page_title: Scanning SQUID microscopy
section_title: Short in a 3D Package
hierarchical_section_title: Scanning SQUID microscopy / Applications / Short in a 3D Package
caption_attribution_description: English: 3D SQUID overlaid XRay
context_page_description: Scanning SQUID microscopy is a technique where a superconducting quantum interference device is used to image surface magnetic field strength with micrometre scale resolution. A tiny SQUID is mounted onto a tip which is then rastered near the surface of the sample to be measured. As the SQUID is the most sensitive detector of magnetic fields available and can be constructed at submicrometre widths via lithography, the scanning SQUID microscope allows magnetic fields to be measured with unparalleled resolution and sensitivity. The first scanning SQUID microscope was built in 1992 by Black et al. Since then the technique has been used to confirm unconventional superconductity in several high-temperature superconductors including YBCO and BSCCO compounds.
context_section_description: Examination of the module shown in Figure 1 in the Failure Analysis Laboratory found no external evidence of the failure. Coordinate axes of the device were chosen as shown in Figure 1. Radiography was performed on the module in three orthogonal views: side, end, and top-down; as shown in Figure 2. For purposes of this paper the top-down x-ray view shows the x-y plane of the module. The side view shows the x-z plane, and the end view shows the y-z plane. No anomalies were noted in the radiographic images. Excellent alignment of components on the mini-boards permitted an uncluttered top-down view of the mini-circuit boards. The internal construction of the module was seen to consist of eight, stacked mini-boards, each with a single microcircuit and capacitor. The mini-boards connected with the external module pins using the gold-plated exterior of the package. External inspection showed that laser-cut trenches created an external circuit on the device, which is used to enable, read, or write to any of the eight EEPROM devices in the encapsulated vertical stack. Regarding nomenclature, the laser-trenched gold panels on the exterior walls of the package were labeled with the pin numbers. The eight miniboards were labeled TSOP01 through TSOP08, beginning at the bottom of the package near the device pins.
  Pin-to-pin electrical testing confirmed that Vcc Pins 12, 13, 14, and 15 were electrically common, presumably through the common exterior gold panel on the package wall. Likewise, Vss Pins 24, 25, 26, and 27 were common. Comparison to the xray images showed that these four pins funneled into a single wide trace on the mini-boards. All of the Vss pins were shorted to the Vcc pins with a
  resistance determined by the I-V slope at approximately 1.74 ohms, the low resistance indicating something other than an ESD defect.
  Similarly electrical overstress was considered an unlikely cause of failure as the part had not been under power since the time it was qualified at the factory. The three-dimensional geometry of the EEPROM module suggested the use of magnetic current imaging (MCI) on three, or more flat sides in order to construct the current path of the short within the module. As noted, the coordinate axes selected for this analysis are shown in Figure 1.
caption: Figure 3: A magnetic current image overlay on an x-ray image of the EEPROM module. Thresholding was used to show only the strongest current at the capacitor of the TSOP08 mini-board. Arrows indicate Vcc and Vss pins. This image is in the x-y plane.
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