Brazing The Delicate Craftsman for Precision Joining

Brazing does not melt the base metal but achieves joining by melting low-melting-point brazing filler metal to fill gaps. It features flat welds and small deformation, making it suitable for welding precision components, dissimilar materials, and complex structures. It is indispensable in fields such as electronics, aerospace, and medical equipment. According to the melting point of the brazing filler metal, brazing is divided into two categories: soft brazing and hard brazing.

(I) Soft Brazing: The "Micro-Joining" for Electronic Components

Soft brazing uses brazing filler metal with a melting point below 450°C. The commonly used brazing filler metal is tin-lead alloy (gradually replaced by lead-free tin alloy). Flux is used during welding to remove oxide films and reduce surface tension. It is suitable for precision joining of electronic components, circuit boards, and water pipe joints, among which soldering is the most typical soft brazing technology.

1. Soldering: The "Basic Skill" for Circuit Board Welding

Principle: A soldering iron heats the workpiece (temperature 250-350°C), melting the lead-free tin wire (melting point approximately 227°C). Under the action of the flux, the molten tin fills the gap between the component pins and the circuit board pads, forming a solder joint after cooling.

Operational Points:

Pre-Welding Cleaning: Use sandpaper to polish the component pins and pads to remove oxide layers; wipe the circuit board with alcohol to remove oil stains and avoid cold soldering.

Heating Technique: First, bring the soldering iron tip into contact with the workpiece (the junction of the pin and the pad). After heating for 1-2 seconds, feed the tin wire. Avoid directly heating the tin wire, which may cause "cold soldering" (the molten tin fails to fully wet the workpiece).

Solder Joint Control: The amount of tin wire should be "sufficient to fill the gap without overflowing." The solder joint should be "conical." Do not shake the component before cooling to prevent solder joint breakage.

(II) Hard Brazing: The "Reliable Guarantee" for High-Strength Precision Components

Hard brazing uses brazing filler metal with a melting point above 450°C. The commonly used brazing fillers are copper-zinc alloy (brass brazing filler) and silver-based alloy (silver brazing filler). It features high welding temperature and high weld strength, making it suitable for welding high-strength precision components such as cutting tools, heat exchangers, and aero-engine blades.

Operational Points: Preheat the base metal before welding (temperature 300-500°C) to ensure full flow of the brazing filler metal; use flux such as borax and boric acid to remove the oxide film on the base metal surface; perform slow cooling treatment after welding (e.g., placing in an insulation box) to prevent cracks caused by excessive temperature differences.

(III) Selection Strategy and Development Trends of Welding Methods

Faced with a variety of welding methods, how to select the appropriate technology according to actual needs is the key to improving welding quality and efficiency. At the same time, with the development of industrial technology, welding technology is also evolving towards "intelligence and greenization."

(IV) Core Factors for Welding Method Selection

Base Metal Characteristics: For low-carbon steel, priority is given to SMAW and CO₂ welding; for stainless steel, TIG welding and laser welding are preferred; for aluminum alloys, AC TIG welding is selected; for electronic components, soldering is used.

Product Requirements: For precision components (such as aerospace parts), laser welding and TIG welding are chosen; for mass-produced parts.