功率LED芯片表面微结构陶瓷薄膜衬底加工机理

LED (Light-emitting diode) is regarded as a new generation green light source. To solve the challenging technical problems inhered in power LED flip-chip in chip scale packaging (CSP), such as poor bonding between chip and substrate, thermal-mechanical stress damage, high heat flux dissipating and precise preparation of phosphor coating, this project proposes power LED flip-chip in CSP based on ceramic thin film substrate with surface microstructure and its semi-packaged chip array cutting precisely. The effect of the surface microstructure on wettability of interface between substrate and AuSn is investigated. The design theory and optimization method for the ceramic thin film substrate with surface microstructure are established to target for high eutectic soldering strength and interfacial bond strength between copper coating and substrate, low thermal mechanical stress and heat resistance. To achieve collaborative manufacturing of ceramic thin film substrate with high integrity and its surface microstructure, the forming mechanism surface microstructure and its machining conditions are obtained by investigating the effect of edge radius of abrasive particle, multiple stress field coupling and residual stress on brittle-ductile transition of ceramic substrate. The macroscopic deformation mechanism and crack initiation and propagation laws of ceramic thin film substrate coated phosphor layer are investigate to disclose the forming mechanisms of edge chippings and “burrs” during ceramic thin film substrate cutting. On the above bases, the fundamental theory on design, collaborative manufacturing and precision cutting of ceramic thin film substrate with surface microstructure is constructed to provide theoretical foundation and technical support for the innovation and development of LED.

LED是新一代绿色光源。项目针对功率LED倒装-芯片尺寸封装存在的芯片与衬底联结不良、热-机械应力损伤、高热流密度散热、荧光涂层精密制备等技术难题，提出表面具有微结构的陶瓷薄膜衬底的倒装-芯片尺寸封装及其半封装芯片阵列精密切割。研究微结构对衬底表面与熔融金锡合金润湿性的影响，以高的共晶焊接强度和镀铜层-衬底界面粘结强度、低的热-机械应力和热阻为目标，建立陶瓷薄膜衬底及其表面微结构设计理论与优化方法；研究磨粒刃圆半径、多应力场耦合作用和残余应力对陶瓷衬底脆塑转变的影响，研究微结构生成机理和条件，实现陶瓷衬底磨削减薄及其表面微结构协同制造；研究荧光涂层覆盖下的陶瓷薄膜衬底宏观变形机制及裂纹产生和扩展规律，揭示陶瓷薄膜衬底切割时边崩、“毛刺”的形成机理。构建陶瓷薄膜衬底及其表面微结构设计、协同制造、精密切割基础理论，为我国功率LED的创新发展提供理论与技术基础。

LED以其节能、环保、高效、寿命长、光色可调等优点，已成为显示、照明等新一代绿色光源。但LED功率器件由于极高的热流密度极易导致芯片失效甚至烧毁。氮化铝AlN陶瓷热导率高、耐热震，具有优良的介电性能和与单晶硅匹配的热膨胀系数等优点使其成为LED功率器件封装基板理想材料。但氮化铝陶瓷基板硬度高、脆性大，极难加工；且由于润湿性差，易出现焊接空洞，热阻增大导致器件失效，降低产品可靠性等问题。针对这些问题，本研究围绕陶瓷薄膜衬底表面微结构设计与优化、加工机理与形貌控制、LED胶体模压半封装芯片阵列精密切割以及其器件可靠性四个方面展开研究。主要研究内容如下：. 采用压/划痕实验与分子动力学模拟探究AlN陶瓷的加工及去除机理研究。通过压痕实验分析在晶粒各向异性影响下的裂纹产生、扩展规律以及材料塑性流动规律。探究划痕过程中氮化铝陶瓷表面/亚表面的形成特征及材料的各向异性去除机制，并通过分子动力学对不同晶体取向氮化铝陶瓷的变形特征进行分析。建立考虑晶粒各向异性的弹性回复率预测模型以及考虑弹性回复、压头形状的临界深度模型。同时开展玻璃基板表面微结构加工机理研究，在脆性域以及脆塑转变临界区进行先后双刻划实验，揭示划痕之间的裂纹相互影响机制。 . 预加工的微结构表面，通过SEM、AFM等手段表征微结构形貌，采用接触角测定仪测定不同微结构的表面接触角，探究其亲水性。并通过机械加工方法加工出同等粗糙的表面，进行熔融金锡合金浸润性测试。.利用磨削运动学模拟，针对不同的磨粒形状、磨粒排布以及磨粒大小的随机性对磨削过程的影响进行分析。通过逆向分析得到的最优化的排布准则以及磨削力、热、应力和未变形切削厚度的分析。采用激光精密修饰的方法获得优化排布后的有序砂轮，进行磨削实验研究，得到磨粒排布角度与间距对表面形貌的影响。.建立基于表面具有微结构的陶瓷薄膜衬底的功率LED倒装-芯片尺寸封装器件的热-机械应力空间分布模型和三维热分析模型，测试LED器件的光效，功率等性能参数。