Thermal resistance and optical performance of SMD LEDs with traditional package and chip scale package

Light-emitting diodes (LEDs) have been widely used in many fields. As a new packaging form, LED with chips scale package (CSP) has received more and more attention. The heat dissipation of LED devices is the main problem that restricts the application of LED, especially for 2835 Surface Mounted Devices（SMD）LEDs. In this paper, traditional packaging and CSP packaging methods have been used in 2835 SMD LEDs, and the changes of thermal resistance, spectrum, color temperature and color coordinates of the samples under different temperature and current have been studied. The thermal resistance results indicate that the 2835 SMD LEDs with CSP package has better temperature and current stability than that with traditional package. The 2835 SMD LEDs with CSP package have better spectral integrity at different current and temperature condition. The color temperature of the two samples almost changes linearly with increasing current or temperature. The result indicates that the blue light emission from the blue LED chip increases with current increase, which leads to shifting in the chromaticity coordinates to the blue portion in the chromaticity diagram that known as a blue shift mechanism for 2835 SMD LEDs with traditional package. On the contrary, the chromaticity coordinate X of 2835 SMD LEDs with CSP package have increased, which mainly attributed to the reduction of photon reabsorption. The long wavelength phosphor stimulated by more blue light as well as purple light with increasing intensity of current, so the color coordinates moved to the red region.