Pressureless sintering high-density micron silver soldering paste and preparation method and application thereof

Abstract

The invention discloses pressureless sintering high-density micron silver soldering paste and a preparation method and application thereof. The pressureless sintering high-density micron silver soldering paste is formed by selecting the solvent capable of improving the surface activation energy of the micron silver sheets and mixing the solvent with the micron silver sheets with proper sizes according to a certain proportion, so that uniform dispersion of the micron silver sheets can be realized, and the specific solvent is also beneficial to tight combination of the micron silver sheets; at a lower temperature (lt; compared with the prior art, the welding material is sintered at the temperature of 300 DEG C without applying extra pressure, a welding joint with large shear strength and high density can be obtained, an extra binder is not needed, energy consumption and production cost can be reduced, the welding material can serve as a good welding material of a packaging module, a large number of harmful substances cannot be generated in the sintering process, and the welding material is environmentally friendly.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic packaging interconnection materials, and more specifically to a pressureless sintering high-density micron silver solder paste and a preparation method and application thereof. Background Art

[0002] In the early days of the development of electronic packaging technology, the most commonly used interconnection materials were solder alloys and conductive adhesives, and the maximum operating temperature of these connection materials can usually only reach about 150°C. With the increase in the operating temperature of power electronic devices, the method of sintering silver particles has broad application prospects in the packaging field of the device due to its excellent comprehensive performance. Both the size of silver particles and the composition of solder paste will affect the performance of the silver solder paste sintered body. For example, Chinese patent CN112207481A (application publication date 2021.01.12) discloses a pressureless sintering high-density micron silver solder paste, which is made of two micron-sized silver particles and a solvent in a certain ratio. The sintering temperature is 200-225°C. Although a shear strength of more than 30MPa can be obtained at a lower sintering temperature, its porosity is still relatively high (~30%), and the density is not ideal. Among them, the solvent component also has an important influence on the physical properties of the silver solder paste, including viscosity and fluidity. The evaporation and removal process of the solvent during the sintering process will affect the performance of the silver solder paste after sintering. The solvent component of solder paste can improve the active state of the silver surface and play a vital role in the sintering of solder paste, but there is currently little research on the influence of solvent composition. Summary of the invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of high porosity and low density of the sintered body after sintering of the silver solder paste, and to provide a pressureless sintering high-density micron silver solder paste, which requires a low sintering temperature (<300°C), does not require additional pressure, does not contain additives, does not produce a large amount of harmful substances during the sintering process, and the sintered welding joint also has good shear strength and low density.

[0004] Another object of the present invention is to provide a method for preparing a pressureless sintering high-density micron silver solder paste.

[0005] Another object of the present invention is to provide an application of a pressureless sintering high-density micron silver solder paste.

[0006] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0007] A pressureless sintering high-density micron silver solder paste comprises 80% to 90% of micron silver particles and 10% to 20% of an organic solvent calculated by mass percentage, wherein the micron silver particles are micron silver sheets with a diameter of 1 to 10 μm and a thickness of 0.1 to 2 μm, and the organic solvent is selected from a mixture of 2 to 4 of alcohols, ethers, alkanes and ketones; the alcohol is selected from n-octanol, terpineol, eucalyptol, ethylene glycol, diethylene glycol, triethylene glycol or polyethylene glycol 400; the ether is selected from n-pentyl ether, n-hexyl ether, diethylene glycol diethyl methyl ether, diethylene glycol diethyl ether or diethylene glycol dibutyl ether; the alkane is selected from n-decane, n-undecane or n-dodecane; the ketone is selected from phorone, isophorone, cyclohexanone, 4-methylcyclohexanone or cycloheptanone.

[0008] The present invention provides a pressureless sintering high-density micron silver solder paste. The micron silver particles are selected in suitable shapes and sizes, and the solvent that can improve the surface activity of the micron silver flakes is selected, so that the micron silver flakes can be evenly dispersed and the micron silver flakes can be closely connected. On the one hand, the ether reagent has a relatively low viscosity. After being mixed with a solvent with a relatively high viscosity, the viscosity of the silver solder paste is adjusted to a suitable degree, and it has good printing adaptability; at the same time, the small surface tension of diethylene glycol diethyl ether makes it have excellent adhesion performance, which is conducive to the formation of effective connection between the solder joint and the substrate and the silicon wafer; on the other hand, the organic layer on the surface of the silver particles is characterized by Raman spectroscopy to contain -COOH or -COOM functional groups and a relatively long carbon chain, so the use of hydroxyl, carbonyl solvents or alkanes with long carbon chains can react or dissolve with the organic shell layer, which is conducive to close contact between the silver particles and then densification sintering. The mixed organic solvent can adjust the volatility of the original single solvent silver solder paste, so that the organic solvent evaporates in layers and smoothly, and the porosity of the joint microstructure is significantly reduced. The micron silver solder paste of the present invention does not require additional adhesive or additional pressure, and the silver solder paste requires a lower sintering temperature, so that better shear strength and lower porosity can be obtained.

