纳米颗粒增强无铅钎料的研究进展

Present Research Status of Lead-free Solder Reinforced by Nanoparticles

电子产业的发展离不开封装材料的进步。随着科学技术的进步,电子器件集成度逐渐提高,引脚尺寸和间距不断减小,而电子产品的服役条件也日趋复杂,因此对钎料的性能要求越来越严苛。与无铅钎料相比,传统的SnPb钎料因为成本低廉、性能优异,得到了电子工业的青睐。随着人们环保意识的提高,有毒元素铅在电子产业中的使用受到了限制,推动了电子封装材料朝着无铅化发展。但是目前,无铅钎料合金体系均存在成本高、润湿性差、可靠性不足、熔化特性与生产体系不匹配等问题,难以满足电子工业发展的需要。因此,探索改善无铅钎料性能的方法,研发性能优异的无铅钎料以替代SnPb钎料成为电子封装领域研究的一个热点。目前无铅钎料改性的研究主要集中在微合金化和纳米颗粒增强两个方面。微合金化就是向钎料中添加微量的合金元素,通过改变钎料合金成分来改善钎料的组织性能。无铅钎料微合金化的研究起步较早,目前已经取得了大量的研究成果,添加如Ag、In等元素均可以显著改善钎料的力学性能和可靠性,其中稀土元素由于活性较高,被视为无铅钎料合金化的理想合金元素。但是微合金化只能部分地提高钎料的性能,还不能满足生产的需要。纳米材料以其特殊的尺寸效应和优异的理化特性而受到广泛关注,同时纳米颗粒作为增强材料,在改善金属材料组织性能方面也具有非常明显的作用。将细小的纳米颗粒弥散地分布于钎料基体中,能够显著影响无铅钎料的性能,这也是一个较为新颖的研究方向。常见的纳米增强颗粒主要有金属纳米颗粒、氧化物纳米颗粒、陶瓷纳米颗粒和碳基材料纳米颗粒等。本文综合评述了纳米颗粒增强无铅钎料的研究进展。首先对目前纳米颗粒复合无铅钎料的三种制备方法的工艺特点进行了介绍;然后讨论了不同类型的纳米颗粒对SnAgCu、SnZn、SnBi和SnCu几种应用广泛的无铅钎料组织性能的影响,如微观组织、力学性能、润湿性能、熔化特性和可靠性等,同时对纳米颗粒增强无铅钎料的作用机理进行了分析;最后整理了目前纳米颗粒增强无铅钎料存在的不足,并对其未来的发展趋势进行了分析与展望,以期能够为未来无铅钎料的研究提供一定的参考。

The developme nt of electrical in dustry comes with the improveme nt of packag ing materials. Adva nceme nts in scie nce and tech no logy has put much emphasis on the properties of solder alloy because the electronics is developing towards increasingly higher integrated level, finer pitch and severer service conditions. Compared with lead-free solder alloys, the traditional SnPb solder was widely used in the electrical industry due to its low cost and excellent properties. However the application of Pb is prohibited currently due to its toxicity and lead-free solder alloy has become the trend in electronical packaging material. But presently, lead-free solder alloys have some disadvantages, such as high cost, poor wettability and reliability, unsatisfactory melting property, which fail to meet the demand of electrical industry. Therefore, searching the method to improve the properties of lead-free solder seems to be worthy of attention and is a critical topic for the design of excellent lead-free solder to substitute SnPb solder alloy. So far, researches on modified lead-free solder are concentrated in microalloying and nanoparticles strengthening. Microalloying is to improve the properties of lead-free solder by doping alloy elements, such as Ag, In and rare earth elements. A great number of researches on lead-free solders modified with alloy elements have been carried out in the past decades but they are all proved to only improve a few properties of solders, which do not come up to the expected standard. Nanomaterials have attracted great attention due to their special size and property, and moreover as the ideal reinforcement, nanoparticles could influence the microstructure and performance of metal materials. The properties of lead-free solder alloy could be significantly enhanced by dispersed nanoparticles in solder matrix, the majority of which are metal nanoparticle, oxide nanoparticle, ceramic nanoparticle and carbon-based nanoparticle. In this paper, the present research status of lead-free solder alloy reinforced by nanoparticles is reviewed systematically. First of all, the characteristics of three methods to prepare the composite lead-free solder alloy modified with nanoparticles are introduced. Then the effect of doping nanoparticles on the microstructure and properties of principal lead-free solder alloys is discussed respectively, such as SnAgCu, SnBi, SnZn, SnCu solder. In addition, the strengthening mechanism of nanoparticles is analyzed. Moreover, limitations of lead-free solder reinforced by nanoparticles are summarized and the development trends of researches on lead-free solder alloy reinforced by nanoparticles are forecasted to provide the reference for the future investigation of lead-free solders.