Conductive elastic silver paste suitable for 3D printing elastic probe and its preparation method and application

Abstract

The present invention belongs to the field of 3D printing technology, and specifically relates to a conductive elastic silver paste suitable for 3D printing elastic probes, and a preparation method and application thereof. The present invention adopts low-cost micron-sized silver particles and a polymer elastic matrix to mix and prepare a conductive elastic silver paste, which helps to achieve a higher conductivity. The micron-sized silver particles of the present invention have good interface compatibility with the polymer elastic matrix, which effectively improves the adhesion of the conductive elastic silver paste, avoids the phenomenon of peeling, shedding, and stratification of the silver particles, and further improves the 3D printing performance of the conductive elastic silver paste. The conductive elastic silver paste of the present invention has excellent elastic shrinkage performance while ensuring high conductivity, which helps to realize the preparation of elastic probes with small size, large elastic shrinkage, strong conductivity and low cost through 3D printing technology.

Description

Technical Field

[0001] The present invention belongs to the field of 3D printing technology, and further relates to the field of printed electronic device material technology, and specifically relates to a conductive elastic silver paste suitable for 3D printing elastic probes, and a preparation method and application thereof. Background Art

[0002] In recent years, electronic digital products have become thinner and lighter, and their functions have become more and more powerful. At the same time, semiconductor chip manufacturing technology has made great progress and has entered the field below 3 nanometers. The size of integrated circuits (ICs) is getting smaller and smaller, which has led to an increasing number of chip pins and a continuous decrease in pin spacing, further making wafer preparation, chip or die packaging, and chip testing more and more sophisticated and complex.

[0003] Wafer testing refers to the electrical testing of the chips on the wafer before the wafer is sliced ​​and packaged to confirm whether its electrical characteristics and logical functions meet the specifications, screen out bad chips and mark them, and no longer perform subsequent packaging to avoid wasting resources. The equipment used in wafer testing includes testers, probe stations and probe cards. During wafer testing, the test signal sent by the tester is transmitted to the probe card on the tester through the communication interface. The probes on the probe card contact the solder joints of the chips on the wafer for communication, and the test data is fed back to the tester for comparison, thereby completing the test.

[0004] When testing the chip, the probe needs to frequently contact the contact points on the chip, which can easily cause wear of the probe and affect the service life of the probe. At the same time, because the spacing between the pads on the chip is getting smaller and smaller, and the spacing between the probes on the traditional vertical probe card is large, it is difficult to meet the testing needs of chips with smaller and smaller pad spacing, resulting in increased difficulty and cost in preparing probes with smaller spacing. In addition, because the probe is worn, the size becomes shorter or the chip surface is not flat enough, some probes are not in contact with the chip surface, which is prone to impedance instability and transient disconnection, thereby affecting the accuracy of the test results. In order to ensure the test effect, it is necessary to ensure that the probe has a good anti-mechanical fatigue effect while taking into account that all probes can effectively contact the contact points on the chip at the same time. In view of this, it is necessary to provide an elastic probe to improve the service life of the probe and reasonably and effectively control the manufacturing cost of the probe, which can meet the needs of parallel testing, array arrangement, etc., and also have good contact characteristics and high-frequency transmission characteristics.

[0005] At present, the commonly used methods for manufacturing elastic probes mainly include molding injection molding, hot pressing sintering, UV curing technology, plasma treatment, etc. The molding injection molding method can realize mass production by making a mold of elastic material for injection molding, and the cost is low, but the mold manufacturing is complicated and the mold geometry accuracy is poor. The hot pressing sintering method is to sinter the powder of elastic polymer material under high temperature and high pressure. It does not require any organic solvents and is green and environmentally friendly, but it is easily affected by high temperature, which greatly limits the selection of elastic polymer materials and makes it difficult to prepare elastic probes with refined structures. The use of UV curing technology and plasma treatment to prepare elastic probes is difficult to achieve mass industrial production due to the large investment in manufacturing equipment and high cost. For example, patent CN100487463C discloses a method for preparing a micro-electromechanical system probe card based on an elastic substrate. The method uses secondary photolithography and electroforming processes to sequentially coat polydimethylsiloxane and polyimide on the surface of a glass or silicon substrate to form an elastic substrate, which is used to replace the current cantilever beam and simply supported beam structure to withstand and generate greater stress for piercing the oxide film, and adjust the displacement of the probe by changing the thickness of the elastic substrate. Circuit leads are arranged on the elastic substrate, and the probes are located at the top of the circuit leads and arranged in an array according to the position of the chip pins to be tested. The probe tips correspond to the corresponding chip pin positions one by one. The bottom end of the probe is a circuit lead obtained by electroforming. The circuit lead is connected from the bottom end of the probe to the periphery of the probe card, and the periphery is then connected to the corresponding printed circuit board by spot welding, thereby connecting the signal circuit from the probe to the test machine. This solution has the advantages of simple preparation process, low cost, and high probe density. However, the connection line between it and the external printed circuit board is too long, and spot welding connection is required, resulting in a low yield rate.

