The Use of Thermal Imaging to Assess Electronic Components

An investigation involving the use of thermal imaging has been undertaken, both on trimmed thick film resistors and on wave soldered joints to surface mounted devices. The surface mounted devices were ‘zero‐ohm’ jumpers which in themselves did not generate appreciable heat if current was passed through them, but also at the same time allowed the passage of DC current flow through the soldered joints. Thermal imaging results have shown the degree of current bunching obtained for thick film resistors trimmed using air abrasion. Appreciable changes in heating and hence in current density are not observed until the resistor has been trimmed with a cut extending into approximately 50% of the total width. In the case of soldered joints on surface mounted devices, it was found that thermal imaging techniques could not easily detect appreciable temperature changes and hence the current flow in joints which had previously been subject to stress due to one test or another. As a result, measurements were made on artificially damaged joints in order to determine the degree of damage that was needed for thermal imaging to show any noticeable effect. The joints were cut with a miniature PCB saw (1 mm wide) and it was not until the cut extended through approximately 60% of the soldered joint height that any appreciable thermal effects could be observed. Conclusions are drawn from these observations on the applicability of thermal imaging techniques to the assessment of trimmed resistors and soldered joint analysis.