The Finite Element Modeling And Simulation For Thermomechanical Analysis Of PCBA

Nowadays, with development of the SMT towards the high density and the microminiaturized direction, the high integrated production request of printed circuit board assembly (PCBA) proposes the huge challenge to the reliability of reflow soldering. In the process of reflow soldering of the PCBA, warpage deformation is one of the important problems in the reliability research. And it will cause registration problems in chip placement as well as solder joint failure. Therefore, it has extremely theoretic and practical significant that using the finite element software, ANSYS, the whole process of the reflow soldering of PCBA is simulated by three-dimensional modeling, and thermomechanical analysis of PCBA is deeply carried out for the thermal shock of PCBA in the process of the reflow soldering to find out the most essential reason of warpage for avoiding and reducing the warpage problem of PCBA. In this paper, the laminated board basic theory of compound material mechanics is used to analyzed the thermal strain and the thermal stress of the PCB, and model the warpage of the laminated board under one certain restrict condition. Besides, that the temperature field and the thermal deformation of the PCBA happened in the process of the reflow soldering are modeled by using the finite element method. Furthermore, the soldering process of PCBA in the whole infrared reflow soldering stove is modeled by the finite element software, ANSYS, and is simulated by the three-dimensional modelling. The result of research obtains that: In the process of the reflow soldering, 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, the radical reason of PCBA deformation is deeply analyzed, and the conclusion is that the thermal expansion coefficients of the composing materials of PCBA are different; In the process of reflow soldering, when PCBA comes through different temperature sections to be heated, the distribution of temperature field is asymmetric. Furthermore, because of the difference of the thermal expansion coefficients of the FR-4, the copper foil and the PLCC, each area of PCBA can not expand and shrink freely, which produces heat stress. Both of these result in the warpage deformation of the PCBA; When the PCBA is heated in each temperature section, with the process of time the temperature field of PCBA changed, which causes the change of heat stress. It induces that the warpage of PCBA are different in each temperature section and each period of time. The maximal deformation occurred in the transition from reflow soldering section to cooling section and mostly affected...