[0006] 3D printing, also known as additive manufacturing, is a technology that uses computers to build three-dimensional models of objects and directly perform molding. Compared with traditional molding technology, 3D printing can automatically and accurately manufacture parts of any complex shape through program control, which can greatly reduce processing procedures, shorten processing cycles, increase material utilization, and reduce production costs. It is widely used in electronic products, automobiles, aerospace, medical, military, geographic information, and art design. However, there is no clear solution to use 3D printing technology to manufacture elastic probes with small size, short spacing, large number, large elastic shrinkage, and low cost while ensuring that the probes have good contact characteristics, high-frequency transmission characteristics, and test accuracy.

[0007] 3D printing technology is applied in the microelectronics industry. Conductive slurry is required as the printing material ink for printing. After printing, the final product is obtained by sintering. This puts high demands on the performance indicators of the conductive slurry. The slurry used should have excellent conformality and conductivity on the basis of meeting the smooth discharge of the fine nozzle. In the prior art, conductive metal silver is usually used as a metal powder mixed with commonly used polymers such as polyurethane resin to prepare conductive slurry. Due to its poor adhesion, it is difficult for polyurethane resin and other polymers to fully and effectively coat the conductive metal silver, which makes the conductive metal silver easy to peel off and delaminate with polyurethane resin and other polymers, thereby destroying the conductive path between the metal silver particles, further reducing the conductivity and structural stability of the prepared elastic probe. In addition, the heat resistance temperature of polyurethane resin is between -20℃ and 120℃. Polymers such as polyurethane resin will decompose at 220℃, and the high temperature resistance is poor, which affects its use in electronic equipment. Summary of the invention

[0008] The present invention aims to solve the above problems and provide a conductive elastic silver paste suitable for 3D printed elastic probes and a preparation method thereof, so as to realize the preparation of elastic probes with small size, large elastic shrinkage, strong conductivity and low cost through 3D printing technology, and apply the prepared conductive elastic silver paste to the fields of micro-nano chips, printed electronics, sensors, biological probes, and semiconductor devices.

[0009] To achieve the above-mentioned purpose, the present invention is implemented by the following technical solutions:

[0010] A conductive elastic silver paste suitable for 3D printing elastic probes, comprising silver particles, a polymer elastic matrix and an organic solvent; wherein:

[0011] The particle size of the silver particles is 7 to 15 μm.

[0012] At present, the commonly used conductive silver paste is mainly prepared by mixing nano-scale silver particles with polymer matrix materials such as polyurethane resin or epoxy resin, acrylic resin, etc. Due to the large contact resistance between nano-scale silver particles, the conductivity of the prepared probe is easily reduced, and it is difficult to meet the performance requirements for high-frequency testing. At the same time, due to their ultra-high specific surface area, nano-scale silver particles are very likely to agglomerate and precipitate during the preparation of the slurry, which causes the stability of the slurry to deteriorate and affects the service life of the conductive silver paste. And because it is difficult to disperse evenly, the viscosity of the conductive silver paste is too high, and the conductive silver paste is difficult to flow and spread evenly. It is difficult to accurately control the layer thickness and shape of the product when used for 3D printing, which further increases the difficulty of the preparation process, resulting in unstable product quality and easy clogging of the printing equipment. In addition, the amount of silver particles contained in the conductive silver paste is too much. Due to the high hardness of the silver particles, it is very easy to destroy the flexibility of the polymer matrix material, resulting in a significant decrease in the elasticity of the slurry. At the same time, the interface strength between nano-scale silver particles and the polymer matrix material is relatively weak. Under the action of stress, the nano-scale silver particles are prone to peeling, falling off, and stratification, which destroys the continuity of the polymer matrix material and further reduces the elastic properties of the conductive silver paste.

[0013] In addition, after many experiments, the inventors found that although silver particles mixed with polymer matrix materials such as polyurethane resin, epoxy resin, and acrylic resin can obtain a certain elasticity and good stretchability, the prepared probe is difficult to shrink and has irreversibility, which further limits the application scope of the conductive silver paste. In addition, when it is applied to 3D printed probes, due to the large internal stress generated during the curing and shrinking process, cracks and delamination occur between the conductive silver paste layers, making the final prepared 3D printed probe fragile and fragile, prone to collapse or deformation, difficult to maintain the shape, and unable to achieve precise control of complex size shapes. For example, patent CN116130143A discloses a high temperature resistant elastic conductive silver paste and its preparation method, which is obtained by adding a modified epoxy resin matrix to silver powder to obtain a conductive silver paste with high conductivity, high heat resistance, and good impact resistance.

