A solder for a piezoresistor and a production process thereof

Abstract

The application relates to the technical field of solder, in particular to solder for a pressure-sensitive resistor and a production process thereof. The solder for the pressure-sensitive resistor is composed of the following elements in percentage by weight: a soldering promoting element 0.1-0.5%, an insulating element 0.05-0.35%, a processing promoting element 1.8-4.5%, other trace elements 0.01-0.12%, and the balance of Sn and inevitable impurities; the soldering promoting element is Zn and / or V. The application can enhance the impact toughness and corrosion resistance of Sn by alloying Sn with Zn and / or V, further improve the impact toughness and corrosion resistance under the action of the insulating element and the processing promoting element, and make the solder obtained by combining other trace elements have better impact resistance, corrosion resistance and weldability with the pressure-sensitive resistor.

Description

Technical Field

[0001] This application relates to the technical field of solders, and more specifically, to a solder for varistors and its manufacturing process. Background Technology

[0002] Solder is a general term for metallic alloy materials used to fill welds, weld overlays, etc., including welding wire, welding rods, and brazing filler metals. Typically, the melting temperature of solder used for fusion welding is not lower than the solidus of the base metal, and its chemical composition, mechanical, and thermal properties are very close to those of the base metal, such as various welding rods and flux-cored welding wires. The weld strength is usually not lower than that of the base metal itself.

[0003] A varistor is a resistive device with nonlinear current-voltage characteristics, mainly used for voltage clamping when a circuit is subjected to overvoltage, absorbing excess current to protect sensitive components. The resistive material of a varistor is a semiconductor, therefore it is a type of semiconductor resistor.

[0004] Varistors are typically made primarily of zinc oxide (ZnO). Zinc oxide is a semiconductor material that changes its resistance in response to voltage variations. Besides zinc oxide, varistors may also contain other metal oxides or additives, which help to adjust the material's resistive properties and adapt it to different application requirements. In addition, there are other varistor materials, such as silicon vanadate (SVS) and silicon boride (SiC), each with its own characteristics and application areas.

[0005] Currently, the solder used for varistors mainly contains Ag, In, and Sn as its main components. Although Ag and In can further improve the strength and other properties of Sn, after soldering, there are still phenomena such as easy breakage and cracking at the solder joint, so further research is needed. Summary of the Invention

[0006] To address the aforementioned technical problems, this application provides a solder for varistors and a method for preparing the same.

[0007] In a first aspect, this application provides a solder for varistors, composed of the following elements by weight percentage: Welding promoting elements: 1-5% Insulating element: 0.05-0.35% Processing-promoting elements: 1.8-4.5% Other trace elements: 0.01-0.12% The balance is Sn and unavoidable impurities; The welding-promoting element is Zn and / or V.

[0008] The above-mentioned element composition and dosage ratio are all within the preferred range of this application, and the resulting solder has better impact toughness, reducing the occurrence of damage, cracking and other phenomena. In addition, it is stable when welded to the surface of the varistor, reducing the occurrence of cracking at the welding position. It also has better corrosion resistance and maintains better physical properties even in high temperature and high humidity environments and low temperature environments.

[0009] Zinc (Zn) is a metal with excellent strengthening properties, capable of strengthening alloys through the formation of solid solutions, dislocations, and microstructures. During the crystallization and growth of alloys, zinc can alter the atomic structure and chemical composition, thereby enhancing the alloy's strength and hardness. Furthermore, zinc can form alloys with other metals, creating new crystal structures and chemical compositions that further enhance the alloy's properties. Zinc also possesses excellent corrosion resistance, forming rust-resistant alloys with other metals.

[0010] The main effects of vanadium (V) are solid solution strengthening, grain refinement, improved wear resistance and toughness, increased hardenability, secondary hardening effect, improved resistance to intergranular corrosion, improved weldability, and increased low-temperature strength and impact value. V can significantly improve the red hardness, hardness, and wear resistance of steel, effectively refine grains, and reduce the steel's overheating sensitivity.

[0011] Therefore, the addition of Zn and / or V can play a role in corrosion resistance and impact toughness, reducing corrosion at the welding position of the varistor and stabilizing the solder on the varistor, thus improving its practicality.

[0012] Insulating elements provide excellent insulation, and when combined with other elements, they enable the solder to possess certain semiconductor properties. Therefore, they are easy to solder with varistors without affecting the properties of the varistor.

[0013] Processing-enhancing elements play a better role in promoting processing, making it easier for solder to be alloyed during the production process, and resulting in better mechanical properties after alloying.

