A thermosensitive solder with high controllability and a fuse

Abstract

The application relates to a high-controllability heat-sensitive solder and a fuse, the high-controllability heat-sensitive solder comprising an alloy and a flux, the alloy comprising the following components: In: 18.5 wt%, Ag: (1-3.2) wt%, Cu: (2-3) wt%, and the balance of Sn; or, In: 16.5 wt% or 20 wt%, Ag: (1-3.2) wt%, Cu: (0.2-0.7) wt%, and the balance of Sn; or, In: 18.5 wt%, Ag: (4-6) wt%, Cu: (0.2-0.7) wt%, and the balance of Sn; and the flux comprising the following components: film-forming substances, activators, solvents, and corrosion inhibitors. The high-controllability heat-sensitive solder can improve the controllability of a joint formed by welding, that is, the joint can remain unbroken under a 500kPa spring force at a low temperature threshold of 140 DEG C for 2 hours, and the joint can be broken within 5 minutes at a high temperature threshold of 160 DEG C, and the high-controllability heat-sensitive solder has good welding effect and storage resistance.

Description

Technical Field

[0001] This invention relates to the field of soldering technology, and in particular to a highly controllable thermal solder and a fuse. Background Technology

[0002] The principle of fusing is that when the current exceeds a preset target value, the Joule heat generated by the resistance between the current and the protective metal itself melts the protective alloy and breaks the circuit, thereby protecting the safety of devices, equipment, and personnel. This principle is applied in surge protectors, fuses in automotive and household circuits, thermal fuses in electric kettles and hair dryers, power transmission and distribution systems, and power fuses in industrial equipment. The "spring-triggered fusing structure," composed of a spring and solder joint, has advantages such as fast power-off speed, high reliability, and no risk of electric arc. In the design of fusing devices, the instantaneous heat temperature is generally calculated based on the maximum allowable current, and an alloy with a suitable melting point is selected accordingly. However, selecting solder alloys based solely on melting point in the application of "spring-triggered fusing structures" presents the following problems:

[0003] For example, a spring-triggered fuse with a spring force of 500 kPa was calculated. Its reliability test conditions were as follows: it needed to remain unbroken for 2 hours at 140°C and break within 5 minutes at 160°C. The inventor selected an alloy with a melting point of approximately 160°C for welding to ensure the solder melted and broke at 160°C. However, during application, the solder joint broke before reaching the maximum allowable current, causing the fuse to trip before exceeding the maximum allowable current. Conversely, using an alloy with a melting point much higher than 160°C resulted in the solder joint not breaking within 5 minutes at 160°C, thus losing its circuit protection effect. Therefore, selecting solder alloys based on melting point has limitations in spring-triggered fuse applications. A highly controllable heat-sensitive solder is urgently needed to avoid solder alloys causing tripping at low currents or failing to melt under overload, ensuring the high reliability of spring-triggered fuses. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a highly controllable thermal solder that can improve the controllability of the welded joint to remain unbroken for 2 hours at a low temperature threshold of 140°C under the action of a 500 kPa spring force, and to break within 5 minutes at a high temperature threshold of 160°C.

[0005] The objective of this invention can be achieved by adopting the following technical solutions:

[0006] A highly controllable heat-sensitive solder comprises an alloy and a flux; the alloy contains the following components:

[0007] In: 18.5 wt%, Ag: (1–3.2) wt%, Cu: (2–3) wt%, balance Sn;

[0008] Alternatively, In: 16.5 wt% or 20 wt%, Ag: (1–3.2) wt%, Cu: (0.2–0.7) wt%, balance Sn;

[0009] Alternatively, In: 18.5 wt%, Ag: (4–6) wt%, Cu: (0.2–0.7) wt%, balance Sn;

[0010] The flux comprises the following components: film-forming substance, activator, solvent, and corrosion inhibitor.

