CN112475662A - Nano-silver solder paste, preparation method thereof and application of nano-silver solder paste in chip packaging interconnection structure - Google Patents
Nano-silver solder paste, preparation method thereof and application of nano-silver solder paste in chip packaging interconnection structure Download PDFInfo
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- CN112475662A CN112475662A CN202011297959.8A CN202011297959A CN112475662A CN 112475662 A CN112475662 A CN 112475662A CN 202011297959 A CN202011297959 A CN 202011297959A CN 112475662 A CN112475662 A CN 112475662A
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/24—Selection of soldering or welding materials proper
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
- B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
- B23K35/362—Selection of compositions of fluxes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
- B23K35/40—Making wire or rods for soldering or welding
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Abstract
The invention provides a nano-silver soldering paste and a preparation method thereof, wherein the nano-silver soldering paste comprises flake nano-silver and an organic solvent carrier which are mixed with each other, the organic solvent carrier is a mixture of any two or more than two of ethylene glycol, glycerol, diethylene glycol, triethylene glycol, beta-terpineol, gamma-terpineol and delta-terpineol, and the volume percentage of any one organic solvent is not less than 20%; the preparation method of the nano-silver solder paste comprises the following steps: providing flaky nano silver and an organic solvent carrier, and stirring and mixing the flaky nano silver and the organic solvent carrier to prepare the nano silver soldering paste. The invention also provides application of the nano silver solder paste in a chip packaging interconnection structure. The nano-silver soldering paste provided by the invention has low-temperature sintering performance, can be well applied to the field of electronic packaging of low-temperature welding high-temperature service, and is high in shear strength of a connecting layer formed by sintering the soldering paste, good in combination degree of a connecting interface and uniform and compact in the connecting layer.
Description
Technical Field
The invention belongs to the technical field of high-power electronic device packaging, and particularly relates to a nano-silver solder paste and a preparation method thereof, and application of the nano-silver solder paste in a chip packaging interconnection structure.
Background
The working environment required by the fields of automatic driving, aerospace, high-speed railway, oil and gas exploration and the like is more and more severe, and the corresponding requirements on the chip are higher and higher. Conventional silicon-based chips have not been able to meet the needs of the particular environment in these areas. For this reason, researchers have looked at wide bandgap semiconductors (e.g., SiC and GaN) that are well suited to meet the current demands for high performance chips.
Wide bandgap semiconductors (e.g., SiC and GaN) have very broad application prospects in high power applications, they are capable of normal operation above 250 ℃ and also have very high breakdown voltages and operating frequencies. The melting point of the traditional tin-lead solder is about 230 ℃, so that the traditional solder cannot be used under the condition of exceeding 250 ℃. Recently, nano silver particles are considered as a very potential high-temperature-resistant chip interconnection material and a next-generation high-power device packaging material, and the melting point of the sintered silver is 961.8 ℃, which is the basis of high-temperature service.
For nano silver materials, sintering at low temperatures is achieved by reducing its size and increasing its surface energy. There have been many studies on how to reduce the size of nano silver, but when the size of nano silver is reduced to a certain extent, the high specific surface area causes the coating agent on the surface thereof to become very thick and thus causes the sintering property thereof to be degraded, for example, the shear strength to be significantly reduced. In the aspect of packaging interconnection application, the shear strength of a connecting layer is a very important parameter, the shear strength of the current nano silver solder paste is low, and the shear strength of spherical nano silver particles with the particle size of about 300nm is less than 10MPa after sintering.
In addition, in addition to the size of nano silver affecting the sintering property of the solder paste, the solvent of the solder paste is also a very important factor. Most of the existing solder formulas are single solvent systems, but the single solvent systems are easy to volatilize greatly and rapidly at a certain temperature point, so that internal cavities of a connecting layer formed by sintering are too much and even crack, and the compactness is poor.
Disclosure of Invention
In view of the defects in the prior art, the invention provides a nano-silver solder paste, a preparation method and application thereof, and aims to solve the problems that the existing nano-silver solder paste has low shear strength and poor compactness after being sintered to form a connecting layer.
In order to achieve the above objects, an aspect of the present invention provides a nano silver solder paste, which includes flake nano silver and an organic solvent vehicle mixed with each other, wherein the organic solvent vehicle is a mixture of any two or more selected from the group consisting of ethylene glycol, glycerol, diethylene glycol, triethylene glycol, β -terpineol, γ -terpineol and δ -terpineol, and a volume percentage of any one organic solvent is not less than 20%.
