The hottest laser micro welding technology of copp

Laser micro welding technology of copper materials

connecting conductive parts in order to achieve electrical contact is one of the most common welding applications. It covers almost all industrial applications, such as automobiles, electrical and electronic equipment, and medical equipment. The adopted connection technology needs to comprehensively consider the cost, welding performance and output. With the shrinking size of parts and the gradual improvement of performance requirements, all traditional connection technologies, such as crimping, thermal welding and brazing, are no longer applicable. In contrast, with the advantages of complete, firm and good conductivity of solder joints, positioning welding soon became a necessary standard welding technology

copper is the preferred material because it can effectively conduct energy and transmit signals. The material properties of copper make it very suitable as a conductor, but it is difficult to be welded. In addition, as the size of the parts becomes smaller, the contact has reached the size of "micro welding", which makes it more difficult to weld

micro welding of copper brings great challenges to the heat balance control of these small conductive parts - because it is necessary to ensure the quality of welding and ensure that it will not be overheated or underheated. Can manufacturers meet these requirements at the same time? Yes, it can be achieved by using a green laser welder with a wavelength of 532 nm. Before discussing various optional welding technologies at present, let's first define micro welding: micro welding is the joint of two materials, at least one of which is less than 0.02 inch thick. At present, the optional technologies include: ultrasonic welding technology, resistance welding technology and laser welding technology

ultrasonic welding technology is an effective welding technology, which is used to connect copper plates and other parts; However, this is a process of mechanical connection, which is limited by the mechanical force of parts, interface characteristics, contact geometry, and the shape combination of different parts

resistance welding technology is a practical technology, but it is limited by the contact shape, and it needs to buy small conductive electrodes and maintain them

because both ultrasonic welding and resistance welding require direct contact with parts to produce joints, the total welding time is equal to the braking cycle plus welding time. For large-scale manufacturing, this means a lot of time delay

on the contrary, laser welding is a non-contact processing process, which only requires one-way processing. It can process a small area and weld parts of various shapes. It seems to be very suitable for the welding of copper materials, but there is another problem. At the wavelength of 1064 nm, the reflectivity of copper material is more than 90%. Therefore, in order to overcome the problem of high initial reflectivity, a large power density is required. Once the laser touches the material, the material begins to melt, and the reflectivity will drop rapidly. The power density required at the beginning is much higher than that required during welding, resulting in overheating and evaporation of the material, high porosity at the solder joint, or the formation of a cavity

many different techniques have been used to overcome this reflectivity problem, including pulse shaping, using oxygen assistance, and using coated metals with low reflectivity

laser shaping technology is not very reliable, because there are certain changes in the reflectivity of copper and other conductive parts, so the time point of reducing laser power also needs to be changed accordingly. At present, some technicians have tried to use feedback technology to estimate this time point, but these experiments have not been successful. The use of oxygen as an auxiliary gas has greatly improved the linear copper charge price in Jiangsu, which is now maintained at 1590 ⑴ 630 yuan/ton. The laser penetration rate in welding is maintained because the parts to be welded are covered with a layer of oxide film. However, this technology is not suitable for spot welding, because the auxiliary effect of oxygen must be shown after several consecutive pulses pass. In this way, in the welding of a single point or short weld, this technology cannot provide reliable results. Using a coating with low reflectivity, such as nickel or tin, can indeed reduce the initial reflectivity, but it cannot completely solve the problem, because in the process of laser interaction with copper, it still requires a lot of energy to make the laser coupled to the copper material. Therefore, the machinable range of micro welding is very small

