| As circuits and electronic components are developed toward miniaturization,high density,and high integration,the sizes of solder joints are smaller and smaller.The requirements for the thermal conductivity and the high temperature resistance are becoming higher and higher.The electronics manufacturing industry needs methods of soldering with higher precision and smaller heat-affected areas.Soldering processes and equipments are still important factors affecting the development of the electronics manufacturing industry.Therefore,the development of high-performance soldering equipments is the development trend of the electronic packaging industry.Laser soldering uses laser beam as the energy source.Compared with traditional wave soldering and reflow soldering,it has the advantages of high soldering precision,small heating area,high energy density,good mechanical properties of solder joints and low equipment maintenance cost.In recent years,it has received extensive attentions from the electronics manufacturing and scientific research industries.However,due to the high energy density of the laser beam in laser soldering,it is easy to cause damage when soldering heat-sensitive elements and circuits with low-melting-point elements.In this case,it is especially important to regulate real-time online management of the laser output average energy based on the temperature of the solder joint.Controlling the laser output average energy during the laser soldering process not only ensures that the solder joints have good mechanical properties,but also protects the thermal elements and the electronic circuits.This paper is based on the actual production demand,proposes a laser tin wire soldering system which is based on infrared temperature measurement.The temperature of the solder joint is detected by an infrared thermometer and the PWM input signal of the laser is adjusted by a closed-loop control system to achieve monitoring and controling the solder joint temperature.This paper mainly studies and analyzes the optical system and control system in the infrared temperature measurement laser molten tin-wire soldering system,and finally completes the prototype construction and the soldering performance test.Firstly,based on determining the basic working requirements of the optical system,analyzing the basic theory and functions of the components in the optical system,and the laser,infrared thermometer and CCD industrial camera are selected.Simulation and analysis of laser beam and infrared temperature measurement beam propagating in corresponding medium-optical path.The image plane corresponds to the laser beam spot and infrared temperature measurement is 108 mm from the vertical direction of the center point of the lower surface of the total reflection mirror.The spot radii of the beams are 0.5779 mm and 0.412 mm,respectively.Secondly,the communication architecture scheme between each subsystem is designed and the prototype of the infrared temperature measurement laser molten tin-wire soldering system is completed.In order to ensure the infrared temperature measurement accuracy and the accurate control of the laser beam energy,the causes of the error in the infrared temperature measurement in the optical system are analyzed.Through the comparison experiment,the correction of the infrared temperature measurement value is completed,and the temperature detection interval of the welding process is determined to be [124.56,339.73]°C,the maximum deviation between the correction value and the true value is 4.24 °C,which improves the accuracy of the infrared temperature measurement value during the soldering process.The laser beam power detection is used to calculate the energy conversion efficiency of the laser beam in the optical system,which lays the foundation for the simulation analysis of the closed-loop control system.The control strategy of the closed-loop control system is analyzed and designed,and the preferred control scheme is PID control.There are many factors that interfere with the solder joint temperature during the soldering process.The PID parameters need to be constantly set,and the traditional PID control is difficult to guarantee the control accuracy.Through the welding experiment,the transfer function of the control system is established,and the theoretical and simulation analysis of the traditional PID and fuzzy self-tuning PID control system is carried out.In the simulation analysis,the adjustment time,steady-state error,maximum deviation and maximum overshoot of the fuzzy self-tuning PID control system are better than the traditional PID control.Therefore,fuzzy self-tuning PID control is adopted.Finally,based on the above research results,the soldering effect of the soldering system is explored experimentally.Identify the main factors in the soldering effect,and mainly explore the influence of the feeding speed of the tin wire and the laser action time on the soldering effect.Set the basic parameters of the experiment to: target temperature is 270 °C,laser input voltage is 1.9V,pre-wire speed is 17.7mm/s,pre-wire length is 17.7mm,wire-removal speed is 106mm/s,and wire-removal length is 17.7mm.The wire length is 17.7 mm.Through the single factor test,the influence of the feeding speed of the tin wire and the laser action time on the soldering effect are analyzed.When the laser soldering time is 2 s the surface of the solder joint is smooth,spread evenly.Under these conditions,multiple sets of soldering experiments are carried out.The deviation between the temperature peak detected during the soldering process and the target temperature value is in the interval [17.3,27.8]°C.When the deviation value is stable within [-15,15] °C,the time required is in the interval [0.94,1.42] s.Through the conclusions and prospects,the defects of the prototype are analyzed and suggestions for the later optimization and improvement are put forward. |
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