[0011] According to the inventors' research, the main reason for premature breakage of spring-triggered fuses currently manufactured using alloys with melting points exceeding 160°C is the presence of internal pores in the weld joint. This results in different spring stresses on weld joints of the same area, causing creep deformation and breakage due to the greater stress on the weld joint. Therefore, even if the solder joint temperature does not reach its melting point, the spring-triggered fuse will still break. This invention provides a highly controllable thermosensitive solder comprising a Sn-In-Ag-Cu alloy system. By precisely controlling the proportions of Sn, In, Ag, and Cu, the melting point and creep properties of the thermosensitive solder in this application are improved. Since indium has a relatively high solid solubility in tin, the addition of a certain amount of indium can improve the toughness of the alloy and reduce the thermal expansion coefficient of the solder, allowing the weld joint to adapt to certain mechanical stresses and thermal cycling changes, reducing the risk of cracking before the weld joint reaches its fracture temperature. Simultaneously, the addition of In also affects the melting point of the solder; higher indium content lowers the melting point, increasing the risk of cracking before the weld joint reaches its fracture temperature. The risk of cracking at the fracture temperature is a concern, therefore, selecting an appropriate indium content is crucial. Additionally, adding a certain amount of silver and copper to the alloy system can improve the creep resistance of the weld joint at high temperatures, enhancing the creep resistance of the thermosensitive solder. This allows the weld joint formed by the thermosensitive solder of this application to remain unbroken for 2 hours at a low temperature threshold of 140°C. However, excessively high silver content will increase the Ag3Sn content, reducing the wettability of the solder and affecting the welding quality of the weld joint. Therefore, selecting an appropriate silver and copper content is crucial, requiring a balance to be found between the melting point, creep properties, and wettability of the solder alloy. Furthermore, for the Sn-In-Ag-Cu alloy system, due to its low melting point, the low-temperature activity of ordinary fluxes is insufficient to be fully utilized at lower welding temperatures, resulting in poor wettability with the alloy system and difficulty in achieving good bonding between the Sn-In-Ag-Cu alloy system and the welding interface. In addition, the Sn-In-Ag-Cu alloy system is not resistant to corrosion by ordinary fluxes, leading to a relatively short product shelf life and even requiring low-temperature storage, which presents significant storage challenges. To achieve better welding performance and storage resistance with a highly controllable heat-sensitive solder as described in this invention, a novel flux containing film-forming substances, activators, solvents, and corrosion inhibitors is added for welding the Sn-In-Ag-Cu alloy system. This flux can remove the oxide film during the welding process, enhance wettability, and simultaneously reduce the total void ratio, thus solving the corrosion problem of ordinary fluxes on the Sn-In-Ag-Cu alloy.Therefore, the thermosensitive solder of the present invention, through precise control of the Sn, In, Ag and Cu content and selection of flux, yields a thermosensitive solder with high temperature threshold controllability. When the thermosensitive solder forms a solder joint of a spring-triggered fuse after welding, the solder joint remains unbroken for 2 hours at a low temperature threshold of 140°C under the action of a 500 kPa spring force, and breaks within 5 minutes at a high temperature threshold of 160°C. Compared with conventional solder alloys, it has better controllability.

[0012] Furthermore, the flux components are: 10-30 wt% film-forming substance, 1-12 wt% activator, 40-80 wt% solvent and 0.1-1 wt% corrosion inhibitor.

[0013] Furthermore, the film-forming substance comprises one or more of the following substances: water-white rosin, polymerized rosin, terpene phenol resin, polyurethane resin, icy white rosin, and fully hydrogenated rosin.

[0014] Furthermore, the activator comprises one or more of the following substances: β-carbonylglutaric acid, salicylic acid, benzoic acid, 2-methoxyethylamine hydrochloride, (chloromethylene)dimethylammonium chloride, triethylmethylammonium bromide, benzyltriethylammonium bromide (TEBA), alkylphenol polyoxyethylene ether, fluorocarbon surfactant, and dimethylamine hydrochloride.

[0015] Furthermore, the solvent comprises one or more of the following substances: ethanol, isopropanol, α-terpineol, propylene glycol n-propyl ether, and diethylene glycol dimethyl ether.

[0016] Furthermore, the corrosion inhibitor comprises one or more of the following substances: benzotriazole, heptadecanyl imidazoline, lauryl hydroxyethyl imidazoline, and benzotriazole BTA.

