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Mechanical and Electrical Properties of Sn-3.5Ag Solder/Cu BGA Packages during Multiple Reflows
Koo, Ja Myeong,Lee, Young Ho,Kim, Sun Kyu,Jeong, Myung Yong,Jung, Seung Boo Trans Tech Publications, Ltd. 2005 Key Engineering Materials Vol.297 No.-
<P>The mechanical and electrical properties of the Sn-3.5Ag solder/Cu BGA packages were investigated as a function of number of reflows. A continuous scallop-shaped Cu6Sn5 intermetallic compound (IMC) layer was formed at the solder/Cu interface upon 1 reflow process. After 3 reflows, very thin layer of Cu3Sn IMC was observed at the Cu6Sn5/Cu interface. As the number of reflows increased, the thickness of these IMCs increased with a cube root of reflow time. Shear force slightly increased up to 4 reflows and then gradually decreased with increasing the number of reflows. The maximum shear force was 11.7N when the thickness of the IMC layers was 3.7㎛. The fracture surfaces of all the specimens showed ductile failure characteristics up to 4 reflows, and then the fraction of the brittle IMC fracture increased with the number of reflows. The electrical resistance of the BGA packages increased with the number of reflows.</P>
Mechanical Properties of Copper Hollow Sphere Manufactured by Sintering Process
Koo, Ja Myeong,Jung, Seung Boo Trans Tech Publications, Ltd. 2006 Materials science forum Vol.510 No.-
<P>The polystyrene spheres coated with a slurry, consisting of copper (I) oxide powder, water and PA (poly acrilamide), were reduced to form copper (Cu) hollow spheres at sintering temperatures ranging from 650 to 950 °C under a hydrogen atmosphere. The microstructural evolutions and mechanical properties of the Cu hollow spheres were investigated with the sintering temperature. The increase in the sintering temperature led to the increase in the density and grain size of the spheres. The amount of the residual copper oxide in the samples decreased with increasing sintering temperature. The electrical conductivity, hardness, and compression strength of the hollow spheres increased with increasing sintering temperature.</P>
Koo, Ja-Myeong,Yoon, Jeong-Won,Jung, Seung-Boo John Wiley Sons, Ltd. 2006 Surface and interface analysis Vol.38 No.4
<P>In this study, the interfacial reactions of In–48Sn solder balls on an electroless Ni/immersion Au (ENIG) ball grid array (BGA) substrate during reflow at 170 °C for up to 1800 s were investigated using SEM, transmission electron microscope (TEM) and energy dispersive X-ray spectroscope (EDS) analyses. During the initial 10 s of the reflow process, AuIn<SUB>2</SUB> cubes and a continuous Ni<SUB>3</SUB>(Sn,In)<SUB>4</SUB> intermetallic compound (IMC) layer were formed at the interface between the solder and the substrate. The thickness of the Ni<SUB>3</SUB>(Sn,In)<SUB>4</SUB> layer was found to increase from approximately 140 nm to 1 µm, as the reflow time increased from 10 to 1800 s, respectively. The transformation of Ni to form the Ni<SUB>3</SUB>(Sn,In)<SUB>4</SUB> IMC led to the formation of a P-rich Ni (hereafter Ni<SUB>3</SUB>P) layer between the Ni<SUB>3</SUB>(Sn,In)<SUB>4</SUB> IMC and the ENIG substrate, whose thickness increased with increasing the reflow time. Copyright © 2006 John Wiley & Sons, Ltd.</P>
( Ja Choon Koo ),( Yeo Chang Youn ),( Mi Sun Park ),( Myeong Eun Kim ) 한국임학회 2012 한국임학회 학술발표논문집 Vol.2012 No.-
South Korea is not included in Annex I countries under the Kyoto protocol. However, its greenhouse gas (GHG) emissions were listed 9th highest in the world. South Korean government announced a goal of reducing GHG emissions by 30 percent compared to the business as usual by 2020. In order to achieve this voluntary emission target effectively, public and private sector have tried to introduce appropriate mitigation methods in various sectors such as energy, transportation and so on. In particular, the forest sector can play a significant role in mitigating greenhouse gases through carbon sequestration because about 64% of total land is covered by forest in South Korea. In this background, Korea Forest Service has been preparing a policy instrument to make forest carbon credits be traded in the voluntary carbon market which will be launched in 2015 in South Korea. Before introduction of the carbon market, it is needed to analyze companies` demands and preferences to forest carbon credit in advance. This research aimed to estimate the willingness to pay (WTP) of private companies in South Korea for carbon credits from forest offset projects such as domestic forest management activities and REDD (reducing emissions from deforestation and forest degradation) in developing countries. We postulate null hypotheses that there is no difference in the WTP according to types of forest offset projects. The face to face interview was conducted with 200 companies engaged in various types of business in 2011. 70 valid responses were analyzed to elicit the value of WTP for carbon credits per ton of CO2 equivalent by non-parametric approach (Turnbull estimation). We found that there was a difference in WTP according to the area of forest offset project. Estimated WTPs for forest carbon credits were 4.55~7.86 USD/tCO2 in domestic project and 6.64~11.05 USD/tCO2 in foreign project. These results can contribute to designing forest carbon market considering primary consumers.
