In recent years, the rapid development of the LED industry has led to a diversified development trend in the packaging structure of LEDs. In the direction of miniaturization, CSP LEDs came into being. During the development process, the market for Top-view CSP gradually formed, but the white wall enclosure limited its light extraction rate. In this paper, from the analysis and improvement of the process structure, a kind of enhanced single-sided CSP is proposed, which converts the original side light into a side light, which guides the light and improves the CSP light extraction efficiency. And the feasibility is analyzed from the process.
1 Introduction
As a simple LED package product, CSP has been in full swing in recent years. At the beginning, the focus was on the characteristics of its substrate-free and bond-free wires. This package structure can greatly reduce the packaging process and material costs. The square and the uniform thickness of the fluorescent layer determines the excellent light output consistency of the CSP product. The compact size allows the CSP to have flexible design features on the application side and to meet highly integrated design requirements. Therefore, CSP has attracted the attention of many investors, research institutions and companies [1, 2].
And its shape has developed different structural and morphological characteristics with the application end requirements. The original CSP was developed from the traditional single-sided LED PLC and QFN package form to the five-sided CSP. The five-sided CSP product has high luminous efficiency, low light loss, and a near-field illumination angle of nearly 180°, which is suitable for lighting. However, in the field of backlighting, the lens design for the five-sided light-emitting CSP is difficult, and the blue leakage at the bottom of the five-sided CSP affects the backlight effect. In order to adapt to the application requirements and expand the functional structure, the development of CSP has turned to the trend of reducing the luminous surface, resulting in a single-sided luminous CSP form. However, as the white wall glue blocks the light from the CSP, the CSP front light output efficiency will drop by 10-15%. This paper aims to propose a structure and fabrication method of Top-view CSP, which improves the extraction efficiency of single-sided luminescent CSP.
Figure 1 Five-sided luminous CSP and light distribution curve simulation
2. Top-view CSP structure development
The earliest type of single-sided luminescent CSP was derived from the chip end and was cut after the fluorescent glue coating process on the flip chip wafer. Since the side of the chip is completely untreated, the side leakage blue is very serious. In view of this problem, there are very few applications for such products on the market.
Figure 2 First stage Top-view CSP
In the second stage of the Top-view CSP, the side wall of the flip-chip LED chip was directly shielded by the white wall glue, which caused the problem of low light extraction efficiency. In particular, the a-type structure is based on the development of the first-stage single-sided luminescent CSP. Since the side of the fluorescent glue is also occluded, the light extraction efficiency is greatly reduced; and the fluorescent glue of the b and c products is completely pressed on the chip and the white wall. Above the glue, it is actually an incomplete single-sided light-emitting CSP structure. Although the fluorescent adhesive layer is only 0.1-0.17mm, there is still light leakage in the horizontal direction.
Figure 3 Second stage Top-view CSP
The third-stage Top-view CSP is currently the most common category on the market, with products in this form in Korea, Taiwan, and the mainland. Such products are derived from the five-sided CSP. Since the light emitted from the front side and the side of the chip can be directly excited into the fluorescent glue, the white light conversion efficiency is improved and the light efficiency is improved. However, this product is surrounded by the vertical white wall rubber side wall, and there is still a lot of room for improvement in light extraction.
Figure 4 The third stage Top-view CSP
25*50mm Low Profile White Faceplate
included or excluded keystones for Keystones, or designed with PC board
fixtures and fittings provided
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