LED light source is constituted by the so-called III-V compound well-known epitaxial grain size (chip), the solid-state compounds, by their nature very stable under the conditions of the product specification is not easy to damage, while in general application environment, not from a chemical reaction, and therefore have a longer product life. However, the LED chip LED current must pass by the outside world, and therefore will generally small size of the chip adhesive in specific loading units (or lead frame), and materials such as wire or solder connection chip positive and negative poles, and then wrap the whole contained units with polymer materials, which is the so-called packaging process, the LED lights for a variety of common dolphin after this system Chenghou Cheng tablets. In practical applications, but also depending on the required pieces of LED light particles assembled into modules, and finally the end products with other functional modules combination.
From the foregoing, the failure of an LED products, the cause may come from any part of the product, and therefore to be unraveling in order to find the real cause of failure. For failure from the LED light particles in terms of complete LED light particles, the LED chip itself is very strong, but the cladding chip packaging materials are vulnerable to damage, therefore, the failure of the LED light particles can be attributed to the packaging materials damage or deterioration caused by To fully resolve such failure involves expertise in the field of optics, chemistry, materials science, electronics, physics, and with sophisticated equipment and extensive practical experience in order to confirm the point of failure and derive true due, and then propose improvement measures . The IST for the LED product failure test, the general category of LED failure phenomenon, which also developed a corresponds to the analytical approach, to take this text will be multi-service LED customers experience a share in the past three years:
(1) does not shine: The failure refers to the LED power completely non-luminous. In general, the conductive paths on the circuit (open) “one of the main reasons for failure in this class, confirm the method of the circuit is very simple, common multimeter can verify. However, to find the trip points have to do further analysis, such as: the available X-ray to confirm whether the wire is broken or out of profile structure can check the most die-attach defects observed with SEM (scanning electron microscope) and so on. The second main cause of failure in this class is a “short-circuit (short), which is not really current through the LED chip, but flows through the” heretical “, so luminous LED light particles will naturally not, such as: a result of the electron mobility lead normal diffusion of electrode metal atoms, such as indium-tin oxide (ITO), silver or GaN / InGaN diodes, the barrier metal and so on may occur due to mechanical stress, high current density or corrosive environments such abnormal. The other reason may be the line shifts, climb plastic die-attach adhesive. This failure must take advantage of the IV curve (current – voltage diagram) to determine As for the point of failure can not be checked because the appearance of the above defects, you must first X-ray to confirm; or chemical solution to remove the LED packaging materials, and then carefully examined using optical (OM) or electron microscopy (SEM).
2 color: This type of failure is the status of the LED is not lit, the appearance of color or transparency of the plastic material and new, can be seen with the naked eye, usually used for a period of time or done reliability test. Generally speaking, of discolored areas can be broadly divided into two types in the lead-frame or plastic packaging material, occurred in the lead-frame, usually because the chemical reaction in the surface and the environment, such as oxide or sulfide to distinguish belongs to which relies on the component analysis instruments can be used include EDS (Energy Dispersive X-ray Spectroscope), XPS (X-ray Photoelectron Spectrometer), AES (Augur Electron Spectroscope), etc. Packaging plastic material color, belong to the degradation phenomenon of polymer materials, such as epoxy resin susceptible to high temperature or UV impact yellowing white LED changed to silicone replaced. Analysis such failure should pay special attention, because of the plastic material itself has a certain degree of transparency, sometimes discoloration of the lead frame due to be covered by the plastic material mistaken for plastic materials change color, directed to the wrong direction of improvement.
3 light failure: This failure means the LED light intensity is lower than the new. As described in the previous section, the degree of light failure has become an important indicator to judge the life of LED lighting products, so this type of failure analysis is very important. On the whole, the analysis of failure in this class is very complex, are many factors that affect light intensity, such as chip deterioration, the deterioration of the reflector cup, the plastic material and the decline of delamination, the transparency of the plastic material between the chip and wire joints resistance rise thermal resistance is too high, and so on, in the white LED, you need to consider the problem of the deterioration of the phosphor for white LED typically use one or more phosphors, they will be subject to the influence of heat or moisture and decay and reduce efficiency, causing the output of light and color changes. The analysis techniques include: non-destructive testing, such as visual inspection, LED power curve, the integrating sphere optical characteristics, etc., with the comprehensive judgment of the above data, one by one to exclude infer possible causes, followed by destructive analysis, using samples The preparation of the technical production for the analysis of samples, supplemented by a variety of instruments such as the SAT (Scanning Acoustic Tomography,), sonography, FTIR (Fourier Transform InfraRed) Fourier transform infrared spectroscopy, TEM (Transmission Electron Microscope) transmission electron microscope be verified, in order to really due to the SEM (Scanning Electron Microscope,) and so on.