Overview of Various Failures of Luminaires Assembled with SMD LED Chips

Abstract

This work describes common mistakes that are present in luminaires with light emitting diodes (LED) and suggests possible solutions or rather procedures and points that cannot be omitted during both luminaires manufacture and usage. LED packaging is designed to provide mechanical support, electrical connection, thermal management, spectral transformation, and optical control to the LED dies [1]. The LED chip package therefore brings a large variety of reliability issues that are described in the following work. The quality of wirebonds on an LED with soft chip encapsulant was negatively affected during placement. This is minimized when the setting of the machine is optimal, but further handling must also use softer approach when compared to LED chips with hard shell. Mismatch in coefficient of thermal expansion (CTE) also played a significant role in reliability due to fractures in solder joints as our measurement showed and the improper thermal design caused deterioration in the optics that further led to overheating. Several studies were conducted on the reliability calculations, taking into account theoretical or manufacturer declared properties of various LED chips or high power LED chip arrays [2], [3] or whole lighting system including the driver electronics (calculating with initial power consumption, efficiency of the optical system etc., trying to estimate remaining useful life of the entire system [4], [5]. However, real life situations bring into play other, usually unexpected factors such as improper handling.