof, relates to the technical field of packaging materials, and aims to solve the problems of insufficient gold interface bonding strength, weak stress control on chips such as GaN and the like and poor adhesive dispensing manufacturability of the existing domestic conductive silver adhesive. The preparation method comprises the following steps: S1, reacting a siloxane raw material with a catalyst, and carrying out vacuum distillation to prepare modified polydimethylsiloxane; s2, mixing epoxy resin with the siloxane, and adding a solvent, a catalyst and a curing agent for reaction to prepare organic silicon modified resin; and S3, firstly preparing an oligomeric dispersant and modified silver powder, then adding the modified silver powder into resin in batches, and performing rolling, vacuum distillation and filtration through a three-roller machine to obtain a finished product. The finished product has excellent low stress characteristic, gold interface bonding reliability and stable electric conduction and heat conduction performance, and can meet the packaging requirements of high-end radio frequency and power chips.

Description

Technical Field

[0001] This invention relates to the field of encapsulation materials technology, and specifically to a method for preparing low-stress conductive silver paste. Background Technology

[0002] With the rapid development of wireless communication, new energy vehicles, and the Internet of Things, the application scenarios of radio frequency chips and power chips are constantly expanding, and the performance requirements of key materials in their packaging process are becoming increasingly stringent. Conductive silver paste, as a core packaging material that combines conductivity and adhesion, not only needs to achieve signal transmission and structural fixation between electronic components, but also needs to adapt to the development trends of chip miniaturization and high power, maintaining stable electrical performance and mechanical reliability under high-frequency operating conditions. It has become an important basic material supporting the efficient operation of high-end electronic equipment.

[0003] The current market for conductive silver paste used in high-end radio frequency (RF) and power chips is characterized by a highly closed supply chain for core technologies and products. Domestic companies struggle to obtain key formulas and process parameters, forcing them to rely on imported products to meet production needs. This dependence not only leads to high procurement costs for downstream packaging companies but also exposes them to the risk of supply chain disruptions and technology shortages due to fluctuations in the international situation. This severely restricts the domestic electronics and information industry's demand for self-sufficiency in key materials and hinders the progress of domestic production of RF and power chips.

[0004] Existing domestically produced conductive silver pastes have significant shortcomings in performance and processability, making them unsuitable for the packaging requirements of high-end chips. On one hand, the bonding design for the gold interface is flawed, resulting in insufficient bonding strength and a tendency for chip detachment after curing, compromising the long-term stability of the equipment. On the other hand, materials such as GaN commonly used in RF chips are sensitive to packaging stress, and domestically produced pastes, due to insufficient optimization of the main resin formulation, have weak stress control capabilities, easily leading to chip breakage during curing. Furthermore, some products suffer from excessively high viscosity and poor thixotropy, easily causing defects such as dispensing clogging and stringing, reducing production efficiency and failing to meet the actual needs of large-scale packaging. Therefore, given the limitations of the aforementioned technologies, there is an urgent need to develop a low-stress conductive silver paste and its preparation method. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a low-stress conductive silver paste and its preparation method, which effectively solves the problems of insufficient bonding strength at the gold interface of existing conductive silver pastes, easy chip detachment after curing, and weak stress control capability and easy chip breakage when dealing with chip materials such as GaN that are sensitive to packaging stress.

[0006] The objective of this invention can be achieved through the following technical solutions: On one hand, the present invention provides a method for preparing low-stress conductive silver paste, comprising the following preparation steps: S1: Dimethylcyclosiloxane, hexamethyldisiloxane, phenyltrimethoxysilane, hydroxypolydimethylsiloxane and distilled water are mixed, catalyst A is slowly added, and the reaction is stirred and heated. After the reaction is completed, vacuum distillation is performed to obtain modified polydimethylsiloxane; S2: The epoxy resin and the modified polydimethylsiloxane are mixed, acetone is added and stirred uniformly, catalyst B is added, and the reaction is stirred and heated under nitrogen protection. The curing agent is added, and the temperature is continued to rise. After the target temperature is reached, the reaction is stirred under nitrogen protection to obtain a silicone modified resin; S3: The modified silver powder is added to the silicone modified resin in portions, stirred uniformly, and then subjected to three-roll mill crushing and dispersion to obtain a conductive paste. The conductive paste is vacuum distilled, filtered to remove impurities, and a low-stress conductive silver adhesive product is obtained.

[0007] Further, the preparation method of the modified silver powder is as follows: The silver powder is added to anhydrous ethanol, ultrasonically dispersed, and an oligomeric dispersant is added. The reaction is stirred and heated to obtain a modified silver powder.

[0008] Further, the preparation method of the oligomeric dispersant is as follows: Polyethylene glycol monomethyl ether and mercaptopropionic acid are mixed, p-toluenesulfonic acid is added, and the reaction is stirred and heated under nitrogen protection. After the reaction is completed, the reaction solution is poured into diethyl ether, stirred at room temperature, and then filtered, washed and dried to obtain an oligomeric dispersant.

