【作者】 周健；

【导师】 孙扬善；

【作者基本信息】 东南大学 ， 材料学， 2006， 博士

【摘要】 Pb是一种有毒物质。电子产品中由于使用了大量含Pb的焊料进行封装,因此对人类健康造成了严重的威胁。随着RoHS指令(关于在电子电气设备中限制使用某些有害物质指令)和WEEE指令(关于废旧电子电气设备指令)在欧盟议会获得批准,电子产品在2006年7月1日后将禁止含Pb。因此,世界各国目前正在积极开展无铅焊料领域的研究,其中Sn-Zn系焊料由于熔点最为接近传统焊料,有望成为新一代的无铅焊料。然而,Sn-Zn二元合金在铜表面的润湿性差、且抗氧化性不良,不能直接用于电子产品。近几年来,采用合金化方法改善Sn-Zn系焊料润湿性的研究取得了一定的进展,并且已有少量的Sn-Zn系合金投入实际应用。但是,由于Sn-Zn系合金的润湿性、抗氧化性问题并没有得到根本解决,在实际生产中往往要求增加焊剂活性或气氛保护以帮助焊料获得良好的润湿,因此这种焊料难以被推广应用。本论文以具有应用潜力的Sn-Zn-Bi合金为研究对象,以提高焊料的润湿性为主要研究目标,综合考虑合金的熔点、熔程及力学性能,对Sn-Zn-Bi焊料进行了成分的优化;在此基础上,通过加入少量或微量的其它合金元素(Nd、La、In),进一步提高了Sn-Zn-Bi焊料的润湿性和抗氧化性等性能,形成了具有优良综合性能的成分配方。此外,本文还采用时效的方法研究了几种优选合金与Cu基底焊后接头的界面扩散及界面生长行为,以及扩散反应层的生长对接头剪切强度的影响。合金元素Bi的加入不仅能够降低Sn-Zn系焊料熔体的表面张力,而且能够降低焊料/Cu接头的界面张力,因而提高了Sn-9Zn-xBi焊料的铺展性。当合金中Bi含量达到6%时,最大气泡压力法测得的焊料熔体在240℃下的表面张力接近Sn-40Pb合金的表面张力。理论计算进一步证明Bi能够有效降低Sn-Zn系焊料的表面张力,其作用机理是Bi原子在焊料熔体表面的富集作用。润湿平衡实验表明,Sn-Zn系焊料中添加Bi后,焊料在Cu基底上的润湿力明显提高,而润湿时间明显缩短。运用相关的力学理论推导,可以证明焊料润湿力的提高与焊料/Cu界面的界面张力降低直接相关。虽然Zn含量的增加会导致Sn-Zn-Bi三元合金熔体表面张力提高,但合金在Cu基底上的铺展面积却随Zn含量的增加而增大,这是因为Zn在焊料/Cu表面的优先扩散降低了液-固界面的界面张力。润湿力测试结果表明焊料在Cu基底上的润湿力随Zn含量的提高而增大,但润湿时间明显延长。对接头的组织分析表明,焊料/Cu界面层上的扩散反应区厚度随焊料中Zn含量的提高而增大。正是因为扩散过程需要更长的时间,因此Sn-Zn系焊料在Cu基底上的润湿过程也需要更长的时间。添加微量的稀土元素Nd、La或少量添加元素In能够明显提高Sn-8Zn-3Bi焊料的铺展性,其作用机理与Bi类似。Nd对提高焊料润湿性的作用效果比La、In更加显著。铺展性实验表明:当焊料中Nd的含量为0.1%时,焊料的铺展性接近Sn-40Pb焊料的水平;该焊料的润湿时间只有0.45S,低于Sn-40Pb焊料的润湿时间(0.61S)。Nd的加入能够降低Sn-Zn-Bi合金熔体表面上Zn的含量,减少Zn与O结合的几率。同时,合金熔体表面的Nd与O会发生反应,但形成的速度较慢,阻碍了O向焊料内部的扩散,因此明显提高了Sn-Zn-Bi焊料的抗氧化性。在Sn-Zn-Bi合金中加入La也能够减少ZnO的形成。然而,这种稀土元素自身极易与O结合而形成大量的氧化物,因此La对提高Sn-Zn-Bi合金的抗氧化性的效果并不显著。In在焊料中不易富集于表面,但同样能够使Bi在焊料熔体表面富集,减少ZnO的生成量,从而提高合金的抗氧化性。更多还原

【Abstract】 Tin-lead solders have been widely used in electronics manufacturing for many decades. However, there are environmental and health issues concerning the toxicity of Lead(Pb) present in these Pb-Sn solder alloys. These concerns have inspired a great deal of research to find suitable Pb-free replacement alloys. In Europe, the move towards Lead-free solder alternatives has accelerated because of legislation within the European Union. The European Union has approved the directives on waste from electrical and electronic equipment (WEEE) and restriction of hazardous substances (RoHS), which states that Lead will be banned in electronic products in the European Union from July 1, 2006. Sn-Zn base alloys are widely recommended because of the melting point of the Sn-Zn eutectic alloy is near that of the Sn-Pb eutectic alloy. However, its inferior wettability and easy oxidization are the two main disadvantages.Recently, Sn-Zn-Bi solders with low melting point have come into use in some cases. However, their application is limited by their unsatisfactory wettability and oxidation resistance. In the present paper, it is the main purpose to improve wettability of Sn-Zn-Bi solders. Firstly, the effects of Bi and Zn on wettability, melting behavior and mechanical property of Sn-Zn-Bi alloys have been investigated to find out the optimization Sn-Zn-Bi solder. At the following stage, some trace element has been added into the Sn-Zn-Bi solder to improve oxidation resistance and wettability of the alloy. At last, selected Sn-Zn-Bi-X quaternary alloy have been reflowed to achieve soldering joints. The effect of solder/Cu reactive layer growth on shear strength of aged joints has been investigated.According to the results of surface tension test, surface tension of Sn-Zn alloy melts can be reduced with addition of Bi. The results of surface tension calculation suggest a decrease in the surface tension of Sn-Zn-Bi alloys as a result of the enrichment of the surface with Bi atoms. Wetting force(Fw) and wetting time(tw) on Cu substrate of Sn-Zn-Bi solders have been measured by wetting balance test. With addition of Bi, Fw increase and tw decrease, which indicates wettability of Sn-Zn-Bi alloy has been improved.The addition of Zn increases the surface tension of Sn-Zn-Bi melts. But, because Zn atoms diffuse into Cu, solder/Cu interface tension has been decreased, which helps the solders spread out at Cu substrate. The reactive wetting procedure accompany with diffusion usually needs long time to achieve equilibrium, so wetting time has been prolonged.Nd, La and In are the effective additive elements on increasing wetting area of Sn-Zn-Bi solders. The most effective additive was Nd at 0.10%, because the wetting area is closed to that of Sn-40Pb, and the wetting time has been shortened to 0.45S.Zn atoms have been prevented from oxidation, which results from Zn concentration at the surface of solder melt has been deduced with addition of Nd. Nd atoms have been oxidated instead of Zn. But, the formation of Nd oxidation obviously slower than that of Zn oxidation, which indicates that the diffusion of O atoms into the solder has been impeded. La atoms have been oxidated instead of Zn also. A large mounts of La oxidation has formed, which shows there is no更多还原