- Equipment introduction
Soldering is one of the key processes in the component packaging process. Soldering is divided into manual soldering and automatic soldering. The equipment used for manual soldering is a constant temperature soldering iron, and the general temperature is set to 380~420℃. The early photovoltaic industry basically used manual welding, but now it has been gradually eliminated and changed to automatic welding. Only some special solar cells use manual welding. Automatic welding equipment (commonly known as automatic string welding machine) can automatically and continuously weld the front and back sides of the battery sheet at the same time according to the set parameters, and complete single welding and string welding at one time to form a battery string. Compared with manual welding, the automatic welding speed is fast, the welding quality is reliable, the consistency is good, and the process can be monitored. Wait. An automatic stringer with a capacity of 1200 pieces/hour can replace about 20 operators.
Of course, if there is a problem of poor welding, it often occurs in batches, so automatic welding has extremely high requirements on the stability of the equipment. In China, the automatic string welding machine mainly relied on imports at the beginning. The main products are Technical Team (TT) from Germany and DF series from Toyama Machinery from Japan. Now a large number of domestic automatic string welding machines have emerged, including Pioneer, Autowell, Mavericks, etc. The domestic string welding machine equipment is very cost-effective, the price is less than 1/3 of the foreign equipment, and the technical quality and after-sales service are comparable to those of the foreign equipment. The most critical measurement index of automatic string welding machine is the welding fragmentation rate. Domestic equipment can achieve better than imported equipment in this indicator. The fragmentation rate of imported string welding machine is generally less than 0.25%, while domestic equipment can achieve less than 0.15%.
The main heating methods of solar cell welding include infrared heating, electromagnetic induction heating and hot air heating. German TT, Spain Gorosabel, China Wuxi Pioneer, Ovit and Tianjin Rapido all use infrared heating, while Swiss Komax, American Xcell (Komax reorganization), China Ningxia Mavericks and other companies use electromagnetic induction heating technology, Somont GmbH (Acquired by Meyerberg) The company uses soft-contact electric heating rods for heating, while Japan’s Toyama Machinery uses hot air heating technology.
- Device Workflow
A string welding machine mainly includes a feeding area, a welding area, a discharging area and a welding strip supply area. The main functions of the feeding area are battery feeding, CCD detection, etc. The functions of the welding area are battery heating, welding, transmission, etc., and the functions of the discharging area are mainly to cut and transfer the welded battery strings to the next station. , The main function of the ribbon supply area is to draw, organize and cut interconnect strips, and some also include flux supply.
2.1. Battery feeding
The battery box loading position is located outside the machine, and there is no need to stop the machine to load the material. After the operator sees the loading box being transferred into the equipment, he will put another box of batteries on the loading table.
2.2. Battery feeding and CCD detection
After the battery box reaches the feeding position, the feeding mechanism grabs the batteries one by one to the CCD camera platform for photo detection and positioning. The feeding mechanism is composed of a jacking servo, a lifting electric cylinder (with a suction cup) and a traverse servo, and is equipped with an air knife to prevent the battery from sticking. Generally, CCD detection adopts industrial cameras with more than 3 million pixels. The main functions are as follows:
(1) Defect detection can detect defects such as missing corners, cracks, cracks, and non-parallel grid lines, and the defect level (such as crack depth) can be automatically determined according to the standard set in the computer;
(2) The grid line positioning detects the center of the battery and the position of the main grid line, and matches with the welding tape.
The CCD sends the test results to the robot, and the robot accurately grasps and locates the battery according to the data transmitted by the CCD, puts the bad battery into the bad film box, and the qualified battery is grasped to the conveyor belt, and is detected according to the CCD during the grasping process. As a result, the battery was fine-tuned to make the busbar line aligned with the welding strip, and the positioning accuracy could reach 0.01mm, which effectively avoided the whitening of the busbar line welding.
- Apply the flux
There are two general flux application methods: spraying and immersion. The spraying method is generally that when the robot takes out the solar cell from the camera platform, the flux spraying mechanism sprays the flux on the grid lines on both sides of the battery. In this process, the spraying angle needs to be controlled, otherwise it will be sprayed on the bus line and the back. Outside the range of electrodes, it affects the appearance of the battery and sometimes brings other reliability problems. The immersion method is that when the interconnect strip is pulled from the reel, it is directly passed through a flux soaking box, and then soldered after drying. The two methods have their own advantages and disadvantages. The spraying method needs to adjust the spraying angle after adjusting and switching the specifications of the welding strip. For the immersion method, because the flux is corrosive, the parts of the tooling parts that the welding strip passes through need to be cleaned and maintained frequently. , to prevent corrosion.
- Interconnection strip arrangement and traction
The interconnect strip is bent on the spool, so it needs to be straightened first, then cut, and can be bent to some extent if needed to match the height of the battery from front to back, preventing fragmentation and component work The effect of thermal expansion and contraction in the The stretching amount of the interconnecting strip can be set in the computer program. Too large or too small stretching amount will affect the welding performance. The stretching amount should be set according to the performance of the welding strip and experience. The bending depth and position are generally controlled by small fixtures and can be adjusted manually. The ribbon traction mechanism clamps and positions the cut ribbon on the main grid line of the battery. The accuracy of the ribbon positioning is mainly ensured by the servo motor, linear module and guide mechanism of the ribbon traction mechanism.
- Welding area conveyor belt
The conveyor belt in the welding area is generally made of Teflon material, which is resistant to high temperature and does not stick to tin. In order to reduce the stress caused by the temperature change inside the solar cell, multiple heating plates are installed under the conveyor belt in the welding area, and the cells are preheated in multiple stages at different temperatures before welding, and the cells can also be slowly cooled in multiple stages after welding. The conveyor belt is driven by a servo motor with high stepping precision.
- Heating and Soldering
By heating the front and back sides of the battery at the same time, the interconnecting bars are welded on the busbar and the back electrode of the solar cell at the same time, and the cells are directly welded into strings. In addition to the heating plate under the conveyor belt to preheat the back of the battery, the front of the battery is also heated by infrared or hot air, or electromagnetic heating. Generally, the temperature accuracy of the welding base plate is about ±5℃, and the temperature accuracy of the infrared lamp is about ±10℃.
- Serialization mechanism
The main function of the serial separator is to cut off the welded battery strings according to the required number of series connected batteries, and can automatically and continuously cut off. The cutting and welding are performed synchronously without waiting. It avoids the offset of the welding strips at the beginning and end of the battery string.
- Discharge area
The discharge area is composed of a conveyor belt, a lower suction mechanism, an upper suction mechanism, a traverse mechanism, a finished box support, and a waste box support. The discharge area can be set to check mode or automatic mode. In the inspection mode, the battery string can be flipped to a set angle through the button on the side of the machine, which is convenient for manual inspection; in the automatic mode, each string of battery strings is automatically flipped and delayed for a certain time (usually 5 seconds of detection time is left) Then put it in the finished box.