[0009] Further, in step S1, the amounts of the raw materials are as follows: dimethylcyclosiloxane 70-80 parts, hexamethyldisiloxane 3-5 parts, phenyltrimethoxysilane 5-10 parts, hydroxypolydimethylsiloxane 8-12 parts, distilled water 2-4 parts, and catalyst A 0.05-0.1 parts. Catalyst A is tetramethylammonium hydroxide. The stirring and heating reaction conditions are as follows: nitrogen protection, heating to 80-90°C, stirring speed 200-300 rpm, and reaction time 3-5 h. The vacuum distillation conditions are as follows: temperature 110-130°C, vacuum degree -0.09 MPa to -0.095 MPa, and distillation time 1-2 h.

[0010] Further, in the step S2, the amounts of the raw materials are as follows: 100-110 parts by weight of epoxy resin, 30-50 parts by weight of modified polydimethylsiloxane, 50-80 parts by weight of acetone, 0.5-0.8 parts by weight of catalyst B, and 0.8-1.2 parts by weight of curing agent. Catalyst B is stannous octoate, and the curing agent is dicyandiamide. The conditions for the reaction under nitrogen protection and stirring are as follows: a temperature of 50-60°C, a stirring speed of 300-400 rpm, and a reaction time of 2-3 hours. The target temperature for the subsequent temperature increase is 110-130°C, and the reaction is carried out under nitrogen protection and stirring at this temperature for 1-2 hours at a stirring speed of 200-300 rpm.

[0011] Further, in the step S3, the amounts of the raw materials are as follows: 60-70 parts by weight of modified silver powder and 30-40 parts by weight of silicone modified resin. The modified silver powder is added in 3-5 portions, and each portion is stirred for 10-15 minutes at a stirring speed of 500-600 rpm. The dispersion conditions for the three-roller mill are as follows: the roller spacing is adjusted to 20 μm, 10 μm, and 5 μm in sequence, the rolling is performed for 3-5 times, and the roller temperature is controlled to be 25-30°C. The vacuum distillation conditions are as follows: a temperature of 50-60°C, a vacuum degree of -0.09 MPa to -0.095 MPa, and a distillation time of 1-1.5 hours.

[0012] Further, the amounts of the raw materials for the modified silver powder are as follows: 60-70 parts by weight of silver powder, 200-300 parts by weight of anhydrous ethanol, and 2-3 parts by weight of oligomeric dispersant. The ultrasonic dispersion conditions are as follows: a frequency of 25-35 kHz and a dispersion time of 10-15 minutes. The conditions for heating, stirring, and reaction are as follows: a temperature of 40-50°C, a stirring speed of 400-500 rpm, and a reaction time of 1.5-2.5 hours. The centrifugation conditions are as follows: a speed of 8000-10000 rpm and a centrifugation time of 10-15 minutes. The drying conditions are as follows: a temperature of 50-60°C, a vacuum degree of -0.08 MPa to -0.09 MPa, and a drying time of 2-3 hours.

[0013] Further, the amounts of the raw materials for the oligomeric dispersant are as follows: 50 parts by weight of polyethylene glycol monomethyl ether, 10-11 parts by weight of mercaptopropionic acid, 0.4-0.6 parts by weight of p-toluenesulfonic acid, and 200-300 parts by weight of diethyl ether. The conditions for the reaction under nitrogen protection and stirring are as follows: a temperature of 75-85°C, a stirring speed of 200-300 rpm, and a reaction time of 3.5-4.5 hours. The stirring time at room temperature is 15-20 minutes. The standing time is 25-35 minutes. The washing is performed for 2-3 times with diethyl ether. The drying conditions are as follows: a temperature of 50-60°C, a vacuum degree of -0.08 MPa to -0.09 MPa, and a drying time of 1.5-2.5 hours.

[0014] In another aspect, the present application provides a low-stress conductive silver adhesive prepared by the above method.

[0015] The present application has the following advantages: The low-stress conductive silver adhesive prepared by the present application has excellent low-stress characteristics and gold interface bonding stability. By introducing a phenyl flexible segment into the modified polydimethylsiloxane and utilizing the grafting reaction of hydroxyl polydimethylsiloxane and epoxy resin, the internal stress generated during curing can be effectively reduced, avoiding damage to stress-sensitive chips such as GaN, and the interfacial bonding force with gold-plated chips and gold-plated substrates can be enhanced, reducing the risk of chip falling off and ensuring long-term reliability of the packaging structure.