[0017] The composition and content of flux significantly affect the controllability of the solder joints in spring-triggered fuses formed after welding with heat-sensitive solder. The film-forming substance primarily prevents oxidation; excessive content leads to excessive residue, affecting fuse lifespan and hindering solder spread, resulting in insufficient effective welding area and inability to withstand the low temperature threshold of 140℃ for 2 hours without breaking. Insufficient content results in an incomplete anti-oxidation protective film, similarly preventing the fuse from holding at 140℃ for 2 hours. The activator primarily removes the oxide film from the metal surface; excessive content leads to over-reaction, excessive growth of the IMC layer, and brittle solder joints, reducing the fuse's drop resistance and potentially causing solder joint corrosion. Insufficient content also affects solder wettability. Insufficient flux content can lead to defects such as incomplete soldering and voids, preventing the fuse from maintaining its integrity for 2 hours at the low temperature threshold of 140℃. Solvents primarily dissolve other substances; excessive content can cause spatter and porosity, also preventing the fuse from maintaining its integrity for 2 hours at the low temperature threshold of 140℃, and affecting viscosity, thus impacting the application process and efficiency. Insufficient content affects the dissolution of other substances and can also worsen the storage performance of the flux, making it easier for other components to precipitate. Corrosion inhibitors inhibit post-soldering metal corrosion; excessive content can passivate the surface and reduce solder wettability, preventing the fuse from maintaining its integrity for 2 hours at the low temperature threshold of 140℃. Insufficient content can accelerate corrosion of the solder joint in humid and hot environments, affecting the long-term reliability of the fuse.

[0018] By selecting specific film-forming substances, activators, solvents, corrosion inhibitors and their contents, and matching them with the specific components of the thermosensitive solder alloy of the present invention, when the thermosensitive solder forms a solder joint of a spring-triggered fuse after welding, the solder joint remains unbroken for 2 hours at a low temperature threshold of 140°C under the action of a spring force of 500 kPa, and breaks within 5 minutes at a high temperature threshold of 160°C, with a controllability rate of over 70%.

[0019] Furthermore, the content of each component of the flux is as follows:

[0020] The film-forming substance is: 10-20 wt% water-based rosin and 5-10 wt% polyurethane resin;

[0021] The activator consists of: 1-3 wt% salicylic acid, 0.5-1.5 wt% dimethylamine hydrochloride, 0.5-1.5 wt% benzyltriethylammonium bromide (TEBA), and 0.5 wt% fluorocarbon surfactant.

[0022] The solvent is: 45-50 wt% ethanol, 5-15 wt% α-terpineol, and 10-15 wt% diethylene glycol dimethyl ether.

[0023] And the corrosion inhibitor: 0.5 wt% benzotriazole BTA.

[0024] Organic acid activators are key components in fluxes, with dicarboxylic acids being the most commonly used. These are gentle, slow-reacting, less corrosive, and offer good electrical insulation. The activation temperature of commonly used organic acids in fluxes is generally around 150-250℃. Below 150℃, their effectiveness is reduced, often requiring the addition of multiple organic acids or an increase in their proportion to enhance activity. However, organic acids with high activation temperatures cannot be completely decomposed during soldering. Organic acids remaining on or around the solder joint surface easily absorb moisture, causing electrochemical corrosion. Salicylic acid, as the main activator, has an activation temperature as low as 150℃, slightly lower than common organic dicarboxylic acids in ordinary fluxes, such as oxalic acid (182℃), succinic acid (188℃), phthalic acid (191℃), and tartaric acid (200℃). Its phenolic hydroxyl groups synergistically work with carboxyl groups to efficiently strip the oxide film from the alloy. Simultaneously, salicylic acid can react with In... 3+ Ionic reactions generate indium salicylate, forming a chemical passivation that protects the solder joints. Dimethylamine hydrochloride acts as a low-temperature activation synergist, melting at 120–180°C and gradually decomposing to release free dimethylamine and HCl gas. The HCl gas and salicylic acid form an acid-gas synergistic activation mechanism, improving the oxide film removal efficiency of the low-temperature alloy. Simultaneously, the synergistic solvent evaporation carries away any incompletely decomposed salicylic acid. During the welding heating process, the free dimethylamine and HCl gas form an antioxidant protective atmosphere on the exposed alloy surface, reducing secondary oxidation of the alloy under heating conditions. TEBA carries Br... - Ions enter the organic phase, transporting salicylic acid anions to the hot-soldering interface, increasing the local anion concentration, reducing the welding interface energy, and facilitating the removal of the oxide film on the solder surface. α-Terpineol and diethylene glycol dimethyl ether, as high-boiling-point solvents, can form a vapor-phase protective blanket: blocking oxygen to prevent secondary oxidation of the solder alloy, while simultaneously regulating the solvent evaporation rate and promoting the orderly escape of gas during the melting of the Sn-In-Ag-Cu alloy. Benzotriazole (BTA), as a corrosion inhibitor, reacts with In... 3+ Formation of [In(BTA)3] coordination film (impedance value > 10) 5 Ω·cm 2This method inhibits the electrochemical corrosion of solder during storage. Polyurethane resin, as an auxiliary film-forming resin, softens at 60–80°C to form a sealing layer, reducing accelerated oxidation of the alloy during the preheating stage of welding. Its urethane groups hydrogen-bond with BTA to achieve controlled release of the corrosion inhibitor. This highly controllable heat-sensitive solder, with 5–10 wt% polyurethane resin, not only compatible with and dissolves other components in the formulation but also prevents secondary oxidation of the solder alloy during welding, provides suitable fluxing performance, and does not decompose to release excess gas. Post-weld residues are easily cleaned with water-based or solvent-based cleaning agents. 1–3 wt% salicylic acid gives the heat-sensitive solder high low-temperature activity, effectively removing the oxide film on the solder surface. Its chemical properties are relatively mild, and the low addition ratio makes the Sn-In-Ag-Cu alloy less prone to corrosion during room temperature storage. Its corrosion forms metal oxides; the interface reaction can be optimized by overcoming the kinetic barrier and reducing the interfacial energy through the gas-solid synergistic reaction of salicylic acid-TEBA-HCl; the synergistic effect of 5-15 wt% high-boiling-point solvent α-terpineol and polyurethane resin system improves the gas escape efficiency and greatly reduces the void rate of weld joints; 0.5 wt% benzotriazole BTA forms a BTA-polyurethane hydrogen bond network with polyurethane resin. At room temperature, the hydrogen bonds stabilize BTA molecules and reduce migration. At temperatures above 60°C, the hydrogen bonds break and release BTA to repair damage, achieving dynamic corrosion inhibition and providing long-term corrosion suppression.

