[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

https://tandfonline.com/doi/pdf/10.1080/14686996.2019.1591168

Structure and properties of Sn-Cu lead-free solders in electronics packaging

In this article, the laser-based powder bed fusion ( L -PBF) processing behavior of pure copper powder is evaluated by employing a conventional infrared fiber laser with a wavelength of 1080 nm, a small focal spot diameter of 37.5 µm, and power levels up to 500 W. It is shown that bulk solid copper parts with near full density (ρ Archimedes = 99.3 ± 0.2%, ρ Optical = 99.8 ± 0.1%) can be produced using a laser power of 500 W for the chosen combination of powder particle size, L -PBF settings, and pure copper baseplate. Moreover, at 500 W, parts with a relative density exceeding 99% are manufactured within a volumetric energy density window of 230–310 J/mm3, while laser power levels below 500 W did not produce parts with a relative density above 99%. An analytical model is used to elucidate the L -PBF processing behavior, wherein both conduction and keyhole regimes corresponding to the employed L -PBF settings are identified. The analytical model-based results predict that the bulk solid copper parts with near full density are produced in a keyhole regime prior to the onset of keyhole-induced porosity, which is in accordance with the porosity types observed in the parts. The L -PBF fabricated copper parts exhibit an electrical conductivity of 94 ± 1% compared to the international annealed copper standard (IACS) and demonstrate a tensile strength of 211 ± 4 MPa, a yield strength of 122 ± 1 MPa, and an elongation at break of 43 ± 3% in the as-built condition.

Laser-based powder bed fusion additive manufacturing of pure copper

This paper reviews the recent advances in the experimental and theoretical analysis of the high-temperature spreading of molten metals and oxides. Results obtained in the analysis of simple non-reactive systems are compared with current theories developed for room-temperature liquids. These results outline the critical role in spreading at high-temperature of the local dissipation at the triple solid–liquid–vapor junction. However, in most high-temperature systems, the substrate cannot be described as an ideal solid – rigid and insoluble – and the movement of the triple junctions is accompanied by other phenomena such as ridging, interdiffusion, and chemical reactions (reactive spreading). The effect of these phenomena is outlined and a framework for the theoretical analysis of reactive spreading emerges. This framework is based on the division of the reactive spreading process into its constituent steps, and the identification of the step that drives spreading and controls its kinetics. A key aspect of the analysis is the description of the structure of the triple junction and the identification of the relative kinetics of the movement of the liquid and the other phenomena that accompany spreading.

Kinetics of high-temperature spreading

Nucleation of tin on the Cu6Sn5 layer in electronic interconnections

On the initial stages of phase formation at the solid Cu/liquid Sn-based solder interface

Laser powder bed fusion (L-PBF) of copper alloys with high copper content is difficult due to the high infrared reflectivity and thermal conductivity of these alloys. In this study a simple and scalable method for coating copper powder with tin and nickel is presented, and suggested as an alloying strategy for such alloys. The coated powders were processed in a commercial L-PBF-machine at various scanning speeds. The samples made from coated powders show a lower amount of porosity compared to samples made from in-situ alloyed powders of similar composition.

Laser Powder Bed Fusion of Metal Coated Copper Powders.

Interfacial reaction between solid ɛ-Cu3Sn compound and liquid Sn at 250 °C is studied for the first time. The reaction product formed at the ɛ-Cu3Sn/liquid Sn interface consists of the single η-Cu6Sn5 phase. The growth kinetics of the η phase formed at the incremental ɛ/liquid Sn couple (ɛ/η/Sn configuration) is compared to that of η phase formed at the classical Cu/liquid Sn couple (Cu/ɛ/η/Sn configuration). The experimental method consists first in processing of intimate interfaces by dipping peaces of solid ɛ-Cu3Sn compound and Cu in liquid Sn for 1 s at 250 °C. Afterwards, isothermal holding of such pre-performed couples for 10, 30, 120 and 480 min at 250 °C are performed for both couples. A theoretical analysis of the growth kinetics of η phase and comparison of its growth in both configurations are performed.

Phase growth competition in solid/liquid reactions between copper or Cu 3 Sn compound and liquid tin-based solder

Wetting and spreading kinetics of liquid Sn on Ag and Ag3Sn substrates

The formation of Cu3Sn phase in the soldering reaction is believed to be harmful for the reliability of solder contacts on account of Kirkendall voiding in the compound. In this study, a criterion for the suppression of the growth of this phase by the fast growing scallop-like Cu6Sn5 compound is presented. The average thickness of the η-Cu6Sn5 phase above which the e-Cu3Sn phase starts to grow as a continuous layer at the Cu/Cu6Sn5 interface during liquid Sn/solid Cu interaction has been evaluated from thermodynamic and kinetic considerations.

Oleksii Liashenko

Papers

On the initial stages of phase formation at the solid Cu/liquid Sn-based solder interface

Laser Powder Bed Fusion of Metal Coated Copper Powders.

Phase growth competition in solid/liquid reactions between copper or Cu 3 Sn compound and liquid tin-based solder

Wetting and spreading kinetics of liquid Sn on Ag and Ag3Sn substrates

Cu3Sn suppression criterion for solid copper/molten tin reaction