COB-based failure analysis
2014/11/14
This article describes the COB packaging technology, LED-based lighting products and several common causes of failure mode analysis. And described the prevention and improvement in COB package, the whole lamp structure design application process countermeasures. Can improve product reliability to some extent.LED has been globally recognized as a new generation of environmentally friendly high-tech light, its long life, high reliability is to get the majority of consumers. Although from a technical point of view LED chip theoretical life of up to 100000 Hours, but because of the package, driving, cooling and other technologies applied to the life of the light source or luminaire for general illumination class can only reach 30000 hours, there are many on the market even with no to six months will be a problem of the products. How to improve the reliability of LED lighting products has also been a business problem to be solved.
LED lighting product failure modes can generally be divided into: chip failure, package failure, failure of electrical stress, thermal stress failure, assembly failure. Through the analysis of these phenomena and the failure to improve, we can design and produce high-reliability LED lighting products to help. Based on the COB packaging technology and its application several common reasons for failure are analyzed and described the matter should be paid attention to summarize.
1, based on the characteristics of COB LED products
LED lighting products consists of three main components, namely cooling structure, power supply and lighting parts. Illuminated by the light source portion and a secondary optical light components (such as lenses, mirrors, and the diffusion plate) components.
As LED lighting products in the light part of the core components, is the basis for achieving photovoltaic device performance. The technology is based on a package COB light source, which itself is no longer needed any automatic surface mount process, just to elicit positive and negative welding can be assembled into a simple matrix or lighting. Figure 1 shows its importance in LED lighting products in key components.
These components are, in particular, COB, in most cases, are assembled by hand. This has resulted in the production process is likely to produce more than a potential failure in an automated process.
2. Cause Failure Analysis COB
Based COB LED packaging technology is the multi-chip structure with different string and then wire bonding method to establish an electrical connection between the chip and the substrate, the final package from the use of encapsulants. This structure determines the interior of any single chip COB bad, will result in the remaining surplus chip current load increases, then rising single Vf value, the drive power supply into the output overvoltage condition, the output abnormalities lead flashing until the death of the remaining branches lights. The reason to exclude bad chip itself, in most cases the performance of poor inter-chip bond together, our conventional single-bonded to the bonding wire is divided into five key points ABCDE, and poor bonding is the most common encountered in the actual the reason.