[0016] The low-stress conductive silver adhesive prepared by the present application has stable conductive and thermal conductivity performance and strong process adaptability. With the targeted modification of silver powder by self-made oligomeric dispersant and the multi-stage rolling dispersion process of three-roll mill, the uniform distribution of silver powder in the resin system can be ensured, and stable conductive path and thermal efficiency can be maintained. At the same time, by adjusting the resin formula and solvent dosage, the viscosity and thixotropy of the silver adhesive can be optimized, reducing the plug and wire drawing phenomenon during dispensing, and adapting to the large-scale packaging production process.

[0017] The low-stress conductive silver adhesive prepared by the present application forms a dense and ductile three-dimensional network structure through the crosslinking and curing regulation of dicyandiamide modified silicone resin, which improves the tensile strength and anti-deformation ability of the silver adhesive. Under complex working conditions such as high and low temperature cycles, the silver adhesive can still maintain the stability of conductive and adhesive properties, meeting the reliability requirements of long-term operation of high-end electronic devices. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0019] In the embodiments of the present application, the epoxy resin is E-51 bisphenol A epoxy resin, which is purchased from Wuxi Xihua Chemical Technology Co., Ltd.

[0020] The hydroxyl polydimethylsiloxane used in the following embodiments is Kesheng COSiL F series hydroxyl polysiloxane, product name F-1.5, purchased from Jiangsu Kesheng New Material Co., Ltd.

[0021] The polyethylene glycol monomethyl ether used in the following embodiments is MPEG-500, purchased from Haian Petroleum Chemical Plant in Jiangsu Province.

[0022] The silver powder used in the following examples is QA301 ultra-fine spherical silver powder, which is purchased from Shenzhen Xingshengfeng Technology Co., Ltd.

[0023] The methoxy-terminated polydimethylsiloxane used in the following comparative examples is Jiangsu Kexing New Material Co., Ltd. COSiL® alkoxyl-terminated polysiloxane product J-15.

[0024] Example 1 A preparation method of a low-stress conductive silver adhesive includes the following preparation steps: S1: Add dimethylcyclosiloxane 75 parts, hexamethyldisiloxane 4 parts, phenyltrimethoxysilane 8 parts, Jiangsu Kexing New Material Co., Ltd. COSiL® F series hydroxyl polysiloxane product F-1.5 10 parts, and distilled water 3 parts into a reaction kettle and stir to mix uniformly, slowly add tetramethylammonium hydroxide 0.08 parts, introduce nitrogen gas with a purity of ≥99.99% and control the nitrogen gas flow rate at 50 mL / min, heat to 85°C, start mechanical stirring and control the stirring speed at 250 rpm, and stir at a constant temperature for 4 h under this condition. After the reaction is completed, stop heating, set the distillation temperature to 120°C and the vacuum degree to -0.092 MPa, and vacuum distill for 1.5 h to obtain modified polydimethylsiloxane.

[0025] S2: Add E-51 bisphenol A epoxy resin 105 parts and the prepared modified polydimethylsiloxane 40 parts into a reaction kettle, add acetone 65 parts, start mechanical stirring until mixed uniformly, then transfer the mixture to the reaction kettle, add stannous octoate 0.65 parts, introduce nitrogen gas with a purity of ≥99.99% and control the nitrogen gas flow rate at 50 mL / min, heat to 55°C, start mechanical stirring and control the stirring speed at 350 rpm, and stir at a constant temperature for 2.5 h under this condition. Then add dicyandiamide 1.0 parts, continue to heat to 120°C, adjust the stirring speed to 250 rpm, and stir at this temperature under nitrogen protection for 1.5 h to obtain a silicone-modified resin.

[0026] S3: Put 50 parts of polyethylene glycol monomethyl ether with a specification of MPEG-500 and 10.5 parts of mercaptopropionic acid into a reaction kettle, start mechanical stirring and control the stirring speed at 250 rpm, then add 0.5 parts of p-toluenesulfonic acid, introduce nitrogen gas with a purity of ≥ 99.99% and control the nitrogen flow rate at 50 mL / min, heat to 80°C, and under this condition, stir for 4 h, after the reaction is completed, slowly pour the reaction liquid into 250 parts of ether, stir for 18 min at room temperature, then stand for 30 min, then collect the precipitate by filtering with a Buchner funnel, wash the precipitate with ether twice, and then put the washed precipitate into a vacuum drying oven, control the drying temperature at 55°C and the vacuum degree at -0.085 MPa, and dry for 2 h to obtain an oligomeric dispersant; mix 65 parts of QA301 ultra-fine spherical silver powder and 250 parts of anhydrous ethanol, ultrasonically disperse for 12 min, set the ultrasonic frequency at 30 kHz, then add the ultrasonically dispersed material into the reaction kettle, add 2.5 parts of the prepared oligomeric dispersant, start stirring and control the stirring speed at 450 rpm, heat to 45°C, and under this condition, stir for 2 h, after the reaction is completed, transfer the mixture to a centrifugal stirrer and set the stirring speed at 9000 rpm, centrifuge for 12 min, collect the centrifuged solid particles, put the solid particles into a vacuum drying oven, control the drying temperature at 55°C and the vacuum degree at -0.085 MPa, and dry for 2.5 h to obtain modified silver powder; add 35 parts of the prepared silicone modified resin into a stirring tank, add 65 parts of the prepared modified silver powder in 4 portions, start stirring after adding each portion of the modified silver powder and control the stirring speed at 550 rpm, stir for 12 min, after all the modified silver powder is added and stirred uniformly, transfer the mixed slurry to a three-roll mill, set the roll spacing of the three-roll mill at 20 μm, 10 μm and 5 μm in sequence, control the roll temperature at 28°C, and roll for 4 times to obtain a conductive paste, transfer the conductive paste to a vacuum distillation device, set the distillation temperature at 55°C and the vacuum degree at -0.092 MPa, and vacuum distill for 1.2 h, after the distillation is completed, remove the impurities by suction filtration with a filter membrane with a pore size of 0.5 μm to obtain a low-stress conductive silver adhesive finished product.