[0014] In summary, this application enhances the impact toughness and corrosion resistance of Sn by alloying it with Zn and / or V. Furthermore, the impact toughness and corrosion resistance are further improved by the use of insulating and processing-promoting elements. Combined with other trace elements, the resulting solder possesses excellent impact resistance, corrosion resistance, and weldability to varistor electronics. Therefore, when used for welding varistors, the weld joints are less prone to cracking, breakage, or corrosion, thus improving the practicality of the varistor.

[0015] Preferably, the weight ratio of Zn to V is (1-6):1.

[0016] When Zn and V are compounded in a weight ratio of (1-6):1, they have a synergistic effect, which makes the solder more impact-resistant, corrosion-resistant and weldable to varistor electronics. This reduces the possibility of corrosion, breakage and cracking when used to weld varistor resistors.

[0017] Preferably, the insulating element is Si and / or B.

[0018] Si and B both have excellent insulation, corrosion resistance, and toughening strength. They can also improve the wettability of varistors. Therefore, the addition of Si and / or B improves the impact resistance, corrosion resistance, and weldability of the solder to varistors, thereby reducing the possibility of corrosion, breakage, and cracking when used to solder varistors.

[0019] Preferably, the weight ratio of Si to B is (1-5):1.

[0020] When the Si:B content ratio is (1-5):1, it can play a synergistic role, further enhancing the solder's impact resistance, corrosion resistance, and weldability with varistor electronics. This reduces the possibility of corrosion, breakage, and cracking when used to weld varistor resistors.

[0021] Preferably, the processing-promoting element is one or more of Li, Cu, Al, and Ag.

[0022] Li, Cu, Al, and Ag can all improve the plasticity and toughness of solder, giving the alloy better free deformability and strength, making it easier to weld and process, and also enhancing the corrosion resistance of the solder. Therefore, adding one or more of Li, Cu, Al, and Ag can give the solder both good impact toughness and corrosion resistance, reducing the possibility of corrosion, cracking, and breakage after welding to varistors.

[0023] Preferably, the weight ratio of Li, Cu, Al, and Ag is 1:(1-3):(1-3):(1-2).

[0024] When the content ratio of Li, Cu, Al, and Ag is 1:(1-3):(1-3):(1-2), the resulting solder exhibits better corrosion resistance and impact toughness.

[0025] Preferably, the other trace elements are one or more of Ba, Se, and As.

[0026] Ba, Se, and As all contribute to alloying and effectively increase the density and stiffness of the material, improving its heat resistance, durability, and flame retardancy. Therefore, when one or more of Ba, Se, and As are present, the solder exhibits better corrosion resistance and impact toughness. When used in varistors, this reduces the likelihood of corrosion, cracking, and breakage, thus enhancing the practicality of the varistor.

[0027] Preferably, the weight ratio of Ba, Se, and As is (2-6):(1-5):1.

[0028] When the weight ratio of Ba, Se, and As in the solder is (2-6):(1-5):1, the resulting solder has better corrosion resistance and impact toughness. Therefore, it can also provide better welding stability when used for welding varistors, reducing the possibility of corrosion and cracking, and improving the practicality of varistors.

[0029] Secondly, this application provides a manufacturing process for solder for varistors, which is prepared by the following method: 1) Calculate according to the weight percentage of the elements, weigh the tin powder, heat it to melt, then add the substance containing the processing-promoting element, mix evenly, heat to 600-700℃, hold and melt to obtain alloy liquid A; 2) Add the insulating element and other trace element to the alloy liquid, mix evenly, heat to 950-1050℃, heat and melt, cast into shape, cool, anneal to obtain solder.

[0030] In the above process, after tin powder is melted, a substance containing processing-promoting elements is added, stirred evenly, and then heated to 600-700℃ to continue melting the alloy. To obtain a liquid alloy, a substance containing insulating elements and other trace elements is added, stirred to ensure thorough mixing, and then heated to 950-1050℃ for holding and melting. After cooling, it is cast, forged, cooled, and annealed to obtain the solder. The resulting solder exhibits excellent corrosion resistance and impact toughness, making it easier to weld with varistors and reducing the possibility of corrosion, cracking, or breakage at the welding points of the varistor.

[0031] Preferably, the heat preservation and melting time in step 1) is 2-5 hours; the heat preservation and melting time in step 2) is 1.5-3.5 hours, and the temperature drop is 300-400℃.

[0032] The above melting time ensures thorough and uniform mixing of the materials, promoting the bonding of tin with other elements. Holding at 950-1050℃ for 1.5-3.5 hours further strengthens the bond between the elements, resulting in solder with superior corrosion resistance and impact toughness.

