PCB焊点热循环失效分析和改进设计

针对PCB（印制电路板）焊点在高低温热循环下的失效，建立了传统结构的三维模型和在芯片边角下加锡块的改进设计模型，通过实验测得FR-4的弹性模量和热膨胀系数，用ANSYS计算了PCB在高低温循环下的应力应变，并用修正的Coffin-Manson经验方程计算了焊点的热循环寿命。结果表明，通过在芯片边角下加锡块，PCB焊点的最大等效塑性应变显著降低，其热疲劳寿命得到明显提高.

Fatigue Failure Analysis and Structural Improvement of PCB Solder Joints Under Thermal Cycles

To investigate the fatigue failure of PCB solder joints under thermal impact cycles, a 3D finite element model of PCB with the traditional structure was built. For comparison, an improved structural model with solder pads added at the QFN corners was also built. Based on the measurement of Young’s moduli and thermal expansion coefficients of FR 4 by experiment, the thermo mechanical FE analysis was conducted on the 2 models in ANSYS. The thermal fatigue life of the PCB solder joints was evaluated by means of the modified Coffin Manson equation according to the FEA results. It is found that the peak equivalent plastic strain at the PCB solder joints is significantly reduced after addition of the solder pads at the QFN corners, and the thermal fatigue life of the PCB solder joints was thus greatly improved.