Establishment Of Thermal Equivalent Model For Reflow Soldering And The Simulation Of Reflow Welding Process Reflow Thermal Profile

Reflow welding process is one of the most important steps to ensure the reliability of solder joint.At present,there are three main ways to study the reflow process: trial and error based on the real object,mathematical statistics and virtual simulation.The first two methods will cost a lot of time and material resources.Therefore,the time-saving and labor-saving advantages of virtual simulation of reflow welding process reflow thermal profile become more and more prominent,and gradually become the most direct and effective method to guide the formulation of reflow welding process parameters.However,due to the complex structure of surface assembled printed circuit board PCBA and reflow oven,detailed modeling will lead to too long simulation time and the efficiency cannot be guaranteed.However,the current simplification and accuracy are not enough to guide the process optimization in production.Therefore,how to greatly improve the simulation efficiency while ensuring the calculation accuracy is one of the key meanings in the simulation of reflow welding process reflow thermal profile.In PCBA of printed circuit board produced by SMT,plasticized BGA is a typical component,and also a key component to ensure the reliability of PCBA welding balls as a whole.Generally,the solder joints of BGA are fully welded in the reflow oven,so the solder joint reliability of other components will also be guaranteed.Based on the above reasons,this paper established a thermal equivalent model for the relationship between the structure,material,thermal conductivity,specific heat capacity and density of PCB board and plastic sealed BGA device,and carried out the following work:1.First,the detailed model of the plastic BGA device was established by using the Space Claim module in ANSYS 19.2.In the process of establishing the detailed model of BGA,four important structures of the typical plastic BGA device in the heat transfer process were selected: the plastic shell,the substrate,the chip and the welding ball.After that,the thermal resistance network model was established for plastic BGA,and the calculation expression of the thermal conductivity in the thickness direction of plastic BGA was obtained.Through the formula,the influence parameters of six thermal conductivity were determined,paving the way for the orthogonal test and regression analysis below.In order to improve the efficiency of numerical calculation and simulation,the welding spot of plastic BGA was simplified separately in this paper,and the ball of ball table shape was simplified into a hexahedral shape.BGA structure and material parameters were substituted into the thermal resistance network formula for calculation,and the calculated results were compared with the simulation results for verification.The thermal equivalent simulation model of plastic BGA was established and compared with the simulation results of the detailed model.At the same time,the multilayer PCB board structure was established and the rationality of PCB model in Icepak was verified by numerical calculation and simulation.2.Secondly,the thermal conductivity of the plastic BGA device was numerically simulated by orthogonal test to explore the influence of the six main factors.An orthogonal table with 6 factors and 3 levels was designed based on the orthogonal test method,and 18 groups of simulation tests were carried out.Among them,range analysis shows that the primary and secondary relationship of six key factors influencing the equivalent thermal conductivity of BGA is as follows: the height of the plastic shell above the chip is higher than that of the chip > welded sphere than that of the > substrate.The area of the > chip is higher than that of the > welded sphere.According to the analysis of variance,the significant factors affecting the equivalent thermal conductivity of BGA thickness include the height of the plastic sealed shell above the chip,the area ratio of the welded balls and the height of the substrate.It can be seen from the range analysis and variance analysis that the height of the plastic sealed shell above the chip and the ratio of welded ball area are the main influencing factors.Through the interaction analysis,it is found that the factors affecting the equivalent thermal conductivity in the direction of the thickness of BGA generally interact with each other.Then,multiple nonlinear regression analysis of factors was carried out with 1stopt,and genetic algorithm was used to optimize the factors.Finally,the mathematical model for equivalent calculation of thermal conductivity in the direction of BGA thickness was obtained.3.In the end,use(Wickon)of hot air reflow oven temperature acquisition instrument measuring reflow temperature experiment,using ANSYS Icepak module is established in 19.2 the infrared hot air reflow oven model of 10 temperature area,respectively,to establish the actual production of PCBA circuit board of the model and the equivalent thermal model in detail,the four BGA reflow temperature simulation monitoring center position,the detailed model of the heat flow curve and the flow curve of equivalent simplified model,this paper compares and analyzes thermal equivalent simplified model simulation reflow reflow thermal profile and the measured via comparing the reflow thermal profile,The reflow temperature simulation curves of the simplified model with the same thermal conductivity in different thickness directions of BGA were compared and analyzed.