High-Speed Testing Methods for LEDs
|Publication Date:||1 January 2017|
This report and the Technical Report CIE 225:2017 on optical measurement of high-power light emitting diodes (HP-LEDs, see 3.3) (CIE 2017) are intended to extend the scope of the technical report CIE 127:2007 on Measurement of LEDs (CIE 2007). This document deals with optical measurement of LEDs and high-power LEDs on wafer and at product level using pulse methods in the production environment. It does not describe the measurement methods for laboratories; such information can be found in (CIE 2017). The focus is on measurements during mass LED production for the purpose of LED sorting according to their different optical, colorimetric, and electrical properties, which is often referred to as the binning process. CIE 225:2017 covers the laboratory measurements of high-power LED products using DC methods. Both the pulse methods described in this document and the DC methods described in CIE 225:2017 reference measurements to the junction temperature of the LED.
Due to the very complicated LED production processes, starting from growing the epitaxial layers, via chip processing and final die packaging (die bond, wire bond, encapsulation, etc.) combined with the usage of various materials, it is necessary to test all LEDs to ensure a high quality in terms of specified colour, brightness, and voltage.
Since today's LED manufacturing processes suffer from process variations which are higher than accepted by the market, the LEDs must be sorted into various groups with narrow ranges of brightness, colour and other parameters, such as forward voltage, during the outgoing testing process. This leads to the need for precise and very fast testing methods and test equipment.
All optical and electrical parameters of solid-state light sources are highly temperaturedependent
Purpose of the report
The purpose of this report is to give recommendations for the testing of LEDs during production and the information that should be given to correctly interpret the results of these measurements. This is necessary especially due to the fact that ideal testing of light-emitting areas at a fixed, constant, temperature within around a 10-ms period is not possible. The rated operating conditions applied during the outgoing tests of LEDs at chip or package leve l usually do not and cannot completely correspond to typical operating conditions once the LEDs are assembled in their final application, which provides the thermal management necessary, e.g. for DC operation.
Within this report it will be shown that by proper specification of measurement conditions, including a proper definition of certain time settings, highly reproducible measurement results (necessary for good correlation between different levels of integration) can be achieved.