Mechanism research of shaping microlens array and packaging failure

Jinghong Lu

Shanghai Ultra-precision Optical Manufacturing Engineering Center,

Department of Optical Science and Engineering, Fudan University, Shanghai 200433, China

Abstract

The optical components having complex functions used in precision optics are increasingly small in sizes, which entails particular challenges for the precision production. Conventionally, the high-precision glass-based optical components with a large size can be manufactured via the processes of ultra-precision grinding and polishing economically, however, for the optical components with micro-size and periodical structures, e.g., diffractive optical elements, microlens arrays and so on, the standard manufacturing processes become largely time-consumed and thus costly. As an alternate, the introduction of the precision glass molding (PCM) method has proved to be an effective and economical industrial production-process to produce high-volume and high-precision periodical micro-structures. In this paper, the PCM process for spherical glass-lens arrays was investigated by the finite element method (FEM). From the investigations of the distribution of residual stress, the optimum PCM parameters, e. g. the molding temperature, the molding time and the thickness of glass blank, were obtained, which were found to be 570,114s and 6µm, respectively.

With the increasing market demand and the shrinking pixel of the imaging sensor, the wafer level chip scale packaging (WLCSP) technology has attracted lots of attention recently. The WLCSP technology can cut the cost and reduce the difficulty of the packaging through redistribution line (RDL) and without using under filler which is indispensable in traditional flip-chip technology. However, in the process of the WLCSP assembly, the fatigue crack will be formed within the solders and continue growth with the change of the temperature, and eventually lead to failure due to the mismatching of the coefficient of thermal expansion (CTE) among the constituent materials used in WLCSP. Therefore much effort has been paid to investigate the crack mechanism in the WLCSP process or other effective packaging technology, by experiments or the numerical simulations. In this work, the effects of under bump metallurgy (UBM) materials, solder alloy, and the thickness of the UBM layers on the crack in the WLCSP is investigated by finite element method (FEM).The finite element method (FEM) is employed to investigate the solder crack mechanism in wafer-level chip-scale packaging (WLCSP). The location of the initial crack is calculated and the numerical results are compared to the experimental ones. Moreover, the FEM model is used subsequently to obtain the J-integral as well, a major factor to predict the initial crack growth in solder. This paper investigates the following three aspects, e.g. under-bump metallurgy (UBM) materials, solder alloy, and the thickness of the UBM layers, respectively. By numerical simulations, it is concluded that the 96.5Sn3.5Ag solder and the Au-Ni-Cu-Ti UBM material show an excellent performance in the initial crack growth.

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The Study of Si-ncs on structure, photoluminescence and application in photovoltaic solar cells

Yanli Li

To improve the light emission of silicon is the foundation for the development of silicon-based optoelectronic device and the realization of silicon-based optoelectronic integration. To build the nanostructure is an important method for the enhancement of silicon luminescence. Room temperature visible light emission from porous silicon（PS）and nanocrystal silicon （Si-nc）has opened a new era for optoelectronic integration based on Si. However for PS, the reactivity and fragile due to its porosity and possible pollution from its fabrication process prevent its practical applications in optoelectronical devices. While Si nanocrystals embedded in a SiO₂ matrix (Si-ncs/SiO₂) are considered as one of the most promising Si based light-emitting materials due to their appreciable and stable light emission as well as their robust structure.

Si-ncs/ SiO₂ can be made by many different approaches and the most widely used one is based on phase separation and recrystallization.Sub-stoichiometric silica films （SiO_x）were deposited by different methods and annealed at 1100℃in nitrogen ambient to form Si-ncs/ SiO₂ . In this thesis, we fabricated Si-ncs/ SiO₂ by reactive pulsed laser deposition with subsequent thermal annealing in an inert nitrogen atmosphere. Strong PL was observed at room temperature from Si nanocrystals  with an average diameter of about 5nm at 325nm light excitation. We find that samples deposited in 0.7Pa O₂  after annealing at 1100℃ have the maximum intensity of PL.

The PL intensity can be enhanced by many different approaches. We can take advantage of the superlattices structure or passivate the non-radiative defect centers. There are many methods usually used to suppress the non-radiative recombination channel, such as the hydrogen passivation, oxygen passivation, metal passivation and so on. The PL intensities are enhanced by 2-fold or more in our research with hydrogen passivation and air passivation. Metal and oxygen passivation is further experiments.

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Optical Control of Surface Anchoring and Reorientation of Liquid Crystals via a Plasmon-Enhanced Local Field

施巍

摘要：

纳米光子学研究纳米材料与物质的相互作用，是一门新兴学科。在纳米光子学中，金属纳米材料是最受研究关注的材料，利用金属纳米材料表面等离激元共振效应突破传统光学衍射极限，可以实现微电子与光子在同一芯片上的集成。此外，金属纳米材料表面等离激元共振效应可以增强荧光分子辐射效率，控制纳米颗粒取向和转动，是改变物质物理光学性质的理想选择。本文围绕金纳米颗粒局域表面等离激元共振效应对定向液晶盒中液晶分子光致取向增强效应进行了深入地探讨和研究。发现经金纳米颗粒修饰的液晶盒定向层受到与局域等离激元共振的激光辐照时，会有效降低液晶的锚定能。利用这一新的效应，观察到对应液晶分子转动的光学Fréedericksz相变阈值下降1-2个量级。该效应也使液晶分子响应的动力学过程发生改变，缩短了液晶盒的光响应时间。

Abstract：

Gold nanoparticles deposited on the windows of a liquid crystal (LC) cell were found to be able to reduce the surface anchoring energy of the LC, and hence the threshold for its reorientation phase transition, by 1 to 2 orders of magnitude when a cw pump light was used to excite the local plasmon resonance of the nanoparticles. The effect was due to the disorientation of LC molecules between nanoparticles by the plasmon-enhanced local field that softens the effective surface anchoring. A lightcontrolled variation of surface anchoring energy could provide new opportunities for optoelectronic applications of a LC.

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