Light Emitting Diode (LED) chips are the main components of LED lighting devices. LED is a solid-state semiconductor device that can convert electricity into light. In a wire-bond chip on board (COB), an LED chip is connected to the circuit electrodes via bonding wires. These wires are often thinner than human hair and can break due to thermomechanical damages and aging. The LED chips can also be damaged after repeated use or due to problems in the circuits connected to these chips. X-ray micro-CT (computed tomography) can inspect the wire bonding connection and other potential damages inside of LED chips nondestructively.
Analysis procedure
In this example, a malfunctioning LED package was scanned using a micro-CT scanner, CT Lab HX.
The CT image was compared to the visual observation of the damage.
The internal bonding wires were investigated for damages.
1. CT scan
The malfunctioning LED package shown in the picture was scanned to produce the 3D grayscale CT images.
2. Damaged area observation
The damaged (dark) area observed from the outside of the device showed a partially missing LED chip. The small particles seen around the square LED chips are the surrounding fluorescent material.
3. Bonding wire observation
All bonding wires of about 20 microns in width were seen clearly in this 3D rendered view of the LED package. One of the wires, the one that connects the LED chip to the lead frame, was found broken.
