• 마이크로전자및패키징학회지
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• 제29권4호
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• pp.41-47
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• 2022

Ag sintering technologies have received great attention as it was applied to the inverter of Tesla's electric vehicle Model III. Ag sinter bonding technology has advantages in heat dissipation design as well as high-temperature stability due to the intrinsic properties of the material, so it is useful for practical use of SiC and GaN devices. This study was carried out to understand the sinter joining temperature effect on the robust Ag sintered joints in air without pressure within 10 min. Electroplated Ag finished Cu dies (3 mm × 3 mm × 2 mm) and substrates (10 mm × 10 mm × 2 mm) were introduced, respectively, and nano Ag paste was applied as a bonding material. The sinter joining process was performed without pressure in air with the bonding temperature as a variable of 175 ℃, 200 ℃, 225 ℃, and 250 ℃. As results, the bonding temperature of 175 ℃ caused 13.21 MPa of die shear strength, and when the bonding temperature was raised to 200 ℃, the bonding strength increased by 157% to 33.99 MPa. When the bonding temperature was increased to 225 ℃, the bonding strength of 46.54 MPa increased by about 37% compared to that of 200 ℃, and even at a bonding temperature of 250 ℃, the bonding strength exceeded 50 MPa. The bonding strength of Ag sinter joints was directly influenced by changes in the necking thickness and interfacial connection ratio. In addition, developments in the morphologies of the joint interface and porous structure have a significant effect on displacement. This study is systematically discussed on the relationship between processing temperatures and bonding strength of Ag sinter joints.

• Journal of Mechanical Science and Technology
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• 제15권5호
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• pp.630-638
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• 2001

The electrical resistivity of sinter dusts generated from the steel industry and coal fly ash from the coal power plant has been investigated using the high voltage conductivity cell based on JIS B 9915 as a function of temperature and water content. Dust characterization such as the chemical composition, size distribution, atomic concentration, and surface structure has been conducted. Major constituents of sinter dusts were Fe$_2$O$_3$(40∼74.5%), CaO (6.4∼8.2%), SiO$_2$(4.1∼6.0%), and unburned carbon (7.0∼14.7%), while the coal fly ash consisted of mainly SiO$_2$(51.4%), Al$_2$O$_3$(24.1%), and Fe$_2$O$_3$(10.5%). Size distributions of the sinter dusts were bi-modal in shape and the mass median diameters (MMD) were in the range of 24.7∼137㎛, whereas the coal fly ash also displayed bi-modal distribution and the MMD of the coal fly ash was 35.71㎛. Factors affecting resistivity of dusts were chemical composition, moisture content, particle size, gas temperature, and surface structure of dust. The resistivity of sinter dusts was so high as 10(sup)15 ohm$.$cm at 150$\^{C}$ that sinter dust would not precipitate well. The resistivity of the coal fly ash was measured 1012 ohm$.$cm at about 150$\^{C}$. Increased water contents of the ambient air lowered the dust resistivity because current conduction was more activated for absorption of water vapor on the surface layer of the dust.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.303-304
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• 2006

The mechanical properties of ferrous powder metallurgy (P/M) materials are directly related to their microstructure. Ferrous P/M materials with sufficient hardenability will develop microstructures containing significant percentages of martensite in the as-sintered condition. Recently, sinter-hardening has developed into a highly cost effective production method through hardened P/M parts without the need for additional heat-treatments. This paper reviews the advances of sinter-hardening as well as some key processing parameters such as sintering temperature, cooling rate, tempering required to produce high quality sinter-hardened components. Specific topics including effect of alloying elements, alloying methods, and the Characterization and observation of microstructure are discussed.

• 대한기계학회논문집A
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• 제20권7호
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• pp.2182-2195
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• 1996

Densification characteristics and behavior of tool steel powder compact during high temperature forming processes were investigated under pressure less sintering, sinter forging and hot isostastic pressing. In pressureless sintering, full density was obtained at a closely controlled temperature near the solidus of the material. Finite element calculations from constitutive model for densification by power law creep and diffusional flow were compared with experimental data. Agreements between theoretical calculations and experimental data were good in hot isostatic pressing but not as good in sinter forging.