[0025] Furthermore, the content of each component of the flux is as follows:

[0026] The film-forming substance is: 15 wt% water-based rosin and 5 wt% polyurethane resin;

[0027] The activator consists of: 2 wt% salicylic acid, 1 wt% dimethylamine hydrochloride, 1 wt% benzyltriethylammonium bromide (TEBA), and 0.5 wt% fluorocarbon surfactant.

[0028] The solvents are: 50 wt% ethanol, 10 wt% α-terpineol, and 15 wt% diethylene glycol dimethyl ether.

[0029] And the corrosion inhibitor: 0.5 wt% benzotriazole BTA.

[0030] A fuse made using the aforementioned highly controllable thermistor solder has a joint formed by welding using the aforementioned highly controllable thermistor solder.

[0031] To better understand and implement this invention, the invention will be described in detail below. Detailed Implementation

[0032] The terminology used in the embodiments of this application is for the purpose of describing specific embodiments only and is not intended to limit the embodiments of this application. It should be understood in this application that the described embodiments are only a part of the embodiments of this application, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of the embodiments of this application. The scope of the embodiments of this application is limited only by the appended claims.

[0033] The fracture performance test method of the embodiments or comparative examples of the present invention is as follows: (1) After welding the target device with a weld joint subjected to a spring force of 500 kPa using 50 pieces of thermal solder from each of the embodiments and comparative examples, the device is placed in an oven at 140°C for 2 hours and then taken out to observe whether it is fractured. (2) After welding the target device with a weld joint subjected to a spring force of 500 kPa using 50 pieces of thermal solder from each of the embodiments and comparative examples, the device is placed in an oven at 160°C for 5 minutes and then taken out to observe whether it is fractured. (3) Calculate the fracture controllability rate of the weld joint using thermal solders containing different flux types in Examples 1 to 6 and Comparative Example 1: the number of thermal solders that simultaneously meet the requirements of "no fracture at 140°C" and "fracture at 160°C" divided by the total number of experimental samples of 100 pieces * 100%.

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0035] Example 1

[0036] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0037] In: 20wt%, Ag: 3.2wt%, Cu: 0.5wt%, balance Sn.

[0038] The flux A has the following components: 15wt% water-white rosin, 5wt% polyurethane resin, 2wt% salicylic acid, 1wt% dimethylamine hydrochloride, 1wt% benzyltriethylammonium bromide (TEBA), 0.5wt% fluorocarbon surfactant, 50wt% ethanol, 10wt% α-terpineol, 15wt% diethylene glycol dimethyl ether, and 0.5wt% benzotriazole (BTA).

