【作者】 张宗波；

【导师】 王立鼎； 王晓东；

【作者基本信息】 大连理工大学 ， 机械电子工程， 2010， 博士

【摘要】 聚合物微流控芯片除了具有检测速度快、效率高、试剂用量少、易于实现自动化操作等优点外,还具有材料选择范围广、制作工艺简单、成本低、可一次性使用以及生物兼容性好等优点。目前,它是微型便携分析仪器商业化与产业化发展的主要方向。近年来,针对聚合物微流控芯片的制备技术,国内外展开了大量的研究。用于实验室研究的少量芯片制作已经能够实现,但芯片的大规模、批量化生产,尚存在亟待研究和解决的关键技术问题。其中,芯片的键合是实现其批量化和自动化生产的主要瓶颈问题之一。本文以聚合物微流控芯片的超声波键合技术为研究对象,以提高键合质量和键合方法的创新为主要目的,对超声波键合过程中的产热机理、超声波熔融键合方法以及超声波非熔融键合方法进行了较系统的研究。基于理论分析和数值计算,对超声波作用下聚合物在玻璃态和粘弹态的产热机理分别进行了研究,搭建了温度测试系统,对键合过程中的温度场进行了测量。根据理论分析以及测温试验,提出超声波键合过程中摩擦和粘弹性复合产热机理的新观点。该观点认为,聚合物在玻璃态时,摩擦热是超声波产热的主要原因,也是整个键合过程的启动热源；当材料温度达到玻璃转化温度(Tg)时,粘弹热使局部温度快速升高导致材料熔融,所以粘弹热是使聚合物熔融的主要热源。依据上述产热机理以及测温试验,文章进一步针对超声振幅对温度场的影响进行了研究。结果表明,超声波键合过程中存在临界振幅,当超声振幅低于该临界振幅时,键合区的最高温度始终低于Tg,并能维持在该温度附近。对超声波键合过程中产热机理的明晰和产热特性的把握,为键合质量的提高和键合方法的创新奠定了基础。研究了利用键合辅助结构提高超声波熔融键合质量的方法。设计了三种超声波键合辅助微结构,并对这些复杂的凸凹式三维微结构的制作方法和成形规律进行了研究。通过键合试验,首次利用带熔池和阻流台的配合式辅助键合结构,实现了最小特征尺寸为30μm的微通道键合封装。该方法键合强度接近材料的本体强度、键合时间短(小于0.5s)、键合质量的稳定性和重复性好,适于批量化和自动化生产,但该方法中试件制备复杂,且由于聚合物熔融液的存在,很难用于更小尺度的微结构键合。在产热机理研究的基础上,本文首次提出了基于局部溶解性激活的超声波非熔融键合方法和热辅助超声波非熔融键合方法。利用键合前期摩擦产热速度慢、易于控制的特点,结合有机溶剂的温变溶解特性,采用分子动力学方法,研究了基于局部溶解性激活的超声波非熔融键合机理。并利用异丙醇(IPA)做为辅助溶剂,对PMMA微流控芯片进行了键合试验。与传统的键合方法相比,由于该方法中超声波振幅较低,导能筋不发生熔融,所以不会出现由于熔融液流延造成的键合质量问题。键合过程中除键合区域外,其它部位均保持室温,所以辅助溶剂不像传统的溶剂键合那样,会对微结构造成损坏。研究结果表明,该方法试件制备简单、易于过程控制、微结构变形量小、键合强度高,是一种适用于聚合物MEMS器件键合的新方法。将超声波的产热特点与传统热键合的键合机理相结合,提出了一种无需键合辅助结构的热辅助超声波非熔融键合方法。该方法中,基片与盖片在预加热过程中充分贴合,在超声波作用下界面温度上升并维持在Tg附近,而基片内部的温度却远低于Tg。在界面温度以及超声振动的共同作用下,界面间形成键合。键合试验证明,该方法具有无需键合辅助结构、微结构变形量小、材料适用范围广、可控性高、超声能量在界面自动集中等特点。利用该方法的独特优势,成功实现了对深度只有200nm微通道阵列的键合和多达12层芯片的一次性键合。更多还原