Preferably, the flaky nano silver is triangular flaky nano silver and/or hexagonal flaky nano silver.
Preferably, the flaky nano silver has a particle size of 100 nm-700 nm and a thickness of 20 nm-40 nm.
Preferably, the organic solvent carrier is a mixture of any two selected from the group consisting of ethylene glycol, glycerol, diethylene glycol, triethylene glycol, β -terpineol, γ -terpineol and δ -terpineol, and the volume percentage of any one organic solvent in the organic solvent carrier is not less than 40%.
Preferably, the mass ratio of the flaky nano silver to the organic solvent carrier is 2-10: 1.
another aspect of the present invention is to provide a method for preparing the nano silver solder paste, which comprises: providing the flaky nano silver and the organic solvent carrier, and stirring and mixing the flaky nano silver and the organic solvent carrier to prepare the nano silver soldering paste.
Preferably, the preparation method further comprises: the flaky nano silver is prepared by adopting a liquid phase reduction method.
Preferably, the preparing and obtaining of the flaky nano silver by the liquid phase reduction method specifically comprises:
dissolving a reducing agent in a solvent to obtain a first reaction solution;
adding a silver source precursor into the first reaction solution, and stirring and mixing to form a second reaction solution;
placing the second reaction solution in a reaction kettle, reacting for 2-24 h at the temperature of 140-200 ℃, and carrying out solid-liquid separation after the reaction is finished to obtain a solid-phase product;
sequentially washing and drying the solid-phase product to obtain the flaky nano silver;
wherein the reducing agent is selected from any one of ascorbic acid, hydrazine hydrate, citrate, polyvinylpyrrolidone, sodium sulfite and sodium borohydride; the solvent is selected from any one of ethanol, glycol, water, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone; the silver source precursor is selected from any one of silver acetate, silver carbonate, silver nitrate, silver oxalate and silver lactate; the molar ratio of the reducing agent to the silver source precursor in the second reaction solution is 0.5-10.
Further, the invention also provides an application of the nano silver solder paste in a chip packaging interconnection structure, wherein the chip packaging interconnection structure comprises a first mother sheet, a second mother sheet and a connecting layer for connecting the first mother sheet and the second mother sheet, and the connecting layer is formed by sintering the nano silver solder paste through a sintering process of heating and pressing.
Specifically, in the sintering process, the heating temperature is 150-300 ℃, and the pressing pressure is 1-20 MPa.
The nano-silver soldering paste provided by the embodiment of the invention comprises the mutually mixed flaky nano-silver and an organic solvent carrier, the sintering connection temperature is 150-300 ℃, the melting point (961.8 ℃) of the massive silver is far lower, and the nano-silver soldering paste can be well applied to the field of electronic packaging of low-temperature welding high-temperature service. The organic solvent carrier in the soldering paste adopts a mixed solvent of more than two organic solvents, the bonding degree of a connecting interface of a connecting layer formed after sintering is good, uniform and compact, the void ratio of the connecting layer is below 13%, the shearing strength reaches more than 35MPa, and the high shearing strength is realized, so that the soldering paste can be well applied to the packaging interconnection of electronic devices.
The preparation method of the nano-silver soldering paste provided by the embodiment of the invention has the advantages of simple process flow and easy realization of process conditions, and is beneficial to large-scale industrial application.
Drawings
FIG. 1 is a schematic structural view of a copper-clad ceramic substrate according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a package interconnect structure in an embodiment of the present invention;
FIG. 3 is an SEM image of flaky nano-silver obtained by the preparation of example 1 of the invention;
fig. 4 is an SEM of a cut-out of a package interconnect structure in embodiment 1 of the present invention;
FIG. 5 is an SEM photograph of a shear fracture surface of a connection layer in example 1 of the present invention;
FIG. 6 is an SEM photograph of a shear fracture surface of a tie layer of a comparative example in example 1 of the present invention;
FIG. 7 is an SEM image of flaky nano-silver obtained by the preparation of example 2 of the invention;
fig. 8 is an SEM of a cut surface of a package interconnect structure in embodiment 2 of the present invention;
FIG. 9 is an SEM photograph of a shear fracture surface of a connection layer in example 2 of the present invention;
FIG. 10 is an SEM image of flaky nano-silver obtained by the preparation of example 5 of the invention;
fig. 11 is an SEM image of a cut surface of a package interconnect structure in embodiment 5 of the present invention;
fig. 12 is an SEM image of a shear fracture surface of the connection layer in example 5 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention are described in detail below with reference to the accompanying drawings. Examples of these preferred embodiments are illustrated in the accompanying drawings. The embodiments of the invention shown in the drawings and described in accordance with the drawings are exemplary only, and the invention is not limited to these embodiments.
