Finite element analysis on soldered joint reliability of QFN device

Quarter models of QFN(quad flat non-leaded) were set-up by means of ANSYS software, Anand model was used to establish the constitutive equation of Sn3.0Ag0.5Cu solder, and the reliability of QFN with different solder joint shape was presented.The results indicate that the maximum value of stress is at the package corner, which value change is cyclical and additive.The solder joint reliability of leads with pullback design is poorer than that of the leads non-pullback design that cannot influence the value of plastic work caused by the solder fillet length and land length significantly.The effect of solder thickness is very obviously, and the average plastic work is inversely proportional to solder thickness.The area of center pad soldering has considerable effect to the solder joint reliability, and the size of the area could be increased appropriately in the reflow soldering process.