김명은 ( Myeong Eun Kim ),민경택 ( Kyung Taek Min ),구자춘 ( Ja Choon Koo ) 한국산림과학회 2015 한국산림과학회지 Vol.104 No.1
The purposes of this study are estimating willingness to pay (WTP) of forest owners for the disaster insurance premium for forest products in Korea and investigating factors affecting their WTP. The result with contingent valuation method shows that forest owners’ median WTP is 9,440 KRW/ha·yr. Advanced forest managers including devoted forest managers and forestry successors are willing to pay more for insurance premium compared to non-advanced ones, and those who have experienced disaster in their own forest land have higher WTP than others. WTP of advanced forest managers appears to be 50% higher than that of nonadvanced. These results imply that policy makers should consider advanced forest managers as a priority to introduce the insurance system.
BGA 솔더 접합부의 기계적.전기적 특성에 미치는 리플로우 횟수의 효과
구자명,이창용,정승부,Koo, Ja-Myeong,Lee, Chang-Yong,Jung, Seung-Boo 한국마이크로전자및패키징학회 2007 마이크로전자 및 패키징학회지 Vol.14 No.4
본 연구에서는 리플로우 횟수를 달리하여 Sn-37Pb, Sn-3.5Ag와 Sn-3.5Ag-0.75Cu (all wt.%) BGA 솔더 접합부들을 OSP가 코팅된 Cu 패드 상에 형성시킨 후, 기계적 전기적 특성을 연구하였다. 주사전자현미경 분석 결과, 접합 계면에 생성된 $Cu_6Sn_5$ 금속간화합물 층의 두께는 리플로우 횟수가 증가함에 따라 증가하였다. Sn-Pb와 Sn-Ag-Cu 솔더 접합부의 경우, 3회 리플로우 후 최대 전단 강도를 나타내었으며, Sn-Ag 솔더 접합부의 경우 4회 리플로우 후 최대 전단 강도를 나타내었다. 이후 리플로우 횟수가 10회까지 증가함에 따라 전단 강도는 점차 감소하였다. 리플로우 횟수가 증가함에 따라 전기적 특성은 점차 감소하였다. In this study, the mechanical and electrical properties of three different ball grid array (BGA) solder joints, consisting of Sn-37Pb, Sn-3.5Ag and Sn-3.5Ag-0.75Cu (all wt.%), with organic solderability preservative (OSP)-finished Cu pads were investigated as a function of reflow number. Based on scanning electron microscopy (SEM) analysis results, a continuous $Cu_6Sn5$, intermetallic compound (IMC) layer was formed at the solder/substrate interface, which grew with increasing reflow number. The ball shear testing results showed that the shear force peaked after 3 reflows (in case of Sn-Ag solder, 4 reflows), and then decreased with increasing reflow number. The electrical property of the joint gradually decreased with increasing reflow number.
CMOS 이미지 센서용 Au 플립칩 범프의 초음파 접합
구자명,문정훈,정승부,Koo, Ja-Myeong,Moon, Jung-Hoon,Jung, Seung-Boo 한국마이크로전자및패키징학회 2007 마이크로전자 및 패키징학회지 Vol.14 No.1
본 연구의 목적은 CMOS 이미지 센서용 Au 플립칩 범프와 전해 도금된 Au 기판 사이의 초음파 접합의 가능성 연구이다. 초음파 접합 조건을 최적화하기 위해서, 대기압 플라즈마 세정 후 접합 압력과 시간을 달리하여 초음파 접합 후 전단 시험을 실시하였다. 범프의 접합 강도는 접합 압력과 시간 변수에 크게 좌우되었다. Au 플립칩 범프는 상온에서 성공적으로 하부 Au 도금 기판과 접합되었으며, 최적 조건 하에서 접합 강도는 약 73 MPa이었다. This study was focused on the feasibility of ultrasonic bonding of Au flip chip bumps for a practical complementary metal oxide semiconductor (CMOS) image sensor with electroplated Au substrate. The ultrasonic bonding was carried out with different bonding pressures and times after the atmospheric pressure plasma cleaning, and then the die shear test was performed to optimize the ultrasonic bonding parameters. The bonding pressure and time strongly affected the bonding strength of the bumps. The Au flip chip bumps were successfully bonded with the electroplated Au substrate at room temperature, and the bonding strength reached approximate 73 MPa under the optimum conditions.
Hwang, Min-Ju,Kim, Myeong-Gi,Kim, Sanghoon,Kim, Ye Chan,Seo, Hee Won,Cho, Jung Keun,Park, In-Kyung,Suhr, Jonghwan,Moon, Hyungpil,Koo, Ja Choon,Choi, Hyouk Ryeol,Kim, Kwang Jin,Tak, Yongsug,Nam, Jae-Do Elsevier 2019 Carbon Vol.142 No.-
<P><B>Abstract</B></P> <P>Anti-corrosion metal protection of the 2D structured graphene oxide (GO) was investigated in this study using its intrinsic impermeability against reactive molecules stemming from the small geometric pore size and π-orbital repelling fields of graphene. The electrophoretic deposition (EPD) of GO sheets on metals is an attractive coating method but the negatively-charged GO only allows the anodic EPD process, which makes it difficult to achieve high-quality coating layers due to gas bubbling and electrochemical oxidation of metals. Thus, we imposed the positive charge to GO sheets using <I>p</I>-phenylenediamine (PPD) and successfully carried out the cathodic EPD in the ethanol aqueous solution. The cathodic EPD of GO on cupper provided a linear growth rate with both deposition time and voltage providing the thickness over 6.0 μm in a void-free and robust feature, which could hardly be achieved by other coating methods. Converting the GO coating to the reduced GO (RGO) by thermal reduction, we successfully increased the RGO adhesion strength up to the highest adhesion grade of 5B in the cross-cut adhesion test. An excellent anti-corrosion protection capability of the developed RGO coating was demonstrated by a decreased corrosion current density and increased corrosion potential in potentiodynamic polarization analysis.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>