Quad Flat No-leads (QFN) packaging is one of the most commonly used packaging types for microelectronic devices due to its outstanding thermal performance. However, it is difficult to analyze the thermal performance of QFN packaging because numerical simulations and experiments often require a large amount of time and resources. In this work, an analytical thermal resistance network model for calculating the mean die temperature of eccentric QFN packaging on the printed circuit board (PCB) is presented. Based on the heat dissipation path from the die to ambient, the thermal resistance network is established. The analytical solution of the mean die temperature of QFN packaging is obtained by the analytical expressions of each thermal resistance in the thermal resistance network. Simulations by commercial software ANSYS provide a reference for verification of the present model. The comparison of the results between simulation and analytical solution shows that the network model can calculate the mean die temperature of QFN packaging accurately over wide ranges of PCB’s thermal conductivity and heat transfer coefficient, and the maximum relative error is only 4.73%. The present model is fast and resource-saving to predict the mean die temperature of QFN packaging; moreover, it provides an optimization method for QFN packaging design to achieve good reliability.

Modified polyimide (MPI) flexible printed circuits (FPCs) are used as chip carrier boards. The quality of the FPC directly affects the reliability of the integrated circuit. Furthermore, micro-holes are critical components of FPCs. In this study, an ultraviolet (UV) femtosecond laser is used to drill micro-holes in double-layer flexible circuit boards with MPI as the substrate. The morphology of the micro-hole wall in the copper foil and MPI layer is observed, and the effects of the laser processing parameters on the diameter and depth of the micro-holes are analyzed. The drilling process and mechanism of micro-holes obtained using a UV femtosecond laser in MPI FPCs are discussed. The results show that the morphology of femtosecond laser-machined copper is closely related to the laser energy, and a periodic structure is observed during the machining process. Copper, MPI, and copper oxides are the most common molten deposits in micro-holes during drilling. The depth of the micro-holes increases with an increase in the energy of a single pulse, scanning time, and scanning overlap rate of the laser beam. However, the diameter exhibits no discernible alteration. The material removal rate increased significantly when laser processing was applied to the MPI resin layer.

In order to ensure the reliability of high heat-flux electronic devices, vapor chambers with double-sided uniform radial micro-grooved wicks (DURM) are developed. The driving force model of the working liquid inside the DURM vapor chamber is established. To enhance the driving force of the working liquid, the condensation micro-grooves and evaporation micro-grooves of the DURM vapor chamber are fabricated using an ultraviolet laser and an infrared laser, respectively. In addition, the startup characteristics and temperature uniformity of the DURM vapor chamber and the effect of the depth–width ratio and radiation angle of the micro-grooves and the filling ratio of the DURM vapor chamber on its thermal performance are also investigated. The results indicate that the DURM vapor chamber could maintain good temperature uniformity. Both the evaporation micro-grooved and condensation micro-grooved wicks facilitate the enhancement of the thermal performance of the vapor chamber. The double-sided micro-grooved wick with a larger depth–width ratio and a smaller radiation angle improves the thermal performance of the DURM vapor chamber. However, when the radiation angle is lower than 4°, further reducing the radiation angle has little effect on improving the thermal performance. In addition, an appropriate filling ratio helps reduce the thermal resistance of the vapor chamber under a certain heat load.