[0009] Preferably, the mass percentage of the micron silver particles is 85% to 90%.

[0010] Preferably, the mass percentage of the organic solvent is 10% to 15%, and the difference in the proportion of each solvent in the mixed organic solvent is less than or equal to 2%.

[0011] Preferably, the diameter of the micron silver flakes is 1 to 6 μm, and the thickness is 0.1 to 1 μm.

[0012] Preferably, the solvent is a mixture of 2 to 4 of n-octanol, ethylene glycol, diethylene glycol, triethylene glycol, diethylene glycol diethyl ether, n-hexyl ether, polyethylene glycol 400, terpineol, n-undecane, n-dodecane, isophorone, and 4-methylcyclohexanone.

[0013] A method for preparing a pressureless sintering high-density micron silver solder paste comprises the following steps: firstly, 2 to 4 solvents are mixed evenly, then a certain amount of micron silver flakes are added, and after being stirred evenly by a planetary mixer, the pressureless sintering high-density micron silver solder paste is obtained.

[0014] The present invention also protects the application of the pressureless sintering high-density micron silver solder paste in the field of power device packaging.

[0015] Preferably, the method comprises the following steps:

[0016] The pressureless sintering high-density micron silver solder paste is placed on the material to be soldered, and sintered at 240-300°C for 10-60min, with a heating rate of 21-36°C / min.

[0017] Preferably, the sintering temperature is 250-300° C. The materials to be welded are a surface metallized ceramic substrate and a silver-plated silicon chip; the surface metallized ceramic substrate includes a DBC substrate, a silver-plated DBC substrate, a gold-plated DBC substrate or an iron-nickel-plated DBC substrate.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The pressureless sintering high-density micron silver solder paste is made of micron silver flakes with a certain ratio and a plurality of mixed solvents. The solvent is selected to improve the surface activation energy of the micron silver flakes and adjust the viscosity of the solder paste, and is mixed with a micron silver flake of a suitable size in a certain ratio. In this way, the uniform dispersion of the micron silver flakes can be achieved. The specific solvent is also conducive to the close bonding of the micron silver flakes. The soldering joint with high shear strength, high density and good electrical conductivity can be obtained by sintering at a relatively low temperature (less than 300° C.) without applying additional pressure. No additional adhesive is required, and energy consumption and production cost can be reduced. The soldering paste can be used as a good soldering material for power electronic device packaging, and a large amount of harmful substances will not be generated during sintering. The soldering paste is an environmentally friendly material. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The microscopic cross-sectional morphology structure of the low-temperature pressureless sintering micrometer silver solder joint of the present invention.

[0021] Figure 2 The cross-sectional microscopic morphology of the solder joints after sintering of the pressureless sintered high-density micron silver solder paste prepared in the examples and comparative examples. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0023] Example 1

[0024] A pressureless sintering high-density micron silver solder paste comprises 89% of micron silver flakes, 6% of organic solvent ethylene glycol, and 5% of diethylene glycol diethyl ether calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0025] The method for preparing the pressureless sintering high-density micron silver solder paste comprises the following steps:

[0026] First, ethylene glycol and diethylene glycol diethyl ether are mixed evenly, and then the micron silver flakes and the mixed solvent are placed in a planetary mixer and stirred in vacuum mode for 6 minutes. The pressureless sintering high-density micron silver solder paste is obtained after stirring evenly.

[0027] The prepared micron silver solder paste was printed between the silver-plated silicon chip and the DBC substrate, and then placed on a heating table for pressureless sintering. The sintering temperature was 250°C, the heating rate was 25°C / min, and the sintering time was 30min.

