不同引线数QFP器件焊点等效应力的数值模拟

Simulation on equivalent stress in soldered joints of QFP devices with different leads

关键词:  有限元法  等效应力  寿命预测  四边扁平封装

Key words:  finite element method  equivalent stress  life prediction  quad flat package

摘要:

采用有限元方法对不同引线数QFP器件焊点的等效应力进行了数值模拟,研究发现,热循环后的PCB板有向外翘曲趋势,但变形较小;陶瓷基板上翘趋势较大,总体变形较明显,且其对引线的拉伸力会加剧焊点裂纹的扩展。在最外侧存在焊点最大应变值,QFP器件鸥翼形引线焊点的焊点根部与焊趾处等效应力较大,焊点根部等效应力比焊趾处大,中间区域等效应力最小。理论计算显示QFP100器件应力最小,QFP48次之,QFP32应力最大。焊点拉伸试验结果显示QFP100器件抗拉强度最大,QFP48次之,QFP32最小,与数值模拟结果完全吻合。

Abstract:

Finite element method was used to simulate residual stress in soldered joints of QFP devices with different leads.Results indicate that the PCB is warped outward, but the distortion is small.The ceramic plate is warped upward and the distortion of its integral structure is obvious after thermal cycle.At the same time, the expending of the crack in soldered joint will be aggravated for the pull stress from ceramic plate to the lead. The largest strain value emerges in outside of the soldered joints.The equivalent stress is relatively large in the root and toe of the soldered joint of QFP gull wing lead that the stress is larger in the root than that in the toe, but that in the middle area of the soldered joint is the least.The simulating results show that the largest stress was endured by the soldered joint of QFP with 32 leads, larger stress endured by the soldered joint of QFP with 48 leads, and the least stress endured by the QFP with 100 leads.The tensile test shows that the soldered joint of the QFP device with 100 leads possesses the biggest tensile strength than that of the QFP with 48 leads and the QFP with 32 leads, which is concordant with the numerical simulation results.