Deep analysis of LED failures

The light source of the LED is composed of a so-called III-V compound, which is a well-known epitaxial crystal chip. The solid compound itself is very stable and is not easily damaged under the conditions specified by the product. There is no chemical reaction in the application environment, so it has a long product life. However, in order for the LED chip to emit light, it is necessary to pass current from the outside. Therefore, a chip having a small size is generally attached to a specific stage (or a lead frame) and connected to a chip by a metal wire or a solder material. The positive and negative poles, and then the entire stage is covered with polymer material. This is the so-called packaging process. After this process, it becomes a common LED light particle on the market. In actual application, several LED light particles are assembled into modules as needed, and finally combined with other functional modules to become a terminal product.

As can be seen from the above, the failure of an LED product may originate from any part of the product, so it must be stripped to find the true cause of failure. In view of the failure from the LED lamp particles, the LED chip itself is strong in the complete LED lamp grain, but the package material of the package chip is susceptible to damage. Therefore, the failure of the LED lamp grain can be attributed to the packaging material. Caused by damage or deterioration. To fully understand such failures, involving expertise in the fields of optics, chemistry, materials science, and electronic physics, and with sophisticated instruments and rich practical experience, we can confirm the failure point and derive the true cause, and then propose improvement measures. .

1. No light: This kind of failure means that the LED does not emit light at all when it is energized. In general, the "open" on the conductive path is one of the main causes of this type of failure. The method of confirming the open circuit is also very simple, and can be verified by a common three-meter. However, in order to find the break point, further analysis is necessary. For example, X-ray can be used to confirm whether the wire is broken or detached, and the structure of the cross section can be observed by SEM (scanning electron microscope) to check the defect of the die-shaped portion. Wait. The second main cause of this type of failure is "short". This is because the current does not pass through the LED chip, but flows through the "next door", so the LED lamp particles naturally do not emit light, such as: due to electron migration. Abnormal diffusion of electrode metal atoms, such as indium tin oxide (ITO), silver, or barrier metals in GaN/InGaN diodes, can occur due to mechanical stress, high current density, or corrosive environments. Other reasons may be wire shifting, adhesive gelling, etc. This failure must be determined by the IV curve (current-voltage diagram). As the failure point cannot be checked from the appearance, it needs to be confirmed by X-ray; or the chemical solution is used to remove the LED package material. Check optically (OM) or electron microscopy (SEM).

Short circuit

Open circuit disconnection

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