[0039] Example 2

[0040] A highly controllable heat-sensitive solder comprises an alloy and flux B; the alloy contains the following components:

[0041] In: 20wt%, Ag: 3.2wt%, Cu: 0.5%, balance Sn.

[0042] The flux B has the following components: 20wt% polymerized rosin, 8wt% terpene phenol resin, 3wt% β-carbonylglutaric acid, 3wt% 2-methoxyethylamine hydrochloride, 0.5wt% alkylphenol polyoxyethylene ether, 25wt% ethanol, 40wt% isopropanol, and 0.5wt% heptadecanylimidazoline.

[0043] Example 3

[0044] A highly controllable heat-sensitive solder comprises an alloy and flux C; the alloy contains the following components:

[0045] In: 20wt%, Ag: 3.2wt%, Cu: 0.5%, balance Sn.

[0046] The flux C has the following components: 25wt% rosin, 5wt% benzoic acid, 4wt% (chloromethylene)dimethylammonium chloride, 35wt% ethanol, 30wt% α-terpineol, and 1wt% lauryl hydroxyethyl imidazoline.

[0047] Example 4

[0048] A highly controllable heat-sensitive solder comprises an alloy and flux D; the alloy contains the following components:

[0049] In: 20wt%, Ag: 3.2wt%, Cu: 0.5wt%, balance Sn.

[0050] The flux D contains the following components: 30 wt% fully hydrogenated rosin, 2 wt% benzyl triethylammonium bromide (TEBA), 2 wt% fluorocarbon surfactant, 30 wt% ethanol, 35 wt% propylene glycol n-propyl ether, 0.5 wt% benzotriazole (BTA), and 0.5 wt% heptadecanyl imidazoline.

[0051] Example 5

[0052] A highly controllable heat-sensitive solder comprises an alloy and flux E; the alloy contains the following components:

[0053] In: 20wt%, Ag: 3.2wt%, Cu: 0.5wt%, balance Sn.

[0054] The flux E has the following components: 10 wt% water-based rosin, 10 wt% polyurethane resin, 1 wt% salicylic acid, 1.5 wt% dimethylamine hydrochloride, 1.5 wt% benzyltriethylammonium bromide (TEBA), 0.5 wt% fluorocarbon surfactant, 45 wt% ethanol, 15 wt% α-terpineol, 15 wt% diethylene glycol dimethyl ether, and 0.5 wt% benzotriazole (BTA).

[0055] Example 6

[0056] A highly controllable heat-sensitive solder comprises an alloy and flux F; the alloy contains the following components:

[0057] In: 20wt%, Ag: 3.2wt%, Cu: 0.5wt%, balance Sn.

[0058] The flux F contains the following components: 20 wt% water-based rosin, 10 wt% polyurethane resin, 3 wt% salicylic acid, 0.5 wt% dimethylamine hydrochloride, 0.5 wt% benzyltriethylammonium bromide (TEBA), 0.5 wt% fluorocarbon surfactant, 50 wt% ethanol, 5 wt% α-terpineol, 10 wt% diethylene glycol dimethyl ether, and 0.5 wt% benzotriazole (BTA).

[0059] Example 7

[0060] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0061] In: 16.5 wt%, Ag: 3.2 wt%, Cu: 0.5 wt%, balance Sn.

[0062] The content of each component of flux A is the same as in Example 1.

[0063] Example 8

[0064] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0065] In: 18.5 wt%, Ag: 4 wt%, Cu: 0.5 wt%, balance Sn.

[0066] The content of each component of flux A is the same as in Example 1.

[0067] Example 9

[0068] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0069] In: 18.5 wt%, Ag: 6 wt%, Cu: 0.5 wt%, balance Sn.

[0070] The content of each component of flux A is the same as in Example 1.

[0071] Example 10

[0072] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0073] In: 18.5 wt%, Ag: 3.2 wt%, Cu: 3 wt%, balance Sn.

[0074] The content of each component of flux A is the same as in Example 1.

[0075] Example 11

[0076] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0077] In: 18.5 wt%, Ag: 3.2 wt%, Cu: 2 wt%, balance Sn.

[0078] The content of each component of flux A is the same as in Example 1.

[0079] Example 12

[0080] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0081] In: 18.5 wt%, Ag: 1 wt%, Cu: 3 wt%, balance Sn.

[0082] The content of each component of flux A is the same as in Example 1.

