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In recent years, market demand has promoted the development of technology. Nowadays, when electronic products are becoming more and more refined, traditional soldering iron welding and wave soldering can no longer meet the welding of all electronic products. Laser soldering is because of its non-contact welding. Can adapt to more welding space, excellent electro-optical efficiency conversion and fine energy control, are more and more applied to the electronic assembly link. There are many types of lasers. The infrared semiconductor laser with a wavelength of 904-940nm is selected for laser soldering, and the power is generally 5-200W.
Semiconductor laser is a device that generates laser light by using a certain semiconductor material as a working substance. . Its working principle is to realize non-equilibrium current carrying between the energy band of semiconductor material (conduction band and valence band) or between the energy band of semiconductor material and the energy level of impurity (acceptor or donor) through a certain excitation method The number of particles is inverted. When a large number of electrons and holes in the state of population inversion recombine, stimulated emission occurs. There are three main excitation methods for semiconductor lasers, namely, electrical injection, optical pumping and high-energy electron beam excitation. Electrical injection semiconductor lasers are generally semiconductor surface junction diodes made of gallium arsenide (GaAs), cadmium sulfide (CdS), indium phosphide (InP), zinc sulfide (ZnS) and other materials, which are forward biased The current is injected for excitation, and stimulated emission occurs in the junction plane area.
The photoelectric efficiency of semiconductor lasers is more advantageous than fiber lasers. Semiconductor diode lasers are a very practical and important type of lasers. It is small in size, long in life, and can be pumped by simple injection current. Its working voltage and current are compatible with integrated circuits, so it can be monolithically integrated with it. And you can directly modulate the current with frequencies up to GHz to obtain high-speed modulated laser output. Due to these advantages, semiconductor diode lasers have been widely used in laser communications, optical storage, optical gyroscopes, laser printing, ranging and radar.
In addition, its continuous output wavelength covers the range of infrared to visible light, and the optical pulse output is up to 50W (bandwidth 100ns), which is an ideal choice for semiconductor lasers used in laser soldering. Semiconductor infrared lasers are commonly used in laser soldering, and most of them are lasers with a wavelength of 915nm+5nm. It belongs to the near-infrared band and has a good thermal effect. Its unique beam uniformity and laser energy continuity are uniform to the pad. The heating and rapid heating effect is remarkable. It has the advantages of high welding efficiency, precise control of the welding position, and good consistency of solder joints. It is very suitable for precision welding of small and micro electronic components, complex structure circuit boards and PCB boards.
The temperature closed-loop control system is used to monitor and control the quality of solder. The advanced laser soldering equipment is equipped with a real-time temperature detection unit. The temperature of the solder joint is detected in real time through an infrared sensor, and the analog-to-digital conversion is sent to the control computer through temperature changes. The situation monitors the formation process of the solder joints, or changes the laser power in real time to control the formation and quality of the solder joints. When the temperature rises too fast, the laser output can be cut off immediately to ensure that the leads of the device are not burned. The image monitor can observe the position of the laser and the lead as well as the welding process, and can record or take pictures of the soldering process. The output power of the laser is set by the control computer and can be programmed to ensure the accuracy of the heating energy.
