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Fe-Cr-Ni 오스테나이트계 스테인리스강의 미소편석과 잔류 δ-페라이트 양에 대한 계산
이혁모,이용득,김선구,서정룡,배준수 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.3
In equilibrium, 304 stainless steel has only γ-austenite phase below about 1170℃ and solutes are uniformly distributed in γ-austenite. Due to incomplete solid-state diffusion, it has retained δ-ferrite as well as γ-austenite and the solute distribution becomes inhomogeneous in each phase. To further understand the solidification behavior of 304 stainless steel, the variation of δ-ferrite amount with temperature and the solute concentration in each phase across the phase boundary are calculated in this study. The calculated solute contents at the interface are in good agreement with experimental data available. It is shown that the equilibrium calculation using 304 steel composition itself produces better results than using equivalent composition. The calculated amounts of retained δ-ferrite using 304 equivalent composition are somewhat higher than experimentally observed values. Much better agreement between calculation results and experimental data is expected if more reliable experimental data can be obtained.
Ni 층의 두께에 따른 Sn-3.5wt%Ag 솔더 합금의 계면 반응
이혁모,최원경 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.11
Sn-3.5Ag (compositions are all in weight percent unless specified otherwise) solder alloys were soldered on the various substrates of bare Cu plate, Cu plate/Ni(2㎛), Cu plate/Ni(4㎛), and bare Ni plate. The morphology, composition and phase identification of the intermetallic compounds(IMC) at the interface were examined using Scanning Electron Microscopy(SEM) and X-ray diffraction(XRD). With varying the Ni layer thickness, various IMCs were formed, which were Cu_6Sn_5 on bare Cu plate, metastable NiSn₃ + Ni₃Sn₄ on Cu plate/Ni(2㎛), Ni₃Sn₄ on Cu plate/Ni(4㎛) and Ni₃Sn + Ni₃Sn₄ on bare Ni plate. And it was also observed that the wetting behavior was dependent on the Ni layer thickness. Such phenomena seemed to be caused by the type of IMCs differently formed on each substrate. As the soldering time was increased, the changes of the IMC morphology and the wetting behavior were observed on the various substrates. Therefore it was postulated that the Ni layer thickness should be considered as an important parameter in the interfacial reaction and the wetting behavior.
시효 처리에 의한 42Sn-58Bi 솔더와 무전해 Ni-P/치환 Au UBM 간의 계면 반응
조문기,이혁모,부성운,김태규,Cho Moon Gi,Lee Hyuck Mo,Booh Seong Woon,Kim Tae-Gyu 한국마이크로전자및패키징학회 2005 마이크로전자 및 패키징학회지 Vol.12 No.2
42Sn-58Bi 솔더(이하 wt.$\%$에 의한 표기)와 무전해 Ni-P/치환 Au under bump metallurgy (UBM) 간의 계면 반응을 intermetallic compound (IMC)의 형성과 성장, UBM의 감소, 그리고 범프 전단강도의 영향 관점에서 시효 처리 전 후에 어떠한 변화가 생기는 지를 알아보고자 하였다. 치환 Au 층을 $5{\mu}m$ 두께의 무전해 Ni-P ($14{\~}15 at.\%$ P)위에 세 가지 각기 다른 두께, 즉 $0{\mu}m$(순수한 무전해 Ni-P UBM), $0.1{\mu}m$, $1{\mu}m$로 도금하였다. 그 후 42Sn-58Bi 솔더 범프를 세 가지 다른 UBM 구조에 스크린프린팅 방식으로 형성하였다. 범프 형성 직후에는 세 가지 다른 UBM구조에서 솔더와 UBM 사이에 공통적으로 $Ni_3Sn_4$ IMC (IMC1) 만이 형성됐다. 하지만, 이를 $125^{\circ}C$에서 시효 처리를 할 경우 특이하게 Au를 함유한 UBM 구조에서는 $Ni_3Sn_4$ 위로 또 다른 4원계 화합물 (IMC2)이 관찰되었다. 원자 비로 $Sn_{77}Ni{15}Bi_6Au_2$인 4원계 화합물로 확인되었다. $Sn_{77}Ni{15}Bi_6Au_2$ 층은 솔더 조인트의 접합성에 매우 치명적인 영향을 미쳤다. 시효 처리를 거친 Au를 함유한 UBM 구조에서 솔더 범프의 전단 강도 값은 시효 처리 전에 비해 $40\%$ 이상의 감소를 보였다. The interfacial reaction between 42Sn-58Bi solder (in wt.$\%$ unless specified otherwise) and electroless Ni-P/immersion Au has been investigated before and after thermal aging, with a focus on formation and growth of an intermetallic compound (IMC) layer, consumption of under bump metallurgy (UBM), and bump shear strength. The immersion Au layer with thicknesses of 0 (bare Ni), 0.1, and $1{\mu}m$ was plated on the $5{\mu}m$ thick electroless Ni-P ($14{\~}15 at.\%$P) layer. Then, the 42Sn-58Bi solder balls were fabricated on three different UBM structures by screen-printing and pre-reflow. The $Ni_3Sn_4$ layer (IMC1) was formed at the joint interface after pre-reflow for all the three UBM structures. On aging at $125^{\circ}C$, a quaternary phase (IMC2) was observed above the $Ni_3Sn_4$ layer in the Au-containing UBM structures, which was identified as $Sn_{77}Ni{15}Bi_6Au_2$ (in at.$\%$). The thick $Sn_{77}Ni{15}Bi_6Au_2$ layer deteriorated the integrity of the solder joint and the shear strength of the solder bump was decreased by about $40\%$ compared with non-aged joints.