Research On Soldering Process And Solder Forming Control Method Under The Action Of Electric-thermal-mechanical Couplin

In the connection of electronic devices,solder contacts can realize the electrical connection between electronic components on the one hand,play the role of signal transmission and circuit conduction,on the other hand,play the role of mechanical support.As the traditional hot pressure welding adopts pneumatic pressure method,there are problems of large fluctuation range of pressure control and low control precision,which is easy to cause defects such as solder overflow,solder offset and solder floating welding.The strength and surface quality of solder joint are important factors to evaluate solder joint quality.Therefore,it is of great significance to deeply analyze the forming process of solder joints in hot pressing solder joints under the action of electrothermal coupling and explore the control method of improving solder joints forming.Firstly,the servo pressure control system is constructed based on STM32 core controller.The hardware circuit and software program of the system are designed to realize the real-time control of welding process and the dynamic parameter supervision of the process.Orthogonal experiment was designed to optimize the welding condition and probe into the influence of welding parameters on the quality of solder joints.The results show that the welding pressure has the greatest influence on the forming effect of solder joints.Too small pressure leads to low heat transfer efficiency in the welding process,unable to form an effective and complete solder contact;Excessive pressure not only leads to solder overflow resulting in lap short circuit,but also causes solder contact surface indentation too deep,solder forming height is insufficient,residual stress concentration after solder spot welding,macro appearance gloss difference defects.A collaborative control strategy of temperature,pressure and displacement was proposed to realize the dynamic control of solder joint forming process.The results show that the surface shape of solder joints is improved obviously.Under the cooperative control of multiple parameters,the solder joint strength increases first and then decreases.The forming height of solder joint is positively correlated with the strength of solder joint,which realizes the precise control of the forming height of solder joint during the welding process.The results show that the servo pressure control system is stable and reliable.The temperature-displacement-pressure cooperative control method improves the solder joint quality,and the solder joint forming is more beautiful,stable and reliable.Solder joints at different welding temperatures and welding time were obtained,and the effects of technological parameters on the microstructure evolution and mechanical properties of solder joints were analyzed.By SEM and EDS analysis,the typical interfacial structure was Cn₆Sn₅.When the welding temperature is too low or welding time is insufficient,the rougher the intermediate layer of solder contact,the lower the strength of solder contact,solder contact fracture mode is mainly brittle fracture;With the increase of welding temperature and welding time,the microstructure of solder joint intermediate layer gradually changes from scallop shape to relatively flat interface,and the fracture mode of solder joint changes from brittle fracture mode to brittle ductile mixed fracture mode.When the welding pressure is 12 N,the welding time is 4000 ms,and the welding temperature is420℃,the strength reaches 35 N.The integral value of welding current increases and the welding energy accumulates continuously.The integral value is proportional to the mechanical properties of solder joints.