Preparation method of silver-based high-temperature brazing filler metal for low-temperature connection of patch type heterogeneous materials

Abstract

The invention relates to a preparation method of silver-based high-temperature brazing filler metal for low-temperature connection of patch-type heterogeneous materials, which is characterized by comprising the following steps: step 1, weighing soluble silver salt, adding the soluble silver salt into a solvent, and uniformly mixing the solvent and the soluble silver salt according to the weight ratio of 1: 1-10: 1; performing ultrasonic treatment for at least 10 minutes to completely dissolve the soluble silver salt to obtain a precursor solution; wherein the soluble silver salt is silver nitrate or silver acetate; the solvent comprises water or alcohol; the silver-based high-temperature brazing filler metal prepared through the method has the advantage of being easy to synthesize, compared with a traditional silver nano material synthesis step, time consumed by the synthesis process is greatly shortened, the yield of the nano material is increased, and the method is suitable for large-scale preparation.

Description

Technical Field

[0001] The invention belongs to the technical field of solder preparation for heterogeneous material connection, and specifically provides a method for preparing a silver-based high-temperature solder for patch-type heterogeneous material low-temperature connection. Background Art

[0002] The lightweight of electronic packaging technology and the miniaturization of electronic devices have promoted the miniaturization and high integration of electronic products. Compared with the traditional through-hole plug-in electronic packaging technology, the surface mount technology (SMT) does not need to insert the pins into the substrate during packaging, but is loaded on a plane, realizing the double-sided utilization of the substrate, greatly improving the degree of circuit integration. At the same time, smaller and thinner leads replace the thick pins, bringing higher wiring density and excellent electrical characteristics.

[0003] The Pb-based solder used in the traditional electronic packaging field cannot meet the heat dissipation requirements of high-power density packaging systems due to its low thermal conductivity and poor electrical conductivity. At the same time, the low melting point of Pb-based alloys means that the corresponding devices can only be used at low operating temperatures, and the high-temperature reliability is extremely poor. In contrast, silver nanomaterials have become a packaging interconnect material that has attracted much attention in recent years because of their melting point and sintering temperature far lower than that of bulk materials and their high-temperature resistance after sintering is similar to that of bulk silver. At the same time, silver has an extremely low resistivity (10 -8 Ωm) and extremely high thermal conductivity (429W / mK) for good electrical and thermal connections.

[0004] However, when silver nanomaterials are currently used in electronic packaging, they are mostly used as fillers, mixed with binders, dispersants, passivation layers, covering agents, solvents, etc. to make slurry, which is applied to the packaging interface and connected with the assistance of pressure and temperature. One of the disadvantages of silver nano slurry is that the preparation of the slurry depends on the pre-synthesis of silver nanomaterials, while the synthesis process of traditional nanomaterials is time-consuming and has low yield, making it unsuitable for mass production. Secondly, in order to ensure that the slurry has good printability when used, a large amount of binders and organic solvents with organic polymer materials as the main components are also introduced in the preparation of the slurry. These polymer materials often need to be completely decomposed at higher temperatures, which brings more harsh conditions to sintering. After the organic matter is decomposed, it is easy to form holes in the joint structure, affecting the mechanical, electrical, thermal properties and reliability of the joint. Summary of the invention

[0005] An object of the present invention is to provide a method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials, so as to solve the problems existing in the prior art.

[0006] A method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials, characterized in that it comprises the following steps:

[0007] Step 1, weighing a soluble silver salt and adding it to a solvent, uniformly mixing the solvent and the soluble silver salt in a weight ratio of 1:1 to 10:1; ultrasonically treating for at least 10 minutes to completely dissolve the soluble silver salt to obtain a precursor solution; wherein the soluble silver salt is silver nitrate or silver acetate; and the solvent comprises water or alcohol;