It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme according to the present invention are shown in the drawings, and other details not so relevant to the present invention are omitted.
The embodiment of the invention firstly provides nano-silver soldering paste which comprises flake nano-silver and an organic solvent carrier which are mixed with each other, wherein the organic solvent carrier is a mixture of any two or more than two of ethylene glycol, glycerol, diethylene glycol, triethylene glycol, beta-terpineol, gamma-terpineol and delta-terpineol, and the volume percentage of any one organic solvent in the organic solvent carrier is not less than 20%.
In a preferred scheme, the flaky nano silver is triangular flaky nano silver and/or hexagonal flaky nano silver. The particle size of the flaky nano silver is 100 nm-700 nm, and the thickness of the flaky nano silver is 20 nm-40 nm.
In a preferred embodiment, the organic solvent carrier is a mixture of any two selected from the group consisting of ethylene glycol, glycerol, diethylene glycol, triethylene glycol, β -terpineol, γ -terpineol and δ -terpineol, and the volume percentage of any one organic solvent in the organic solvent carrier is not less than 20%. More preferably, the volume percentage of any one organic solvent in the organic solvent carrier is not less than 40%.
In a preferred scheme, the mass ratio of the flaky nano silver to the organic solvent carrier is 2-10: 1.
the embodiment of the invention also provides a preparation method of the nano-silver soldering paste, which comprises the following steps: providing the flaky nano silver and the organic solvent carrier, and stirring and mixing the flaky nano silver and the organic solvent carrier to prepare the nano silver soldering paste.
In the preferred scheme, the flaky nano silver is prepared and obtained by adopting a liquid phase reduction method. The method specifically comprises the following steps:
s10, dissolving the reducing agent in the solvent to obtain a first reaction solution. Wherein the reducing agent is selected from any one of ascorbic acid, hydrazine hydrate, citrate, polyvinylpyrrolidone, sodium sulfite and sodium borohydride; the solvent is any one selected from ethanol, ethylene glycol, water, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone.
And S20, adding the silver source precursor into the first reaction liquid, and stirring and mixing to form a second reaction liquid. The silver source precursor is selected from any one of silver acetate, silver carbonate, silver nitrate, silver oxalate and silver lactate; the molar ratio of the reducing agent to the silver source precursor in the second reaction solution is 0.5-10.
S30, placing the second reaction solution in a reaction kettle, reacting for 2-24 h at the temperature of 140-200 ℃, and carrying out solid-liquid separation after the reaction is finished to obtain a solid-phase product.
And S40, sequentially washing and drying the solid phase product to obtain the flaky nano silver. Specifically, the solid-phase product is washed by deionized water firstly, then washed by ethanol, and freeze-dried after the washing is finished, so that the flaky nano silver is obtained.
Further, the embodiment of the present invention also provides an application of the nano silver solder paste in a chip package interconnection structure, where the chip package interconnection structure includes a first mother chip, a second mother chip, and a connection layer for connecting the first mother chip and the second mother chip, where the connection layer is formed by sintering the nano silver solder paste through a sintering process of heating and pressing.
Specifically, the first and second mother substrates are, for example, DBC substrates (copper-clad ceramic substrates), and as a specific example, as shown in fig. 1, the DBC substrate includes a ceramic base 1, a copper layer 2, a nickel layer 3, and a gold layer 4, which are sequentially disposed.