[0033] In summary, this application has the following beneficial effects: 1. This application uses Zn and / or V to alloy Sn, which can enhance its impact toughness and corrosion resistance. Under the action of insulating elements and processing-promoting elements, its impact toughness and corrosion resistance are further improved. Combined with other trace elements, the resulting solder has better impact resistance, corrosion resistance and weldability to varistor electronics. Therefore, when used for welding varistors, the weld joints are less likely to crack, break or corrode, thus improving the practicality of varistors.

[0034] 2. Si and B have good insulation, corrosion resistance, and toughening strength. They can also improve the wettability of varistor. Therefore, the addition of Si and / or B improves the impact resistance, corrosion resistance, and weldability of the solder to varistor, thereby reducing the possibility of corrosion, breakage, and cracking after welding varistor. Detailed Implementation

[0035] The present application will be further described in detail below with reference to the embodiments.

[0036] Examples 1-22 A manufacturing process for solder used in varistors, comprising the following steps: 1) Calculate according to the weight percentage of the elements, weigh the tin powder, heat it to melt, then add the substance containing the processing element and the welding element, mix evenly, heat to 600-700℃, hold and melt to obtain alloy liquid A; 2) Add the insulating element and other trace element to the alloy liquid, mix evenly, heat to 950-1050℃, hold for melting, cast into ingots, and let cool naturally to 80℃ after being taken out of the furnace; heat to 150℃, put into 15℃ water to cool to 35℃, then heat to 75℃, put into 15℃ water to cool to 28℃, take it out, and use a fan to dry the surface moisture to obtain solder.

[0037] The heat preservation and melting time in step 1) is 2-5 hours; the heat preservation and melting time in step 2) is 1.5-3.5 hours.

[0038] Specifically, in the processing, the heating temperature of step 1) is preferably 650℃ and the holding and melting time is 3h; the heating temperature of step 2 is preferably 980℃ and the holding and melting time is 2.8h.

[0039] The welding-promoting elements can be one or both of zinc powder and vanadium powder; The substance containing insulating elements can be composed of one or both of nano boron oxide powder and nano silica powder; The substance containing processing-promoting elements may be composed of one or more of lithium oxide, copper oxide powder, aluminum oxide powder, and metallic silver powder; Substances containing other trace elements may be composed of one or more of barium oxide, selenium powder, and copper-arsenic alloy powder.

[0040] The weight percentages of the target chemical components in Examples 1-22 are different, as shown in Tables 1 and 2. Table 1. Weight percentage (%) of the target chemical elements in Examples 1-11 Table 2. Weight percentage (%) of the target chemical elements in Examples 12-22 Comparative Example Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Zn is replaced with an equal amount of Sn.

[0041] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Si is replaced with an equal amount of Sn.

[0042] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that Ba is replaced with Sn in equal amounts.

[0043] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that Cu is replaced by an equal amount of Zn.

[0044] Performance testing Detection methods / test methods 1. Drop test The solders obtained in Examples 1-22 and Comparative Example 5 were used to weld varistors. The welded varistors were then placed in a salt spray chamber with a humidity of 85%, a temperature of 50°C, and a salt water content of 5%. After 7 days, the welded varistors were subjected to drop tests, and the number of drops when cracks or breaks occurred at the welded position was recorded.

[0045] In high-temperature, high-salt, and high-humidity environments, metal surfaces are prone to developing localized holes and pits, leading to localized corrosion and consequently affecting the material's mechanical properties.

[0046] Drop test: The drop test was conducted in accordance with the standard JESD2-B111, using a Daisy chain BGA soldered test link, and was tested under a 1500G drop condition.

[0047] 2. Performance Testing The solders obtained from Examples 1-22 and Comparative Examples 1-4 were cut into corresponding test samples, and then the following performance tests were performed: Test (1): The impact toughness will be tested, and the specific data will be recorded as A; Test (2): Place the test sample in a salt spray chamber. The humidity inside the salt spray chamber is 85%, the temperature is 50℃, and the salt water content is 5%. After 7 days, test the impact toughness and record the data as B. Calculate the rate of change of impact toughness. Rate of change of impact toughness = |(AB) / A|*100%. Subtract B from A and then divide by A. Multiply the absolute value of the obtained value by 100% to obtain the rate of change of impact toughness.

