Eun-Beom Jeon

Bi-axial fracture strength characteristic of an ultra-thin flash memory chip

Recently, ultra-thin chips with thicknesses of under 35??m have emerged as an option for thinner, high performance electronic devices. For reliable electronic devices and high throughput packaging processes, the mechanical properties of ultra-thin chips need to be accurately understood. In this study, the fracture strength of an ultra-thin flash memory chip was measured using a ball-on-ring (BOR) test. To evaluate and validate the bi-axial strength in the BOR test, a finite element analysis was performed. It was compared with the analytical solution based on Hertzian contact theory. Flash memory chip specimens with different thicknesses were prepared and their bi-axial strengths were tested with respect to various wafer thinning process parameters such as grinding speed and polishing time. Raman spectroscopy was used to characterize the residual stress generated during the wafer thinning process. The surface roughness of the silicon wafer was measured using an atomic force microscope under various wafer thinning conditions. From the study, the fracture strength characteristics of the ultra-thin chip could be established as a function of the wafer thinning parameters.

Ultra-fast annealing to reduce the residual stress in ultra-thin chips using flash light

The continuing trend of miniaturization in electronic equipment includes demands for thinner and smaller semiconductor devices with higher performance. To ensure the reliability of electronic devices and to enable high-throughput packaging processes, the mechanical properties of ultra-thin chips need to be accurately understood. One important consideration is the residual stress generated during wafer thinning due to the shear force between the grinding wheel and polish pad; this stress can degrade the fracture strength of ultra-thin devices. To reduce this residual stress, we developed a flash light irradiation annealing technique, including optimization of the irradiation conditions of flash light energy, pulse number and pulse duration. The distributions of residual stresses within ultra-thin flash memory chips before and after the annealing were measured using Raman spectroscopy, and their fracture strength was measured using a ball-on-ring test. Also, transmission electron microscopy (TEM) analysis and beam transfer function tests were performed to investigate the changes in mechanical properties and changes to the silicon lattice effected by the annealing. The ultra-fast flash light annealing was found to reduce the residual stress of ultra-thin chips by 50%, thereby improving their fracture strength by 20% compared to unannealed chips.

Investigation of damping in the polymer concrete sleeper for use in reduction of rolling noise from railway

The purpose of this study was to measure damping of various polymer concretes to be used as sleepers for railway. The polymer concretes consisted of epoxy monomer, hardener and aggregates. Various polymer concrete specimens were made by changing epoxy resin weight ratio and curing temperature. The dynamic properties of the polymer concrete specimens were measured by using beam-transfer function method. To predict reduction performance of the polymer concrete sleepers, an infinite Timoshenko beam model was investigated after applying measured concrete properties. The moving loads from rotating wheels on railway due to different roughness were utilized in railway vibration analysis. The vibration response was predicted from which the effects of supporting stiffness and loss factor of sleeper were investigated. The radiated sound power was predicted using calculated rail vibration response. Consequently, the sound power levels were compared for rails supported by different polymer concrete sleepers. The resu...

Analysis of Interfacial Peeling of an Ultrathin Silicon Wafer Chip in a Pick-Up Process Using an Air Blowing Method

The ultrathin integrated circuit (IC) chip ejecting and pick-up process plays an important role in advanced packages since the success ratio and productivity are determined by the delamination of chips from the adhesive tape substrate. As thinning of the IC chip occurs, chip cracking between the adhesive tape and ultrathin IC chip increases due to the low strength of the ultrathin IC chip in the die pick-up process. In this paper, the interfacial adhesion strength and energy release rate between an ultrathin IC chip and base tape were measured by a 90° peel test as a function of the peeling velocity. Also, an index was defined to characterize the competing fracture behavior between the delamination of the chip from the adhesive tape and chip cracking. Finite-element analysis of the die pick-up process with a virtual crack-closure technique was performed to predict stable peeling off of the chip with respect to the velocity of the chip holder as well as the pressure of the blown air considering the interfacial energy release rate and chip strength. The results show that the velocity of the chip holder and the pressure of the blown air should be lower than 50 mm/min and 90 kPa, respectively.