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Light emitting diodes (LEDs) are today standard and mature light sources. They have several key advantages, like small size, low energy consumption and long lifetime. However, high reliability of the LED system is required to achieve long lifetime of the light source. Thermo-mechanical stress due to temperature cycle causes failure of electronic systems. The electronic component itself or the interconnect device, e.g. printed circuit board (PCB) might fail. In many cases, the weakest link is found to be the solder interconnect between package and the board. Cracking of the interconnect causes an open contact and the system fails. In this paper we compare the existing methods to investigate LED interconnect failures during temperature cycle tests like the simple “light-on-test”, electric resistance measurement and the shear test. We describe and introduce the transient thermal analysis as a measurement method. We present the first reliability data analysis with transient thermal analysis of ceramic high power LED packages on Al-IMS during air to air thermal shock test (−40°C to +125°C) and correlate it with cross sections. We demonstrate the sensitivity of the thermal analysis to detect solder joint failures of the assembly. We compare the results with electric resistance measurements and light on tests and show that the resolution is significantly higher compared to the methods applied today. The sensitivity of the method enables us to detect the crack in a solder joint much earlier than the final failure of the joint, i.e. the open contact.

AbstractÀLight emitting diodes (LEDs) are today standard and mature light sources. They have several key advantages such as small size, low energy consumption, and long lifetime. However, high reliability of the LED system is required to achieve long lifetime of the light source. Thermomechanical stress due to temperature cycling causes failure of electronic systems. The electronic component itself or the interconnect device, for example, the printed circuit board (PCB), might fail. In many cases, the weakest link is found to be the solder interconnect between the package and the board. Cracking of the interconnect causes an open circuit and the system fails. In this paper the existing methods are compared in order to investigate LED interconnect failures during temperature cycle tests such as the simple light-on test, electric resistance measurement, and the shear test. This paper describes and introduces transient thermal analysis as a measurement method. This paper presents the first reliability data analysis with transient thermal analysis of ceramic high power LED packages on printed circuit boards, that is, insulated metal substrates, during the air-to-air thermal shock test (2408C to +1258C) and correlates it with cross sections. This work demonstrates the sensitivity of the thermal analysis to detect solder joint failures of the assembly. This paper compares the results with electric resistance measurements and light-on tests and shows that the resolution is significantly higher compared with the methods applied today. The sensitivity of the method enables the detection of a crack in a solder joint much earlier than the final failure of the joint, that is, the open circuit.

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