[0014] Therefore, the present invention provides a conductive elastic silver paste suitable for 3D printing elastic probes, including silver particles, a polymer elastic matrix and an organic solvent. Among them, the particle size of the silver particles is 7 to 15 μm. The inventors use low-cost micron-sized silver particles and a polymer elastic matrix to mix and prepare conductive elastic silver paste. Since the micron-sized silver particles are small in size, the contact area is large, and the contact resistance is small, it is helpful to achieve a higher conductivity. At the same time, the micron-sized silver particles have a small specific surface area, are not prone to oxidation and deterioration, and are not prone to agglomeration and sedimentation during the preparation of the conductive elastic silver paste. They have good stability and dispersibility, and good process reproducibility. In addition, the interface compatibility between the micron-sized silver particles and the polymer elastic matrix is ​​good, which improves the adhesion of the conductive elastic silver paste, effectively avoids the phenomenon of peeling, falling off, and stratification of the silver particles, and further improves the 3D printing performance of the conductive elastic silver paste.

[0015] Preferably, a conductive filler is also included.

[0016] As further preferred, the conductive filler is a combination of one or more of conductive polymers, metals, alloys, and carbon nanomaterials.

[0017] Preferably, the conductive filler is a combination of one or more of carbon nanotubes, carbon nanowires, graphite, graphene, carbon black, nickel carbon, silver, silver-coated aluminum, and silver-coated copper.

[0018] Adding conductive fillers to the conductive elastic silver paste helps to improve the conductivity while enhancing the mechanical strength and wear resistance of the prepared conductive elastic probe. At the same time, the addition of conductive fillers is conducive to improving the fluidity of the conductive elastic silver paste, enhancing the adhesion between micron-sized silver particles and the polymer elastic matrix, and further effectively improving the quality and molding effect of the 3D printed elastic probe. In addition, the filling of an appropriate amount of conductive fillers helps to reduce the cost of the conductive elastic silver paste.

[0019] Among them, carbon nanotube conductive fillers have excellent conductive properties and can form a conductive network in the conductive elastic silver paste, which reduces the overall resistance of the conductive elastic silver paste, thereby effectively improving its conductive properties. In addition, carbon nanotube conductive fillers have extremely high elastic modulus and strength, which helps to enhance the mechanical properties of the polymer elastic matrix and effectively extend the service life of the conductive elastic silver paste. At the same time, the addition of carbon nanotube conductive fillers helps to increase the viscosity and fluidity of the conductive elastic silver paste, further improve the tensile strength and fatigue resistance of the elastic probe, and effectively improve the accuracy and quality of the 3D printed elastic probe. In addition, because the specific surface area of ​​carbon nanotube conductive fillers is relatively large and they have strong chemical inertness, they can effectively improve the stability and antioxidant properties of the conductive elastic silver paste.

[0020] Preferably, the added mass of the conductive filler accounts for 5-25% of the mass of the conductive elastic silver paste.

[0021] When the added mass of the conductive filler is less than 5% of the mass of the conductive elastic silver paste, it is difficult to form a good conductive network structure, resulting in a large resistance of the conductive elastic silver paste and reduced conductivity. At the same time, due to the small amount of conductive filler added, the interaction between the conductive filler and the polymer elastic matrix is ​​weakened, resulting in reduced mechanical strength and stability of the conductive elastic silver paste, further affecting its service life.

[0022] When the added mass of the conductive filler is higher than 25% of the mass of the conductive elastic silver paste, excessive conductive filler is prone to agglomeration and sedimentation, resulting in poor uniformity of the conductive elastic silver paste, unstable conductivity, and decreased mechanical strength and tensile strength. In addition, excessive conductive fillers can easily increase the viscosity of the conductive elastic silver paste, making it difficult to accurately control the layer thickness and shape of the elastic probe when used for 3D printing, further increasing the difficulty of the preparation process, resulting in unstable quality of the elastic probe and easy clogging of the printing equipment. Excessive conductive fillers will also cause waste of resources and increase the production cost of the conductive elastic silver paste.

[0023] Preferably, the added mass of the silver particles accounts for 55-90% of the mass of the polymer elastic matrix.

[0024] When the added mass of silver particles is less than 55% of the mass of the polymer elastic matrix, the polymer elastic matrix occupies most of the space in the conductive elastic silver paste, causing the conductive performance of the conductive elastic silver paste to be significantly reduced. At the same time, the addition of too little silver particles makes the dispersion of silver particles in the conductive elastic silver paste worse, resulting in a decrease in the mechanical properties and stability of the conductive elastic silver paste.

[0025] When the added mass of silver particles is higher than 90% of the mass of the polymer elastic matrix, the amount of silver particles added is too much, the cost of the conductive elastic silver paste increases and it is easy to waste resources. Too many silver particles can easily lead to reduced fluidity and dispersibility of the conductive elastic silver paste, while reducing its elasticity, further affecting the 3D printing performance of the conductive elastic silver paste.

[0026] Preferably, the silver particles are a combination of one or more of silver flakes, silver powder and silver balls.

[0027] The morphology of silver particles will affect the performance of conductive elastic silver paste. Silver flakes have a large specific surface area, which helps to improve the conductivity and mechanical strength of conductive elastic silver paste. At the same time, silver flakes have good plasticity and stretchability, which makes the 3D printed elastic probe have better flexibility and elasticity, and further improves the test accuracy of the elastic probe. Silver powder has good dispersibility, but it is very easy to agglomerate and settle in the conductive elastic silver paste, resulting in increased viscosity, affecting the conductive properties and mechanical strength of the conductive elastic silver paste, and increasing the difficulty of processing. Silver balls have better fluidity and excellent processing performance, but they are easily subjected to extrusion, shear and other forces during the preparation of conductive elastic silver paste, causing the morphology of the silver balls to change and the stability of the conductive elastic silver paste to decrease.

