MECHANICAL RELIABILITY AND THERMAL DESIGN STUDIES OF QFN PACKAGES
Authors: Dongji Xie, Ph.D., Younes Shabany, Ph.D., Jonathan Wang, and Sammy Yi Company: Flextronics Date Published: 10/11/2007
Abstract: In this paper, a design of experiment (DoE) was employed to characterize the center pad impact on electrical connection, thermal and mechanical performance. Both simulation and experimental work were performed and described in detail in this paper. The product is a wireless application module with fully function. Thermal modeling was conducted for the Quad flat no lead (QFN) in a wireless application. The results show a significant temperature rise without thermal pads and may not be usable for certain applications. As drop test and bending failures are the main failure mechanism for QFN, reliability assessment is focused on those two items. It is believed that the mechanical failure would be impacted greatly by the center pad area when they are soldered. Both numerical simulation and experimental work are performed and shown in this study. Assembly was done using a daisy chain package and different pad configuration in order to monitor the failure during drop and bending. It is shown from this work that thermal pads are necessary and preferred in the application of high power device and big package. However, partially soldering pads could be used to compromise the electrical, thermal and mechanical performance. A modified QFN structure is proposed to that application to ensure a better mechanical and thermal performance can be achieved.