Difference between soft and hard brazing consumables

Soft brazing consumables and hard brazing consumables are two types of core materials in the brazing process, and their differences are mainly reflected in melting point, composition, properties, application scenarios and process requirements.

Melting point and classification criteria

Soft brazing consumables have melting points below 450°C, while hard brazing consumables have melting points above 450°C. For example, a common tin-lead alloy soft brazing material has a melting point of only 183°C, while silver-based hard brazing materials have melting points ranging from 600-970°C. This categorisation is not absolute, but 450°C has become the industry's common dividing line to distinguish between the two types of materials in terms of process and application.

Compositional system

Soft brazing materials are dominated by low melting point metals such as tin, lead, bismuth and indium. Traditional tin-lead alloys (e.g. Sn63Pb37) are widely used due to good wettability and conductivity, but due to the toxicity of lead, lead-free tin-based alloys (e.g. Sn96.5Ag3Cu0.5) are gradually becoming mainstream. Hard brazing materials, on the other hand, are based on high melting point metals such as silver, copper, aluminium and nickel. Silver-based brazing material by adding copper, zinc and other elements to adjust the performance, taking into account the strength and manufacturability; copper-phosphorus brazing material using phosphorus self-brazing agent properties, reduce welding costs.

Physical properties and strength

The tensile strength of soft brazing material is usually lower than 70MPa, and the plasticity is good, but the bearing capacity is limited. Hard brazing material tensile strength is generally more than 200MPa, some high-end alloys up to 500MPa, and high temperature performance. For example, silver-based brazing consumables remain stable above 600°C, while soft brazing consumables tend to soften and fail at high temperatures.

Application Scenario

Soft brazing materials are mainly used in electronic packaging, electrical connectors and food instruments. In the electronics industry, tin-silver-copper brazing materials (e.g. Sn96.5Ag3Cu0.5) are widely used for chip soldering because of their moderate melting point (219°C) and good conductivity. Hard brazing materials, on the other hand, are used in scenarios such as aerospace, refrigeration equipment and rail transport. For example, silver-based brazing consumables are used for joining aero-engine components, while aluminium-based brazing consumables are dedicated to welding aluminium alloys to meet the demands of extreme working conditions.

Process characteristics

Soft brazing materials can be used with simple tools such as soldering irons and hot air guns, and the soldering temperature is usually controlled at 30-80°C above the melting point of the brazing material to avoid oxidation of the base material. Hard brazing materials need to use flame brazing, vacuum brazing and other high-temperature processes, and often with borax, boric acid and other brazing flux to remove oxides and promote wetting. For example, oxyacetylene flame brazing temperatures of up to 3000°C are suitable for joining high melting point metals.

Environmental trends

The transition to lead-free soft brazing is accelerating, with low-temperature alloys such as FL170FL200, high-reliability alloys such as FR209 and nanoparticle-reinforced brazing materials becoming hot research topics. The hard brazing sector is focusing on the reduction of hazardous elements such as cadmium and the development of vacuum brazing technology to reduce pollution. For example, the European Union has banned the use of cadmium-containing brazing materials in the electronics industry, promoting the development of silver-based brazing materials in the direction of low-cadmium or cadmium-free.

The core difference between soft brazing material and hard brazing material lies in the melting point and strength, and the selection is mainly based on the working temperature of the weldment, load requirements and process feasibility. As technology advances, both continue to evolve in terms of composition optimisation and environmental performance.