基于相分离的Al@Sn-Bi核壳型球粒一步法制备工艺

发布时间：2018-01-23 13:57

本文关键词： Al-Bi Al-Bi-Sn 核壳型凝固相分离表面偏析　出处：《上海交通大学》2011年硕士论文　论文类型：学位论文

【摘要】：随着电子产品向“轻、薄、短、小”及多功能方向发展,先进封装技术向着小型化、高密度和细间距方向演进,因此,焊球的导电性和散热性不足、易产生封装缺陷等问题日益突出。一个较好的解决办法是采用以高强高导电高熔点材料为核心的核壳型焊球,但因目前此类焊球主要采用电镀法制备,因此其应用受到严重制约。本文研究了Al-Bi-(Sn)偏晶合金的相分离和凝固行为,探讨了核壳组织的形成和影响机理,获得了Al@Sn-Bi核壳型球粒及其一步法制备工艺,为核壳型金属颗粒包括电子封装用焊球的制备和应用奠定了基础。首先,针对Al-Bi二元体系,采用射流断裂法研究了合金成分、过热度、硅油温度、液滴飞行距离和液滴尺寸的影响。结果表明,由于表面偏析,不同成分的Al-Bi合金颗粒壳层总是由富Bi相组成。颗粒有圆环型和月食型核壳两种形貌。通过ANSYS软件模拟液滴的温度场,并计算第二相小液滴的运动速率,发现只有当冷却速度和温度梯度精确地配合,才会使Marangoni和Stokes运动速率相平衡,从而能获得圆环型核壳组织。对于Al-65.5Bi (in wt.%)合金,当熔体过热度为100 K,液滴自由飞行距离为3 mm,硅油为常温时,直径0.9 mm左右的颗粒基本能获得圆环型核壳形貌,否则易获得月食型核壳形貌。根据上述分析,总结并图解了Al-Bi合金的凝固路径和核壳形貌的形成过程。此外,还发现核壳型Al-65.5Bi合金球粒的整体与内核直径满足关系式:Dcore=0.9137 Dparticle-0.0312,线性相关度为0.96。其次,对于Al-Bi-Sn合金,研究了7种成分,发现成分点位于液相难混溶区内和边界上都易于获得核壳形貌。随着过热度降低和硅油温度提高,颗粒由三层变成两层同心和两层偏心核壳形貌。对于(Al34.5Bi65.5)67.8Sn32.2合金颗粒,当过热度为100 K,飞行距离为30 mm,硅油温度为283-473 K时,易形成完好核壳组织。其壳层由Sn-Bi基合金组成,熔化范围为407-431 K,符合低温无铅焊料的熔化温度要求;其核层由Al-Sn基合金组成,熔化温度为823-844 K左右,有利于提高导电导热性并在封装过程中保证共面性。通过示差扫描量热仪研究了Al-Bi-Sn合金的相变行为,并结合能谱分析和电镜观察,总结并图解了Al-Bi-Sn合金的凝固路径和核壳组织形成过程。
[Abstract]:With the development of electronic products in the direction of "light, thin, short, small" and multifunction, advanced packaging technology has evolved towards miniaturization, high density and fine spacing. Therefore, the electric conductivity and heat dissipation of solder balls are insufficient. A better solution is to adopt core-shell solder ball with high strength and high conductivity and high melting point material as the core, but at present, this kind of solder ball is mainly prepared by electroplating. Therefore, its application is seriously restricted. The phase separation and solidification behavior of Al-Bi-nn monotectic alloy are studied, and the formation and influence mechanism of core-shell microstructure are discussed. The Al@Sn-Bi core-shell spherical particles and their one-step preparation process were obtained, which laid a foundation for the preparation and application of core-shell metal particles, including solder balls for electronic packaging. Firstly, the effects of alloy composition, superheat, silicone oil temperature, droplet flying distance and droplet size on Al-Bi binary system were investigated by jet fracture method. The particle shell of Al-Bi alloy with different composition is always composed of Bi-rich phase. The particles have two morphologies: annular and lunar eclipse core-shell. The temperature field of droplets is simulated by ANSYS software. The moving rate of the second phase droplet is calculated. It is found that the velocity of Marangoni and Stokes will be balanced only when the cooling rate and temperature gradient are matched accurately. The circular core-shell structure can be obtained. For the Al-65.5Bi alloy, the free flying distance of the droplet is 3 mm when the melt superheat is 100K. When the silicon oil is at room temperature, the core-shell morphology of ring type can be obtained basically by the diameter of 0.9 mm particles, otherwise it is easy to obtain the core-shell shape of lunar eclipse type. The solidification path and core-shell morphology of Al-Bi alloy were summarized and illustrated. It is also found that the whole core diameter of core-shell Al-65.5Bi alloy is equal to the kernel diameter of 0.9137 Dparticle-0.0312. The linear correlation was 0.96. Secondly, for the Al-Bi-Sn alloy, 7 compositions were studied. It was found that the core-shell morphology was easily obtained in the liquid phase inmiscible region and at the boundary, with the decrease of superheat and the increase of the temperature of silicon oil. The particles changed from three layers to two layers of concentric and two layers of eccentric core-shell morphologies. For Al34.5Bi65.5A67.8Sn32.2 alloy particles, the superheat was 100K. When the flying distance is 30 mm and the temperature of silicon oil is 283-473 K, it is easy to form perfect core-shell structure. The shell layer is composed of Sn-Bi base alloy and melting range is 407-431 K. Meet the melting temperature requirements of low temperature lead-free solder; The nuclear layer is composed of Al-Sn base alloy and the melting temperature is about 823-844K. The phase transformation behavior of Al-Bi-Sn alloy was studied by differential scanning calorimeter (DSC) and observed by EDS and electron microscope. The solidification path and core-shell structure formation process of Al-Bi-Sn alloy were summarized and illustrated.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2011
【分类号】：TG146.21

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