Development of a new low-stress hyperred LED encapsulant

The development of a transparent encapsulant for a hyperred LED is presented. The encapsulant was evaluated and compared with various encapsulants from several suppliers. All encapsulants were evaluated by monitoring the behavior of the LEDs in laboratory quality tests and performing failure analysis. The correlation between chemistry and final optical and mechanical properties of the encapsulant, plus their influence on the lifetime of the LED crystal, is elucidated. Three failure mechanisms are commonly observed: corrosion, mechanical stress, and open circuits due to wire breaking. By careful selection of chemistry and optimization of processing and manufacturing procedures, these can be circumvented. The resulting LED has a high light output, good stability during operation under various conditions, and few open circuits in temperature cycling, even after 200 cycles. Finally, the encapsulant does not show any yellowing under extreme weathering conditions or during lifetime.<
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