Current Leakage Detection – Tools and Techniques
One of the single most common failures that plague modern electronic devices is current leakage. This leakage can manifest in many ways; some devices may exhibit normal functionality with excessive power consumption, while others may stop working altogether. This is partly due to the multitude of different causes for current leakage – improper processing, packaging, or handling (in the form of electrostatic discharge damage) can result in defects that will draw excessive current, as can electrical overstress of a device in the field. Since current leakage is such a common failure mode, a good failure analyst will have many different tools to assist in the detection and isolation of defects that may cause anomalous current draw.
One of the most common techniques for detecting current leakage is the use of a liquid crystal whose properties change with temperature. All defects that draw excessive current will give off a thermal signature due to the process of Joule heating; by applying a film of liquid crystal onto the surface of a failing semiconductor die and applying power, an analyst can isolate a defect visually by looking for changes in the crystal caused by the heat from the anomaly. Another technique that works similarly is fluorescent microthermal imaging, in which a compound whose fluorescence changes depending on temperature is painted onto a device and a high-gain camera system is used to detect minute changes in the li9ght emitted by the compound. For more precise measurement of temperature, infrared cameras can be used to detect even the most minute changes in a device’s temperature (which, of course, allows for the isolation of even smaller defects).
In addition to techniques based on the detection of heat produced by current leakage, some tools work by measuring the current drawn by a device directly under various conditions. Techniques like Laser or Thermally Induced Voltage Alteration (LIVA / TIVA) work by measuring the current draw of a device very precisely, then bombarding the part with energy in the form of a laser beam. When this energy interacts with a defect, the amount of current drawn by the device may go up or down depending on the type of problem causing the current draw. These changes can be mapped onto an image of the device, which can then be used for further analysis.
Current leakage detection is a key capability for failure analysis of any electronic device. By isolating a site that draws excessive current, an analyst is able to zero his or her efforts in on a single point, digging into a problem and finding the root cause of failure.
Derek Snider is a failure analyst at Insight Analytical Labs, where he has worked since 2004. He is currently an undergraduate student at the University of Colorado, Colorado Springs, where he is pursuing a Bachelors of Science degree in Electrical Engineering.