[0083] Example 13

[0084] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0085] In: 18.5 wt%, Ag: 2 wt%, Cu: 2 wt%, balance Sn.

[0086] The content of each component of flux A is the same as in Example 1.

[0087] Example 14

[0088] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0089] In: 18.5 wt%, Ag: 4 wt%, Cu: 0.7 wt%, balance Sn.

[0090] The content of each component of flux A is the same as in Example 1.

[0091] Example 15

[0092] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0093] In: 18.5 wt%, Ag: 6 wt%, Cu: 0.7 wt%, balance Sn.

[0094] The content of each component of flux A is the same as in Example 1.

[0095] Example 16

[0096] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0097] In: 18.5 wt%, Ag: 4 wt%, Cu: 0.2 wt%, balance Sn.

[0098] The content of each component of flux A is the same as in Example 1.

[0099] Example 17

[0100] A highly controllable heat-sensitive solder comprises an alloy and flux A; the alloy contains the following components:

[0101] In: 18.5 wt%, Ag: 6 wt%, Cu: 0.2 wt%, balance Sn.

[0102] The content of each component of flux A is the same as in Example 1.

[0103] Comparative Example 1

[0104] A heat-sensitive solder includes an alloy and flux O; the alloy comprises the following components, calculated by weight percentage:

[0105] In: 20wt%, Ag: 3.2wt%, Cu: 0.5wt%, balance Sn.

[0106] The composition of flux O is as follows: 25 wt% natural rosin and 75 wt% ethanol.

[0107] Comparative Example 2

[0108] A heat-sensitive solder includes an alloy and flux A; the alloy comprises the following components:

[0109] In: 20wt%, Ag: 2.8wt%, balance Sn.

[0110] The content of each component of flux A is the same as in Example 1.

[0111] Comparative Example 3

[0112] A heat-sensitive solder includes an alloy and flux A; the alloy comprises the following components:

[0113] In: 25wt%, Ag: 3.2wt%, Cu: 0.5wt%, balance Sn.

[0114] The content of each component of flux A is the same as in Example 1.

[0115] Comparative Example 4

[0116] A heat-sensitive solder includes an alloy and flux A; the alloy comprises the following components:

[0117] In: 18.5 wt%, Ag: 3.2 wt%, Cu: 0.5 wt%, balance Sn.

[0118] The content of each component of flux A is the same as in Example 1.

[0119] Comparative Example 5

[0120] A heat-sensitive solder includes an alloy and flux A; the alloy comprises the following components:

[0121] In: 18.5 wt%, Ag: 1 wt%, Cu: 0.5 wt%, balance Sn.

[0122] The content of each component of flux A is the same as in Example 1.

[0123] Comparative Example 6

[0124] A heat-sensitive solder includes an alloy and flux A; the alloy comprises the following components:

[0125] In: 18.5 wt%, Ag: 3.2 wt%, Cu: 0.2 wt%, balance Sn.

[0126] The content of each component of flux A is the same as in Example 1.

[0127] Comparative Example 7

[0128] A heat-sensitive solder includes an alloy and flux A; the alloy comprises the following components:

[0129] In: 18.5 wt%, Ag: 3.2 wt%, Cu: 0.7 wt%, balance Sn.

[0130] The content of each component of flux A is the same as in Example 1.

[0131] Comparative Example 8

[0132] A heat-sensitive solder includes an alloy and flux A; the alloy comprises the following components:

[0133] In: 18.5 wt%, Ag: 2 wt%, Cu: 0.5 wt%, balance Sn.

[0134] The content of each component of flux A is the same as in Example 1.

[0135] The controllable fracture rate of welded joints formed by using thermal solders with different flux types in Examples 1-6 and Comparative Example 1 is shown in Table 1 below; the fracture effect of welded joints formed by using thermal solders with different alloy types of the same flux A is shown in Table 2 below.

