Photothermal activated failure mechanism in polymer-based packaging of low power InGaN/GaN MQW LED under active storage

Article history: Received 22 May 2015 Received in revised form 15 June 2015 Accepted 23 June 2015 Available online xxxx GaN-based LEDs often use polymermaterial as chip coating. The most used polymer coatings are siloxane-based materials such as poly(methyl-phenyl-silixane) – PMPS – or poly(dimethylsiloxane) — PDMS. Although their thermal properties offer great possibilities to justify their integration in optoelectronic devices, pellicular effect may occur. This paper points out a pellicular failuremechanism occurring inMQWGaN-based LED submitted to active storage (1500 h/30 mA/85 °C) determined from their environment stresses. Before aging, an absorption/ reemission fluorescence process has been extracted. By performing fluorescence analysis, we have found out the cause of such mechanism coming from silicone oil (polymer coating). Additional physico-chemical analyses, consisting of H NMR and MALDI-TOF mass spectrometry, have been investigated to work out the origin of the absorption/reemission process. The presence of low molecular weight molecules (LMWM) playing the role of fluorophoremolecules is responsible for it. After aging, 65% optical power losses have been reported. A combination of electro-optical characterizations andphysico-chemical analyses has led to themain failuremechanismextraction that is the molecular change of silicone oil activated by photothermal phenomenon. Such pellicular failure mechanism has been suggested to be linked to polymerization or cross-linking of silicone oil usually present in GaN-based LEDs. © 2015 Elsevier Ltd. All rights reserved.