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.

Efficient solutions for hot-rolling mill modernizations and upgrades

The recent steel boom was characterized by a steep increase in world wide hot-rolling capacity.Still new hot-rolling mills are scheduled to start production during the coming years.Existing plants,which may be in operation since decades,have to compete with brand-new equipment and technology in terms of product quality and production efficiency.SMS Siemag have developed and successfully applied overall modernization concepts for hot-rolling mills as well as well-defined upgrade packages dedicated particularly to the improvement of product quality and the enlargement of product range.This paper describes the general methods of how SMS Siemag approaches hot-rolling mill modernization projects for maximum customer benefit and describes examples for overall modernization concepts as well as for powerful upgrade packages which have been put into operation during the recent years.

Discharge Characteristics of Bubbles at Interface Between AIN Ceramic and FC-72 Liquid

In order to evaluate the insulation of two-phase immersion cooling in the HV power electronic package,the insulation degradation of the dielectric interface induced by bubbles is investigated.In this paper,a test strategy with 50 Hz unipolar DC and AC combined voltage for partial discharge(PD)at boiling interface of AlN ceramic is proposed.The insulation threshold of an AlN ceramic surface is acquired in several dielectric environments,such as air,FC-72 liquid(FC-72,a Fluorinert^(TM) from 3^(TM)),FC-72 vapor,and boiling state of FC72.This reveals the deterioration of boiling on the insulation of the surface immersed in the dielectric refrigerant.To investigate the mechanism of the PD feature at the boiling interface,the PD patterns of the unrestricted bubble and the accumulated bubble are acquired and contrastively analyzed.Combined with the feature of the back discharge and the bubble behavior,the charged vapor-ceramic interface is relatively stable due to the accumulated vapor layer.This stability of the charged vaporceramic interface is broken if the bubble is unrestricted.Besides,it is discovered that the vapor-liquid interface inside the bubble may be another charged interface,which can also trigger a back discharge.

Optimal design analysis for thermal performance of high power 2.5D package

Based on ANSYS and Icepak softwares, the numerical analysis method is used to build up the thermal analysis model of the 2.5D package, which contains a high power CPU chip. The focus of the research is on the determination of the contributing factors and their effects on the thermal resistance and heat distribution of the package. The parametric analysis illustrates that the substrate conductivity, TIM conductivity and fin height are more crucial for heat conduction in the package. Furthermore, these major parameters are compared and analyzed by orthogonal tests, and the optimal solution for 2.5D integration is proposed. The factors＇ influence patterns on thermal resistance, obtained in this article, could be utilized as a thermal design reference.