[0027] Example 2 S1: Put 70 parts of dimethylcyclosiloxane, 3 parts of hexamethyldisiloxane, 5 parts of phenyltrimethoxysilane, 8 parts of hydroxyl polysiloxane with product name F-1.5, and 2 parts of distilled water into a reaction kettle and stir to mix uniformly, slowly add 0.05 parts of tetramethylammonium hydroxide, introduce nitrogen gas with a purity of ≥ 99.99% and control the nitrogen flow rate at 50 mL / min, heat to 80°C, start mechanical stirring and control the stirring speed at 200 rpm, and under this condition, stir for 3 h, after the reaction is completed, stop heating, set the distillation temperature at 110°C and the vacuum degree at -0.09 MPa, and vacuum distill for 1 h to obtain modified polydimethylsiloxane.

[0028] S2: E-51 bisphenol A epoxy resin 100 parts and prepared modified polydimethylsiloxane 30 parts were added to the reaction kettle, then acetone 50 parts was added and mixed, mechanical stirring was started until the mixture was uniform, then the mixture was transferred to the reaction kettle, stannous octoate 0.5 parts was added, nitrogen gas with a purity of ≥99.99% was introduced and the nitrogen flow rate was controlled at 50 mL / min, the temperature was raised to 50°C, mechanical stirring was started and the stirring speed was controlled at 300 rpm, under these conditions, constant temperature stirring was carried out for 2 h, then dicyandiamide 0.8 parts was added, the temperature was raised to 110°C, the stirring speed was adjusted to 200 rpm, and under this temperature, nitrogen protection stirring was carried out for 1 h, to obtain a silicone modified resin.

[0029] S3: Polyethylene glycol monomethyl ether with a specification of MPEG-500 50 parts and mercaptopropionic acid 10 parts were added to the reaction kettle, mechanical stirring was started and the stirring speed was controlled at 200 rpm, then p-toluenesulfonic acid 0.4 parts was added, nitrogen gas with a purity of ≥99.99% was introduced and the nitrogen flow rate was controlled at 50 mL / min, the temperature was raised to 75°C, under these conditions, constant temperature stirring was carried out for 3.5 h, after the reaction was completed, the reaction liquid was slowly poured into 200 parts of ether, stirred at room temperature for 15 min, then placed for 25 min, then the precipitate was collected by filtration with a Buchner funnel and washed twice with ether, the washed precipitate was placed in a vacuum drying oven, the drying temperature was controlled at 50°C and the vacuum degree was controlled at -0.08 MPa, and dried for 1.5 h, to obtain an oligomeric dispersant; QA301 ultrafine spherical silver powder 60 parts and anhydrous ethanol 200 parts were mixed and ultrasonically dispersed for 10 min, the ultrasonic frequency was set at 25 kHz, then the ultrasonically dispersed material was added to the reaction kettle, the prepared oligomeric dispersant 2 parts was added, stirring was started and the stirring speed was controlled at 400 rpm, the temperature was raised to 40°C, under these conditions, constant temperature stirring was carried out for 1.5 h, after the reaction was completed, the mixture was transferred to a centrifugal stirrer and the stirring speed was set at 8000 rpm, centrifuged for 10 min, the centrifuged solid particles were collected, placed in a vacuum drying oven, the drying temperature was controlled at 50°C and the vacuum degree was controlled at -0.08 MPa, and dried for 2 h, to obtain a modified silver powder; the prepared silicone modified resin 30 parts was added to a stirring tank, the prepared modified silver powder 60 parts was added in 3 portions, stirring was started after each addition of the modified silver powder and the stirring speed was controlled at 500 rpm, and stirred for 10 min, after all the modified silver powder was added and stirred uniformly, the mixed slurry was transferred to a three-roll mill, the three-roll mill roll spacing was set at 20 μm, 10 μm and 5 μm in sequence, and the roll temperature was controlled at 25°C, and rolled 3 times, to obtain a conductive slurry, the conductive slurry was transferred to a vacuum distillation device, the distillation temperature was set at 50°C and the vacuum degree was set at -0.09 MPa, and vacuum distilled for 1 h, after the distillation was completed, impurities were removed by suction filtration with a filter membrane with a pore size of 0.5 μm, to obtain a low-stress conductive silver adhesive finished product.

