Reflow Temperature Analysis Of PCB Assembly In Reflow Soldering

With the miniaturization and high density of electronic components,SMT technology has developed rapidly because of its high integration.As a key process in SMT,the setting of reflow process parameters affects the reliability of PCB assembly.Reflow process parameters mainly shows the control of reflow temperature.In order to obtain the reflow temperature which satisfied the requirements of different PCB assembly,rich experience and many tests are needed to adjust the reflow oven parameters.This process consumes a lot of manpower,material resources and time.Aiming at the problem of parameter setting of reflow oven in reflow soldering of PCB assembly,this article bases on the method of theoretical analysis and finite element simulation to model and simulate the temperature field of 20 PCB assembly under 10 groups of reflow oven parameter setting.The reflow temperature of specific points on typical components of PCB assembly is obtained.The influence of PCB structure parameters,component layout,component size and reflow oven parameter setting on PCB assembly is studied.The parameter setting method of reflow oven is summarized,and the reliability of simulation results is verified by experiments.The main work of this paper can be summarized as follows:1.Firstly,the finite element model of 20 PCB assembly is established in ANSYS Workbench,and the equivalent material parameters of PCB and solder are calculated.Then,it is based on the heating mode and structure of the reflow oven used in this paper to deduce the convective heat transfer coefficient of PCB assembly in the reflow oven,and verify the rationality of the value of convective heat transfer coefficient by the temperature measurement of thermocouple.Finally,through the finite element simulation,the reflow temperature of specific points on typical components of 20 PCB assembly under 10 groups of different reflow oven parameters is obtained.2.Through finite element simulation,the influence of PCB structure parameters,component layout and component size on PCB reflow temperature is explored.The results show that:(1)In the PCB structure parameters,the thermal conductivity of PCB mainly affects the reflow peak temperature of solder in the center of BGA device,and the thickness of PCB affects the reflow peak temperature of solder.When the length of PCB is greater than 2.5times of the length of component,it does not affect the reflow peak temperature of solder.The reflow peak temperature at the center of solder increases with the increase of PCB thermal conductivity,and the reflow peak temperature of solder decreases with the increase of PCB thickness.(2)The layout of components has less significant effect on the reflow temperature peak,which mainly affects the overall temperature field of PCB assembly.(3)The larger the volume of BGA devices,the lower the reflow temperature peak.3.Through the reflow temperature of 20 PCB assembly under 10 groups of different reflow oven parameters,the influence of reflow oven parameters on the reflow temperature of PCB assembly is analyzed,and the following conclusions are obtained:(1)For assembly 1,the parameters of the fifth group of reflow oven meets the welding requirements of Sn63Pb37 solder.It is found that the temperature of the last heating zone of reflow oven increases by10℃,the peak temperature of solder increases by about 7℃,and the temperature of the last heating zone of the reflow oven increases by 5℃,the solder peak temperature increases by about 4℃.The solder peak temperature decreases with the increase of the conveyor chain speed.(2)By comparing the reflow temperature of 20 components under the setting of reflow oven parameters of group 5,group 8 and group 9,it is found that changing the setting of reflow oven parameters affects similarly the reflow peak temperature of different PCB assembly,and the parameter setting method of reflow oven is summarized.4.The temperature curve tester is used to verify 10 groups of simulation results of 5assemblies under two groups of different reflow oven parameters.In the heating stage,the error between the simulation results and the experimental results is within 5℃.It can be considered that these 10 groups of simulation results are reliable.It also shows that the temperature field of PCB assembly and the reflow temperature curve of specific points on PCB assembly which obtained by finite element simulation are reliable.