Nondestructive Evaluation of Thermal Phase Growth in Solder Ball Microjoints by Synchrotron Radiation X-Ray Microtomography
Nondestructive Evaluation of Thermal Phase Growth in Solder Ball Microjoints by Synchrotron Radiation X-Ray Microtomography
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DOI：
10.1115/1.2804093
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发表时间：
2007-12
影响因子：
1.6
通讯作者：
Hiroyuki Tsuritani;T. Sayama;K. Uesugi;Takeshi Takayanagi;T. Mori
中科院分区：
文献类型：
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作者：
Hiroyuki Tsuritani;T. Sayama;K. Uesugi;Takeshi Takayanagi;T. Mori
在高密度封装技术中，最重要的问题之一是将大规模集成电路芯片从电气和机械上连接到印刷电路板的微关节的可靠性。高空间分辨率无损检测方法的发展有望提高可靠性。在日本最大的同步辐射设备“Super Photon ring-8 GeV”（SPring-8）上开发了一种名为SP-μCT的x射线微断层扫描系统。本文采用SP μ ct技术对焊接球微接头的微观结构演变进行了无损评价，即热循环加载导致的相生长。模拟倒装芯片中的微焊点，采用常规回流焊工艺，将直径为100 μm的Sn-Pb共晶焊锡球连接到钢针上，制备了微焊点样品。通过观察在目标连接固定点连续获得的CT图像来确定相生长过程。在重建的CT图像中，根据x射线线性衰减系数的估定值，识别出Sn-Pb共晶焊料中组成相的分布。因此，SP-μCT获得的显微结构图像为评价焊点的可靠性提供了以下有用的信息。首先，每个阶段都不涉及分散的粒子，而是像海绵一样的三维整体结构。第二，相位的增长以这样一种方式进行，即平均相位尺寸的四次方与周期数成比例地增加。最后，在连接界面附近，由于热膨胀失配引起的局部热应变导致了显著的相生长，相生长速度比其他区域更快。
In high-density packaging technology, one of the most important issues is the reliability of the microjoints connecting large scale integrated circuit chips to printed circuit boards electrically and mechanically. The development of nondestructive testing methods with high spatial resolution is expected to enhance reliability. An X-ray microtomography system called SP-μCT has been developed in Super Photon ring-8 GeV (SPring-8), the largest synchrotron radiation facility in Japan. In this work, SP-μCT was applied in the nondestructive evaluation of microstructure evolution, that is, the phase growth due to thermal cyclic loading in solder ball microjoints. Simulating solder microjoints used in a flip chip, specimens were fabricated by joining a Sn-Pb eutectic solder ball 100 μm in diameter to a steel pin in the usual reflow soldering process. The phase growth process was determined by observing the computed tomography (CT) images obtained consecutively at the fixed point of the target joining. In the reconstructed CT images, the distribution of the constituent phases in the Sn-Pb eutectic solder was identified based on the estimation value of the X-ray linear attenuation coefficient. Consequently, the microstructure images obtained nondestructively by SP-μCT provided us with the following useful information for evaluating the reliability of the solder microjoints. First, each phase involves not dispersing particles but a three-dimensional monolithic structure like a sponge. Second, the phase growth proceeds in such a way that the average phase size to the fourth power increases proportionally to the number of cycles. Finally, in the vicinity of the joining interface, more rapid phase growth occurs compared to the other regions because local thermal strain due to the mismatch of thermal expansion leads to a remarkable phase growth.