The nano-silver solder paste provided by the embodiment of the invention is coated on the connecting surface of the first mother substrate and/or the second mother substrate (for example, the connecting surface of the DBC substrate in fig. 1 is the upper surface of the gold layer 4) to form a solder paste coating, then the first mother substrate and the second mother substrate are stacked according to the connecting surface, so that the solder paste coating is located between the first mother substrate and the second mother substrate, and then a sintering process is performed to sinter the solder paste coating to form the connecting layer. As a specific example, referring to the package interconnection structure shown in fig. 2, the first mother substrate 10 and the second mother substrate 20 are both selected as DBC substrates as shown in fig. 1, the solder paste coating is sintered to form a connection layer 30 between the first mother substrate 10 and the second mother substrate 20, and the connection layer 30 connects the first mother substrate 10 and the second mother substrate 20 to each other.
In a specific scheme, pulse hot-press welding or ultrasonic hot-press welding can be used for heating and pressing the stacked structure, so that the nano silver soldering paste is sintered to complete interconnection. Wherein, the heating temperature can be 150 ℃ to 300 ℃, and the pressing pressure can be 1MPa to 20 MPa.
The above-mentioned nano-silver solder paste and the method for preparing the same will be described below with reference to specific examples, and it will be understood by those skilled in the art that the following examples are only specific examples of the above-mentioned nano-silver solder paste and the method for preparing the same of the present invention, and are not intended to limit the entirety thereof.
Example 1
0.888g of polyvinylpyrrolidone is dissolved in 200ml of N, N-dimethylformamide, 1.689g of silver nitrate is added after complete dissolution by stirring, and the mixture is stirred and mixed to form a reaction solution. And (3) placing the reaction solution in a reaction kettle, and reacting for 4 hours at the temperature of 180 ℃. And after the reaction is finished, washing with deionized water, washing with ethanol, and finally freeze-drying to obtain the flaky nano-silver.
Fig. 3 is an SEM image of the nano silver flakes prepared in this example, and as shown in fig. 3, the nano silver flakes prepared in this example include triangular flake nano silver and hexagonal flake nano silver, and the hexagonal flake nano silver is relatively large. The particle size range of the flaky nano silver prepared by the embodiment is 100 nm-300 nm, and the thickness is 20 nm-50 nm.
And mixing the prepared flaky nano silver with a mixed organic solvent carrier of ethylene glycol and beta-terpineol according to a mass ratio of 5:1, and stirring and mixing for 30min in a mixer to prepare the nano silver soldering paste. Wherein, in the mixed organic solvent carrier, the volume ratio of the glycol to the beta-terpineol is 1: 1.
The nano-silver solder paste prepared by the method is applied to the packaging interconnection of electronic devices. In particular, referring to fig. 2, both the first and second masters in the package interconnect structure are selected to be DBC substrates.
First, the master is processed: and ultrasonically washing the DBC substrate (the first master plate and the second master plate) in ethanol for 3min to remove impurities on the surface of the DBC substrate, and airing.
Then, the nano silver paste prepared in this embodiment is uniformly coated on the connecting surface of the DBC substrate and then stacked to obtain a "sandwich" structure of the DBC substrate/nano silver solder paste coating/DBC substrate.
And then, carrying out low-temperature sintering welding on the stacked structure of the DBC substrate/the nano-silver soldering paste coating/the DBC substrate at the pressure of 10MPa and the connection temperature of 300 ℃, wherein the pressure holding time is 20min, and the nano-silver soldering paste coating is sintered to form a connection layer. After cooling, the package interconnect structure as shown in fig. 2 is obtained.
Fig. 4 is an SEM image of a cross section of the package interconnect structure in this embodiment, and it can be known that the connection of the connection layer is uniform and dense, and the porosity is calculated to be 5.1% through the test. The connection layer of this example was subjected to a shear fracture test, and fig. 5 is an SEM of the shear fracture surface of the connection layer. Through testing, the shear force of the connection layer formed by sintering the nano-silver solder paste of the embodiment was measured to be 49.8MPa after cooling (wherein, 5 test samples were prepared according to the embodiment, and the test data is the average value of the 5 test samples).
It should be noted that the performing the shear fracture test on the connection layer specifically includes: fixing the sample on a fixing clamp of a shear force tester, controlling the tester to push and compress the sample at a speed of 100 microns per second to perform a shear fracture test, and reading from the shear force tester to obtain corresponding shear force when the sample is fractured.
As a comparative example, the organic solvent carrier in this example was replaced with a single solvent using only ethylene glycol, and the remaining conditions were exactly the same as in this example. The solder paste obtained in the comparative example has a porosity of 32.69% and a shear force of 17.5MPa after sintering to form a connection layer, and an SEM image of a fracture surface is shown in fig. 6.
