【作者】 陈强；

【导师】 李国元；

【作者基本信息】 华南理工大学 ， 微电子学与固体电子学， 2011， 硕士

【摘要】 电子封装无铅化的进展很快,世界各国的研究者已开发出不同的可替代铅锡合金的无铅合金系,其中Sn-Ag、Sn-Cu以及Sn-Ag-Cu合金被认为最有希望替代铅锡合金。但目前的研究结果表明它们只能在某些性能上达到或超过铅锡合金,其综合性能上仍不能媲美铅锡合金,且随着微电子产品的持续小型化,这些无铅合金的某些弱点逐渐显露并限制着无铅焊点可靠性的提高。因此,目前尚没有一种合金焊料能满足现代电子封装超微化发展所要求的各项性能。因此研发高可靠性无铅焊料和研究影响无铅互连可靠性的关键问题是高密度微电子封装的重要课题。该项目在Sn3.0Ag0.5Cu焊料中掺入锑、稀土钇以及稀土化合物LaB6。实验结果表明,添加锑可以显著改善焊料的润湿性能,使焊料与铜的接触角减小8o;微量的稀土元素(低于0.1wt%)也能够有效地改善焊料的润湿性能。同时,稀土能够细化合金中的金属间化合物晶粒,能提高焊点的机械性能。Sb具有抑制界面化合物生长的作用,但是同时加入Sb与稀土Y的焊料中,其界面化合物的生长却是比只含Sb而不含Y的焊点的界面化合物生长快。可能的原因是Sb与Y反应生成Sb-Y化合物,抑制了Sb发挥作用。Sn3.0Ag0.5Cu焊料掺入0.4wt%的锑或0.1wt% LaB6时的实验结果表明:在润湿反应时间少于700s时,其界面化合物的厚度与时间成线性或抛物线关系,其中Sn3.0Ag0.5Cu 0.4Sb0.10LaB6/Cu界面处的Cu6Sn5层生长速度最慢,其对阻碍界面原子的互扩散能力应是最强的;固态反应阶段,根据各种老化温度下界面互扩散系数的比较,得出界面化合物层的生长快慢排序如下:Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu<Sn3.0Ag0.5Cu0.4Sb/Cu<Sn3.0Ag0.5Cu0.10LaB6/Cu <Sn3.0Ag0.5Cu/Cu计算了各种界面的Cu-Sn化合物的激活能,结果表明:Sn3.0Ag0.5Cu/Cu界面Cu-Sn化合物的激活能最高,为92.79kJ,其次是Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu和Sn3.0Ag 0.5Cu0.10LaB6/Cu,分别是85.14kJ和84.91kJ,而Sn3.0Ag0.5Cu0.4Sb /Cu界面的Cu-Sn化合物激活能最小,只有75.57kJ。综合考虑各界面互扩散系数随温度变化情况,发现在老化温度范围以内(≤190℃), Sn3.0Ag0.5Cu0.4Sb 0.10aB6/Cu的扩散系数都是最小的,因而其界面化合物的生长速率最慢。更多还原

【Abstract】 With increasing concerns on environmental protection and human being health, lead-free solders have been increasingly used to replace the Pb-containing solders in the field of microelectronic packaging. Many different lead-free solder alloy systems, such as Sn-Ag, Sn-Ag-Cu, Sn-Cu, Sn-Ag-Bi, have been developed and are currently being used as promising alternatives to the Sn-Pb solders. However,the comprehensive properties of all the existing lead-free solders are not as well as that of the Sn37Pb solder. Among the varieties of lead-free solders, the Sn-Ag-Cu family is regarded as the most promising candidate for replacement of Sn-Pb solders, because it has superior mechanical properties of strength, elongation, creep, and fatigue resistance than Sn-Pb solders.As the trendence of high density packaging goes on, the size of each I/O decreases so as to supply more input/output (I/O) for a constant packaging area. In this case, the reliability problems caused by the over growth of intermetallic compound (IMC, of brittle property) in Sn-Ag-Cu solder joints due to their higher reflow temperature must be solved.In the present research, Sb、rare earth yttrium and LaB6 were added to the Sn3.0Ag0.5Cu solder paste. It is found that Sn3.0Ag0.5Cu0.8SbXY, with X ranging between 0.05 and 0.1, has the best wettability on Cu substrate. The growth rate of IMC increases as the amount of yttrium increase from 0wt% to 0.25wt% in the Sn3.0Ag0.5Cu0.8SbXY/Cu system during aging.When the yttrium concentration is increased from 0.25wt% to 0.5wt%, the IMC thickness decreases. Further increase in the RE concentration just results in a slightly increasement of the IMC thickness. The possible reason for this result is that Sb reacts with Y to form Sb-Y compounds and finally the effect of Sb on the growth of IMC weakens. Secondly,0.4wt% Sb and/or 0.1wt% LaB6 were added to the same solder paste used in the firet step and let all the four kinds of solder joints to go through the multi-reflowed and aging process. IMC growth during reflow process was studied and compared their growth rate during the aging process. Results show that solder joints with 0.4wt% Sb and 0.1wt% LaB6 has the minmum interdiffusion coefficient among the four kinds of solder joints in our experimential temperature range. In addition, the activation energy of the Cu-Sn compound was calculated. It is found that the Cu-Sn compound of the Sn3.0Ag0.5Cu/Cu solder joint has the maximum activation energy of 92.79kJ. The other three activation energys are 75.57 kJ, 84.91kJ, 85.14kJ for Sn3.0Ag0.5Cu0.4Sb/Cu, Sn3.0Ag0.5Cu0.10LaB6/Cu and Sn3.0Ag0.5Cu 0.4Sb0.10LaB6/Cu respectively. Although the Sn3.0Ag0.5Cu/Cu has the maximum activation energy, the activation energy of Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu just lower down a little bit.With a much more less diffusion constant D0, it has the minmum interdiffusion coefficient in the experimental range.更多还原