[0028] Preferably, a modification aid is also included.

[0029] Preferably, the modification aid is any one of a silane coupling agent and a surfactant, or a combination of both.

[0030] As further preferred, the silane coupling agent is any one of KH-550, KH-560, KH-570, KH-602, KH-792, A-151, A-171, A-172, or a combination of two thereof.

[0031] The use of KH-550, KH-560, KH-570, KH-602, KH-792, A-151, A-171, and A-172 silane coupling agents helps to form stable chemical bonds between micron-sized silver particles, conductive fillers, and polymer elastic matrices, and improves the bonding strength and durability between micron-sized silver particles, conductive fillers, etc. and polymer elastic matrices. At the same time, the heat resistance and oxidation resistance of the conductive elastic silver paste are improved. In addition, the addition of the above-mentioned silane coupling agents effectively improves the interface properties between micron-sized silver particles, conductive fillers, and polymer elastic matrices, thereby avoiding the aggregation and deposition of micron-sized silver particles and conductive fillers, further improving the uniformity and stability of the conductive elastic silver paste, and promoting the improvement of the mechanical properties of the 3D printed elastic probe.

[0032] As further preferred, the surfactant is any one of AEO3 phosphate ester, AEO7 phosphate ester, AEO9 phosphate ester, or a combination of two thereof.

[0033] AEO3 phosphate ester, AEO7 phosphate ester, and AEO9 phosphate ester surfactants have excellent surface activity and dispersibility, which effectively promote the uniform and stable dispersion of micron-sized silver particles and conductive fillers in the polymer elastic matrix, thereby improving the conductive properties of the conductive elastic silver paste. In addition, AEO3 phosphate ester, AEO7 phosphate ester, and AEO9 phosphate ester surfactants have excellent adhesion, which helps to enhance the adhesion between micron-sized silver particles, conductive fillers and the polymer elastic matrix, and further improve the stability and reliability of the conductive elastic silver paste.

[0034] Preferably, the polymer elastic matrix is ​​a combination of one or more of polysiloxane elastomer, polyurethane elastomer, silicone rubber elastomer, epoxy resin elastomer, SEBS and SBS.

[0035] Selecting the above materials as the polymer elastic matrix helps to ensure the wear resistance, corrosion resistance and high temperature resistance of the conductive elastic silver paste while further improving its elasticity and flexibility, so that it is suitable for various high-strength and high-temperature applications. Among them, polysiloxane elastomer has excellent flexibility and wear resistance; polyurethane elastomer has excellent elasticity, wear resistance and corrosion resistance. At the same time, it has high tensile strength and elongation at break, which helps to improve the 3D printing processing performance of conductive elastic silver paste.

[0036] Preferably, the organic solvent is a combination of one or more of dimethylamine, dimethylformamide, tetrahydrofuran, N-methylpyrrolidone, benzene and toluene.

[0037] The selection of the above-mentioned organic solvents is helpful to reduce the surface tension and viscosity of the conductive elastic silver paste, effectively improve the interfacial compatibility between the silver particles and the polymer elastic matrix, and promote the uniform dispersion of the silver particles in the polymer elastic matrix to avoid agglomeration and sedimentation. At the same time, the appropriate addition of organic solvents is conducive to reducing the viscosity of the conductive elastic silver paste, promoting its fluidity to increase, which is conducive to the extrusion and molding of the conductive elastic silver paste in the process of 3D printing elastic probes, and further improving the dimensional accuracy and quality of the elastic probes after 3D printing.

[0038] The method for preparing the conductive elastic silver paste suitable for 3D printing elastic probes as described above comprises the following steps: dispersing silver particles and a polymer elastic matrix in an organic solvent, optionally adding a conductive filler to the organic solvent, and mixing to obtain the conductive elastic silver paste.

[0039] Preferably, the silver particles and the polymer elastic matrix are dispersed in an organic solvent at a temperature of 50 to 90°C.

[0040] When silver particles and a polymer elastic matrix are dispersed in an organic solvent at low temperature (temperature below 50°C), the polymer elastic matrix has a high viscosity and poor fluidity, which easily causes uneven dispersion of silver particles in the polymer elastic matrix, further leading to agglomeration and sedimentation. At the same time, when the temperature is too low, the interface bonding between the silver particles and the polymer elastic matrix is ​​weak, the adhesion of the silver particles is reduced, and the reaction activity between the silver particles and the polymer elastic matrix is ​​reduced, resulting in a decrease in the conductivity of the conductive elastic silver paste.

[0041] When silver particles and a polymer elastic matrix are dispersed in an organic solvent at high temperature (temperature above 90°C), the polymer elastic matrix is ​​easily decomposed by heat, which affects the service life of the conductive elastic silver paste. At the same time, when the temperature is too high, the cross-linking and curing reaction rate of the polymer elastic matrix is ​​too fast, which is not conducive to the fluidity of the conductive elastic silver paste, further affecting the subsequent processing and molding effect of the elastic probe.