Therefore, the organic solvent carrier in the embodiment of the invention adopts the solder obtained by mixing the organic solvent, the void ratio of the connecting layer formed by sintering is smaller, the compactness of the connecting layer is improved, and the shearing force is also greatly improved.
Example 2
1.65g of polyvinylpyrrolidone is dissolved in 200ml of N, N-dimethylacetamide, 1.689g of silver nitrate is added after complete dissolution by stirring, and the mixture is stirred to form a reaction solution. And (3) placing the reaction solution in a reaction kettle, and reacting for 4 hours at the temperature of 180 ℃. And after the reaction is finished, washing with deionized water, washing with ethanol, and finally freeze-drying to obtain the flaky nano-silver.
Fig. 7 is an SEM image of the flaky nano silver prepared in this example, and as shown in fig. 7, the flaky nano silver prepared in this example includes triangular flaky nano silver and hexagonal flaky nano silver, and the triangular flaky nano silver is relatively large. The particle size range of the flaky nano silver prepared by the embodiment is 100 nm-600 nm, and the thickness is 20 nm-50 nm.
And mixing the prepared flaky nano silver with a mixed organic solvent carrier of ethylene glycol and beta-terpineol according to a mass ratio of 5:1, and stirring and mixing for 30min in a mixer to prepare the nano silver soldering paste. Wherein, in the mixed organic solvent carrier, the volume ratio of the glycol to the beta-terpineol is 3: 2.
The nano-silver solder paste prepared by the method is applied to the packaging interconnection of electronic devices. In particular, referring to fig. 2, both the first and second masters in the package interconnect structure are selected to be DBC substrates.
First, the master is processed: and ultrasonically washing the DBC substrate (the first master plate and the second master plate) in ethanol for 3min to remove impurities on the surface of the DBC substrate, and airing.
Then, the nano silver paste prepared in this embodiment is uniformly coated on the connecting surface of the DBC substrate and then stacked to obtain a "sandwich" structure of the DBC substrate/nano silver solder paste coating/DBC substrate.
And then, carrying out low-temperature sintering welding on the stacked structure of the DBC substrate/the nano-silver solder paste coating/the DBC substrate at the pressure of 10MPa and the connection temperature of 275 ℃, wherein the pressure holding time is 20min, and the nano-silver solder paste coating is sintered to form a connection layer. After cooling, the package interconnect structure as shown in fig. 2 is obtained.
Fig. 8 is an SEM image of a cross section of the package interconnection structure in this embodiment, and it can be known from the SEM image that the bonding degree of the connection interface of the connection layer is good, the connection layer is uniform and dense, and the void ratio is 8.25% by test calculation. The connection layer of this example was subjected to a shear fracture test in accordance with the test method of example 1, and fig. 9 is an SEM of the shear fracture surface of the connection layer. Through testing, the shear force of the connection layer formed by sintering the nano-silver solder paste of the embodiment was measured to be 41.9MPa after cooling (wherein, 5 test samples were prepared according to the embodiment, and the test data is the average value of the 5 test samples).
As a comparative example, the organic solvent vehicle in this example was replaced with a single solvent using only β -terpineol, and the remaining conditions were exactly the same as in this example. The solder paste obtained by the comparative example had a void ratio of 26.94% and a shear force of 22.51MPa after firing to form a connection layer.
Therefore, the organic solvent carrier in the embodiment of the invention adopts the solder obtained by mixing the organic solvent, the void ratio of the connecting layer formed by sintering is smaller, the compactness of the connecting layer is improved, and the shearing force is also greatly improved.
Example 3
Dissolving 3g of sodium citrate into 200ml of water, adding 1g of silver carbonate after completely dissolving the sodium citrate by stirring, and stirring and mixing the mixture to form a reaction solution. And (3) placing the reaction solution in a reaction kettle, and reacting for 12 hours at the temperature of 150 ℃. And after the reaction is finished, washing with deionized water, washing with ethanol, and finally freeze-drying to obtain the flaky nano-silver.
The flaky nano silver prepared by the embodiment comprises triangular flaky nano silver and hexagonal flaky nano silver. The particle size range of the flaky nano silver prepared by the embodiment is 100 nm-400 nm, and the thickness is 20 nm-40 nm.