[0030] Example 3 S1: Add 80 parts of dimethylcyclosiloxane, 5 parts of hexamethyldisiloxane, 10 parts of phenyltrimethoxysilane, 12 parts of COSiL®F series hydroxyl polysiloxane (product name F-1.5), and 4 parts of distilled water to the reactor and stir until homogeneous. Slowly add 0.1 parts of tetramethylammonium hydroxide, introduce nitrogen gas with a purity ≥99.99% and control the nitrogen flow rate at 50 mL / min, raise the temperature to 90℃, turn on the mechanical stirrer and control the stirring speed at 300 rpm, and stir the reaction at a constant temperature for 5 hours. After the reaction is completed, stop heating, set the distillation temperature to 130℃ and the vacuum degree to -0.095 MPa, and vacuum distill for 2 hours to obtain modified polydimethylsiloxane.

[0031] S2: Add 110 parts of E-51 bisphenol A epoxy resin and 50 parts of the prepared modified polydimethylsiloxane to a reaction vessel, then add 80 parts of acetone and mix. Turn on mechanical stirring until the mixture is uniform. Then transfer the mixture to a reaction vessel, add 0.8 parts of stannous octoate, introduce nitrogen gas with a purity ≥99.99% and control the nitrogen flow rate at 50 mL / min, raise the temperature to 60℃, turn on mechanical stirring and control the stirring speed at 400 rpm, and stir under this condition for 3 hours. Then add 1.2 parts of dicyandiamide, continue to raise the temperature to 130℃, adjust the stirring speed to 300 rpm, and stir under nitrogen protection at this temperature for 2 hours to obtain organosilicon modified resin.

[0032] S3: Add 50 parts of polyethylene glycol monomethyl ether (MPEG-500 specification) and 11 parts of mercaptopropionic acid to a reaction vessel. Turn on the mechanical stirrer and control the stirring speed at 300 rpm. Then add 0.6 parts of p-toluenesulfonic acid. Purge with nitrogen gas of ≥99.99% purity at a flow rate of 50 mL / min. Heat to 85℃ and stir under this condition for 4.5 h. After the reaction is complete, slowly pour the reaction solution into 300 parts of diethyl ether. Stir at room temperature for 20 min and let stand for 35 min. Then use a Buchner funnel to measure the mixture. The precipitate was collected by filtration and washed three times with diethyl ether. The washed precipitate was then placed in a vacuum drying oven at 60°C and -0.09 MPa for 2.5 hours to obtain the oligomerizing dispersant. 70 parts of QA301 ultrafine spherical silver powder and 300 parts of anhydrous ethanol were mixed and ultrasonically dispersed for 15 minutes at a frequency of 35 kHz. The ultrasonically dispersed material was then added to a reaction vessel, along with 3 parts of the prepared oligomerizing dispersant. Stirring was started at 500 rpm, and the temperature was increased. The mixture was stirred at 50℃ for 2.5 hours. After the reaction, the mixture was transferred to a centrifuge at 10,000 rpm for 15 minutes. The solid particles were collected and placed in a vacuum drying oven at 60℃ and -0.09 MPa for 3 hours to obtain modified silver powder. 40 parts of the prepared organosilicon modified resin were added to a mixing tank, followed by 70 parts of the prepared modified silver powder in 5 separate additions. Stirring was started after each addition of modified silver powder, and the mixture was controlled to maintain a constant temperature. The stirring speed was 600 rpm, and the stirring time was 15 min. After all the modified silver powder was added and stirred evenly, the mixed slurry was transferred to a three-roll mill. The roller spacing of the three-roll mill was set to 20 μm, 10 μm and 5 μm respectively, and the roller temperature was controlled at 30℃. The mill was rolled 5 times to obtain a conductive slurry. The conductive slurry was then transferred to a vacuum distillation device. The distillation temperature was set to 60℃ and the vacuum degree was set to -0.095 MPa. Vacuum distillation was carried out for 1.5 h. After distillation, the slurry was filtered with a filter membrane with a pore size of 0.5 μm to remove impurities and obtain the low-stress conductive silver paste product.

[0033] Comparative Example 1 Compared with Example 1, this comparative example did not add phenyltrimethoxysilane in step S1, and the remaining steps and parameters were the same. This comparative example will not be repeated here. The final product is a low-stress conductive silver paste.

