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이기주,Dongxu Tang,K. Park,조원승 대한금속·재료학회 2010 METALS AND MATERIALS International Vol.16 No.1
Porous Y-doped (Ba,Sr)TiO3 ceramics were prepared by the spark plasma sintering of (Ba,Sr)TiO3 powders with different amounts of carbon black, and by subsequently burning out the carbon black acting as a pore precursor. The microstructure, PTCR and gas-sensing characteristics for porous Y-doped (Ba,Sr)TiO3 ceramics were investigated. Spark plasma sintered (Ba,Sr)TiO3 ceramics revealed a very fine microstructure containing submicron-sized grains with a cubic phase and revealed an increased porosity after the carbon black was burned out. As a result of reoxidation treatment, the grain size of the (Ba,Sr)TiO3 ceramics increased to a few μm and the cubic phase transformed into a tetragonal phase. The phase transformation of (Ba,Sr)TiO3ceramics was affected by grain size. The PTCR jump in the (Ba,Sr)TiO3 ceramics prepared by adding 40vol.% carbon black showed an excellent value of 4.72 × 106, which was ten times higher than the PTCR jump in (Ba,Sr)TiO3 ceramics. The electrical resistivity of the porous (Ba,Sr)TiO3 ceramics was recovered as the atmosphere changed from a reducing gas (N2) to an oxidizing gas (O2) under consecutive heating and cooling cycles.
카본블랙을 첨가하여 제조한 다공성 BaTiO<sub>3</sub>계 세라믹스의 미세구조 및 PTCR 특성 변화
이기주,당동욱,조원승,Lee, Ki-Ju,Tang, Dongxu,Cho, Won-Seung 한국분말야금학회 2011 한국분말재료학회지 (KPMI) Vol.18 No.1
As a pore precursor, carbon black with different content of 0 to 60 vol% were added to (Ba,Sr)$TiO_3$ powder. Porous (Ba,Sr)$TiO_3$ ceramics were prepared by pressureless sintering at $1350^{\circ}C$ for 1h under air. Effects of carbon black content on the microstructure and PTCR characteristics of porous (Ba,Sr)$TiO_3$ ceramics were investigated. The porosity of porous (Ba,Sr)$TiO_3$ ceramics increased from 6.97% to 18.22% and the grain size slightly decreased from $7.51\;{\mu}m$ to $5.96\;{\mu}m$ with increasing carbon black contents. PTCR jump of the (Ba,Sr)$TiO_3$ ceramics prepared by adding carbon black was more than $10^5$, and slightly increased with increasing carbon black. The PTCR jump in the (Ba,Sr)$TiO_3$ ceramics prepared by adding 40 vol% carbon black showed an excellent value of $9.68{\times}10^5$, which was above two times higher than that in (Ba,Sr)$TiO_3$ ceramics. These results correspond with Heywang model for the explanation of PTCR effect in (Ba,Sr)$TiO_3$ ceramics. It was considered that carbon black is an effective additive for preparing porous $BaTiO_3$ based ceramics. It is believed that newly prepared (Ba,Sr)$TiO_3$ cermics can be used for PTC thermistor.
이기주,김근수,가차와키스가누마,Lee, Ki-Ju,Kim, Keun-Soo,Suganuma, Katsuaki 한국마이크로전자및패키징학회 2010 마이크로전자 및 패키징학회지 Vol.17 No.4
차세대 패키징 기술을 실현하기 위해서는 극복해야 할 기술적인 과제들이 많이 존재한다. 그 중에서 솔더 접합부의 EM에 의한 고장은 오랜전부터 알려진 과제이지만, 고밀도화, 파인핏치화, 발열문제가 심각해지면서 현실적인 문제로 인식되기 시작했다. 더욱이 솔더가 무연화 되면서 다양해진 구성원소들의 영향에 대한 연구가 시작되었다. 지금까지의 연구결과를 종합해보면 Sn-Pb 공정솔더 보다 무연솔더는 EM에 대한 저항성이 강한 것으로 보여진다. 하지만, 무연솔더 접합부에서 발생하는 EM현상에 대해서는 아직 밝혀지지 않은 부분이 많다. 보이드의 핵 생성 및 성장속도와 전기저항의 급격한 변화와의 관계, Sn 결정립의 방향과 전류밀도에 따른 마이그레이션 속도계수와 수명예측기술, 각종 무연솔더와 시험조건에서의 언더필의 효과 등에 관한 다양한 연구가 필요하다. 또한 무연 플립칩 패키지의 총체적인 신뢰성 확보를 위해, EM과 반도체칩 내부배선의 발열에 기인하는 Thermomigraton, 응력에 기인하는 Stress-migration과의 상관관계에 대한 연구도 요구된다. The electromigration phenomenon in lead-free flip-chip solder joint has been one of the serious problems. To understand the mechanism of this phenomenon, the crystallographic orientation of Sn grain in the Sn-Ag-Cu solder bump has been analyzed. Different time to failure and different microstructural changes were observed in the all test vehicle and bumps, respectively. Fast failure and serious dissolution of Cu electrode was observed when the c-axis of Sn grain parallel to electron flow. On the contrary of this, slight microstructural changes were observed when the c-axis of Sn perpendicular to electron flow. In addition, underfill could enhance the electromigration reliability to prevent the deformation of solder bump during EM test.