[0042] The conductive elastic silver paste suitable for 3D printing elastic probes as described above, or the conductive elastic silver paste obtained by the preparation method as described above, is used in the fields of precision 3D printing, micro-nano chips, printed electronics, sensors, biological probes, and semiconductor devices.

[0043] Therefore, the present invention has the following beneficial effects:

[0044] (1) The present invention uses low-cost micron-sized silver particles mixed with a polymer elastic matrix to prepare a conductive elastic silver paste, which helps to achieve higher conductivity;

[0045] (2) The micron-sized silver particles of the present invention have good interfacial compatibility with the polymer elastic matrix, which effectively improves the adhesion of the conductive elastic silver paste, avoids the phenomenon of peeling, shedding and stratification of the silver particles, and further improves the 3D printing performance of the conductive elastic silver paste;

[0046] (3) The conductive elastic silver paste of the present invention has excellent elastic shrinkage performance while ensuring high conductivity, which helps to realize the preparation of elastic probes with small size, large elastic shrinkage, strong conductivity and low cost through 3D printing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is a scanning electron microscope image of the conductive elastic silver paste of the Ag-PDMS system in Example 1.

[0048] Figure 2 This is a scanning electron microscope image of the conductive elastic silver paste of the Ag-PDMS system in Example 5.

[0049] Figure 3 This is a schematic diagram of an elastic probe with large elasticity prepared by 3D printing technology using the conductive elastic silver paste in Example 9.

[0050] Figure 4 This is a scanning electron microscope image of the conductive elastic silver paste of the Ag-TPU system in Example 9. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments of the specification. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0052] Example 1

[0053] A conductive elastic silver paste suitable for 3D printing elastic probes, comprising the following components in percentage by mass:

[0054] Micron-sized silver particles: silver flakes, average particle size 11μm; mass percentage 85%;

[0055] High molecular elastic matrix: polydimethylsiloxane (PDMS) solution with a solid content of 96% (wherein the solid content of the PDMS solution is 95-98%, most preferably 96%), and the solvent is dimethylamine (DMA); the mass percentage of the high molecular elastic matrix is ​​15%;

[0056] Silane coupling agent: KH-560, mass percentage is 1%;

[0057] Conductive filler: carbon nanotubes, 10% by mass;

[0058] Solvent: dimethylamine (DMA), balance.

[0059] The method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above comprises the following steps:

[0060] (S.1) 2 g of polydimethylsiloxane (PDMS) was added to 3 mL of dimethylamine solvent, and then 0.2 mL of KH-560 was added, stirred evenly and heated to 60°C. After the reaction was completed, the filtrate was filtered using a 1-10 μm needle filter and the filtrate was collected to obtain a surface-modified polydimethylsiloxane (PDMS) substrate;

[0061] (S.2) Add 2 g of carbon nanotubes to the polydimethylsiloxane (PDMS) matrix obtained in step (S.1), stir evenly, then add 17 g of silver flakes, continue stirring evenly and filter to obtain a conductive elastic silver paste of the Ag-PDMS system. The scanning electron microscope image of the conductive elastic silver paste of the Ag-PDMS system in this embodiment is as follows: Figure 1 As shown. Figure 1 It can be seen that the density of silver flakes is relatively high, which is beneficial to increase the contact points to provide pathways for electron transmission and improve conductivity; at the same time, it is observed that the silver flakes are evenly dispersed in the organic carrier and no obvious agglomeration is observed.

[0062] Example 2

[0063] The difference between this embodiment and embodiment 1 is that:

[0064] Micron-sized silver particles: silver flakes, with an average particle size of 7 μm. Others are the same as in Example 1.

[0065] Example 3

[0066] The difference between this embodiment and embodiment 1 is that:

[0067] Micron-sized silver particles: silver flakes, with an average particle size of 15 μm. Others are the same as in Example 1.

[0068] Example 4

[0069] The difference between this embodiment and embodiment 1 is that:

[0070] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 13 g of silver flakes are added after stirring evenly in step (S.2), so that the mass percentage of the silver flakes is 65%. The rest is the same as in Example 1.

[0071] Example 5

[0072] The difference between this embodiment and embodiment 1 is that:

[0073] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probes as described above, 11 g of silver flakes are added after stirring evenly in step (S.2), so that the mass percentage of the silver flakes is 55%. The rest is the same as in Example 1. The scanning electron microscope image of the conductive elastic silver paste of the Ag-PDMS system in this embodiment is as follows Figure 2 As shown. Figure 2 It can be seen that the silver content is low. Figure 2 The silver flakes are distributed loosely, the probability of continuous transmission of electron energy is low and the slurry shows low thixotropy.

[0074] Example 6

[0075] The difference between this embodiment and embodiment 1 is that:

[0076] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 18 g of silver flakes are added after stirring evenly in step (S.2), so that the mass percentage of the silver flakes is 90%. The rest is the same as in Example 1.