[0008] Step 2, weighing a polymethacrylate solution and a reducing agent, adding them to a solvent, and ultrasonically treating for at least 5 minutes to obtain a reducing agent solution; wherein the ratio of the polymethacrylate solution, the reducing agent and the solvent is, by weight: taking 0.1 to 10 parts of the reducing agent, 0.02 to 0.08 parts of the polymethacrylate solution, and adding them to 20 parts of the solvent; wherein the reducing agent is ascorbic acid, sodium citrate, glucose or polyvinyl pyrrolidone; the solvent is water or an alcohol solvent; the mass fraction of the polymethacrylate solution is 10% to 50% aqueous solution, and the polymer atomic weight is greater than 9000; the polymethacrylate is sodium polymethacrylate;

[0009] Step 3, adding the solution obtained in step 1 to the solution obtained in step 2, and standing in a container for at least 30 seconds to obtain a silver-based flaky structure;

[0010] Step 4: Clean the silver-based thin sheet structure obtained in step 3 with a solvent, dry it, and obtain a silver-based high-temperature solder sheet. The cleaning solvent is water or an alkane solvent.

[0011] In the step 3, the adding method is one-time adding; standing for at least 30 seconds until the silver-based thin sheet is formed; the container used is a culture dish or a corresponding container is used according to the shape of the substrate to be welded, so as to obtain a welding piece shape that is easy to weld;

[0012] In the step 4, the number of times of washing with the solvent is 2 to 5 times; the drying method is one or more combinations of room temperature drying, freeze drying, and supercritical drying.

[0013] The silver-based high-temperature solder sheet prepared in step 4 can be used for patch sintering or welding. During the sintering or welding process, since there is no need to use organic matter for printing regulation, the introduction of organic matter is reduced, thereby achieving connection of heterogeneous materials at low temperature.

[0014] The silver-based high-temperature solder can be used for welding SiC chip-DBC substrate, copper-aluminum, silver-copper heterogeneous materials and homogeneous materials.

[0015] The mass fraction of the polymethacrylate solution in step 2 is 25% to 35% aqueous solution.

[0016] The present invention has at least the following beneficial effects:

[0017] (1) The silver-based high-temperature solder prepared by the present invention has the advantage of being easy to synthesize. Compared with the traditional synthesis steps of silver nanomaterials, the synthesis process time is greatly reduced, the output of nanomaterials is increased, and it is suitable for mass production.

[0018] (2) The silver-based high-temperature solder prepared by the present invention is suitable for patch welding connection. There is no need to introduce high-molecular organic solvents and adhesives during the welding or packaging process, which reduces the influence of high-molecular organic matter on the welding / packaging temperature and joint strength. At the same time, the shape of the silver-based high-temperature solder can change with the shape of the container, so that the silver-based high-temperature solder welding sheet is suitable for welding / packaging on complex curved surfaces.

[0019] (3) The silver-based high-temperature solder prepared by the present invention can be used for connecting SiC chips & DBC substrates, copper-aluminum, silver-copper heterogeneous materials and homogeneous materials, and has a wide range of applications.

[0020] (4) The sintered body obtained after welding the silver-based high-temperature solder prepared by the present invention has a high melting point similar to that of the silver bulk, which can meet the needs of low-temperature connection and high-temperature service of high-power devices. The present invention greatly increases the high-temperature reliability of the connection layer; at the same time, its electrical properties and thermal conductivity are similar to those of bulk silver, which can achieve good electrical and thermal connections. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 , which are digital photos of solder sheets of different sizes obtained after cutting the silver-based solder sheet prepared in Example 1 of the present invention;

[0022] Figure 2 , which are digital photos of silver-based high-temperature solders of different shapes obtained after reaction refining using different containers in the present invention;

[0023] Figure 3 , is a scanning electron microscope (SEM) image of the SiC chip-DBC substrate packaged using silver-based high-temperature solder in the present invention. DETAILED DESCRIPTION

[0024] In order to achieve these purposes and other advantages according to the present invention, a method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials is provided, comprising the following steps:

[0025] Step 1, weighing a soluble silver salt, adding it to a solvent, and ultrasonically treating it for at least 10 minutes to obtain a precursor solution;

[0026] Step 2, weighing a polymethacrylate solution and a reducing agent, adding them to a solvent, and ultrasonically treating for at least 5 minutes to obtain a reducing agent solution;

[0027] Step 3, adding the solution obtained in step 1 to the solution obtained in step 2, and standing in a container such as a petri dish for at least 30 seconds to obtain a silver-based thin sheet structure;

[0028] Step 4: Clean the silver-based thin sheet structure obtained in step 3 with a solvent, dry it, and obtain a silver-based high-temperature solder sheet.