[0034] Comparative Example 2 Compared with Example 1, in step S1, "COSiL® F series hydroxyl polysiloxane with product name F-1.5" is replaced with "COSiL® alkoxy-terminated polysiloxane with product name J-15". All other steps and parameters are the same, and will not be repeated in this comparative example. The final product is a low-stress conductive silver paste.

[0035] Comparative Example 3 Compared with Example 1, in this comparative example, the "self-made oligomer dispersant in S3" in step S1 is replaced with "sodium dodecylbenzenesulfonate". All other steps and parameters are the same, and will not be repeated in this comparative example. The final product is a low-stress conductive silver paste.

[0036] Comparative Example 4 Compared with Example 1, the preparation of the oligomer dispersant in this comparative example omits p-toluenesulfonic acid, while the remaining steps and parameters are the same. The details of this comparative example will not be repeated here. The final product is a low-stress conductive silver paste.

[0037] Comparative Example 5 Compared with Example 1, this comparative example did not add dicyandiamide in step S2, and the remaining steps and parameters were the same. The details of this comparative example will not be repeated here. The final product is a low-stress conductive silver paste.

[0038] The performance of the low-stress conductive silver paste products prepared in Examples 1-3 and Comparative Examples 1-5 was tested, and the results are recorded in Table 1.

[0039] 1. Shear force detection at the gold interface: Referring to GB / T7124-2008 "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)", a gold-plated silicon chip with a size of 2mm×2mm×0.3mm (gold layer thickness 500nm) was selected as the substrate A, and a gold-plated oxygen-free copper substrate with a gold layer thickness of 800nm ​​and a size of 20mm×10mm×2mm was selected as the substrate B. Conductive silver paste was uniformly coated on the gold-plated bonding area (2mm×2mm) of the substrate for each sample, and the coating thickness was controlled at 30μm. After the gold-plated chip was attached, a 500g weight was applied for pressure holding, and curing was completed according to the sample curing conditions (120℃ / 1.5h). After cooling to room temperature (25℃), a universal testing machine (model: WDW-5) was used to apply tensile force along the shear direction at a loading speed of 1mm / min until the chip separated from the substrate. The maximum load value (unit: kg) was recorded. Five parallel samples were tested for each sample, and the arithmetic mean was taken as the gold interface shear force.

[0040] 2. Detection of residual adhesive at the gold interface: After the gold interface shear force test was completed, the separated gold-plated chip and gold-plated substrate were collected. Using a metallographic microscope (model: OLYMPUS GX51) at 200x magnification, the residual adhesive on the bonding surface of the chip and substrate was observed. The area of ​​conductive silver paste remaining on the bonding surface was measured using the microscope's built-in image analysis system, and calculated according to the formula… The initial bonding area is calculated to be 2mm × 2mm = 4mm²; three separated chip-substrate pairs are selected for each sample for testing, and the arithmetic mean is taken as the percentage of residual adhesive at the gold interface.

[0041] 3. Thermal conductivity detection: Referring to GB / T22588-2008 "Measurement of thermal diffusivity or thermal conductivity by flash method", each sample conductive silver adhesive is made into a circular thin sheet sample with a diameter of 12.7 mm and a thickness of 2 mm according to the curing condition (120℃ / 1.5h), and the sample surface is ensured to be flat and bubble-free; a laser flash thermal conductivity instrument (model: NETZSCH LFA467) is used to emit a laser pulse to one side of the sample under the condition of room temperature (25℃) and nitrogen protection (flow rate 50mL / min), and the temperature change curve of the other side is recorded, and the thermal diffusivity is calculated by the software of the instrument, and the thermal conductivity (unit: W / (m·K) is calculated according to the formula "D=α·ρ·c" combined with the density (measured by Archimedes drainage method) and the specific heat capacity (measured by differential scanning calorimeter DSC-60) of the sample. Each sample is tested 3 times, and the arithmetic mean value is taken.

[0042] 4. Young's modulus detection: Referring to GB / T1040.1-2006 "Determination of tensile properties of plastics - Part 1: General principles", each sample conductive silver adhesive is made into a dumbbell-shaped standard sample (gauge length 25mm, width 4mm, thickness 2mm) according to the curing condition (120℃ / 1.5h); the sample is placed in a constant temperature environment box (temperature control is 25℃±1℃) for 1h, and then installed on a universal material testing machine (model: WDW-5), and a tensile force is applied at a stretching speed of 5mm / min, and the stress-strain curve of the sample is recorded; 3 different stress points are selected in the elastic stage of the curve, and the elastic modulus is calculated according to the formula "E=σ / ε", and 5 groups of parallel samples are tested for each sample, and the arithmetic mean value is taken as the Young's modulus at 25℃ (unit: MPa).