【Abstract】 Polymer microfluidic chips not only have the advantages of high-speed, high-throughout, small sample consumption and easy to realize automatic operation as other microfluidic devices, they also have their inimitable advantages such as wide choices of materials, ease of fabrication, low cost, disposability and good bio-compatibility and so on. Therefore, polymer microfluidic chips are considered as the most potential for the commercialization and industrialization of portable analytical instruments. Many techniques for the fabrication of polymer microfluidic chips have been studied in the last decay. And small batches of chips used for research in the lab can be realized by these techniques. However, there are still some technical issues in the mass production. Bonding is one of the bottlenecks among these issues. In order to meet the bonding requirements of microfluidic chips and other polymer MEMS devices, ultrasonic bonding methods and the bonding mechanism were systematically studied in this thesis.Based on theoretical analysis and numerical calculation, the heating mechanisms of polymer under ultrasonic vibration in glassy state and viscoelastic state were studied. The temperature field during ultrasonic bonding process was measured. Based on the calculation and experiment results, a new frictional composited with viscoelastic heating mechanism was presented. It reveals that facial friction rather than viscoelastic heat initially start the bonding process in glassy state. Viscoelastic heat becomes dominant when temperature reaches Tg (glass transition temperature) of the material. Viscoelastic heat provides most required heat during the process. Temperature fields at different ultrasonic amplitudes were also discussed based on numerical calculations and temperature measuring experiments. The results indicates that there exists a critical amplitude for the given material and dimensions of energy director. The peak temperature become constant and the polymer does not melt when ultrasonic amplitude is lower than the critical amplitude no matter how long the bonding time is. These findings give a more clear understanding of heating mechanisms in ultrasonic bonding. And it will contribute to the improvement of bonding quality and method innovation of ultrasonic bonding.In order to improve the bonding quality of melt based ultrasonic bonding method, different bonding auxiliary microstructures were designed. The fabrication of these complex 3-D microstructures was also studied. Based on bonding experiments, the mating style design including molten bath and flowing block was successfully used to hermetically bond the microchannels with characteristic dimension of 30μm. This method shows many advantages such as very high bonding strength (near the body strength of the material), short bonding time (less than 0.5 s) and stable bonding quality. However, the melt of polymer make it difficult to improve the bonding accuracy further using this method.Based on the research of heating mechanism, the non-melt ultrasonic bonding method was firstly proposed. And two novel non-melt ultrasonic bonding methods were presented in this thesis. They were local solubility activated non-melt ultrasonic bonding method and thermal assisted non-melt ultrasonic bonding method.The bonding mechanism of the local solubility activated non-melt ultrasonic bonding method was studied according to the heating process under low amplitude ultrasonic and molecular dynamics simulation. PMMA microfluidic chips were successfully bonded with isopropanol (IPA) as the assisted solvent. Comparison to traditional ultrasonic bonding method, lower amplitude was used in this method, which prevented melting of polymer and deformation of microchannel. Additionally, most part of the PMMA substrates kept at room temperature except for the interface between the energy director and cover substrate during the bonding process. So IPA did not damage the microstructures as in common solvent bonding method. The experimental results indicated many advantages of this method such as easy to fabricate the substrates, good controllability of the process, low deformation of the microstructures and high bonding strength. It is a novel bonding method for polymer MEMS devices. However, high selectivity for the polymer and solvent greatly limited the usage of this method.A thermal assisted non-melt ultrasonic bonding method without bonding auxiliary structures was proposed according the heating properties during ultrasonic bonding and the bonding mechanism of traditional thermal bonding method. Temperature of the interface rose to around Tg as a result of friction heating from ultrasonic vibration, while the bulk temperature of the substrates was still well below Tg. Combined with ultrasonically oscillating pressure, bonding formed at the interface with little deformation of microstructures. Bonding experiments indicated some advantages of this method such as needless of bonding auxiliary structures, low deformation of the microstructures, good controllability of the process, suitable for almost all thermoplastics and automatically focus of ultrasonic energy at the interface. Considering the special advantages of this method, planar nanochannel array with depth of 200 nm was successfully bonded using this method. And multilayer microfluidic devices with as many as 12 layers were also bonded together at one time using this method.更多还原