[0048] All the above experiments were performed 5 times and the average value was taken. The impact toughness was referenced to GB / T 229-2007 "Metallic Materials Charpy Pendulum Impact Test Method". The impact energy absorbed by the V-notch specimen under the 2mm pendulum blade is shown in Table 3. Table 3. Experimental data of Examples 1-22 and Comparative Examples 1-4 Combining Example 1 and Comparative Example 1 with Table 3, it can be seen that the number of drops and impact toughness of Example 1 are higher than those of Comparative Example 1. After high temperature, high humidity and high salt corrosion, the change rate of impact toughness of Example 1 is not much different from that of Comparative Example 1. This indicates that the Zn contained in the solder of this application can further improve the impact toughness of the solder and obtain better corrosion resistance.

[0049] Combining Example 1 and Comparative Example 2 with Table 3, it can be seen that the number of drops and impact toughness of Example 1 are higher than those of Comparative Example 2. Moreover, after high temperature, high humidity and high salt corrosion, the change rate of impact toughness of Example 1 is smaller than that of Comparative Example 2, indicating that the solder of this application contains Si, which can further improve impact toughness and corrosion resistance.

[0050] Combining Example 1 and Comparative Example 3 with Table 3, it can be seen that the number of drops and impact toughness of Example 1 are higher than those of Comparative Example 3. Moreover, after high temperature, high humidity and high salt corrosion, the change rate of impact toughness of Example 1 is smaller than that of Comparative Example 3, indicating that the solder of this application contains Ba, which can further improve impact toughness and corrosion resistance.

[0051] Combining Example 1 and Comparative Example 4 with Table 3, it can be seen that the impact toughness of Example 1 is higher than that of Comparative Example 4. After high temperature, high humidity and high salt corrosion, the change rate of impact toughness of Example 1 is not much different from that of Comparative Example 3. This indicates that the solder of this application contains Cu, which can further improve the impact toughness and obtain better corrosion resistance.

[0052] Combining Examples 1 and 4-6 with Table 3, it can be seen that the number of drops and impact toughness of Examples 4-6 are higher than those of Example 1. After high temperature, high humidity and high salt corrosion, the change rate of impact toughness of Examples 4-6 is smaller than that of Example 1. This indicates that when Zn and V are contained in this application, they have a synergistic effect, which improves the weldability of the solder to the varistor, and at the same time makes the solder have better impact toughness and corrosion resistance.

[0053] Combining Examples 5 and 7-9 with Table 3, it can be seen that the number of drops and impact toughness of Examples 7-9 are higher than those of Example 5. After high temperature, high humidity and high salt corrosion, the change rate of impact toughness of Examples 7-9 is smaller than that of Example 5. This indicates that the solder containing both B and Si has further improved impact toughness and better corrosion resistance.

[0054] As can be seen from the comparison of Examples 8 and 16-18 and Table 3, the number of drops and impact toughness of Examples 16-18 are higher than those of Example 8. After high temperature, high humidity and high salt corrosion, the change rate of impact toughness of Examples 16-18 is smaller than that of Example 8. This indicates that the solder containing both B and Si has further improved impact toughness and better corrosion resistance.

[0055] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A solder for a varistor, characterized in that, Composed of the following weight percentages of elements composition: Welding promoting elements: 0.1-0.5% Insulating element: 0.05-0.35% Processing-promoting elements: 1.8-4.5% Other trace elements: 0.01-0.12% The balance is Sn and unavoidable impurities; The welding-promoting element is composed of Zn and V in a weight ratio of (1-6):1; The processing-promoting element is one or more of Li, Cu, Al, and Ag; The other trace elements are one or more of Ba, Se, and As; The insulating element is composed of Si and B in a weight ratio of (1-5):

1.

2. The solder for a varistor according to claim 1, characterized in that: The weight ratio of Li, Cu, Al, and Ag is 1:(1-3):(1-3):(1-2).

3. The solder for a varistor according to claim 1, characterized in that: The weight ratio of Ba, Se, and As is (2-6):(1-5):

1.

4. A manufacturing process for a solder for a varistor as described in any one of claims 1-3, characterized in that, It is prepared by the following method: 1) Calculate according to the weight percentage of the elements, weigh the tin powder, heat it to melt, then add the substance containing the processing element and the welding element, mix evenly, heat to 600-700℃, hold and melt to obtain alloy liquid A; 2) Add the insulating element and other trace elements to the alloy liquid A, mix evenly, heat to 950-1050℃, hold for melting, cast into shape, cool, and anneal to obtain solder.

5. The manufacturing process of solder for a varistor according to claim 4, characterized in that: The holding and melting time in step 1) is 2-5 hours; the holding and melting time in step 2) is 1.5-3.5 hours, and the temperature drop is 300-400℃.

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