[0136] Table 1

[0137]

[0138] Table 2

[0139]

[0140] As shown in Table 2, one embodiment of the present invention comprises the following components: In: 18.5 wt%, Ag: (1-3.2) wt%, Cu: (2-3) wt%, with the balance being Sn; or, In: 16.5 wt% or 20 wt%, Ag: (1-3.2) wt%, Cu: (0.2-0.7) wt%, with the balance being Sn; or, In: 18.5 wt%, Ag: (4-6) wt%, Cu: (0.2-0.7) wt%, with the balance being Sn; and flux, including a highly controllable heat-sensitive solder containing film-forming substances, activators, solvents, and corrosion inhibitors of specific components and contents. The weld joint formed after welding is able to remain unbroken for 2 hours under a low temperature threshold of 140°C under a spring force of 500 kPa, and break within 5 minutes under a high temperature threshold of 160°C. As shown in Table 1, when the ordinary flux used in Comparative Example 1 was used in conjunction with the Sn-In-Ag-Cu alloy of the present invention for welding, the weld joint remained unbroken for 2 hours at a low temperature threshold of 140°C under a spring force of 500 kPa, but the fracture controllability rate was 0 at a high temperature threshold of 160°C within 5 minutes. This indicates that the Sn-In-Ag-Cu alloy of the present invention needs to be used in conjunction with a novel flux containing specific components and amounts of film-forming substances, activators, solvents, and corrosion inhibitors for welding. To improve the controllability of the weld joint of the thermosensitive solder under a spring force of 500 kPa, maintaining its integrity for 2 hours at a low temperature threshold of 140°C, and breaking within 5 minutes at a high temperature threshold of 160°C; the solder comprises 45–50 wt% ethanol, 5–15 wt% α-terpineol, 10–15 wt% diethylene glycol dimethyl ether; 10–20 wt% water-based rosin, 5–10 wt% polyurethane resin; 1–3 wt% salicylic acid, 0.5–1.5 wt% dimethylamine hydrochloride, 0.5– The flux, comprising 1.5 wt% benzyltriethylammonium bromide (TEBA), 0.5 wt% fluorocarbon surfactant, and 0.5 wt% benzotriazole (BTA), combined with the Sn-In-Ag-Cu alloy of this invention, enables the fracture controllability rate of the weld joint of the thermosensitive solder to reach over 98%. It also contains 50 wt% ethanol, 10 wt% α-terpineol, 15 wt% diethylene glycol dimethyl ether, 15 wt% water-based rosin, 5 wt% polyurethane resin, 2 wt% salicylic acid, and 1 wt% dimethylamine hydrochloride. The flux A, consisting of 1 wt% benzyltriethylammonium bromide (TEBA), 0.5 wt% fluorocarbon surfactant, and 0.5 wt% benzotriazole BTA, combined with the Sn-In-Ag-Cu alloy of the present invention, enables the fracture controllability rate of the weld joint of the heat-sensitive solder to reach 100%. It is the preferred flux composition of the present invention that maintains the response control without fracture for 2 hours at a low temperature threshold of 140°C under the action of a 500 kPa spring force and fractures within 5 minutes at a high temperature threshold of 160°C.

[0141] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A highly controllable heat-sensitive solder, comprising an alloy and a flux, characterized in that: The alloy comprises the following components: In: 18.5 wt%, Ag: (1~3.2) wt%, Cu: (2~3) wt%, balance Sn; Alternatively, In: 20wt%, Ag: (1~3.2)wt%, Cu: (0.2~0.7)wt%, balance Sn; Alternatively, In: 18.5 wt%, Ag: (4~6) wt%, Cu: (0.2~0.7) wt%, balance Sn; The flux comprises the following components: Film-forming substances: 10~20wt% water-based rosin, 5~10wt% polyurethane resin; Activators: 1~3wt% salicylic acid, 0.5~1.5wt% dimethylamine hydrochloride, 0.5~1.5wt% benzyltriethylammonium bromide, 0.5wt% fluorocarbon surfactant; Solvents: 45-50 wt% ethanol, 5-15 wt% α-terpineol, 10-15 wt% diethylene glycol dimethyl ether; Corrosion inhibitor: 0.5wt% benzotriazole.

2. The highly controllable thermal solder according to claim 1, characterized in that: The content of each component in the flux is as follows: The film-forming substance is: 15 wt% water-based rosin and 5 wt% polyurethane resin; The activator consists of: 2 wt% salicylic acid, 1 wt% dimethylamine hydrochloride, 1 wt% benzyltriethylammonium bromide, and 0.5 wt% fluorocarbon surfactant. The solvents are: 50 wt% ethanol, 10 wt% α-terpineol, and 15 wt% diethylene glycol dimethyl ether. And the corrosion inhibitor: 0.5wt% benzotriazole.

3. A fuse, characterized in that: It has a joint formed by welding using the highly controllable thermosensitive solder as described in any one of claims 1 to 2.

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