Techniques for analyzing LEDs
A first step in doing failure analysis of Light Emitting Diodes (LEDs) is recognizing the failure symptoms. Often the LEDs fail to produce any light or flicker due to intermittent electrical contact within the device.
Failure analysis of LEDs often finds that the LEDs fail due to de-bonding of the lens material from the cup or the surface of the die due to thermal stress resulting from a large thermal expansion mismatch between the lens material and the other materials used in their construction. At SEM Lab, Inc. our LED failure analysis typically involves creating microsections and performing SEM/EDS analysis to characterize these failures.
Below is a summary paper describing various LED failure modes that have been seen here at SEM Lab, Inc. These failures resulted in intermittent conditions and included die attach failure, die cracking, wedge bond failure and ball bond failure. In most cases, these LED failures are induced by mechanical or thermo-mechanical stresses.