Electronics Design Validation through Infrared Measurements

Reliability Challenges in Test Equipment: Overheating PCB Components Under Investigation

A manufacturer of electronic test equipment is experiencing reliability issues with its waveform analyzer, which is suspected to be caused by overheating components on one of the printed circuit boards (PCBs) within the chassis.

Comprehensive research is conducted on all electronic components on the suspect board to ascertain their maximum operating temperatures. The board is then mounted on a test stand and powered to replicate the conditions during processor-intensive use. Key components are measured with a contact thermometer to determine if any are operating above their maximum temperatures. While all are within their specified limits, several are found to be operating close to their maximum temperatures.

The issue with using thermocouples for temperature measurement on very small structures, such as an surface-mount device (SMD), is that they need to reflect the true temperature of the electronics accurately. For small PCB components, the thermal mass is quite small. Compared to these small SMD components, a thermocouple has enough thermal capacity to influence the component’s temperature while being tested. The thermocouple and its wiring draw heat away from the electronics component, resulting in lower temperature readings than the actual temperature of the SMD component without the thermocouple. Consequently, this leads to the measurement of smaller temperature amplitudes in static conditions and inaccurate thermal dynamics readings.

It is concluded that temperature testing within the equipment chassis is necessary to account for the impact of internal temperatures in an enclosed casing on component temperatures. Remote temperature measurements are deemed challenging due to potential line-of-sight obstructions caused by the equipment enclosure.

Optimizing Temperature Measurements in Electronic Enclosures with Infrared Technology

In general, the thermographic inspection of electronic components and assemblies is an established test procedure for failure detection and quality management, from developing initial prototypes to serial production. This method detects various issues, such as hotspots and atypical temperature distributions on the surface of printed circuit boards, integrated circuits, and multichip modules. It will identify increased abnormal contact resistances, hidden cracks in joints, power losses due to RF mismatch, incorrect thermal connections of heat sinks, short circuits, and soldering defects such as cold solder joints.

In this application, an infrared camera, used with IR transmissive materials, accurately assesses the temperatures of all critical board components while replicating a typical operating environment within the equipment enclosure (chassis). A top cover section is removed and tested with several infrared transmissive materials, starting with Saran wrap. The Saran wrap proves highly transmissive in the infrared region, attenuating less than 10% of the signal. Still, it flutters when the instrument fan is engaged, and its durability poses some problems. Zinc Selenide is considered the best solution due to its durability and ability to permit visual observation. Still, the cost of a window large enough to cover the entire PC board is prohibitive. Calcium Fluoride infrared windows, commonly used for electrical switchgear infrared testing, are the best solution. Although their infrared transmission is less than that of ZnSe, this can be accounted for when producing accurate measurements. The metal housings of the infrared windows make them easy to mount into the metal enclosure, and their affordability allows several windows to gather data on all key components. Two devices are immediately determined to be operating over temperature due to their mounting locations next to other heat-producing devices and inadequate airflow to disperse heat from hot devices.