【作者】 蔡志祥；

【导师】 曾晓雁；

【作者基本信息】 华中科技大学 ， 物理电子学， 2009， 博士

【摘要】 随着厚膜传感器不断向着微型化、集成化、非标准化方向的发展，厚膜传感器制造业迫切需要发展一种能在无掩膜的条件下，快速制备出小尺寸、高精度、高可靠性传感器的新技术。在国家“863”高技术研究发展计划资助项目和国家自然科学基金的资助下，本文在国内外率先提出微笔-激光复合直写快速制造厚膜传感器技术，实现了在陶瓷基板上集成制造厚膜温度传感器、微加热器和厚膜气敏传感器，并系统研究了复合直写过程中的关键科学问题。主要研究结果总结如下：本文将微笔直写技术与激光微熔覆电子浆料技术相结合，利用微笔直写技术将浆料按图形轨迹预置在基板上，烘干后，激光沿微笔运动轨迹对浆料进行加热，再用有机溶剂清洗激光未辐照区域，就得到所要图形。选用激光微熔覆作为微笔直写的后续工艺，不仅不需要将整个样品放炉中高温烧结，还可以进一步缩小微笔直写线条的线宽，制得更精细的图形。目前微笔直写后，激光微熔覆制得的厚膜PTC热敏电阻最小线宽为40μm。根据微笔-激光复合直写技术的基本特点，研究并开发出相应的复合直写设备。该设备主要由Nd：YAG准连续激光器、微笔直写系统和三维运动工作台组成。在机床Z轴上合理设计激光光路和微笔安装工位，将激光加工与微笔直写集成到同一台机床上，由数控系统控制工作平台的运动速度与方向，完成微笔直写和激光微熔覆工作。其中，控制系统采用“NC嵌入PC”型开放式数控结构，适应数控系统发展的潮流，使整个复合直写系统具有很大的灵活性和可移植性。配备了“旁轴CCD+监视器”的工件定位系统，采用直写标记法测定微笔与激光的相互坐标，确保不同加工工具加工轨迹重合。该系统还可以供其它激光精密加工使用。用流变学理论分析、建立了微笔直写电子浆料成型的理论模型。用正交实验的方法，对影响微笔直写线宽的主要工艺参数进行了排序，按主次顺序排列，依次为浆料粘度、直写速度、笔头内径、驱动气压、笔头端面到基板表面的垂直距离。影响膜厚的主要因素是笔头端面到基板表面的垂直距离。通过对厚膜PTC热敏电阻浆料、电热浆料和气敏浆料热分析，证明了功能电子浆料在激光微熔覆过程中的变化特征与炉中烧结相似。激光功率密度对功能电子浆料电性能影响规律与炉中烧结温度对其影响规律相似。激光微熔覆电子浆料的过程实质上就是激光与电子浆料的热耦合过程，过程中有液相出现，由于激光束与浆料作用的时间极短，该过程实质是瞬时液相烧结。激光强度分布的不均匀性会导致浆料膜层出现波状起伏的现象；膜层较厚时，冷却的不均匀会造成膜层表面开裂。系统地分析了激光微熔覆热敏电阻浆料、电热浆料和气敏浆料的质量控制规律。目前激光微熔覆制得的厚膜PTC热敏电阻电阻-温度系数可达2965×10^-6/℃，其性能与传统的炉中烧结相当。激光功率密度和后续热处理温度对PTC热敏电阻方阻和电阻温度系数影响较大，激光功率密度最佳值为1．5×10⁶W/cm²，后续热处理温度最佳值为400℃。激光微熔覆制备的微加热器加热温度最高可达到500℃，“螺旋”形微加热器升温、降温速度分别为7℃s^-1和4℃s^-1。激光功率的大小对SnO₂气敏膜的微观结构和气敏性能有重要的影响。激光微熔覆制备的气敏膜在工作温度250℃下对2000ppm酒精蒸汽的响应度最大，为8．6，其响应时间和恢复时间分别为7s和20s；传统烧结的气敏膜（膜厚为8．5μm）响应度为7．4，响应时间和恢复时间分别为10s和25s；并尝试用TO-6管对气敏传感器进行了封装，证明了微笔-激光复合直写的器件与传统封装工艺是相容的。本文所研究开发的微笔-激光复合直写技术开辟了一种快速、无掩模、制造效率高的柔性直写厚膜传感器新途径。该技术在新品研发和小批量非标生产厚膜传感器场合，比传统工艺方法生产成本更低，生产效率更高，具有十分广阔的发展空间和应用前景。更多还原