And mixing the prepared flaky nano silver with a mixed organic solvent carrier of glycerol and beta-terpineol according to the mass ratio of 3:1, and stirring and mixing for 30min in a mixer to prepare the nano silver soldering paste. Wherein, the volume ratio of the glycerol to the beta-terpineol in the mixed organic solvent carrier is 1: 4.
The nano-silver solder paste prepared by the method is applied to the packaging interconnection of electronic devices. In particular, referring to fig. 2, both the first and second masters in the package interconnect structure are selected to be DBC substrates.
First, the master is processed: and ultrasonically washing the DBC substrate (the first master plate and the second master plate) in ethanol for 3min to remove impurities on the surface of the DBC substrate, and airing.
Then, the nano silver paste prepared in this embodiment is uniformly coated on the connecting surface of the DBC substrate and then stacked to obtain a "sandwich" structure of the DBC substrate/nano silver solder paste coating/DBC substrate.
And then, carrying out low-temperature sintering welding on the stacked structure of the DBC substrate/the nano-silver soldering paste coating/the DBC substrate at the connection temperature of 250 ℃ under the pressure of 3MPa, wherein the pressure holding time is 20min, and the nano-silver soldering paste coating is sintered to form a connection layer. After cooling, the package interconnect structure as shown in fig. 2 is obtained.
The connection layer of this example was subjected to void ratio calculation and shear fracture test with reference to the test manner of example 1, and through the test, the void ratio of the connection layer formed by sintering the nano-silver solder paste of this example was 11.24% and the shear force was 39.34MPa (wherein, 5 test samples were prepared and obtained according to this example, the test data was an average value of 5 test samples).
Example 4
Dissolving 1.8g of ascorbic acid into 200ml of ethanol, adding 1.66g of silver acetate after the ascorbic acid is completely dissolved by stirring, and stirring and mixing to form a reaction solution. And (3) placing the reaction solution in a reaction kettle, and reacting for 8 hours at the temperature of 160 ℃. And after the reaction is finished, washing with deionized water, washing with ethanol, and finally freeze-drying to obtain the flaky nano-silver.
The flaky nano silver prepared by the embodiment is triangular flaky nano silver. The particle size range of the flaky nano silver prepared by the embodiment is 120 nm-400 nm, and the thickness is 20 nm-50 nm.
And mixing the prepared flaky nano silver with the mixed organic solvent carrier of glycerol and diethylene glycol according to the mass ratio of 7:1, and stirring and mixing for 30min in a mixer to prepare the nano silver soldering paste. Wherein, the volume ratio of the glycerol to the diglycol in the mixed organic solvent carrier is 3: 2.
The nano-silver solder paste prepared by the method is applied to the packaging interconnection of electronic devices. In particular, referring to fig. 2, both the first and second masters in the package interconnect structure are selected to be DBC substrates.
First, the master is processed: and ultrasonically washing the DBC substrate (the first master plate and the second master plate) in ethanol for 3min to remove impurities on the surface of the DBC substrate, and airing.
Then, the nano silver paste prepared in this embodiment is uniformly coated on the connecting surface of the DBC substrate and then stacked to obtain a "sandwich" structure of the DBC substrate/nano silver solder paste coating/DBC substrate.
And then, carrying out low-temperature sintering welding on the stacked structure of the DBC substrate/the nano-silver soldering paste coating/the DBC substrate at the connection temperature of 250 ℃ under the pressure of 10MPa, wherein the pressure holding time is 20min, and the nano-silver soldering paste coating is sintered to form a connection layer. After cooling, the package interconnect structure as shown in fig. 2 is obtained.
The connection layer of this example was subjected to void ratio calculation and shear fracture test with reference to the test manner of example 1, and through the test, the void ratio of the connection layer formed by sintering the nano-silver solder paste of this example was 9.61%, and the shear force was 40.39MPa (wherein, 5 test samples were prepared and obtained according to this example, the test data was an average value of 5 test samples).
Example 5
8.69g of polyvinylpyrrolidone is dissolved in 200ml of DMF, 3.03g of silver oxalate is added after the polyvinylpyrrolidone is completely dissolved by stirring, and the mixture is stirred and mixed to form a reaction solution. And (3) placing the reaction solution in a reaction kettle, and reacting for 2 hours at the temperature of 200 ℃. And after the reaction is finished, washing with deionized water, washing with ethanol, and finally freeze-drying to obtain the flaky nano-silver.
