基于焊点形态预测与塑性应变计算的工艺参数对QFP焊点可靠性影响分析

选取焊盘长度、焊盘宽度、钢网厚度和间隙高度4个工艺参数作为关键因素,采用水平正交表L25(56)设计了25种不同参数组合的208脚、0.5mm引脚间距四方扁平封装(Quad Flat Package:QFP)器件焊点;建立了这25种焊点的三维形态预测模型和三维有限元分析模型;对热循环加载条件下QFP焊点进行了非线性有限元分析,基于塑性应变采用Coffin-Manson方程计算了25种不同焊点形态的QFP焊点热疲劳寿命;针对热疲劳寿命计算结果,进行了极差分析与方差分析。结果表明,最优的工艺参数组合为焊盘长度1.25mm,焊盘宽度0.30mm,钢网厚度0.125mm,间隙高度0.05mm;在置信度为90%的情况下,焊盘长度对QFP焊点可靠性具有显著影响而焊盘宽度、钢网厚度、间隙高度对可靠性无显著影响。

Study on the impact of process parameters on the reliability of quad flat package solder joints based on shape prediction and plastic strain calculation

The pad length,the pad width,the stencil thickness and the stand-off were selected as four control factors.By using an L_(25)(5~6) orthogonal array,the solder joints of a 0.5mm lead pitch,208-pin quad flat package(QFP) component which have 25 different process parameters' levels combinations were designed.The 3D shape prediction models and the 3D finite element analysis models of all the 25 QFP solder joints were developed.Using ANSYS performed the nonlinear finite element analysis of the QFP solder joints under thermal cycles.The thermal fatigue life of QFP solder joint was calculated using Coffin-Manson equation based on the plastic strain.Based on the calculated thermal fatigue life results,the range analysis and the variance analysis were performed.The results of study show that the best level combination of process parameters that results in the longest fatigue life is the pad length of 1.25mm,the pad width of 0.30mm,the stand-off of 0.05mm and the stencil thickness of 0.125mm.With 90% confidence the pad length has a significant effect on the reliability of QFP solder joints whereas the pad width,the stand-off and the stencil thickness have little effect on the reliability of QFP solder joints.