Packaging design for improving the uniformity of Chip scale package (CSP) LED luminescence. (July 2021)

• Record Type: Journal Article
• Authors: Jiang, Nan; Liu, Huizi; Zou, Jun; Guo, Chunfeng; Li, Wenbo; Shi, Mingming; Yang, Bobo; Liu, Yiming; Guo, Bin
• Is Part Of: Microelectronics and reliability. Volume 122(2021)
• Publication Date: 2021-07
• Subjects: Chip scale packages -- Flip-chip LED -- Light intensity distribution -- Fabrication technology; Electronic apparatus and appliances -- Reliability -- Periodicals; Miniature electronic equipment -- Periodicals; Appareils électroniques -- Fiabilité -- Périodiques; Équipement électronique miniaturisé -- Périodiques; Electronic apparatus and appliances -- Reliability; Miniature electronic equipment; Periodicals; 621.3815
• DOI: 10.1016/j.microrel.2021.114136
• Languages: English
• ISSNs: 0026-2714

Abstract

Abstract: In order to realize small package size, uniform performance and high manufacture efficiency, a chip scale packaging (CSP) technology has been developed by controlling the thickness of the phosphor film in this paper. Five CSP LEDs with different thicknesses of 4 side faces are prepared. Optical tests and thermal simulations were carried out to evaluate the performance of the five samples. The measurement results indicate that: 1) When the absorption of the blue light reached a certain extent, the luminous flux and correlated color temperature gradually decreased with the increase of the thickness of the film; 2) the color temperature of the CSP LED will reach the best uniformity when the ratio of thickness of top film to that of side film is close to 2:1; 3) when the ratio of thickness of top film to that of side film is not less than 2:1, the effective light angle can reach about 160°; 4) the thermal management for prepared CSP samples shows a slight decrease in temperature as the side film's thickness increases; 5) the aging test result shows that the thinner the package thickness is, the stronger the aging resistance will be. Highlights: A new chip scale package process has opened up our understanding of chip scale package, with this special process, we can arbitrarily change the package thickness of any light-emitting surfaces of the chip, therefore, the specific light-emitting demand can be achieved by controlling the ratio of the top surface package thickness to the side package thickness. Experimental results show that this method of packaging with fluorescent film pressing and cutting can get a different light distribution curve, namely, saddle shaped light distribution, which means that this kind of CSP LEDs has a wider light angle than the traditional packaging. Especially when the upper surface film thickness and the side film thickness ratio are not less than the 2:1, the effective luminous angle can reach about 160°, The results also show that when the ratio of the upper surface package thickness and side package thickness reaches 2:1, the correlated color temperature change at a different angle of the CSP LED can be the minimum, close to 7%, What's more, when the concentration of the phosphor in the encapsulated film is the same, the decrease of the thickness of the film can not only lead to the increase of temperature but also the increase of anti-aging ability. In summary, we conclude that when the surface thickness and the thickness of the package side reaches 2:1, the CSP LED can achieve a wide light-emitting angle, the most uniform correlated color temperature distribution, relatively uniform temperature distribution, and an acceptable anti aging capacity.