[0077] Example 7

[0078] The difference between this embodiment and embodiment 1 is that:

[0079] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 1 g of carbon nanotubes is added in step (S.2) so that the mass percentage of the carbon nanotubes is 5%. The rest is the same as in Example 1.

[0080] Example 8

[0081] The difference between this embodiment and embodiment 1 is that:

[0082] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 3 g of carbon nanotubes are added in step (S.2) so that the mass percentage of the carbon nanotubes is 15%. The rest is the same as in Example 1.

[0083] Example 9

[0084] A conductive elastic silver paste suitable for 3D printing elastic probes, comprising the following components in percentage by mass:

[0085] Micron-sized silver particles: a combination of silver flakes and silver balls, with an average particle size of 11 μm and a mass percentage of 70%;

[0086] High molecular elastic matrix: polyurethane (TPU) solution with a solid content of 60% (wherein the solid content of the TPU solution is 50-90%, most preferably 60%), and the solvent is dimethylformamide (DMF); the mass percentage is 30%;

[0087] Surfactant: AEO9 phosphate, mass percentage is 1%;

[0088] Conductive filler: carbon nanotubes, 10% by mass;

[0089] Solvent: dimethylformamide (DMF), balance.

[0090] The method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above comprises the following steps:

[0091] (S.1) 4 g of polyurethane (TPU) was added to 6 mL of dimethylformamide solvent, heated in a water bath at 60° C. for 3 to 4 h and stirred evenly, then filtered using a 1 to 10 μm needle filter and the filtrate was collected, then 0.2 mL of AEO9 phosphate was added, and stirring was continued to obtain a surface-modified polyurethane (TPU) matrix;

[0092] (S.2) Add 2g of carbon nanotubes to the polyurethane (TPU) matrix obtained in step (S.1), stir evenly, then add 14g of a combination of silver flakes and silver balls, continue stirring evenly and filter to obtain a conductive elastic silver paste of the Ag-TPU system. The elastic probe with large elasticity and shrinkage prepared by 3D printing technology using the conductive elastic silver paste of this embodiment is shown in FIG. Figure 3 The SEM image of the conductive elastic silver paste of the Ag-TPU system in this embodiment is shown in FIG. Figure 4 As shown. Figure 4 It can be seen that the silver flakes are evenly dispersed in the silver ball particles, which is conducive to forming a good conductive path. The smaller particle size of the silver ball makes the overall slurry more delicate, which can improve the passability of the material and the smoothness of the printed line. Figure 3 It can be seen that the elastic probe with large elasticity and shrinkage prepared by 3D printing technology using the conductive elastic silver paste in this embodiment shows excellent thixotropy, and the printed line has a smoother surface and good uniformity.

[0093] Example 10

[0094] The difference between this embodiment and embodiment 9 is that:

[0095] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 12 g of the silver flake and silver ball composition is added in step (S.2) so that the mass percentage of the silver flake and silver ball composition is 60%. The rest is the same as in Example 9.

[0096] Embodiment 11

[0097] The difference between this embodiment and embodiment 9 is that:

[0098] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 18 g of the silver flake and silver ball composition is added in step (S.2) so that the mass percentage of the silver flake and silver ball composition is 90%. The rest is the same as in Example 9.

[0099] Example 12

[0100] The difference between this embodiment and embodiment 9 is that:

[0101] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 1 g of carbon nanotubes is added in step (S.2) so that the mass percentage of the carbon nanotubes is 5%. The rest is the same as in Example 9.

[0102] Embodiment 13

[0103] The difference between this embodiment and embodiment 9 is that:

[0104] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, 5 g of carbon nanotubes are added in step (S.2) so that the mass percentage of the carbon nanotubes is 25%. The rest is the same as in Example 9.

[0105] Embodiment 14

[0106] The difference between this embodiment and embodiment 9 is that:

[0107] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, the water bath heating reaction temperature in step (S.1) is 50° C. The rest is the same as in Example 9.

[0108] Embodiment 15

[0109] The difference between this embodiment and embodiment 9 is that:

[0110] In the method for preparing the conductive elastic silver paste suitable for 3D printing elastic probe as described above, the water bath heating reaction temperature in step (S.1) is 90° C. The rest is the same as in Example 9.

[0111] Comparative Example 1

[0112] The difference between this comparative example and Example 1 is:

[0113] The average particle size of the silver flakes in this comparative example is 6 μm, and the rest is the same as in Example 1.

[0114] Comparative Example 2

[0115] The difference between this comparative example and Example 1 is:

[0116] The average particle size of the silver flakes in this comparative example is 16 μm, and the rest is the same as in Example 1.

[0117] Comparative Example 3

[0118] The difference between this comparative example and Example 1 is:

[0119] The mass percentage of the silver flakes in this comparative example is 50%, and the rest is the same as in Example 1.

[0120] Comparative Example 4

[0121] The difference between this comparative example and Example 1 is:

[0122] The mass percentage of the silver flakes in this comparative example is 95%, and the rest is the same as in Example 1.

