In modern industry, there is an increasing demand for efficient processing and/or electrical micro-connection of thin metal materials. In many fields, the compatibility of materials or processes is not sufficient for conventional heat treatment, such as welding, brazing, and soldering, or the use of adhesives and mechanical fasteners is not desired. This situation may be very common in the energy storage industry, because next-generation batteries, which are key components of the emerging power battery industry, require the use of thin foils to make cathodes and anodes. In the consumer electronics industry, high-density packaging and miniaturization continue to promote innovation and also pose challenges to traditional connection technologies.

From the laser's point of view, there are many challenges that make the micro-welding of thin metal materials extremely difficult. To successfully weld, it is necessary to avoid weld penetration, deformation and bending, all of which require careful control of the heat input of the process. In the traditional laser deep penetration welding process, overcoming the material threshold usually requires a higher average power. The average power required for welding of high-reflective materials and dissimilar metals may be higher. One of the basic problems is whether to use a thermal conduction welding process or a deep penetration welding process. In heat conduction welding, heat sources with larger width and weaker strength tend to produce higher heat input and heat affected zone. Therefore, it is generally not recommended as a solution to the problem of sheet metal welding. During deep penetration welding, a highly concentrated and high-strength heat source can minimize the molten pool, thereby helping to control the heat input. Therefore, the adjustment of deep penetration welding parameters is essential to obtain high-quality results.

One method widely used in welding is to use nanosecond (ns) pulsed fiber lasers. These short-pulse, high-peak intensity lasers may be more suitable for marking, engraving, and other material removal processes, so intuitively, they may have the opposite effect when used in the material welding process. But the pulse control provided by the main oscillator power amplifier (MOPA) has excellent parameter flexibility, thus realizing possible metal bonding processing methods. Nanosecond pulsed fiber lasers operate with pulse energy from a few microjoules to> 1mJ, pulse duration range 10-1000ns, and can reach peak power> 10 kilowatts, operating at frequencies up to 4MHz, which is clearly different from continuous wave (CW ) And even quasi-CW (QCW) long pulse lasers, but many still operate within these ranges.

The use of nanosecond micro-welding as a welding tool is suitable for many applications and is also suitable for overcoming welding challenges from foils to dissimilar metals. The joining of thin metal foils (<50μm) is particularly challenging because it requires a very delicate energy balance, which is sufficient to melt the metal, but cannot generate significant vaporization and plasma. Foil materials are easy to use lap joints for welding. In this process, close contact between the foil materials is a necessary condition for good results, but this poses a major challenge to the fixture. Today's battery production process has many strict requirements for the welding of multilayer foils. The existing technology is ultrasonic welding, but manufacturers increasingly hope to use laser welding to improve production efficiency, quality and improve foil stacking restrictions. Lasers offer many potential solutions, but infrared (IR) nanosecond lasers have proven to be able to weld up to 20 layers of copper or aluminum foil using a 200W EP-Z laser, but eliminating porosity in this application is highly challenging.

The high peak power of nanosecond pulsed fiber lasers means that it can easily enter high anti-metals such as copper with a small average power. Using the nanosecond micro-soldering process as an alternative to soldering, the study of directly attaching components to copper printed circuit board (PCB) tracks has shown great promise. At present, copper wires up to 150μm thick have been successfully attached to deposition tracks >60μm without any obvious delamination with the FR4 substrate. This provides an alternative to the bonding of heat-sensitive components or components whose operating temperature may exceed the traditional welding limit.