• 한국세라믹학회지
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• 제34권12호
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• pp.1247-1253
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• 1997

Sinter-active yttria powders were prepared by a solution precipitation with using a self-decomposing precipitation agent NH2CONH2(urea). The cold-pressed powders can be sintered to full density and the microstructure of grains less than 200 nm at a temperature as low as 120$0^{\circ}C$. The activity of the yttria powder has been controlled by varying nucleation conditions during precipitation and by minimizing formation of aggregates. The type of precursor is decisive in preparation of a sinter-active oxide powder, and urea is desirable as a precipitation agent for an active yttrium oxide powder.

• 한국재료학회지
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• 제4권1호
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• pp.37-43
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• 1994

Y-BA-Cu-O계 고온초전도체의 미세조직을 가공과 열처리로써 제어하여 조직의 배향화와 치밀화를 기하여 높은 임계전류밀도($J_c$)를 갖는 초전도체의 개발을 목적으로sinter forging법으로 Y-BA-Cu-O/Ag 고온초전도복합체를 제조하였다. sinter forging을 통하여 고온 초전도체의 미세조직의 texture화를 가져왔으며, 이 경우 (123)결정립의 C축 방위가 단일축의 압축방향으로 배향화 되었다. 한편, texture의 orientation facter는 고온일수록, 압력이 클수록 크고, 조직의 배향화도 뚜렷하였으며 그에 따라 $J_c$역시 증가하였다. 이러한 결과로 미루어 결정의 배향도는 $J_c$를 좌우하는 중요한 변수라고 사려되었다. 또한 sinter forging 시킨Y-MA-Cu-O/Ag 복합체의 on set온도는 sinter forging온도에 크게 의존치 않았으나, 고온일수록 off set 온도($T_c\;^{zero}$)가 다소 떨어졌다. 한편, 첨가된 Ag는 주고(123)결정입계에 존재하였으며, 이들이 (123)결정립간의 결합을 촉진시켜 임계전류밀도를 크게 향상시켰으며, Y-BA-Cu-O/Ag 복합체의 $J_c$는 2,000 A/$\textrm{cm}^2$ 이상이었다.

• 대한기계학회논문집A
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• 제21권8호
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• pp.1175-1187
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• 1997

Densification behavior and grain growth of zirconia powder compacts are investigated under high temperature. Experimental data are obtained for zirconia powder under pressureless sintering, sinter forging and hot isostatic pressing. The constitutive equations by Kwon et al. are used for diffusional creep and grain growth. The constitutive equations by McMeeking and co-workers are also included to study the effect of power-law creep. These constitutive equations are implemented into a finite element program (ABAQUS) to investigate the friction effect during sinter forging and the canning effect during hot isostatic pressing. The agreements between experimental data and finite element results are very good in pressureless sintering and hot isostatic pressing, but not as good in sinter forging.

• 대한기계학회논문집A
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• 제24권11호
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• pp.2749-2761
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• 2000

Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing. Finite element results by using the proposed model also well predicted experimental data in the literature for densification behavior of nanocrystalline zirconia powder during pressureless sintering and sinter forging.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.987-988
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• 2006

The processes of P/M affect the properties of sintered gears. The different techniques of P/M lead to the different properties of sintered gears. This paper summarizes new progress in powder metallurgy for sintered gears. These progresses include warm compaction, high velocity compaction, sinter hardening, high temperature sintering, infiltration, CNC powder press and surface densification etc.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.363-368
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• 2000

Densification, grain growth, and phase transformation of nanocrystalline ceramic powder were investigated under pressureless sintering, sinter forging, and hot pressing. A constitutive model for densification of nanocrystalline ceramic powder was proposed and implemented into a finite element program (ABAQUS). A grain growth model was also proposed by including the effect of applied stress on grain growth when phase transformation occurs. Finite element results by using the proposed models well predicted densification behavior, deformation, and grain growth of nanocrystalline titania powder during pressureless sintering, sinter forging, and hot pressing.