Role of Cu in dissolution kinetics of Cu metallization in molten Sn-based solders

Huang, Mingliang; Loeher, Thomas; Ostmann, A.; Reichl, H.

doi:10.1063/1.1925317

Cited by 86 publications

(39 citation statements)

References 12 publications

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“…This can take place either when time is very short or when the solder volume is very large. According to a recent study by Huang et al, 15 the dissolution rate of a thin Cu foil (106 m thick) dipped into a large amount (500 g) of Sn3.5Ag at 250°C is quite high, reaching 8.7 m/min. Because the Cu foil was attacked by the solder on both surfaces, the single-side dissolution rate should then be 4.35 m/min.…”

Section: Discussionmentioning

confidence: 99%

Pronounced electromigration of Cu in molten Sn-based solders

et al. 2008

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The high local temperature in flip-chip solder joints of microprocessors has raised concerns that the solder, a low melting temperature alloy, might locally liquefy and consequently cause failure of the microprocessors. This article reports a highly interesting electromigration behavior when the solder is in the molten state. A 6.3 × 10 3 A/cm 2 electron current was applied to molten Sn3.5Ag solder at 255°C through two Cu electrodes. The high current density caused rapid dissolution of the Cu cathode. The dissolved Cu atoms were driven by electrons to the anode side and precipitated out as a thick, and sometimes continuous, layer of Cu 6 Sn 5 . The applied current caused the dissolution rate of the Cu cathode to increase by one order of magnitude. A major difference between the electromigration in the solid and molten state was identified to be the presence of different countering fluxes in response to electromigration. For electromigration in the molten state, the back-stress flux, which was operative for electromigration in the solid state, was missing, and instead a countering flux due to the chemical potential gradient was present. An equation for the chemical potential gradient, d/dx, required to balance the electromigration flux was derived to be d/dx ‫ס‬ N°z*eJ, where N°is Avogadro's number, z* is the effective charge of Cu, e is the charge of an electron, is the resistivity of the solder, and J is the electron current density.

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Section: Discussionmentioning

confidence: 99%

Pronounced electromigration of Cu in molten Sn-based solders

et al. 2008

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“…The Cu atoms dissolved quickly during the reflow of the molten-Sn to solid-Cu reaction system. 16 Therefore, the melting of the pre-solder dissolved many Cu atoms during reflow. After multiple reflows, molten 37Pb-63Sn reached the outer rim of the Ni UBM.…”

Section: Cross-sectional Observationmentioning

confidence: 99%

Fundamental Study of the Intermixing of 95Pb-5Sn High-Lead Solder Bumps and 37Pb-63Sn Pre-Solder on Chip-Carrier Substrates

Chang

Lin

Lai

et al. 2009

Journal of Elec Materi

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This study investigated the intermixing of 95Pb-5Sn solder bumps and 37Pb-63Sn pre-solder in flip-chip solder joints. The reaction conditions included multiple reflows (up to ten) at 240°C, whereby previously soldercoated parts are joined by heating without using additional solder. We found that the molten pre-solder had an irregular shape similar to a calyx (i.e., a cup-like structure) wrapped around a high-lead solder bump. The height to which the molten pre-solder ascended along the solid high-lead solder bump increased with the number of reflows. The molten pre-solder was able to reach the under bump metallurgy (UBM)/95Pb-5Sn interface after three to five reflows. The molten pre-solder at the UBM/95Pb-5Sn interface generated two important phenomena: (1) the molten solder dewetted (i.e., flowed away from the soldered surface) along the UBM/95Pb-5Sn interface, particularly when the number of reflows was high, and (2) the molten pre-solder transported Cu atoms to the UBM/95Pb-5Sn interface, which in turn caused the Ni-Sn compounds at the chip-side interface to change into (Cu 0.6 Ni 0.4 ) 6 Sn 5 .

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“…However, in view of increasing environmental and health concerns, alternative solder alloy systems need to be considered. For electronic parts and devices, solder joints provide electrical conductivity and suitable mechanical strength [8,9]. So that the aim of the present work to study the effect of indium additions and rapid solidification on the structure, melting temperature, microhardness and micro-creep of Sn-Zn eutectic lead free solder alloy.…”

Section: Introductionmentioning

confidence: 99%

Effect of indium content and rapid solidification on microhardness and micro‐creep of Sn‐Zn eutectic lead free solder alloy

Shalaby¹

2010

Cryst. Res. Technol.

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The Sn-Zn alloys have been considered as lead-free solders. In this paper, the effect of 0.0, 0.5, 1.0, 1.5 and 2.0 wt.% Indium as ternary additions on melting temperature, structure, microhardness and micro-creep of the Sn-9Zn lead-free solders were investigated. It is shown that the alloying additions of Indium to the Sn-Zn binary system result in a suppression of the melting point to 187.9 °C. From x-ray diffraction analysis, a new intermetallic compound phase, designated β-In 3 Sn is detected. The formation of an intermetallic compound phase causes a pronounced increase in the electrical resistivity and mechanical strength. Also, an interesting connection between dynamic Young's modulus and the axial ratio (c/a) of the unit cell of the β-Sn was found in which Young's modulus increases with increasing the axial ratio (c/a). The ternary Sn-9Zn-xIn exhibits creep resistance superior to Sn-9Zn binary alloy. The better creep resistance of the ternary alloy is attributed to solid solution effect and precipitation of In 3 Sn in the Sn matrix. The addition of small amounts of In is found to refine the effective grain size and consequently, improves hardness. The 89%Sn-9%Zn-2%In alloy is a lead-free solder designed for possible drop-in replacement of Pb-Sn solders.

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Role of Cu in dissolution kinetics of Cu metallization in molten Sn-based solders

Cited by 86 publications

References 12 publications

Pronounced electromigration of Cu in molten Sn-based solders

Pronounced electromigration of Cu in molten Sn-based solders

Fundamental Study of the Intermixing of 95Pb-5Sn High-Lead Solder Bumps and 37Pb-63Sn Pre-Solder on Chip-Carrier Substrates

Effect of indium content and rapid solidification on microhardness and micro‐creep of Sn‐Zn eutectic lead free solder alloy

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