in order to form a good and stable laser welding point on the surface of copper material, we find out the problem of theoretical and experimental analysis that hinders the good welding conference. The theme is the interaction of friction, wear and fatigue phenomena, and the root cause of the result - material reflectivity. When the wavelength changes from 1064 nm to 532 nm, the reflectivity of copper and other materials is greatly reduced (see Table 1). According to its conversion principle, 532 is divided into 2-band slope method, integration method, parallel comparison method, voltage 1 frequency conversion method and successive comparison method, which makes the laser beam continuously coupled to the copper material, and stabilizes the welding process. Figure 1 shows the comparison of results after welding copper materials without coating with 1064 nm and 532 nm lasers. When 532 nm laser is used, it has high accuracy and repeatability on copper materials; According to relevant national or international standards, it can be used to test the welding effect of tensile, contraction, bending, shear and spalling of various materials, which is comparable to the welding result of 1064 nm laser on steel materials

in order to successfully micro weld copper materials, a green laser with a wavelength of 532 nm must be used. There are two ways to achieve this wavelength. The most common way is to use a Q-switched laser, but such a laser does not have enough pulse energy for welding. The newer technology is to use a nd:yag pulse laser, which produces a 532 nm laser with a peak power of 1.5 kW and a pulse width of 5 ms. This provides enough welding energy to penetrate copper plates with a thickness of 350 microns. Such energy is sufficient in most micro welding applications. Another advantage of using nd:yag pulse laser transmitted by optical fiber is the low brightness of the beam, which improves the degree of light absorption at the focal spot and avoids the instability caused by the formation of too hot spots in the center of the solder joint

many application fields

there are great differences in the size, shape and material of electrical connections in products. Therefore, here are some examples to illustrate the performance and advantages of 532 nm laser welding

semiconductor connection Figure 2 shows 0.0015 inch thick gold-plated copper wire welded to the metal plate. Because the copper wire is relatively wide in the transverse direction, but its thickness is very small, it is necessary to use a relatively large light spot for welding. In this case, the laser with long pulse width and low peak power can provide better energy flow, and the low brightness of the beam makes the flat copper wire evenly heated over the entire transverse width

the connection between the plane and the circular end point laser processing has a high degree of flexibility, especially when the processed joints and the geometry of both ends are different. Figure 3 shows the welding point between the gold-plated copper connector with rectangular side and the silver plated copper wire. The welding point is "pipe" shaped, and a welding point is formed between one end of the line and the top. The coupling between the laser beam and the round top of the copper wire and the plane of the copper plate makes the whole welding process very reliable. Similarly, due to the low brightness of the laser beam, the whole processing process is more conducive to the joining of parts

wire to plane connection another welding configuration is to weld solid and bunched wires. When the wire is welded to the thin plate, both the wire and the plate must constantly absorb the laser energy at the same time to ensure the fixity of the solder joint (Fig. 4). Similarly, when welding a beam of wires, the distribution of the wires must be controlled to ensure the absorption of the whole beam of wires to the laser

welding of frame in mass production, the key to welding different joints on the frame is welding quality and welding speed. Because laser welding is a non-contact process, it is very conducive to large-scale production and processing. After integrating the movement of the laser beam, it can get many solder joints in one second (see Figure 5)

welding between different materials when the welded materials have different absorption rates, it often happens that the materials with high absorption rates overheat, resulting in material splashing or holes. Usually, the way to overcome this problem is to prefer one of the materials when processing. However, for small parts, even small uneven absorption will lead to overheating of welding. If the laser with the wavelength of 532 nm is used, the energy balance of the welding process can be achieved because the reflectivity of the two parts is closer, so the weldability can be greatly improved (as shown in Figure 6)

summary

the welding of copper material is a relatively difficult process, and micro copper welding makes the processing more difficult. Laser welding is a practical technology to realize the bonding process of copper materials. It adopts a non-contact processing method, which is very suitable for automatic processing. However, the reflectivity of copper at 1064 nm wavelength is very high, which hinders the realization of laser processing. In order to overcome this difficulty, we use 532 nm green nd:yag laser welding machine, which provides an effective method for large-scale micro welding of copper materials and other conductive materials

the authors Geoff Shannon and Paul severloh are from Miyachi UNITEK company in the United States, and their company address is:. (end)