Study of strip-filling for old room and pillar mining goaf
According to the problems of land resources destruction and environmental pollution caused by the collapse of old room and pillar mining goaf, a goaf security evaluation model was established and applied to the safety assessment of a colliery in Ordos city. The results indicated that the room and pillar mining goafs in this coal mine area would fail with time passing. To solve the problems, with analyzing the structural characteristics and activation mechanism of old room and pillar mining goaf, based on the theory of strip mining, a new method of strip-filling for controlling subsidence of old room and pillar mining goaf was put forward and used in designing of the strip-filling plan of the colliery, the filling effect prediction have been worked out. It demonstrates that the strip-filling method is economically feasible.
Study on the Comprehensive Assessment of the Western Regions Ecological Environment
In recent years,the ecological environment in the western regions of China has been in a severe situation on the whole because of the inherent frangibility of western regions ecological environment on the one hand,and the man-made,economic,political and legal factors on the other hand.Therefore,the western region would shoulder double duties of environmental protection and economic development.Faced with the double tasks,the western region should adopt interactive model of development and establish the index system of comprehensive assessment on its ecological environment,so as to implement double wins in environmental protection and economic development and improve its ecological environment,at the same time realize the sustainable development of western regions ecological environment,economics as well as society.
Ultrathin Wafer Pre-Assembly and Assembly Process Technologies: A Review
Ultrathin silicon wafer technology is reviewed in terms of the semiconductor applications, critical challenges, and wafer pre-assembly and assembly process technologies and their underlying mechanisms. Mechanical backgrinding has been the standard process for wafer thinning in the semiconductor industry owing to its low cost and productivity. As the thickness requirement of wafers is reduced to below 100 μm, many challenges are being faced due to wafer/die bow, mechanical strength, wafer handling, total thickness variation (TTV), dicing, and packaging assembly. Various ultrathin wafer processing and assembly technologies have been developed to address these challenges. These include wafer carrier systems to handle ultrathin wafers; backgrinding subsurface damage and surface roughness reduction, and post-grinding treatment to increase wafer/die strength; improved wafer carrier flatness and backgrinding auto-TTV control to improve TTV; wafer dicing technologies to reduce die sidewall damage to increase die strength; and assembly methods for die pick-up, die transfer, die attachment, and wire bonding. Where applicable, current process issues and limitations, and future work needed are highlighted.