[0043] Table 1: Performance test results of low-stress conductive silver adhesive finished product The low-stress conductive silver adhesive finished product of examples 1-3 has excellent comprehensive performance, and presents a balanced and high-quality situation matching the gradient optimization of raw material dosage in terms of gold interface bonding reliability, low-stress characteristics, thermal conductivity efficiency and structural mechanics stability, which is due to the synergistic design of key raw materials and precise regulation of process parameters in the preparation process, from the introduction of flexible segments of modified polydimethylsiloxane, the construction of crosslinked network of silicone modified resin, to the stable dispersion of modified silver powder, forming a complete system with complementary functions, which can meet the core needs of high bonding strength, low curing internal stress and stable thermal conductivity performance of conductive silver adhesive in high-end radio frequency and power chip packaging, and adapt to the long-term stable operation requirements of stress-sensitive chips such as GaN and gold interface packaging.

[0044] ​​Comparative Example 1 and Example 1 can be compared, Comparative Example 1 is not added phenyl trimethoxysilane, missing the ability to introduce flexible modified polydimethylsilane phenyl segment, leading to the resin system rigidity significantly enhanced, not only weaken the silver glue and gold interface between the adhesion, but also makes the silver glue after curing the internal stress increases, ultimately reflect the gold interface adhesion performance and low stress characteristics of the double decline, thus proving the phenyl trimethoxysilane on the balance of silver glue rigidity and flexibility, the key role of optimizing the adhesion effect of gold interface.

[0045] Comparative Example 2 and Example 1 can be compared, Comparative Example 2 with alkoxyl terminated polysiloxane instead of hydroxyl polydimethylsiloxane, due to the alkoxyl group cannot be effectively grafted with epoxy group in epoxy resin, destroy the formation of "epoxy-silicone" interpenetrating network, leading to the silver glue internal interface bonding force is greatly weakened, both reduce the adhesion strength with gold interface, but also affect the stability of the thermal conductivity, fully illustrate the importance of hydroxyl terminated structure to ensure the grafting compatibility of resin system, maintain the comprehensive performance of silver glue.

[0046] Comparative Example 3 and Example 1 can be compared, Comparative Example 3 with sodium dodecyl benzene sulfonate instead of self-made oligomeric dispersant, because the market dispersant only contains a single lipophilic group, lack of self-made dispersant "silver site-resin segment" of the dual functional group design, can not realize the stable dispersion and close combination of silver powder in resin, leading to the aggregation of silver powder, not only reduce the thermal efficiency, but also slightly weaken the adhesion effect of gold interface, highlight the self-made oligomeric dispersant on the targeted optimization of silver powder dispersibility and interface bonding force.

[0047] Comparative Example 4 and Example 1 can be compared, Comparative Example 4 in the preparation of oligomeric dispersant, omit p-toluene sulfonic acid, due to the lack of catalysis of protonic acid, the esterification reaction of polyethylene glycol monomethyl ether and mercaptopropionic acid can not be fully carried out, leading to the incomplete structure of the dual functional group of oligomeric dispersant, its ability to disperse silver powder, adapt to the resin is significantly decreased, and then the adhesion strength of silver glue and the thermal conductivity of gold interface are negatively affected, proving that p-toluene sulfonic acid has a key catalytic value to ensure the integrity of the structure of oligomeric dispersant and the performance of the standard.

[0048] The above content is only an example and description of the concept of the present application. Those skilled in the art can make various modifications or supplements to the described specific embodiments or use similar ways to replace them, as long as they do not deviate from the concept of the invention or exceed the scope defined by the present claims, which shall belong to the protection scope of the present application.

Claims

1. A method for preparing a low-stress conductive silver paste, characterized in that, The preparation steps include: S1: Mix dimethylcyclosiloxane, hexamethyldisiloxane, phenyltrimethoxysilane, hydroxypolydimethylsiloxane and distilled water, slowly add catalyst A, stir and react under heating, vacuum distill after the reaction to obtain modified polydimethylsiloxane; S2: Mix epoxy resin and modified polydimethylsiloxane, stir and mix uniformly after adding acetone, add catalyst B, stir and react under heating under nitrogen protection, add curing agent, continue to heat, stir and react under nitrogen protection after the temperature reaches the target temperature to obtain silicone modified resin; S3: Add modified silver powder into the silicone modified resin, stir uniformly, perform three-roll mill crushing and dispersion to obtain conductive paste, vacuum distill the conductive paste, remove impurities by filtration to obtain low-stress conductive silver adhesive finished product.

2. The method for preparing a low-stress conductive silver paste according to claim 1, characterized in that, The preparation method of the modified silver powder is as follows: Add silver powder into anhydrous ethanol, ultrasonically disperse, add oligomeric dispersant, stir and heat under heating, centrifuge and dry after cooling to obtain modified silver powder.