【Abstract】 With the development of thick-film sensors towards miniaturization, integration and non-standardization, it is very important to develop a new processing technology, which can rapidly fabricate sensor with small-size, high precision, high reliability and no mask. With the support of National "863" Hi-Tech Research & Development Program of China and National Natural Science Foundation of China, a method of thick-film sensor fabrication by Micropen-Laser hybrid direct writing technique was presented in this paper firstly. With this novel method, thick-film temperature sensor, microheater and gas sensor were fabricated directly on ceramic substrates. At the same time, the concerned key scientific problems on the hybrid direct writing fabrication were studied systematically. Following are the main results on the project:This novel method combined Micropen direct writing technology and laser microcaldding electronic paste technology. Firstly, electronic paste was direct written or deposited on substrate by Micropen according to the designed pattern. Then it was dried by a heater. After that the laser beam was utilized to irradiate the coating according to Micropen movement track. Finally, the un-irradiated paste was removed by organic solvent and the pattern was left. Laser microcladding was selected as a post process, which can be used not only to functionalize the component but also to generate the fine pattern. It does not require the patterns and substrate to be post processed at high temperatures. At present, the minimum line width of thick-film PTC thermistor fabricated by Micropen-Laser hybrid direct writing was 40μm.Novel special equipment for Micropen-Laser hybrid direct writing technology was developed and manufactured on the basis of hybrid direct writing characteristics. This equipment was composed of Nd:YAG lasers, Micropen direct-write system and a 3-dimensional worktable. Laser beam delivery system and Micropen were installed on Z-axis of equipment. The scanning speed and directions were controlled by a numeric control system, by which Micropen direct writing and laser micro cladding process can be accomplished. The Open System Architecture of "NC embedded in PC" was used in the control system, which made the system more flexible and transplantable. "off-axis CCD + monitor" was used as workpiece position system. To measure the correlative coordinates between Micropen and laser beam, a simple method using direct-write marker was devised, which ensures that the movement tracks of Micropen and laser beam coincide with each other. Moreover, this equipment can be used in other fields such as laser precision machining, laser micro manufacturing and so on.The theoretical model of Micropen direct writing was established through rheology theoretical analysis. The sequence of the main process parameters which affect the line width is shown below in the order from primary to secondary: the viscosity of paste, the direct writing speed, the diameter of Micropen tip, gas pressure and the tip-to-substrate distance. It is obtained by orthogonal experiment. The main parameter which greatly affects the direct writing film thickness is the tip-to-substrate distance.Transformation character of functional electronic paste in the process of laser microcladding is similar to the process of furnace sintering accordint to the thermal analysis experiment. Laser power density has the similar effect on electrical properties as the temperature of furnace sintering. Laser microcladding electronic paste is essentially the thermal coupling process of laser beam withelectronic paste. There is liquid phase emerged during laser process. In essence, this process is an instantaneous liquid phase sintering during laser irradiation. The non-homogeneous distribution of the laser power intensity resulted in fluctuant phenomenon in the paste film during laser irradiation. The cracks can be found in the thick films when the film layer is thicker and the cooling process is non-uniform.The basic mechanisms of how to control the film quality of thermistor paste, galvanothermy paste and gas sensing paste by laser microcladding were studied systematically. The thermistors fabricated by laser microcladding exhibited excellent electrical performance and resistance tolerance equivalent to traditional oven-fired electrical paste. The TCR of thermistors reaches the maximum value of 2965×10^-6/°C. Laser power density and the temperature of post-heat treatment had a great effect on sheet resistivities and TCR of thermistor. Optimal values of laser power density and temperature of post-heat treatment are 1.5×10^-6W/cm² and 400°C , respectively. The highest temperature of microheaters exceeded 500°C. The heating and cooling rates of the spiral-shaped microheater are about 7°C s^-1 and 4°C s^-1, respectively. The operating temperature has an obvious influence on the sensitivity of the sensor to ethanol vapor and the peak sensitivity occurs at operating temperature of 250°C. The sensitivity to 2000ppm ethanol vapor reaches a maximum value of 8.6, while that of screen-printed sample with 8.5μm thickness is 7.4. The measured response and recovery time of the sample was 7s and 20s, respectively, and 10s and 25s, respectively, for the sample fabricated by screen-printing. The gas sensor fabricated by laser microcaldding was packaged by TO-6 tube, which proved that the sensor fabricated by Micropen-Laser hybrid direct writing technology was compatible with traditional packaging technology.Summing up above mentioned, Micropen-Laser hybrid direct writing technology has created a new way for thick-film sensor fabrication with fast, maskless and high efficiency. Under the conditions of new product research and development, small-scale non-standardization production, this technique will be accepted by the industrial enterprises because of its low cost and high efficiency in comparison with traditional processes, which has a broad space for development and bright application prospects.更多还原