[0028] Example 2

[0029] A pressureless sintering high-density micron silver solder paste comprises 90% of micron silver flakes, 5% of an organic solvent n-undecane, and 5% of diethylene glycol diethyl ether calculated by mass percentage, wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0030] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1.

[0031] Example 3

[0032] A pressureless sintering high-density micron silver solder paste comprises 90% of micron silver flakes and 5% each of organic solvents terpineol and diethylene glycol diethyl ether calculated by mass percentage; wherein the diameter of the micron silver flakes is 5μm and the thickness is 0.1μm.

[0033] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1.

[0034] Example 4

[0035] A pressureless sintering high-density micron silver solder paste comprises 90% of micron silver flakes and 5% of organic solvents, isophorone and diethylene glycol diethyl ether, calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0036] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1, except that it is interconnected with the silver-plated silicon chip and the silver-plated DBC substrate.

[0037] Example 5

[0038] A pressureless sintering high-density micron silver solder paste comprises 88% of micron silver flakes, 4% of an organic solvent pineneol, 4% of ethylene glycol, and 4% of diethylene glycol diethyl ether in terms of mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0039] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1.

[0040] Example 6

[0041] A pressureless sintering high-density micron silver solder paste comprises 88% of micron silver flakes, 4% of an organic solvent isophorone, 4% of ethylene glycol and 4% of diethylene glycol diethyl ether calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0042] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1.

[0043] Example 7

[0044] A pressureless sintering high-density micron silver solder paste comprises 88% of micron silver flakes, 3% of solvent pineol, 3% of ethylene glycol, 3% of diethylene glycol, and 3% of n-undecane calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0045] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1.

[0046] Example 8

[0047] A pressureless sintering high-density micron silver solder paste comprises 88% of micron silver flakes, 3% of isophorone solvent, 3% of ethylene glycol, 3% of n-dodecane and 3% of n-hexyl ether calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0048] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1.

[0049] Example 9

[0050] A pressureless sintering high-density micron silver solder paste is the same as Example 2, except that the subsequent sintering temperature is 275°C.

[0051] Example 10

[0052] A pressureless sintering high-density micron silver solder paste is the same as Example 2, except that the silver solder paste is printed between the silver-plated silicon chip and the iron-nickel-plated DBC substrate, and the subsequent sintering temperature is 300°C.

[0053] The preparation method of the pressureless sintering high-density micron silver solder paste and other sintering parameters are the same as those in Example 1.

[0054] Comparative Example 1

[0055] The preparation method of a micron silver solder paste is the same as that of Example 1, except that the solvent is replaced by ethylene glycol.

[0056] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those in Example 1.

[0057] Comparative Example 2

[0058] A pressureless sintering high-density micron silver solder paste comprises 89% of micron silver flakes and 11% of diethylene glycol diethyl ether as a solvent calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0059] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those of Example 2, except that the solvent is replaced by a single solvent, diethylene glycol diethyl ether.

[0060] Comparative Example 3

[0061] A pressureless sintering high-density micron silver solder paste comprises 89% of micron silver flakes and 11% of solvent n-undecane calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0062] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those of Example 3, except that the solvent is replaced by a single solvent, n-undecane.

[0063] Comparative Example 4

[0064] A pressureless sintering high-density micron silver solder paste comprises 89% of micron silver flakes and 11% of solvent pineol calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0065] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those of Example 3, except that the solvent is replaced by a single solvent, pinene alcohol.

[0066] Comparative Example 5

[0067] A pressureless sintering high-density micron silver solder paste comprises 89% of micron silver flakes and 11% of isophorone solvent in terms of mass percentage; the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0068] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those of Example 4, except that the solvent is replaced by a single solvent, isophorone.

[0069] Comparative Example 6

[0070] A pressureless sintering high-density micron silver solder paste comprises 89% of micron silver flakes and 11% of solvent diethylene glycol calculated by mass percentage; wherein the diameter of the micron silver flakes is 5 μm and the thickness is 0.1 μm.

[0071] The preparation method and sintering parameters of the pressureless sintering high-density micron silver solder paste are the same as those of Example 7, except that the solvent is replaced by a single solvent, diethylene glycol.

[0072] Performance Testing

[0073] 1. Test methods

[0074] Shear strength: The shear strength test was carried out at room temperature using a push-pull tester (MFM1200, Try precision) with a shear speed of 100 μm / s.