3. The method of claim 2, wherein the low-stress conductive silver paste is prepared by mixing the silver powder, the glass frit, the organic vehicle, and the dispersant, and then performing a ball milling process. The preparation method of the oligomeric dispersant is as follows: Mix polyethylene glycol monomethyl ether and mercaptopropionic acid, add p-toluenesulfonic acid, stir and react under heating under nitrogen protection, pour the reaction solution into diethyl ether after the reaction, stir at room temperature, filter, wash and dry after standing to obtain oligomeric dispersant.

4. The method of claim 1, wherein the low-stress conductive silver paste is prepared by mixing silver powder, glass frit, and an organic vehicle. In the step S1, the dosages of the raw materials are respectively 70-80 parts of dimethylcyclosiloxane, 3-5 parts of hexamethyldisiloxane, 5-10 parts of phenyltrimethoxysilane, 8-12 parts of hydroxypolydimethylsiloxane, 2-4 parts of distilled water and 0.05-0.1 parts of catalyst A; catalyst A is tetramethylammonium hydroxide; the stirring and reaction under heating conditions are as follows: under nitrogen protection, the temperature is increased to 80-90℃, the stirring speed is 200-300 rpm, and the reaction time is 3-5 h; the vacuum distillation conditions are as follows: the temperature is 110-130℃, the vacuum degree is -0.09 MPa to -0.095 MPa, and the distillation time is 1-2 h.

5. The method of claim 1, wherein the low-stress conductive silver paste is prepared by mixing silver powder, glass frit, and an organic vehicle, and then performing a drying process, a calcination process, and a milling process. In the step S2, the dosages of the raw materials are respectively 100-110 parts of epoxy resin, 30-50 parts of modified polydimethylsiloxane, 50-80 parts of acetone, 0.5-0.8 parts of catalyst B and 0.8-1.2 parts of curing agent; catalyst B is stannous octoate, and the curing agent is dicyandiamide; the stirring and reaction under heating conditions under nitrogen protection are as follows: the temperature is 50-60℃, the stirring speed is 300-400 rpm, and the reaction time is 2-3 h; the target temperature for the continued heating is 110-130℃, the stirring speed is 200-300 rpm, and the nitrogen protection stirring and reaction time is 1-2 h at this temperature.

6. The method of claim 1, wherein the low-stress conductive silver paste is prepared by mixing silver powder, glass frit, and an organic vehicle. In the step S3, the amount of each raw material is 60-70 parts of modified silver powder, 30-40 parts of silicone modified resin, by weight; the modified silver powder is added for 3-5 times, and stirred for 10-15 minutes after each addition, at a stirring speed of 500-600 rpm; the three-roll mill grinding and dispersion conditions are: the roll spacing is adjusted to 20 μm, 10 μm and 5 μm in sequence, and grinding is performed for 3-5 times, with the roll temperature controlled at 25-30°C; the vacuum distillation conditions are: temperature 50-60°C, vacuum degree -0.09 MPa to -0.095 MPa, and distillation is performed for 1-1.5 hours.

7. The method of claim 2, wherein the low-stress conductive silver paste is prepared by mixing silver powder, glass frit, and an organic vehicle, and then performing a drying process, a calcination process, and a milling process. The raw materials of the modified silver powder are 60-70 parts of silver powder, 200-300 parts of anhydrous ethanol and 2-3 parts of oligomeric dispersant, by weight; the ultrasonic dispersion conditions are: frequency 25-35 kHz, and dispersion is performed for 10-15 minutes; the heating and stirring conditions are: temperature 40-50°C, stirring speed 400-500 rpm, and reaction is performed for 1.5-2.5 hours; the centrifugation conditions are: speed 8000-10000 rpm, and centrifugation is performed for 10-15 minutes; and the drying conditions are: temperature 50-60°C, vacuum degree -0.08 MPa to -0.09 MPa, and drying is performed for 2-3 hours.

8. The method of claim 3, wherein the low-stress conductive silver paste is prepared by mixing silver powder, glass frit, and an organic vehicle, and then performing a drying process, a calcination process, and a milling process. The raw materials of the oligomeric dispersant are 50 parts of polyethylene glycol monomethyl ether, 10-11 parts of mercaptopropionic acid, 0.4-0.6 parts of p-toluenesulfonic acid and 200-300 parts of diethyl ether, by weight; the nitrogen-protected heating and stirring reaction conditions are: temperature 75-85°C, stirring speed 200-300 rpm, and reaction is performed for 3.5-4.5 hours; the room temperature stirring time is 15-20 minutes; the standing time is 25-35 minutes; the washing is performed with diethyl ether for 2-3 times; and the drying conditions are: temperature 50-60°C, vacuum degree -0.08 MPa to -0.09 MPa, and drying is performed for 1.5-2.5 hours.

9. A low-stress conductive silver adhesive prepared by the method of any one of claims 1-8.

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