CQFP器件板级温循可靠性的设计与仿真

温度循环是考核封装产品板级可靠性的重要试验之一。陶瓷四边引脚扁平封装(CQFP)适用于表面贴装,由于陶瓷材料与PCB热膨胀系数的差异,温循过程中引线互联部分产生周期性的应力应变,当陶瓷壳体面积较大时,焊点易出现疲劳失效现象。CQFP引线成形方式分顶部成形和底部成形两类。针对CQFP引线底部成形产品在板级温循中出现的焊接层开裂现象,采用有限元方法对焊接层的疲劳寿命进行了预测分析。采用二次成形方法对引线进行再次成形以缓解和释放热失配产生的应力。仿真和试验结果显示,引线二次成形有利于提高焊接层的温循疲劳寿命。与引线底部成形相比,当引线采用顶部成形时,焊接层的温循疲劳寿命显著提高。

Design and Simulation of Board Level Reliability for CQFP Device in Thermal Cycling

Thermal cycling is an important test for board level reliability analysis of IC packages. Ceramic Quad Flat Package(CQFP)is mostly used for surface mounting applications. Due to the thermal expansion coefficient difference, periodic strain and stress occurs on the solder joints which may cause the solder joint fatigue failure when the package area is large. Lead forming could be realized from the upper side or the underside of the ceramic. Solder joint cracking was observed for a CQFP product with lead forming from the downside in thermal cycling, and Finite Element Method(FEM)is used to predict the fatigue life of the solder joint. Lead shape is optimized with the secondary forming method to alleviate the thermal stress. Both the simulation and test results show that the secondary method is effective in improving the board level reliability of CQFP device. When the lead forming starts from the upper side of the ceramic, there is a significant improvement in solder joint fatigue life.