Indium (In) has a relatively low melting point (157°C) and can form a series of low-melting-point eutectic solders with elements such as Sn (tin), Pb (lead), and Ag (silver). This helps avoid the impact of high temperatures on products during packaging and soldering processes. Indium-based solders have high corrosion resistance in alkaline media and excellent wetting ability with both metals and non-metals. The solder joints formed with indium have advantages such as low electrical resistance and high plasticity, making them suitable for matching packaging of materials with different coefficients of thermal expansion. Therefore, indium-based solders are primarily used in the packaging of electronic vacuum devices, glass, ceramics, and low-temperature superconducting devices. Pure indium and indium-based alloy solders are often used as connecting materials and thermal interface materials for bonding ceramic components to PCBs due to their excellent thermal conductivity, low melting point, and outstanding softness and ductility.
Indium-based solders possess good physical properties, with solder joints that exhibit excellent fatigue resistance, reliable mechanical strength, and tensile strength. They have high corrosion resistance in alkaline and saline media, making them suitable for welding equipment in the chlor-alkali industry. Additionally, they have high electrical conductivity; the electrical conductivity of indium-based solders is comparable to or even higher than that of Sn-Pb alloys, preventing signal loss at solder joints and meeting the requirements of electronic connections. Indium-based solders also have good compatibility. During the soldering process, they demonstrate excellent soldering performance with the copper, tin, silver, gold, and nickel coatings on PCB pads, as well as with the coatings on component leads. Moreover, they are compatible with different types of fluxes. Indium solder prevents the phenomenon of gold embrittlement; when soldering gold-plated products, using tin-based solder can cause the gold from the plated components to be drawn into the joint, forming brittle metallic compounds. In such cases, indium-based solder is generally recommended to prevent gold loss and penetration, thereby enhancing the reliability of the solder joints. Due to its excellent wetting ability with non-metals, indium solder can be used for soldering glass, ceramic, quartz, and other non-metallic products in electronic, low-temperature physics, and vacuum systems. Its wide melting point range allows the production of various types of indium-based alloy products with melting points ranging from a few tens of degrees to over 300 degrees, catering to the needs of different fields.