Development Of Laser Micro-welding Device Of Flex Lead With Solder Paste

In accelerometer,flex lead is an important part of signal transmission between moving objects.Because the diameter of flex lead is very small,and it is currently manual welding,This method results in poor consistency of solder joints and low production efficiency.In order to realize the automation of flex lead micro-welding and obtain products with good consistency of welding joints,this paper systematically studies the micro-welding mode of flex lead,and puts forward a complete set of welding scheme,then designs and builds a welding experimental device,and through continuous experiments,good welding process and key process parameters are summarized.Finally,good conductivity solder joints with diameter of about 0.2mm are obtained.By choosing solder paste as solder and laser as heating source,a set of welding experimental device was designed.It mainly includes solder paste liquid separation module,laser heating module,vision module,infrared temperature measurement module,signal and data processing module.The solder paste segregation module is mainly used to transport trace solder paste quantitatively to the area to be soldered.The laser heating module is mainly used to heat solder paste according to the specified power curve,so that it melts and solidifies to form solder joints.The visual module is mainly used to realize the functions of visual positioning,visual measurement and monitoring of welding process.The infrared temperature measurement module is used to monitor the temperature changes of welding joints in the welding process,which provides the basis for the subsequent improvement of welding effect.The signal and data processing module mainly relies on industrial computer and related software to save,analyze and process visual information and temperature information in the experimental process.In order to perfect the welding function of the system and improve the welding quality,a series of calibration work and related experiments have been carried out.Firstly,the experiment of solder paste emissivity measurement is designed and implemented,and the temperature measurement error of the system under this emissivity is measured.The emissivity of the solder paste used in the experiment is 0.8978,and the relative error of temperature measurement is about ±1%.Then,the calibration experiment of the pixel size of the visual system is carried out,and the result shows that the pixel size is 2.74 um x 2.73 um.After that,the coaxiality measurement and calibration experiments of laser energy center and system vision center are carried out,it is found that the center deviation values of the two systems are different under different spot sizes.By recording several sets of deviation data,It is found that no matter how the size of the spot changes,there is a linear relationship between the difference of their central coordinates.It can be concluded that the relationship between the central axis of vision system and the central axis of laser energy is heterogeneous.Further experiments show that the central position will not change when the magnification of the lens is changed with the same spot size.Then,the infrared temperature measurement experiment of small solder joints was carried out.It was found that the temperature curve and laser power curve had the same tendency when the solder paste heated by laser,but there was a temperature explosion zone in the initial stage.The subsequent experiments showed that the temperature explosion zone was caused by the initial state of solder paste.Then,the solder paste heating experiment was carried out,and four kinds of common problems in the welding process were summarized,and the corresponding solutions were put forward.Finally,the experiment of conductivity measurement of solder joints is designed and implemented.The results show that the conductivity of solder joints is good.Through continuous optimization and improvement,the solder joints with a diameter of about 0.2 mm and good conductivity were finally obtained.