Inline Rth control: Short time thermal transient evaluation for high power LEDs

As junction-to-case thermal resistance RthJC is a primary performance and reliability parameter for high power light emitting diodes (LED) an accurate specification of this value is of paramount importance. Currently thermal transient characterization methods are reserved to research and quality laboratories. Especially the thermal calibration procedure requires an enormous effort of time. Therefore the RthJC specification of a high volume production is based on a statistical approach. However, high test coverage or even a single unit test is desired. This paper presents a method for inline Rth control for high power LEDs. By skipping the conventional thermal calibration procedure the method compares the measured response of the device under test with a completely thermal characterized reference curve of a reference device. It enables to detect variations in thermal interface materials, e.g. failures in the thermal adhesive attach, with sufficient accuracy within some hundred milliseconds testing time. The achieved measurement results verify the applicability of inline Rth control in a high volume production.