Examples of Defects of LED Products/Chip Capacitor

Lighting failure [Failure of LED product]

I-V characteristic of LED
I-V characteristic of LED

Thermal expansion of mold resin due to continuous lighting may cause sequential non-lighting.

Possible causes are:

  1. Connection failure at the 1st bonding portion;
  2. Break at the 1st bonding neck portion; (Grain coarsening due to the thermal effect during bonding)
  3. Break at the 2nd bonding portion (Corrosion, joint failure, effects during resin molding, etc.)
Cross section of LED Cross section of LED
1st bonding portion 1st bonding portion
SIM image of 1st bonding neck portion SIM image of 1st bonding neck portion

SIM:Scanning Ion Microscope

Internal electrode crack [Failure of chip capacitor]

chip capacitor Chip capacitor

Crack may be generated in the internal electrode area of the chip capacitor, causing a failure.

Due to the warp of the mounting substrate, crack may be generated starting from the solder joint on the bottom of the chip capacitor. If a crack is generated crossing electrodes, failures such as short-circuit and insulation degradation will become apparent.

The base material of the chip capacitor is ceramic such as barium titanate which is a dielectric, and many internal electrodes are laminated inside the chip capacitor. Therefore, due to a shock such as bending, crack is easily generated.

Cracking of the chip capacitor may be generated at the time of the dividing of the mounted substrate and similar occasions.

Cross sectional view of cracking of the chip capacitor Cross sectional view of cracking of the chip capacitor
Crack starting point Crack starting point
Crack may be generated due to the warp of the mounting substrate
Crack may be generated due to the warp of the mounting substrate

Short circuit between internal electrodes [Failure of chip capacitor]

Chip capacitor Chip capacitor Cross-section of the chip capacitor Cross-section of the chip capacitor

Short-circuited chip capacitor was found at the market.

As the examination result of the cross section of the chip capacitor, it was found that the portion between the internal electrodes was short-circuited. As stress over the withstand voltage is not applied to this chip capacitor, and the failure is dependent on the lot of the chip capacitor. Therefore, it is presumed that the short-circuit was caused by a poor insulation between the internal electrodes.

The portion between the internal electrodes is short-circuited, causing a crack on the dielectric.

Optical microscope obsevation of chip capacitor cross section Optical microscope obsevation of chip capacitor cross section

On another product in the same lot On another product in the same lot

On another product in the same lot, a slight trace of short-circuit is recognized on the internal electrode.

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