Finite Element Analysis On Reliability Of Vertical Interconnection Of 3D Packaging Power Module

Power module is one of the most important components in power electronic system. With the rapid development of large-scale and ultra-large-scale integrated circuit technology, new electronic materials technology, as well as the Si P(System in Package) technology, people put forward higher requirements for the package of power module. It is quite different from the solder joints in a 2D packaging module that in a 3D-Si P power module using vertical interconnection technology between substrates, solder joints not only interconnect the circuit, but also provide mechanical support for the stacked structure. Solder joints need to withstand mechanical shock, vibration and other reliability problems. In addition, with the increase of packaging density, the heat generated by the circuit is more difficult to dissipate, which makes the solder joints bearing more stress caused by the CTE(Coefficient of Thermal Expansion) mismatch. All of these put forward higher requirements for the reliability of the solder joints in a 3D-Si P power module. Power module packages with smaller size, higher performance, and higher reliability play a pivotal role in both civilian use and military purposes. Especially for aerospace electronics field, in which the electronics modules need to be more reliable and bear greater environment stress, the reliability of the vertical interconnected structure of the 3D packaging power module is more important.In this paper, finite element simulation method was used to study the reliability of the 3D-Si P power module with vertical interconnected substrates in thermal cycling test and constant acceleration test based on the finite element simulation platform ANSYS 15.0. The viscoplastic properties of the solder were studied. After that, APDL(ANSYS Parameter Design Language) was used in the modeling task of the package structure. The temperature distribution, the law of deformation and stress change, as well as solder joint life prediction were studied in the thermal cycling test. Besides, the law of deformation and the law of stress and strain change in the constant acceleration test were analyzed. At last, the parameters of the 3D package structure were optimized.The results showed that the packaging structure had a periodic deformation during the thermal cycling test. The upper solder joints were mainly affected by the tilt of the transition board and the bending of the upper substrate, and the von Mises stress in the middle position was higher than that of the edge position. By contrast, the lower solder joints were mainly affected by the tilt of the transition board and CTE mismatch between transition board and DBC(Direct Bonded Copper) substrate, and the von Mises in the edge position was higher than that of the middle position. The weakest position of the package was at the corner of the lower solder joints where the thermal fatigue life of the joint was the lowest, and more stress concentrated at the interface between the solder joints and DBC substrate. In each cycle, the maximum von Mises stress of the solder joints was gradually increased. The stress relaxation and the increase of the plastic strain at high temperature was significantly higher than that at low temperature. In the constant acceleration test, the weakest position of the package was at the corner of the upper joints, and more stress concentrated at the interface between the solder joints and upper substrate. The maximum von Mises stress of the weakest element appeared at the end of the acceleration phase, while the maximum von Mises plastic strain was at the end of the uniform phase and the maximum plastic strain energy density was at the end of the decelerating phase. The results of packaging structure optimization showed that joints with tall and slender shape(smaller diameters and larger heights of solder balls, and larger diameters of pads) had higher reliability in thermal cycling test, while joints with bigger overall size(larger diameters and heights of solder balls and larger diameters of pad) had higher reliability in constant acceleration test. According this rule, the optimized parameters of the package were proposed and the reliability test obtained expected results.