【作者】 谈发堂；

【导师】 乔学亮；

【作者基本信息】 华中科技大学 ， 材料科学与工程， 2006， 博士

【摘要】 导电胶作为传统铅锡焊料的一种替代品,因具有环境友好、操作温度低、间距细及工艺步骤少等优点,而引起人们的广泛关注。和无铅焊料相比,导电胶具有更好的柔性度,抗蠕变性和能量吸收性。但是,导电胶也有很多缺点,如体电阻率高、接触电阻不稳定和抗冲击性能差等。本文研究了导电粒子的制备与表征、光亮片状银粉的表面行为、导电胶中的界面行为,探讨了提高导电胶的电性能与机械性能的方法。以水合肼为还原剂还原硝酸银溶液制备球形或类球形银粉。研究了反应条件与环境因素如反应物浓度、配比、反应物滴加速度、搅拌速度、反应温度、分散剂用量等对银粉几何形态、性能的影响。优化后的制备工艺为:反应温度为室温,还原剂浓度2.1mol/L,硝酸银浓度0.35 mol/L,滴加时间40分钟,搅拌速度1000rpm,水合肼与硝酸银摩尔比6:1,分散剂PVP与硝酸银的重量比为0.9。通过对还原银粉进行球磨制备光亮片状银粉,研究了球磨液体介质、球磨助剂、球磨时间等对光亮片状银粉的粒径、粒径分布与形貌的影响。实验表明,以水为球磨液体介质、油酸为球磨助剂,球磨48小时能得到质量很好的光亮片状银粉。利用差示扫描热分析法研究了光亮片状银粉被溶剂与醇酸混合溶液处理前后的热性能,利用傅立叶红外光谱对油酸与光亮片状银粉表面进行了表征,利用扫描电镜和能谱分析仪EDAX对被醇酸混合溶液处理前后的片状银粉的表面进行了形貌观察和成份分析。结果表明,球磨后光亮片状银粉表面的油酸不是物理吸附的油酸,而是化学吸附在银粉表面的一层有机润滑层,是油酸和银粉相互作用产生的有机银盐。不同的溶剂与溶液对光亮片状银粉表面的去除效率不同。本研究首次发现,醇酸混合溶液能完全去除光亮片状银粉表面的有机银盐。其去除机理为:醇酸混合溶液中的H+首先和光亮片状银粉表面的有机银盐反应,生成油酸和无机银盐,油酸溶于醇,无机银盐溶于水溶液,直至有机银盐被完全去除为止。光亮片状银粉表面的油酸被完全去除后,在相同银粒子填充量的情况下,能提高导电胶的体电阻率。通过添加偶联剂能改善导电粒子与树脂间的相容性,不同的偶联剂对导电胶性能的影响不同,本研究中添加硅烷偶联剂KH-570能提高导电胶的电导率和剪切强度,而添加钛酸脂偶联剂NDZ-401的导电胶的电导率的变化不大。扫描电镜照片显示添加偶联剂的导电胶的导电粒子与树脂基体间的结合更紧密。导电填料中添加适量的低熔点合金有助于导电胶电导率的提高,导电填料中低熔点合金的最佳含量为20 wt%左右。低熔点合金在导电胶固化阶段熔化,在银粒子间形成冶金连接。更多还原

【Abstract】 Electrically conductive adhesives (ECAs), an alternative for traditional tin/lead (Sn/Pb) solders, have gained much attention owing to their environmentally friendly profits, lower temperature processing, finer pitch printing and more flexible and simpler processing over traditional tin/lead (Sn/Pb) solders. In addition, compared with lead-free solders, electrically conductive adhesive systems exhibit greater flexibility, creep resistance and energy damping. At the same time, ECAs have drawbacks such as high volume resistivity, unstable contact resistance under environmental aging conditions and limited impact resistance of the adhesive interconnections. In this paper, silver conductive fillers were prepared and characterized, the surface behavior of bright silver flakes and interfacial behavior in electrically conductive adhesives were studied, and methods for improving the electrical and mechanical properties of ECAs were also discussed.Spherical or sphere-like silver powders were prepared by a reduction process of the silver nitrate solution with hydrazine hydrate as the reducing agent. Influences of reaction condition and environmental parameters, on the size and shape properties of silver powders were studied, such as concentration of reactants, weight ratio of reducing agent to AgNO3, reaction temperature, adding speed of reactant, agitating speed and weight ratio of dispersant PVP to AgNO3 The optimum reaction conditions were determined: reaction temperature is room tempeture, concentration of AgNO3 is 0.35 mol/L, concentration of reductant is 2.1mol/L, adding time is 40min, agitating speed is 1000rpm, mole ratio of reducing agent to AgNO3 is 6:l , and weight ratio of dispersant PVP to AgNO3 is 0.9. Bright silver flakes were obtained by ball milling as prepared silver powders.Thermal properties of bright silver flakes before and after treatment by different solvents and chemicals were characterized by Differential Scanning Calorimetry (DSC) technique. Fourier transform infrared spectroscopy (FT-IR) was used to characterize the chemical structures of oleic acid and the trace amount of organic lubricants on the silver flakes surface. The morphology of silver flakes before and after treatment by a mixture of alcohol and diluted acid was observed by SEM. Elemental compositions of silver flakes before and after treatment were analyzed by EDAX. It shows that the organic lubricant on the surface of bright silver flakes is not the oleic acid physisorbed on the surface of silver flakes, but a chemisorbed lubricant layer, salt of silver with oleic formed during milling process. Efficiency of different solvents and chemicals on the removal of lubricant on the surface of silver flakes is different. To the best of our knowledge, it was the first time for us to find a method to fully remove the lubricant on the surface of silver flakes. A mixture of alcohol and diluted acid can fully remove the chemisorbed lubricant. The mechanism of the removal is that the H+ in the mixture of alcohol and acid firstly reacts with the salt, resulting in oleic acid and an inorganic silver salt, and the oleic dissolves in alcohol and the inorganic silver salt dissolves in water. The reaction processes until the full consumption of the salt, the chemisorbed lubricant on the surface of bright silver flakes.It was found that with the full removal of lubricants on the surface of silver flakes, the electrical conductivity is improved at the same weight filler loading. Compatibility of silver flakes filled epoxy system can be improved by adding coupling agents. It was also found that the added coupling agents have different effects on the electrical, aging and lap shear properties of ECAs. According to this study, the use of silane coupling agent KH-570 had a significant electrical conductivity improvement and lap shear strength increase before and after the aging test. But for the titanate coupling agent NDZ-401, the properties of the ECA have no significant change. Scanning electron microscopy studies revealed a strong adhesion/bonding between the filler and the matrix for coupling agent added ECAs.Adding some low melting point alloy in the fillers is helpful for the improvement of electrically conductivity of ECAs, in this study, the proper weight ratio of LMPAs in fillers is about 20%. The LMPA fillers melt and form metallurgical interconnections between the Ag flakes during the curing of ECAs.更多还原