Fig. 10 is an SEM image of the flaky nano silver prepared in this example, and as shown in fig. 10, the flaky nano silver prepared in this example includes triangular flaky nano silver and hexagonal flaky nano silver, and the triangular flaky nano silver is relatively large. The particle size range of the flaky nano silver prepared by the embodiment is 100 nm-500 nm, and the thickness is 20 nm-50 nm.
And mixing the prepared flaky nano-silver with a mixed organic solvent carrier of triethylene glycol and delta-terpineol according to the mass ratio of 8:1, and stirring and mixing for 30min in a mixer to prepare the nano-silver soldering paste. Wherein, in the mixed organic solvent carrier, the volume ratio of the triethylene glycol to the delta-terpineol is 4: 1.
The nano-silver solder paste prepared by the method is applied to the packaging interconnection of electronic devices. In particular, referring to fig. 2, both the first and second masters in the package interconnect structure are selected to be DBC substrates.
First, the master is processed: and ultrasonically washing the DBC substrate (the first master plate and the second master plate) in ethanol for 3min to remove impurities on the surface of the DBC substrate, and airing.
Then, the nano silver paste prepared in this embodiment is uniformly coated on the connecting surface of the DBC substrate and then stacked to obtain a "sandwich" structure of the DBC substrate/nano silver solder paste coating/DBC substrate.
And then, carrying out low-temperature sintering welding on the stacked structure of the DBC substrate/the nano-silver solder paste coating/the DBC substrate at the connection temperature of 225 ℃ under the pressure of 10MPa for 20min, and sintering the nano-silver solder paste coating to form a connection layer. After cooling, the package interconnect structure as shown in fig. 2 is obtained.
Fig. 11 is an SEM image of a cross-section of the package interconnect structure in this embodiment, and it can be understood that the bonding degree of the connection interface of the connection layer is good, and the uniform and dense voids of the connection layer are 11.75%. The connection layer of this example was subjected to a shear fracture test, and fig. 12 is an SEM of the shear fracture surface of the connection layer. Through testing, the shear force of the connection layer formed by sintering the nano-silver solder paste of the embodiment was measured to be 37.78MPa after cooling (wherein, 5 test samples were prepared according to the embodiment, and the test data is the average value of the 5 test samples).
Example 6
0.888g of polyvinylpyrrolidone is dissolved in 200ml of N-methylpyrrolidone, 1.689g of silver nitrate is added after complete dissolution by stirring, and the mixture is stirred and mixed to form a reaction solution. And (3) placing the reaction solution in a reaction kettle, and reacting for 24 hours at the temperature of 140 ℃. And after the reaction is finished, washing with deionized water, washing with ethanol, and finally freeze-drying to obtain the flaky nano-silver.
The flaky nano silver prepared by the embodiment is mainly hexagonal flaky nano silver, the particle size range of the flaky nano silver is 200 nm-500 nm, and the thickness of the flaky nano silver is 20 nm-50 nm.
And mixing the prepared flaky nano silver with a mixed organic solvent carrier of glycerol and gamma-terpineol according to the mass ratio of 10:1, and stirring and mixing for 30min in a mixer to prepare the nano silver soldering paste. Wherein, in the mixed organic solvent carrier, the volume ratio of the triethylene glycol to the delta-terpineol is 3: 7.
The nano-silver solder paste prepared by the method is applied to the packaging interconnection of electronic devices. In particular, referring to fig. 2, both the first and second masters in the package interconnect structure are selected to be DBC substrates.
First, the master is processed: and ultrasonically washing the DBC substrate (the first master plate and the second master plate) in ethanol for 3min to remove impurities on the surface of the DBC substrate, and airing.
Then, the nano silver paste prepared in this embodiment is uniformly coated on the connecting surface of the DBC substrate and then stacked to obtain a "sandwich" structure of the DBC substrate/nano silver solder paste coating/DBC substrate.
And then, carrying out low-temperature sintering welding on the stacked structure of the DBC substrate/the nano-silver solder paste coating/the DBC substrate at the pressure of 20MPa and the connection temperature of 175 ℃, wherein the pressure holding time is 20min, and the nano-silver solder paste coating is sintered to form a connection layer. After cooling, the package interconnect structure as shown in fig. 2 is obtained.
