The Dynamics of IR

IR imaging is based on the fundamental principle that when current flows through an electrical circuit it dissipates heat in resistive elements. By measuring the resulting radiated heat pattern with an IR camera, information about the current flow in the circuit can be obtained. The current pattern will be the same, within a statistically acceptable variation, for all properly functioning PCBAs (Figure 2).

However, defects, such as faulty, missing, misaligned or misplaced components, parts of wrong value or polarity, and opens or shorts, inevitably will disturb the flow of current directly or indirectly because of their effect on other components. Any current flow disturbance affects the PCBA's radiated thermal signature, causing some portions of the circuit to appear abnormally hot and/or other portions appear abnormally cold. By comparing these signatures with those of "good" assemblies, the anomalous hot/cold regions can be located quickly and easily.

Because the PCBA is imaged, its entire surface, regardless of component density, is "probed" simultaneously with a surface resolution determined by the imaging capability of the IR camera(s). Today's IR test systems can probe a 16 x 24" board effectively with more than 153,000 virtual IR probes in less than 15 seconds. Except for tooling pins to position the board accurately and repeatedly and power connections, there is no physical contact with the board under test. Hence, set-up time and fixturing costs are minimal.