[0075] Conductivity: A 40×10×0.12 mm strip sample was printed on a glass slide for conductivity testing, and the conductivity of the sample was tested using a four-probe resistance meter (Loresta-GX MCP-T700, Nittoseiko Analytech).

[0076] Viscosity: The viscosity of the silver solder paste was tested using a rotational rheometer (MCR302, Anton Paar). The rotor of the instrument was immersed in 8g of silver solder paste. After adjusting the level of the rotor of the equipment and the automatic calibration of the instrument, a certain speed was set. The viscosity value read was between 40% and 60% of the range, which was the effective value. The measurement time was set to 500s.

[0077] 2. Test results

[0078] Table 2 Shear performance test results of micron silver solder joints prepared in various embodiments and comparative examples

[0079]

[0080]

[0081] Table 3 Test results of conductivity of micron silver solder joints prepared in some embodiments and comparative examples

[0082]

[0083]

[0084] As can be seen from Table 2, the pressureless sintering high-density micron silver solder paste prepared by the present invention has a high shear strength and good density after sintering. Different organic solvents were used in the above-mentioned embodiments and comparative examples, and there were certain differences in the results of the obtained welded joints, indicating that the organic solvent plays a certain role in the sintering process. In Examples 1 to 8, the silver solder paste uses organic solvents of different mixed formulas, while only one alcohol organic solvent is used in Comparative Examples 1 and 4, and the shear strength of the joint is greatly reduced compared with Examples 1 to 8, and the corresponding porosity is significantly increased. Mixed organic solvents can adjust the volatility and wetting ability of the silver solder paste, which is beneficial to improve the mechanical properties of the sintered silver joint and slow down the formation of macropores. In Comparative Example 1, the solvent used is ethylene glycol. Due to the high surface tension and viscosity of ethylene glycol, the micron silver flakes cannot be well dispersed in ethylene glycol alone, nor can they promote the close connection between the micron silver flakes. At the same sintering temperature, the shear strength of the welded joint is low, and it can be seen that the selection of organic solvents is crucial. In Table 3, Examples 3 and 9 are silver solder pastes prepared from the same organic solvent and sintered at different temperatures. As the sintering temperature increases from 250°C to 275°C, the shear strength of the solder joint increases slightly, and its conductivity increases from 1.57×10 7 S / m increased to 1.60×10 7 S / m, which is about the conductivity of pure silver (6.3×10 7 S / m). For different silver solder pastes sintered at the same temperature, Example 8 exhibited the best shear strength and the best conductivity, followed by Examples 6 and 7. The shear strength of the silver solder joints prepared in the comparative examples using a single solvent did not exceed 30 MPa. Among them, the conductivity of Comparative Examples 1, 4, and 6 was less than one-eighth of that of pure silver, significantly lower than that of other examples; although the conductivity of Comparative Examples 2, 3, and 5 could reach 10 7 The results of the embodiment 10 are shown in Table 1, which is only slightly lower than the results of other embodiments, but the joint shear strength is only about 13MPa, and the mechanical properties are significantly lower than those of other embodiments. Embodiment 10 is to interconnect the micron silver solder paste with the iron-nickel plated DBC substrate, and the results show that the sintered silver can form an effective connection with the iron-nickel plated layer.

[0085] The above results show that the pressureless sintering high-density micron silver solder paste of the present invention requires a low sintering temperature, can obtain a good interconnection effect, reduce energy consumption, and does not produce harmful substances.

[0086] Cross-section of interconnected sintered structures using silver solder paste Figure 1As shown, the upper side is a silver-plated silicon chip, the lower side is a direct-bonded copper ceramic substrate (silver-plated DBC) with a silver-plated surface, and the middle is a porous silver sintered body. Figure 2 The microscopic cross-sections of sintered bodies prepared by different organic solvent silver solder pastes correspond to (a) Example 1; (b) Example 8; (c) Comparative Example 1; (d) Comparative Example 2. Figure 2 It can be seen that the sintered solder joints of the embodiments all show a reliable interconnected structure with good density, especially the sintered structure of Example 7 clearly shows a higher density than other examples, indicating that a reliable sintered joint is obtained after sintering. First, the surface tension of pine alcohol and diethylene glycol diethyl ether is relatively low, so the spreading performance of silver is better; second, alcohols such as pine alcohol, ethylene glycol, and diethylene glycol can react with the organic shell layer on the surface of silver particles, which is conducive to the close connection between silver particles; and thirdly, the volatilization temperature of the mixed solvent has a gradient, and the volatilization temperatures of different organic solvents are different. During the heating process, diethylene glycol diethyl ether, ethylene glycol, pine alcohol, and diethylene glycol are volatilized from low to high in layers, so that the overall volatilization rate of the silver solder paste becomes gentle, which is conducive to reducing the formation of pores. The comparative examples are all silver solder pastes prepared by a single solvent. They will volatilize quickly and in large quantities at a certain temperature during sintering, which will result in larger pores in the sintered body.

