Simulation For Lead-free Solder In The Reflow Welding Of PCB Warpage Deformation

Along with the information times is coming, electronic product which is interrelated with people's life is emerged in endlessly, those electronic product are benefit for people ,but also destroy people's health and environment. Therefor, to considerate protect environment and health,spread lead-free welding in electronic manufacturing is imperatived.At present the melt temperature of lead-free solder is 217℃, which 34℃higher than solder of Sn-Pb,therefor, use suitably lead-free solder, how to reducing the warpage of PCB in the circumstances of temperature is higher is the important problems. In this paper , Sn3.5Ag0.75Cu is research object, in different temperature setting, simulate temperature field,warpage deformation and thermomechanical analysis in the whole process of the reflow soldering of PCB, accordingly make sure the appropriate welding procedure,and compared with warpage deformation under the circumstances of solder of Sn-Pb.In this paper, the temperature field of the PCB happened in the process of the reflow soldering are modeled by using the finite element method, and the laminated board basic theory of compound material mechanics is used to analyze the thermal strain and the thermal stress of the PCB, and model the warpage of the laminated board under one certain restrict condition. Furthermore, in different temperature setting , simulated temperature field,warpage deformation and thermomechanical analysis the soldering process of PCB by the finite element software, ANSYS.The result of research obtains that: In the process of the reflow soldering, with different temperature setting, the pictures of temperature field distribution, warpage deformation status and stress distribution along with time variation are obtained; Through the contrast study of these pictures, we know in the temperature seeting of"flat", the deformation is declined; the radical reason of PCB deformation is deeply analyzed, and the conclusion is that the thermal expansion coefficients of the composing materials of PCB are different; In the process of reflow soldering, when PCB comes through different temperature sections to be heated, the distribution of temperature field is asymmetric, PCB can not expand and shrink freely, which produces heat stress. which causes the warpage of PCB. Moreover, through the intensively thermomechanical analysis of PCBA in the process of reflow soldering above, some methods are given to reduce the warpage.