First, the process parameters of laser welding 1. Power density Power density is one of the most critical parameters in laser processing. With higher power density, the surface layer can be heated to the boiling point in the microsecond time range, resulting in a large amount of vaporization. Therefore, high power density is beneficial for material removal processes such as punching, cutting, and engraving. For lower power density, it takes several milliseconds for the surface temperature to reach the boiling point. Before the surface vaporizes, the bottom layer reaches the melting point, which is easy to form a good fusion welding. Therefore, in conduction laser welding, the power density is in the range of 104~106W/cm2. 2. Laser pulse waveform Laser pulse waveform is an important issue in laser welding, especially for thin sheet welding. When the high-intensity laser beam hits the surface of the material, 60-98% of the laser energy on the metal surface will be reflected and lost, and the reflectivity varies with the surface temperature. During the action of a laser pulse, the reflectivity of metals varies greatly. 3. Laser pulse width Pulse width is one of the important parameters of pulsed laser welding. It is not only an important parameter that is different from material removal and material melting, but also a key parameter that determines the cost and volume of processing equipment. 4. Influence of defocus amount on welding quality Laser welding usually requires a certain degree of defocusing, because the power density in the center of the spot at the laser focus is too high, and it is easy to evaporate into a hole. On the planes away from the laser focus, the power density distribution is relatively uniform. There are two ways of defocusing: positive defocusing and negative defocusing. The focal plane is located on the workpiece. The above is positive defocusing, otherwise it is negative defocusing. According to the geometrical optics theory, when the positive and negative distances are equal, the power density on the corresponding plane is approximately the same, but the shape of the molten pool obtained is actually different. When the defocus is negative, a larger penetration depth can be obtained, which is related to the formation process of the molten pool. Experiments show that when the laser is heated for 50~200us, the material begins to melt, forming a liquid phase metal and vaporizing it, forming a market-pressure steam, which is ejected at a very high speed, emitting a dazzling white light. At the same time, the high concentration of vapor makes the liquid metal move to the edge of the molten pool, forming a depression in the center of the molten pool. When the defocus is negative, the internal power density of the material is higher than that of the surface, and it is easy to form stronger melting and vaporization, so that the light energy can be transmitted to the deeper part of the material. Therefore, in practical applications, when the penetration depth is required to be large, when using negative defocus to weld thin materials, positive defocus should be used. 2. Laser welding process method 1. Welding between islands Including butt welding, end welding, center penetration fusion welding, center penetration fusion welding and other 4 process methods. 2. Wire to wire welding Including wire-to-wire butt welding, cross welding, parallel lap welding, T-welding and other 4 process methods. 3. Welding of wire and block components The connection between the metal wire and the block element can be successfully realized by laser welding, and the size of the block element can be arbitrary. During welding, attention should be paid to the geometrical dimensions of the filamentary elements. 4. Welding of Tong metal Welding different types of metals addresses weldability and weldability parameter ranges. Laser welding between different materials is only possible with certain material combinations. Laser brazing The connection of some components is not suitable for laser welding, but the laser can be used as a heat source to implement soft soldering and brazing, which also has the advantages of laser welding. There are many ways to use brazing. Laser soldering is mainly used for the welding of printed circuit boards, especially for chip component assembly technology. 3. Compared with other methods, the use of laser soldering has the following advantages 1. Due to local heating, the components are not prone to thermal damage and the heat-affected zone is small, so soldering can be performed near the heat-sensitive components. 2. Using non-contact heating, melting the bandwidth, without any auxiliary tools, it can be processed after the double-sided components are equipped on the double-sided printed circuit board. 3. Good stability in repeated operation. The flux has little pollution to welding tools, and the laser irradiation time and output power are easy to control, and th