QFN封装分层失效与湿-热仿真分析

Simulation Analysis of Delamination Failure and Thermal-Moisture for QFN Package

采用湿度敏感度评价试验及湿-热仿真方法,分析了温湿度对于QFN封装分层失效的影响。通过C-SAM和SEM等观察发现,QFN存在多种分层形式,分层大多发生在封装内部材料的界面上,包括封装塑封材料和芯片之间的界面、塑封材料和框架之间的界面等。此外,在封装断面研磨的SEM图像上发现芯片粘结剂内部有空洞出现。利用有限元数值模拟的方法,对QFN封装的内部湿气扩散、回流过程中的热应力分布等进行了模拟,分析QFN分层失效的形成原因。结果表明,由于塑封器件材料、芯片、框架间CTE失配,器件在高温状态湿气扩散形成高气压条件下易产生分层。最后提出了改善QFN分层失效的措施。

Moisture sensitivity is used for evaluating the test and the wet-thermal simulation method,the effects of temperature and humidity on the failure of QFN package is analyzed.Several delamination modes are found by temperature humidity test with C-SAM and SEM methods,and most delamination are in the interface between different assembly materials,including the interface between mold compound and die and the other interface between mold compound and leadframe;a few voids are also appeared in the adhesive material.At the same time,FEA method was used to simulate the moisture diffusion,and thermal stress distribution in the process of reflow.The main reason of package＇s moisture absorption and delamination were researched by numerical simulation.The results indicate that moisture absorption,vapor pressure and CTE mismatch are the major driven force for interface delamination.Finally,resolutions for improving delamination failure of QFN are given.