Evolution of tin whiskers and subsiding grains in thermal cycling
Evolution of tin whiskers and subsiding grains in thermal cycling
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DOI：
10.1007/s10853-013-7788-5
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发表时间：
2014-02
影响因子：
4.5
通讯作者：
Ying Wang;J. Blendell;C. Handwerker
中科院分区：
文献类型：
--
作者：
Ying Wang;J. Blendell;C. Handwerker
研究了在具有Cu中间层的Si衬底上的Sn薄膜在空气中从−40 ° C到85 °C的热循环过程中最多250个循环的表面形貌的演变，包括晶须形成、晶界开裂和下沉晶粒，并与室温老化产生的表面形貌进行了比较。跟踪多个区域，并随时间监测这些区域内的晶须的面密度和晶粒形态，以进行室温老化和热循环次数的增加。在室温老化过程中，晶须密度随时间增加，直到镀后约3周达到饱和。至于热循环，观察到的晶须密度首先增加，但随后由于晶须夹断现象而降低。在热循环过程中形成的晶须的特征包括沿晶须面内晶界沿着形成深凹槽（“晶须根部”），晶须半径随着它们的生长而减小，晶须上的条纹环垂直于晶须生长方向，相应的条纹沿着膜中的凹槽表面，尽管与它们相应的晶须上的那些相比具有不同的空间周期性，以及晶须夹断，因为随着晶须半径减小，晶须变得易于断裂。在室温老化过程中形成的晶须没有显示这样的开槽或夹断。晶须夹断模型，提出了解释所观察到的形态变化和由此产生的晶须密度在热循环过程中的减少，与计算的晶须生长速率，同意与实验观察。
The evolution of surface morphology, including whisker formation, grain boundary cracking, and subsiding grains, was studied in Sn thin films on Si substrates with a Cu interlayer during thermal cycling from −40 to 85 °C in air for up to 250 cycles and was compared with surface morphologies resulting from room temperature aging. Multiple areas were tracked, and the areal density of whiskers and the grain morphologies within these areas were monitored over time for room temperature aging and with increasing number of thermal cycles. During room temperature aging, the whisker density increased with time until saturation ~3 weeks after plating. As for thermal cycling, the whisker density was observed first to increase but then to decrease as a result of a whisker pinch-off phenomenon. The characteristic features of whiskers formed during thermal cycling included the formation of deep grooves along the in-plane grain boundaries of whiskers (“whisker root”), a decrease in whisker radii as they grew, striation rings on whiskers perpendicular to the whisker growth direction, corresponding striations along grooved surfaces in the film, albeit at different spatial periodicities than those on their corresponding whiskers, and whisker pinch-off as whiskers became prone to fracture as their radii decreased. Whiskers formed during room temperature aging did not display such grooving or pinch-off. A whisker pinch-off model was proposed to explain the observed morphological changes and the resulting decrease in whisker density during thermal cycling, with a calculated whisker growth rate that agrees with the experimental observation.