Thermally induced voltage alteration (TIVA) is an imaging technique which uses a laser beam to pinpoint the location of electrical shorts on a device. The laser induces local thermal gradients in the device, which result in changes to the amount of power that the device uses.
A laser is scanned over the surface of the device while it is under electrical bias. The device is biased using a constant current source, and the power supply pin voltage is monitored for changes. When the laser strikes an area containing a short circuit, localized heating occurs. This heating changes the resistance of the short, resulting in a change in power consumption of the device. These changes in power consumption are plotted onto an image of the device in locations corresponding to the position of the laser at the time that the change was detected.
Original text: http://en.wikipedia.org/wiki/Thermal_laser_stimulation#Optical_beam_induced_resistance_change
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