Identification of Failure Mechanisms and Activation Energies of Opto Devices

Many types of opto electronic devices (couplers and light emitting diodes) are being used in space and military projects. This study reports on optocouplers and light emitting diodes (LED´s). A total of 2300 opto devices from five manufacturers was tested. These devices were subjected to rated, step stress, and accelerated tests of thermal cycle, high temperature, vibration and operating life to determine their failure mechanisms and associated activation energies. Previous studies and ALERT´s have shown that optocouplers had a high intermittent failure rate in thermal cycle. The manufacturers have devoted considerable effort to their redesign and improved testing to eliminate this problem. This study reveals that this problem has been eliminated with the exception of one manufacturer, and the designs are quite capable of passing 400 cycles from ¿55°C to +125°C. The optocouplers did not fail in mechanical tests, such as shock, acceleration and vibration. The predominant failure m-odes were found in operating life at selected temperatures between 25°C and +225°C. Typically these were degraded electrical parameters and open bonds attributed to high temperature exposure. The failed parts were analyzed to identify specific failure mechanisms for study and for the calculation of activation energies. The activation energies were calculated for the functional elements of the devices and ranged from . 42 eV to 1.3 eV.