[0123] Comparative Example 5

[0124] The difference between this comparative example and Example 1 is:

[0125] The mass percentage of the carbon nanotubes in this comparative example is 4%, and the other contents are the same as those in Example 1.

[0126] Comparative Example 6

[0127] The difference between this comparative example and Example 1 is:

[0128] The mass percentage of the carbon nanotubes in this comparative example is 16%, and the other contents are the same as those in Example 1.

[0129] Comparative Example 7

[0130] The difference between this comparative example and Example 1 is:

[0131] In this comparative example, no carbon nanotubes were added, and the other contents were the same as those in Example 1.

[0132] Comparative Example 8

[0133] The difference between this comparative example and Example 9 is:

[0134] The micron-sized silver particles in this comparative example are only silver flakes and do not contain silver balls. Other aspects are the same as those in Example 9.

[0135] Comparative Example 9

[0136] The difference between this comparative example and Example 9 is:

[0137] The mass percentage of the silver flake and silver ball composition in this comparative example is 55%, and the rest is the same as in Example 9.

[0138] Comparative Example 10

[0139] The difference between this comparative example and Example 9 is:

[0140] The mass percentage of the silver flake and silver ball composition in this comparative example is 95%, and the rest is the same as in Example 9.

[0141] Comparative Example 11

[0142] The difference between this comparative example and Example 9 is:

[0143] In this comparative example, no carbon nanotubes were added, and the other conditions were the same as those in Example 9.

[0144] Comparative Example 12

[0145] The difference between this comparative example and Example 9 is:

[0146] The mass percentage of the carbon nanotubes in this comparative example is 4%, and the rest is the same as that in Example 9.

[0147] Comparative Example 13

[0148] The difference between this comparative example and Example 9 is:

[0149] The mass percentage of the carbon nanotubes in this comparative example is 26%, and the rest is the same as that in Example 9.

[0150] Comparative Example 14

[0151] The difference between this comparative example and Example 9 is:

[0152] The water bath heating reaction temperature in step (S.1) of this comparative example is 45°C, and the rest is the same as in Example 9.

[0153] Comparative Example 15

[0154] The difference between this comparative example and Example 9 is:

[0155] The water bath heating reaction temperature in step (S.1) of this comparative example is 95°C, and the rest is the same as in Example 9.

[0156]

Performance test

[0157] The performance test method is as follows:

[0158]

Resistivity test

[0159] Use Ruike Weiye FT-340 four-probe square resistance tester to measure the resistivity of conductive elastic silver paste. The specific method is:

[0160] ① The prepared conductive elastic silver paste is coated on the glass original plate by a coating machine and sintered at 300℃ for 60min in air atmosphere to obtain a conductive elastic silver film; ② The thickness of the conductive elastic silver film sample after high-temperature sintering is measured with the help of a step meter; ③ The corresponding parameters are set in the square resistance meter, and the four-probe probe is adjusted to press down vertically above the sample to be tested and touch lightly; ④ After the reading is stable, the square resistance, resistivity and other data are recorded.

[0161]

Adhesion test

[0162] The prepared conductive elastic silver paste was coated on a glass substrate by a coating machine, and sintered at 300° C. for 10 min in an air atmosphere to obtain a conductive elastic silver film;

[0163] ② Using ASTM D3359-2017 as the test standard, use a grid knife to cut the surface of the test piece at a cutting speed of 20-50mm / s; ③ Rotate the test piece 90° and repeat the above operation on the cut to form a grid pattern;

[0164] ④ Use a soft brush to brush the diagonal lines on both sides of the grid pattern, brushing lightly 5 times each;

[0165] ⑤Use 3M 600-1PK test tape to perform peel test and evaluate the adhesion performance of the material.

[0166]

Tensile Strength Test

[0167]

Experimental results characterization

[0168] The conductive elastic silver paste of the Ag-PDMS system prepared according to the formula and preparation method in Examples 1 to 8 and Comparative Examples 1 to 7 was subjected to the above-mentioned performance test. The test results are shown in Table 1 below.

[0169] Table 1

[0170]

[0171]

[0172] From the data analysis in Table 1, it can be seen that adding 85% by mass of silver flakes with an average particle size of 11μm to the PDMS elastic matrix and then adding 10% carbon nanotubes can obtain a conductive elastic silver paste with relatively balanced electrical properties, elasticity, and adhesion; when the silver content is constant, the larger the particle size, the greater the probability of contact between the sheets, the better the conductivity, and the larger silver flakes can be used as connecting bridges in the elastic matrix to obtain greater tensile strength. However, considering that this article is to develop an elastic silver paste suitable for 3D printing, larger silver particles will bring a series of problems such as poor discharge passability, and the comprehensive optimal particle size is 11μm; too high a content of silver powder and conductive filler can improve the electrical properties, but because the powder is difficult to disperse evenly and cannot be well infiltrated with the elastic matrix, it will affect its elasticity. If the content is too low, it is difficult to obtain more rational electrical properties.

