Reliability test and failure analysis of high power LED packages

A new type application specific light emitting diode （LED） package （ASLP） with freeform polycarbonate lens for street lighting is developed, whose manufacturing processes are compatible with a typical LED packaging process. The reliability test methods and failure criterions from different vendors are reviewed and compared. It is found that test methods and failure criterions are quite different. The rapid reliability assessment standards are urgently needed for the LED industry. 85℃/85 RH with 700 mA is used to test our LED modules with three other vendors for 1000 h, showing no visible degradation in optical performance for our modules, with two other vendors showing significant degradation. Some failure analysis methods such as C-SAM, Nano X-ray CT and optical microscope are used for LED packages. Some failure mechanisms such as delaminations and cracks are detected in the LED packages after the accelerated reliability testing. The finite element simulation method is helpful for the failure analysis and design of the reliability of the LED packaging. One example is used to show one currently used module in industry is vulnerable and may not easily pass the harsh thermal cycle testing.

Thermal Performance Analysis of LED with Multichips

The package and system level temperature and thermal stress distributions of 10 W light emitting diode （LED） with 4 chips and 100 W LED with 100 chips were investigated using finite element analysis. The chips were arranged on a Si sheet which is soldered on the copper/diamond composite slug with very high conductivity. The experimental results show that the maximal temperature appears in the chips of both two high power LEDs packages. Compared with the 10 W LEDs package with 4 chips array, the heat issue caused by stacking and coupling of the heat in 100 W LEDs package with 100 chips array is more serious. The chip temperature in the center of the array is much higher, and it decreases with the distance between the chip and the center of LEDs increases. Great thermal stress lies between the chips and the solder, which will reduce the reliability of the package.

Thermal diffusivity of light-emitting diode packaging material determined by photoacoustic piezoelectric technique

Thermal property is one of the most important properties of light-emitting diode （LED）. Thermal property of LED packaging material determines the heat dissipations of the phosphor and the chip surface, accordingly having an influence on the light-emitting efficiency and the life-span of the device. In this paper, photoacoustic piezoelectric （PAPE） technique has been employed to investigate the thermal properties of polyvinyl alcohol （]？VA） and silicon dioxide, which are the new and the traditional packaging materials in white LED, respectively. Firstly, the theory of PAPE technique has been developed for two-layer model in order to investigate soft materials; secondly, the experimental system has been set up and adjusted by measuring the reference sample; thirdly, the thermal diffusivities of PVA and silicon dioxide are measured and analysed. The experimental results show that PVA has a higher thermal diffusivity than silicon dioxide and is a better packaging material in the sense of thermal diffusivity for white LED.

Ceramic-metal package for high power LED lighting

High power light-emitting diodes （LEDs） lighting has drawn a great interest in the field of street light system in recent years. Key parameters for successful launching of LED street light in the commercial market are price and light efficiency, respectively, and they are greatly influenced by the materials and design factors used in high power LED package. This article presents a new design and materials processing technology to realize the solution of LED packaging with advantageous in price and performance. Cost effective materials and processing technology can be realized via thick film glass-ceramic insulating layer and silver conductor. Highly effective thermal design using direct heat dissipation to heat sink in LED package is demonstrated.

A Low Temperature Vulcanized Transparent Silane Modified Epoxy Resins for LED Filament Bulb Package

In this work, low-temperature vulcanized, transparent silane modified epoxy resins for LED filament bulb package were prepared. Firstly, transparent silane modified epoxy resins were produced through a controllable sol-gel method using γ-（2,3-epoxypropoxy）propytrimethoxysilane and dimethyldiethoxylsilane. The features of the reaction were investigated and the products were characterized in detail. Subsequently, various curing agents were explored to prepare transparent silane modified epoxy resins. The silane modified epoxy resins cured by PEA-230 at a fairly low temperature（40 °C/2 h then 60 °C/1 h） exhibited excellent thermal stability with a thermal degradation temperature as high as 316.5 °C and adjustable hardness between 40-60 shore A. The application tests showed the materials obtained were good candidates for LED filament bulb package.

Packaging technology of LEDs for LCD backlights

We design a package patterned with red and green emitting phosphors excited by a blue LED to emit tri-basic mixing color.For high backlight display quality, we compare several phosphors.According to our measurements, green phosphors 0752G, 0753G and red phosphor 0763R are preferred for producing a good backlight source.Compared to RGB-LED backlight units, this frame typically benefits the lighting uniformity, and can sim-plify the structures.It also provides higher color render and better CCT than the traditional package method of a yellow phosphor with a blue chip.However, its light efficiency needs to be further improved for the use of backlights for LCDs.

Comparison of the copper and gold wire bonding processes for LED packaging

Wire bonding is one of the main processes of the LED packaging which provides electrical interconnec- tion between the LED chip and lead frame. The gold wire bonding process has been widely used in LED packaging industry currently. However, due to the high cost of gold wire, copper wire bonding is a good substitute for the gold wire bonding which can lead to significant cost saving. In this paper, the copper and gold wire bonding processes on the high power LED chip are compared and analyzed with finite element simulation. This modeling work may provide guidelines for the parameter optimization of copper wire bonding process on the high power LED packaging.