[0087] In addition, the proportion of each mixed solvent is equal or the difference is less than or equal to 2%, which can effectively adjust the viscosity of the solder paste, so that it has good fluidity and wettability during printing and mounting. If the viscosity of the silver solder paste is too large, it is easy to stick and cause warping, and if it is too small, it is difficult to accurately control the printed shape. The viscosity range suitable for printing is 50-200 Pa·s. The viscosity of the silver solder paste with a similar ratio of composite solvents is significantly lower than that of the silver solder paste prepared with a single alcohol solvent, and higher than that of the silver solder paste prepared with a single ether solvent, as shown in Table 4. The composite solvent silver solder paste has a certain fluidity, and it only needs to be scraped once to print it flat on the substrate. After stopping printing, the viscosity is large enough to maintain the shape, and it has good printability. At the same time, the uniform solvent ratio can make the solder paste volatilize evenly during the sintering and heating process, avoiding a large amount of volatilization within a certain temperature range to produce too many pores and cracks, and improving the density and strength of the solder joint.

[0088] Table 4 Different solvent composition silver solder paste at a shear rate of 5s -1 Viscosity

[0089] Viscosity (Pa·s) Example 1 88.9 Example 3 69.2 Example 6 90.1 Comparative Example 1 373 Comparative Example 2 27.7 Comparative Example 4 170

[0090] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A pressureless sintering high-density micron silver solder paste, characterized in that: The invention comprises 80% to 90% of micron silver particles and 10% to 20% of an organic solvent calculated by mass percentage, wherein the micron silver particles are micron silver sheets with a diameter of 1 to 10 μm and a thickness of 0.1 to 2 μm, and the organic solvent is selected from a mixture of 2 to 4 of alcohols, ethers, alkanes and ketones; the alcohol is selected from n-octanol, terpineol, eucalyptol, ethylene glycol, diethylene glycol, triethylene glycol or polyethylene glycol 400; the ether is selected from n-pentyl ether, n-hexyl ether, diethylene glycol diethyl methyl ether, diethylene glycol diethyl ether or diethylene glycol dibutyl ether; the alkane is selected from n-decane, n-undecane or n-dodecane; the ketone is selected from phorone, isophorone, cyclohexanone, 4-methylcyclohexanone or cycloheptanone.

2. The pressureless sintering high-density micron silver solder paste according to claim 1, characterized in that: The micron silver particles are micron silver flakes with a diameter of 1 to 6 μm and a thickness of 0.1 to 1 μm.

3. The pressureless sintering high-density micron silver solder paste according to claim 1, characterized in that: The mass percentage of the micron silver particles is 85% to 90%.

4. The pressureless sintering high-density micron silver solder paste according to claim 1, characterized in that: The total mass percentage of the organic solvent is 10% to 15%, and the difference in the proportion of each solvent in the mixed organic solvent is less than or equal to 2%.

5. The method for preparing the pressureless sintering high-density micron silver solder paste according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: firstly, 2 to 4 kinds of solvents are mixed evenly, then micron silver flakes are added, and after vacuum stirring evenly, pressureless sintering high-density micron silver solder paste is obtained.

6. Application of the pressureless sintering high-density micron silver solder paste according to any one of claims 1 to 4 in the field of wide bandgap semiconductor device packaging interconnection.

7. The use according to claim 6, characterized in that: The steps include: The pressureless sintering high-density micron silver solder paste is placed on the material to be soldered, and sintered at 240-300°C for 10-60min, with a heating rate of 21-36°C / min.

8. The use according to claim 6, characterized in that: The sintering temperature is 250-300°C.

9. The use according to claim 6, characterized in that: The materials to be welded are a surface metallized ceramic substrate and a silver-plated silicon chip; the surface metallized ceramic substrate includes a DBC substrate, a silver-plated DBC substrate, a gold-plated DBC substrate or an iron-nickel-plated DBC substrate.

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