[0173] The conductive elastic silver paste of the Ag-TPU system prepared according to the formula and preparation method in Examples 9 to 15 and Comparative Examples 8 to 15 was subjected to the above performance test. The test results are shown in Table 2 below.

[0174] Table 2

[0175] Group Square resistance (mΩ / □) Resistivity (μΩ·cm) Adhesion Tensile strength(MPa) Example 9 90.5 181 5B 7.1 Example 10 354.5 709 5B 4.7 Embodiment 11 37 74 3B 2.7 Example 12 104.5 209 5B 6.1 Embodiment 13 84.5 169 4B 4.4 Embodiment 14 103.5 207 3B 3.6 Embodiment 15 93.5 187 2B 8.0 Comparative Example 8 106 212 5B 6.8 Comparative Example 9 Non-conductive / 5B 3.3 Comparative Example 10 10.5 21 2B 1.2 Comparative Example 11 118.5 237 5B 5.4 Comparative Example 12 105 210 5B 5.5 Comparative Example 13 75.5 151 4B 3.7 Comparative Example 14 100.5 201 3B 2.7 Comparative Example 15 99.5 199 2B 8.2

[0176] From the data analysis in Table 2, it can be seen that by swelling the TPU elastic matrix at 60°C and adding 70% by mass of silver flakes and silver balls with an average particle size of 11μm, and then adding 10% of carbon nanotubes, a conductive elastic silver paste with relatively balanced electrical properties, elasticity and shrinkage properties, and adhesion that meets the needs of 3D printing can be obtained; nano silver balls can be evenly dispersed between the silver flakes and the elastic matrix, which is more conducive to the formation of an electronic connection network than the pure silver flake system, and can improve the conductivity to a certain extent. At the same time, the silver balls can make the overall performance of the paste more delicate, which is conducive to 3D printing. Printing output; If the content of silver powder and conductive filler is too high, although it can improve the electrical properties, it will affect its elasticity due to the difficulty in dispersing evenly. If the content is too low, it is difficult to obtain more rational electrical properties; temperature will affect the degree of cross-linking between polymer elastomers, and at the same time affect the volatilization of organic solvents during stirring. At 45°C, the degree of cross-linking of TPU is insufficient, and it is difficult to obtain ideal elastic and shrinkage properties and weather resistance. At 95°C, the degree of cross-linking of TPU is too high and the residual solvent content of the system is low. The fluidity of the elastomer is poor and it is harder after curing. When rotating 90° and making the second cut in the 100-grid test, the whole piece is easy to fall off.

[0177] The above description is only a detailed description of the preferred embodiments and principles of the present invention. For ordinary technicians in this field, according to the ideas provided by the present invention, there will be changes in the specific implementation methods, and these changes should also be regarded as the protection scope of the present invention.

Claims

1. A conductive elastic silver paste suitable for 3D printing elastic probes, characterized in that: It includes silver particles, a polymer elastic matrix and an organic solvent; wherein, The particle size of the silver particles is 7 to 15 μm; It also includes a conductive filler, which is a combination of one or more of carbon nanotubes, carbon nanowires, graphite, graphene, carbon black, nickel carbon, silver, silver-coated aluminum, and silver-coated copper, and the added mass of the conductive filler accounts for 5-15% of the mass of the conductive elastic silver paste; The added mass of the silver particles accounts for 70-85% of the mass of the polymer elastic matrix; The silver particles and the polymer elastic matrix are dispersed in an organic solvent at a temperature of 60 to 90°C.

2. The conductive elastic silver paste suitable for 3D printing elastic probe according to claim 1, characterized in that: The silver particles are a combination of one or more of silver flakes and silver balls.

3. The conductive elastic silver paste suitable for 3D printing elastic probe according to claim 1, characterized in that: Also includes modification aids.

4. The conductive elastic silver paste suitable for 3D printing elastic probe according to claim 3, characterized in that: The modification aid is any one of a silane coupling agent and a surfactant or a combination of both.

5. The conductive elastic silver paste suitable for 3D printing elastic probe according to claim 1, characterized in that: The polymer elastic matrix is ​​a combination of one or more of polysiloxane elastomer, polyurethane elastomer, silicone rubber elastomer, epoxy resin elastomer, SEBS and SBS.

6. The conductive elastic silver paste suitable for 3D printing elastic probe according to claim 1, characterized in that: The organic solvent is a combination of one or more of dimethylamine, dimethylformamide, tetrahydrofuran, N-methylpyrrolidone, benzene and toluene.

7. The method for preparing a conductive elastic silver paste suitable for 3D printing elastic probes according to any one of claims 1 to 6, characterized in that: The following steps are involved: Silver particles and a high molecular elastic matrix are dispersed in an organic solvent, and a conductive filler is added into the organic solvent, and the conductive elastic silver paste is obtained after mixing.

8. The conductive elastic silver paste suitable for 3D printing elastic probes as described in any one of claims 1 to 6, or the conductive elastic silver paste obtained by the preparation method according to claim 7, in the fields of precision 3D printing, micro-nano chips, printed electronics, sensors, biological probes, and semiconductor devices.

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