[0029] Preferably, in step 1, the precursor solution is uniformly mixed in a weight ratio of solvent to soluble silver salt of 1:1 to 10:1, and the solution is ultrasonically treated to dissolve the silver salt.

[0030] Preferably, in the preparation of the precursor solution, the soluble silver salt includes but is not limited to silver nitrate, silver acetate, etc. The solvent includes but is not limited to water, alcohols, and other organic solvents.

[0031] Preferably, in step 2, the reducing agent solution is prepared by taking 0.1 to 10 parts of reducing agent and 0.02 to 0.08 parts of polymethacrylate solution by weight, adding them to 20 parts of solvent, and subjecting the reaction container to ultrasonic treatment to dissolve the silver salt.

[0032] Preferably, in the preparation of the reducing agent solution, the reducing agent includes but is not limited to ascorbic acid, sodium citrate, glucose, and polyvinyl pyrrolidone. The solvent includes but is not limited to water, alcohols, and other organic solvents. The polymethacrylate includes but is not limited to sodium polymethacrylate.

[0033] Preferably, in step 2, the polymethacrylate solution is a 10% to 50% aqueous solution by mass, and the polymer atomic weight is greater than 9000. In step 3, the adding method is one-time adding; standing for at least 30 seconds until the silver-based thin sheet is formed; the container used includes but is not limited to a culture dish, and the corresponding container can be used according to the shape of the base to be welded, so as to obtain a welding piece shape that is easy to weld. In step 4, the number of times of washing with solvent is 2 to 5 times; the drying method is one or more combinations of room temperature drying, freeze drying, and supercritical drying.

[0034] Preferably, the silver-based high-temperature solder sheet prepared in step 1 can be used for patch sintering. During the sintering process, since there is no need to use organic matter for printing regulation, the introduction of organic matter is reduced, so that the connection of heterogeneous materials can be achieved at low temperature.

[0035] Preferably, the silver-based high-temperature solder can be used for welding heterogeneous materials such as SiC chip-DBC substrate, copper-aluminum, silver-copper and the like, as well as homogeneous materials.

[0036] Preferably, the sintered body obtained after welding with silver-based high-temperature solder has a high melting point close to that of the silver bulk body, which can meet the demand for low-temperature connection and high-temperature service of high-power devices.

[0037] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0038] Embodiment 1:

[0039] A method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials comprises the following steps:

[0040] Step 1: Weigh 14 g silver nitrate and 20 g deionized water into a beaker and sonicate for 10 minutes to completely dissolve them.

[0041] Step 2: Weigh 0.136 g ascorbic acid, 0.02 g sodium polymethacrylate solution, and 20 g deionized water into a beaker, and sonicate for 5 minutes to completely dissolve them.

[0042] Step 3, adding the solution obtained in step 1 to the solution obtained in step 2, and standing in a culture dish for at least 30 seconds to obtain a thin sheet of silver structure;

[0043] Step 4: Wash the thin sheet structure repeatedly with deionized water for 5 times, and freeze-dry it to obtain a silver-based high-temperature solder sheet.

[0044] Figure 1 This is the macroscopic morphology of the silver-based high-temperature solder sheet. As can be seen from the figure, the sheet can be cut into different sizes. Figure 2 The silver-based high-temperature solders of different shapes were obtained after reaction and standing in different containers, proving that the shape of the solder can be controlled by using containers, thereby obtaining solder sheets suitable for different welding / packaging substrates. Figure 3 This is the SEM image of the SiC chip and DBC substrate after welding using silver-based high-temperature solder. Effective connection of heterogeneous materials was achieved at 300°C.

