Phosphor settling phenomena exists during the phosphor coating process in the light emitting diode (LED) packaging industry. It is perceived that phosphor settling will affect the concentration of the phosphor, and consequently the concentration will influence the optical performance of phosphor-converted white LED light source. In this paper, an experiment based on the real packaging process was conducted to investigate the phosphor settling phenomena. It was found that the concentration variation of the phosphor embedded in the silicone matrix was very small (less than 1%). Based on the observation of the experiments, the effect of the phosphor settling in the silicone matrix on light extraction efficiency (LEE), correlated color temperature (CCT), angular color uniformity (ACU) and light intensity distribution curve (LIDC) was investigated and discussed by the three dimensional Monte Carlo ray-tracing simulations. It was discovered that the effect of the phosphor settling on the optical performance could be neglected when using the present packaging process.Highlights► Phosphor settling was studied by experiments based on the real packaging process. ► The concentration variation of the phosphor embedded in silicone was very small. ► Optical effects of phosphor settling at room temperature curing can be neglected. ► Some suggestions to the LED packaging industry were also provided.

Effects of tilt angles of reflective cup structure and phosphor surface geometries on light extraction efficiency and angular color uniformity (ACU) of phosphor converted light emitting diodes (pcLED) are investigated by Monte Carlo ray-tracing simulations. It is found that tilt angles of reflective cup and phosphor surface geometries affect the light extraction efficiency and the ACU distinctly. When the tilt angle varied from 60° to 15°, the light extraction efficiency of LED can achieve the improvements of 13.87%, 18.25% and 14.79% respectively, when the phosphor surface geometry is concave, flat and convex, respectively. It is also found the variety law of phosphor concentrations with the change of tilt angles and phosphor surface geometries to maintain a fixed correlated color temperature (CCT).

Optical constants, including scattering coefficient, absorption coefficient, asymmetry parameter and reduced scattering coefficient, of cerium-doped yttrium aluminium garnets (YAG:Ce) phosphor blended with SiO2 particle for white light-emitting diode (LED) packages were calculated based on Mie theory in this study. Calculation processes were presented in detail. Variations of the optical constants with the changes of phosphor weight fraction, dopant weight fraction, phosphor particle radius and SiO2 particle radius, were shown and analyzed separately. It was found that the asymmetry parameter is the intrinsic characteristic of the particles, and the increase of the phosphor weight fraction (or concentration) will lead to the increase of the optical constants. It was also discovered that the increase of the dopant weight fraction will enhance the scattering coefficient, but result in the decreases of the reduced scattering coefficient and the absorption coefficient.

An analytical thermal resistance network model is developed for calculating mean die temperature of a typical BGA packaging. The thermal resistance network is established based on heat dissipation paths from die to ambient. Every thermal resistance in the network can be calculated by analytical expressions. The proposed model is applied to a typical BGA packaging. Simulations to obtain the die temperature of the packaging were also done by COMSOL. The data comparison shows that the mean die temperatures calculated by the present model are very close to the ones obtained by simulations. It is demonstrated that the proposed model can be used to predict the mean die temperature of BGA packaging accurately. This proposed model is simple and resource-saving for the semi-conductor industry to predict the mean die temperature of typical BGA packaging and also it provides an optimization method to choose materials for good thermal management of BGA packaging.

Quite a few MEMS devices need vacuum packaging technology to guarantee the desirable performance. Developing an absolute vacuum environment for those devices is indispensable. However, it is difficult to monitor the pressure change in vacuum chamber in on-line and real-time mode. A surface micro-machined Pirani gauge for measuring vacuum pressure inside vacuum packaging in wafer level was presented in this paper. It was designed with a simplified structure and did not need complex circuit. Only a simple Wheatstone bridge circuit is needed, which could be manufactured by conventional CMOS processes. Preliminary tests on this device were conducted. The experimental results show that the Pirani gauge is capable of measuring pressures from atmospheric value to 1 Pa and has a very good linearity in the range from1 Pa to 300 Pa. It demonstrates that the micro-machined Pirani gauge has great potential to be used in wafer level vacuum packaging. Also, the Pirani gauge is able to be the packaging hermeticity detector.