• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.101-106
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• 2003

Recent electronic equipment becomes smaller, more functional, and more complex. According to these trends, LTCC(low temperature co-fired ceramic) has been emerged as a promising technology in packaging industry. It consists of multi-layer ceramic sheet, and the circuit has 3D structure. In this technology via hole formation plays an important role because it provides an electric path for the packaging interconnection network. Therefore via hole quality is very important for ensuring performance of LTCC product. Via holes are formed on the green sheet that consists of ceramic(before sintering) layer and PET(polyethylene Terephthalate) one. In this paper we found the correlation between hole quality and process condition such as ceramic thickness, and tool size. The shear behavior of double layer sheet by micro hole punching which is different from that of single layer one was also discussed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.1555-1558
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• 2005

In this study, we measured cylindricity and Runout of the air bearing spindle, and tested PCB(printed circuit boards) drilling with 0.4mm micro drill at 90,000rpm and 110,000rpm in order to obtain drilling hole error. Results are as follows; The air bearing spindle's Runout was not so high within $10\mu{m}$ from 20,000rpm to 80,000rpm but it grew after 80,000rpm. Drilling hole size error was 9% at 80,000rpm and 12% at 110,000rpm because of spindle's Run out. Drilled hole shape falsified more 110,000rpm than 90,000rpm.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.4 no.4
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• pp.42-49
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• 1995

It is not clearly known how defects or inclusions of a low carbon steel affect a fatigue strength. We study this issue using SM15C materials. The investigation is carried out by a quantitative evaluation, and experimental findings are: (1) a fatigue limit of A series smooth specimen is 205MPa, and that of B, C, D series is 245MPa, 304MPa and 245MPa, respectively. (2) the fatigue limit varies with respects to the stress distribution I the vicinity of a defects and crack. (3) the micro hole creates a half-circular shape crack, while the hole depth is not critical to the fatigue strength, (4) considering the fatigue strength, the hole diameter is more significant than the hole depth, and (5) Fatigue limit of artificially defected specimen is lower than that of a flawless one (5-10%), however, there exist allowance size and depth of defect which don't get to influence at fatigue limit.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.11a
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• pp.317-318
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• 2008

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2003.10a
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• pp.386-390
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• 2003

As a trial of application of hydrostatic pressure in micro fomring, burr-free punching has been conducted by means of hydro-mechanical procedure. Even though it is in beginning stage, result of the hydro-mechanical punching is promising. Hydrostatic pressure helps delay fracture initiation and makes it possible to get clean shearing surface. Without any burr on both side of sheet, smooth holes are archived as intended. To verify the significance of hydro-mechanical punching, conventional punching is performed under similar conditions and relatively larger portion of fracture surface is detected in the punching hole. Despite the quality of sidewall is not good enough, it might be possible to make the hole shaped upright, reduce the roll-over radius and minimize the fracture surface by optimizing process parameters.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.13 no.3
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• pp.61-67
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• 2004

In micro hole punching process the burr occurs inevitably, but the burr must be minimized in order to improve the quality and accuracy of the product. In this study, magnetic field-assisted polishing technique is applied to remove the burr which exists in nozzles for ink-jet printer head and proved to be a feasible for deburring by experiment. The deburring characteristics of sheet metals was investigated changing with polishing time and magnetic abrasive size. After the deburring, the burr size has remarkably reduced and roundness of the hole also has improved.

• Journal of the korean Society of Automotive Engineers
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• v.11 no.1
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• pp.51-56
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• 1989

This study was performed to investigate the effect of defect on fatigue strength under the stress of rotary bending. The specimens were made of low carbon steel having artificial microholes, namely, single micro-hole and two adjacent micro-holes as natural defects, and the effects of the diameter of hole and the distance between the holes on fatigue strength have been investigated. The obtained result can be summarized as follows: 1, The critical defect means the largest size of defect that does not affect fatigue limit, and correspondes to the size of defect leading to final fracture under fatigue limit of smooth specimen. The size of defect which has an effect on fatigue limit is larger than that of critical defect. 2, The defect larger than the critical defect affects fatigue strength for as a kind of size effect, and the physical meaning of size effect of defect is considered same as the one of notch effect.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.10a
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• pp.329-333
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• 2003

In micro hole punching process the burr occurs inevitably, but the burr must be minimized in order to improve the quality and accuracy of the product. In this study, magnetic field assisted polishing technique is applied to remove the burr which exists in nozzles for ink-jet printer head and proved to be a feasible for deburring by experiment. The deburring characteristics of sheet metals was investigated changing with polishing time. After the deburring, the burr size has remarkably reduced and roundness of the hole also has improved.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.5 s.176
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• pp.1288-1296
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• 2000

In this study, fatigue crack behavior between arbitrarily located defects was investigated by experiment. Especially, stress interaction between micro hole defects and fatigue cracking, and fatigue crack initiation life following the variation of location of micro hole defects were considered. In addition, crack initiation position by micro hole stress interaction and the relationship between stress concentration factor and fatigue initiation life are studied in detail.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.4 no.1
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• pp.18-23
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• 2005

This paper reports experimental results on microdrilling process for silicon parts used in semiconductor equipments. An experimental system was developed consisting of a high speed precision machine, microscope system, and project profile instrument. The experimental results indicate that the amount of chipping at the entrance and exit of micro hole decreases as the spindle speed increases up to 18,000 rpm. At higher spindle speed, however, the amount of chipping increases rapidly. The amount of chipping and infeed rate show proportional relationship up to 20 m/min of infeed rate. Beyond that infeed rate, however, sudden increase in the amount of chipping has occurred.