Development of a nondestructive miniature X-ray system for the inspection of through silicon via in 3-dimensional stacked semi-conductor packaging

Abstract

A new concept for a non-destructive testing device using a novel carbon nanotube (CNT) based miniature X-ray tube is proposed. The device can be used for small-scale internal inspection of objects. To investigate the effectiveness of the proposed concept, the device was fabricated and its performance was systematically analyzed. The non-destructive testing device consists of a CNT based miniature X-ray tube, a scintillator, an optical lens, and a detector. The size of the focal spot needed to identify objects as small as $5$ $\mu m$ was calculated through simulation. An electron optics simulation software, E-GUN, was used to optimize the geometries of both the focusing cup and the X-ray target to achieve the desired focal spot size of X-ray tube. CNT based miniature X-ray tube was fabricated using the brazing process and an NdFeB focusing lens was used to further reduce the focal spot size. XR images were obtained using the fabricated device and the spatial resolutions of the images were evaluated using the modulation transfer function. The fields of view (FOV) per probe are $7.1$ $mm^2$ and $1.8$ $mm^2$ when using a 5x optical lens and a 10x optical lens, respectively. The FOV can be increased by increasing the number of probes incorporated into the device. MTF10 values were determined to be $105$ $lp/mm$ and $230$ $lp/mm$ when using 5x optical lens and 10x optical lens, respectively. By using an optical lens to enlarge the XR images, the effect of focal spot was minimized and clear XR images were obtained. The fabricated non-destructive testing device exhibits sufficient capability to effectively inspect the internal components of objects.