The connection layer of this example was subjected to void ratio calculation and shear fracture test in accordance with the test method of example 1, and the void ratio of the connection layer formed by sintering the nano-silver solder paste of this example was 12.15% and the shear force was 36.26MPa (wherein 5 test samples were prepared and the test data was averaged over 5 test samples) by the test.
In summary, the nano-silver solder paste provided by the above embodiment includes the mutually mixed flaky nano-silver and the organic solvent carrier, and the sintering connection temperature is 150 ℃ to 300 ℃, which is far lower than the melting point (961.8 ℃) of the bulk silver, so that the nano-silver solder paste can be well applied to the field of electronic packaging of low-temperature welding high-temperature service. The organic solvent carrier in the soldering paste adopts a mixed solvent of more than two organic solvents, the bonding degree of a connecting interface of a connecting layer formed after sintering is good, uniform and compact, the void ratio of the connecting layer is below 13%, the shearing strength reaches more than 35MPa, and the high shearing strength is realized, so that the soldering paste can be well applied to the packaging interconnection of electronic devices.
The foregoing is directed to embodiments of the present application and it is noted that numerous modifications and adaptations may be made by those skilled in the art without departing from the principles of the present application and are intended to be within the scope of the present application.
Claims (10)
1. The nano-silver solder paste is characterized by comprising flake nano-silver and an organic solvent carrier which are mixed with each other, wherein the organic solvent carrier is a mixture of any two or more of ethylene glycol, glycerol, diethylene glycol, triethylene glycol, beta-terpineol, gamma-terpineol and delta-terpineol, and the volume percentage of any one organic solvent is not less than 20%.
2. The nano-silver solder paste according to claim 1, wherein the nano-silver flakes are triangular flake nano-silver and/or hexagonal flake nano-silver.
3. The nano-silver solder paste according to claim 1, wherein the flaky nano-silver has a particle size of 100 to 700nm and a thickness of 20 to 40 nm.
4. The nano-silver solder paste of claim 1, wherein the organic solvent carrier is a mixture of any two selected from the group consisting of ethylene glycol, glycerin, diethylene glycol, triethylene glycol, β -terpineol, γ -terpineol, and δ -terpineol.
5. The nano-silver solder paste according to any one of claims 1 to 4, wherein the ratio of the flaky nano-silver to the organic solvent carrier by mass is 2 to 10: 1.
6. a method for preparing a nano silver solder paste according to any one of claims 1 to 5, comprising: providing the flaky nano silver and the organic solvent carrier, and stirring and mixing the flaky nano silver and the organic solvent carrier to prepare the nano silver soldering paste.
7. The method of preparing a nano-silver solder paste according to claim 6, further comprising: the flaky nano silver is prepared by adopting a liquid phase reduction method.
8. The method for preparing nano-silver solder paste according to claim 7, wherein the preparing and obtaining the flaky nano-silver by the liquid phase reduction method specifically comprises:
dissolving a reducing agent in a solvent to obtain a first reaction solution;
adding a silver source precursor into the first reaction solution, and stirring and mixing to form a second reaction solution;
placing the second reaction solution in a reaction kettle, reacting for 2-24 h at the temperature of 140-200 ℃, and carrying out solid-liquid separation after the reaction is finished to obtain a solid-phase product;
sequentially washing and drying the solid-phase product to obtain the flaky nano silver;
wherein the reducing agent is selected from any one of ascorbic acid, hydrazine hydrate, citrate, polyvinylpyrrolidone, sodium sulfite and sodium borohydride; the solvent is selected from any one of ethanol, glycol, water, N-dimethylformamide, N-dimethylacetamide and N-methylpyrrolidone; the silver source precursor is selected from any one of silver acetate, silver carbonate, silver nitrate, silver oxalate and silver lactate; in the second reaction solution, the molar ratio of the reducing agent to the silver source precursor is 0.5-10.
9. Use of the nanosilver solder paste of any one of claims 1 to 5 in a chip package interconnect structure comprising a first master and a second master and a connection layer for connecting the first master and the second master, wherein the connection layer is formed by sintering using the nanosilver solder paste of any one of claims 1 to 5 by a sintering process of heating and applying pressure.
10. The use of claim 9, wherein in the sintering process, the heating temperature is 150 ℃ to 300 ℃ and the pressing pressure is 1MPa to 20 MPa.
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