As core components of electrical connections, automotive connector terminals' soldering process directly determines the mechanical strength, electrical performance, and long-term reliability of the connection. Different soldering technologies, through material fusion methods, heat-affected zone control, and process parameter optimization, have varying impacts on connection strength, requiring comprehensive evaluation considering terminal material characteristics and application scenarios.
Traditional soft soldering achieves connection by filling the gap between the terminal and the conductor with molten solder. Its advantages lie in its mature process and low cost, but it also has significant limitations. The bonding between solder and copper terminals is essentially physical wetting, not atomic-level metallic bonding, resulting in bonding strength being significantly affected by flux residue, oxide layer thickness, and ambient humidity. Under vibration or thermal cycling conditions, solder is prone to fatigue cracking, and even brittle fracture due to excessive IMC (intermetallic compound) growth, ultimately leading to a sudden increase in contact resistance or momentary open circuit. This type of process is mostly used in low-vibration, low-current scenarios and cannot meet the stringent reliability requirements of automotive electronics.
Resistance welding involves applying pressure and high current to electrodes, causing localized melting at the contact surface between the terminal and the conductor to form a metallurgical bond. Its advantages include high connection strength and high production efficiency. However, this process relies heavily on the surface condition of the terminal and conductor; the presence of oxide layers or oil contamination can lead to localized overheating or incomplete soldering. Furthermore, resistance welding has a relatively large heat-affected zone, which may cause annealing and softening of the terminal material, reducing its fatigue resistance. To address these issues, modern resistance welding processes employ pulsed current control and multi-stage pressure regulation. By precisely controlling the weld nugget size and heat input, it minimizes thermal damage while ensuring connection strength, and is widely used in the mass production of low-voltage signal terminals in automobiles.
Ultrasonic welding utilizes high-frequency vibration friction to generate heat, enabling atomic diffusion bonding between the terminal and the conductor in a solid state. Its core advantages are the absence of a melting process, a small heat-affected zone, and the elimination of flux. The resulting connection interface is clean and dense, with a bond strength approaching that of the base material, making it particularly suitable for joining dissimilar materials (such as copper-aluminum). Ultrasonic welding requires extremely high surface flatness of the terminal; any tiny protrusion or depression can lead to stress concentration and reduce connection reliability. Optimizing welding head design, vibration frequency, and pressure parameters can significantly improve welding consistency, and this technology is being gradually adopted in automotive high-voltage connector terminals.
Laser welding uses a high-energy-density laser beam as a heat source to achieve rapid fusion bonding between terminals and wires. Its characteristics include high precision, low heat input, and the ability to weld complex structures. The welds formed by this process are narrow and deep, with superior bond strength compared to traditional welding methods, making it particularly suitable for connecting miniature terminals and thin wires. Laser welding places stringent requirements on equipment precision and process control; any focus deviation or power fluctuation can lead to weld defects (such as porosity and cracks), thereby weakening the connection strength. By introducing a real-time monitoring and closed-loop control system, welding parameters can be dynamically adjusted to ensure stable weld quality at each point, meeting the high reliability requirements of automotive electronics.
Miniature TIG welding (non-consumable electrode inert gas welding) uses a high-temperature arc between a tungsten electrode and the workpiece to melt the metal, forming a high-quality weld. This process has lower requirements for product positioning accuracy, is suitable for automated production, and does not require the addition of filler metal during welding, reducing the risk of impurity introduction. Miniature TIG welding presents significant challenges in controlling the molten pool, easily generating spatter and fumes. Optimization of gas protection and welding parameters is crucial to reduce defect rates. In automotive relay terminal welding, this process, with its high precision and low heat-affected zone characteristics, is gradually replacing some traditional welding methods.
The welding process for automotive connector terminals must be selected comprehensively based on material properties, application scenarios, and cost requirements. Soft soldering is suitable for low-requirement scenarios, resistance welding and ultrasonic welding balance efficiency and reliability, while laser welding and miniature TIG welding represent high-end manufacturing directions. In the future, with the introduction of new materials (such as high thermal conductivity alloys) and new processes (such as composite welding), the welding strength and stability of automotive connector terminals will be further improved, providing solid support for intelligent driving and new energy technologies.