[0045] The present invention discloses a method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials, the method comprising:

[0046] (1) The precursor solution is prepared by uniformly mixing a reducing solvent and a silver salt solution; (2) The reducing solvent is prepared by uniformly mixing a solvent, polymethacrylate and a reducing agent; (3) Silver nanomaterials can be quickly synthesized by mixing the reducing solvent and the silver salt solution; (4) When the silver nanomaterials are synthesized in different containers, three-dimensional structures of different shapes can be obtained. In particular, when the container is a container with a large bottom area and a low height (such as a culture dish), a silver-based thin sheet structure suitable for patch sintering can be obtained; (5) The obtained silver-based thin sheet structure is cleaned and dried to obtain a silver-based high-temperature solder. The present invention proposes for the first time a method for preparing a silver-based high-temperature solder suitable for patch-type heterogeneous material connection that can be quickly synthesized. The preparation time of the silver-based solder is less than 5 minutes, and it can be used for connecting heterogeneous materials such as SiC chips and DBC substrates. The effective connection of heterogeneous materials can be achieved below 300°C. The melting point of the weld obtained after the solder is melted and solidified is similar to that of the silver block material, and it is a typical high-temperature solder.

Claims

1. A method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials, characterized in that: The following steps are involved: Step 1, weighing a soluble silver salt and adding it to a solvent, uniformly mixing the solvent and the soluble silver salt in a weight ratio of 1:1 to 10:1; ultrasonically treating for at least 10 minutes to completely dissolve the soluble silver salt to obtain a precursor solution; wherein the soluble silver salt is silver nitrate or silver acetate; and the solvent comprises water or alcohol; Step 2, weighing a polymethacrylate solution and a reducing agent, adding them to a solvent, and ultrasonically treating for at least 5 minutes to obtain a reducing agent solution; wherein the ratio of the polymethacrylate solution, the reducing agent and the solvent is, by weight: taking 0.1 to 10 parts of the reducing agent, 0.02 to 0.08 parts of the polymethacrylate solution, and adding them to 20 parts of the solvent; wherein the reducing agent is ascorbic acid, sodium citrate, glucose or polyvinyl pyrrolidone; the solvent is water or an alcohol solvent; the mass fraction of the polymethacrylate solution is 10% to 50% aqueous solution, and the polymer atomic weight is greater than 9000; the polymethacrylate is sodium polymethacrylate; Step 3, adding the solution obtained in step 1 to the solution obtained in step 2, and standing in a container for at least 30 seconds to obtain a silver-based flaky structure; Step 4: Clean the silver-based thin sheet structure obtained in step 3 with a solvent, dry it, and obtain a silver-based high-temperature solder sheet. The cleaning solvent is water or an alkane solvent.

2. The method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials according to claim 1, characterized in that: In the step three, the adding method is one-time adding; standing for at least 30 seconds until the silver-based thin sheet is formed; the container used is a culture dish or a corresponding container is used according to the shape of the substrate to be welded, so as to obtain a welding piece shape that is easy to weld.

3. The method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials according to claim 1 or 2, characterized in that: In the step 4, the number of times of washing with the solvent is 2 to 5 times; the drying method is one or more combinations of room temperature drying, freeze drying, and supercritical drying.

4. The method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials according to claim 1 or 2, characterized in that: The silver-based high-temperature solder sheet prepared in step 4 can be used for patch sintering or welding. During the sintering or welding process, since there is no need to use organic matter for printing regulation, the introduction of organic matter is reduced, thereby achieving connection of heterogeneous materials at low temperature.

5. The method for preparing a silver-based high-temperature solder for low-temperature connection of patch-type heterogeneous materials according to claim 1 or 2, characterized in that: The silver-based high-temperature solder can be used for welding SiC chip-DBC substrate, copper-aluminum, silver-copper heterogeneous materials and homogeneous materials.

6. The method for preparing a silver-based high-temperature solder for low-temperature connection of heterogeneous materials in patch type according to claim 1, characterized in that: The mass fraction of the polymethacrylate solution in step 2 is 25% to 35% aqueous solution.

Images