Geometric size effect on IMC growth and elements diffusion in Cu/Sn/Cu solder joints

Zhu, Yanan; Sun, Fenglian

doi:10.1108/ssmt-04-2016-0007

Cited by 8 publications

(2 citation statements)

References 15 publications

(18 reference statements)

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“…In lead-free solder joints of microelectronic packaging, Kirkendall voids are often found in Cu 3 Sn intermetallic compound (IMC) near the interface between Cu 3 Sn and Cu after annealing (Gao et al, 2008;Zeng and Tu, 2002;Chan et al, 2013;Zhu and Sun, 2017). Figure 1 is an anin-situ scanning electron microscopy (SEM) photograph of interfacial microstructure between a Cu/Sn/Cu system during isothermal annealing (Park et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

The effect of vacancy on the interfacial diffusion in Cu/Sn lead-free solder joints

Yao

2019

SSMT

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Purpose The purpose of this paper is to investigate the diffusion behaviors of different atoms at the Cu/Cu3Sn interface and the vacancy formation energy, diffusion energy barrier and vacancy diffusion activation energy. Design/methodology/approach The diffusion behaviors of different atoms at the Cu/Cu3Sn interface are analyzed, and the vacancy formation energy, diffusion energy barrier and vacancy diffusion activation energy are obtained using molecular dynamics simulation. The nudged elastic band method is used to evaluate diffusion energy barrier for Cu/Cu3Sn system. Findings It is found that the vacancies in the Cu/Cu3Sn interface promote the interfacial diffusion, and the formation energy of Cu vacancy in the Cu crystal is larger than that in Cu3Sn crystal. In addition, the formation energies of Cu1 vacancy and Cu2 vacancy are close to each other in Cu3Sn crystal, and they are all less than the formation energy of Sn vacancy. Furthermore, the vacancy diffusion barrier and vacancy diffusion activation energy of the Cu/Cu3Sn interface are calculated, and the results show that the vacancy diffusion activation energy of Sn was higher than that of Cu. Finally, by comparison of diffusion activation energies of different diffusion mechanisms, Cu→Cu1vac is the most possible migration path at all temperatures. Originality/value It is concluded that the vacancies in Cu/Cu3Sn interface promote interfacial diffusion, and the activation energy of vacancy diffusion in most diffusion mechanisms decreases with the increase of temperature.

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Section: Introductionmentioning

confidence: 99%

The effect of vacancy on the interfacial diffusion in Cu/Sn lead-free solder joints

Yao

2019

SSMT

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“…Therefore, a coating of Ni over the Cu metallization is often used as a diffusion barrier (Chan et al, 2002). Studies have been reported on the reaction of different solders with Cu substrates (Ju et al, 2014;Zhu and Sun, 2017;Bi et al, 2012;Yan et al, 2016) and Ni/Cu substrates during reflow and ageing (Huang and Lin, 2004;Lee et al, 2005;Mittal and Lin, 2012;Mittal and Lin 2014;Tian et al, 2003). Reaction of Sn-Ag, Sn-Cu and Sn-Bi solders with Ni substrates leads to the formation of Ni 3 Sn 4 IMC, whereas the Sn-Zn solder alloy reacts with Ni to form the Ni 19 Zn 80 Sn IMC (Chan et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Diffusion of elements during reflow ageing of Sn-Zn solder in liquid state on Ni/Cu substrate – theoretical and experimental study

Mittal

Lin²

2018

SSMT

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Purpose This paper aims to study the diffusion of Zn, Ni and Sn in the liquid state during the reflow ageing of the Sn-Zn solder above its melting point on an Ni/Cu substrate in relation to the formation of intermetallic compounds (IMCs). Design/methodology/approach The Sn-Zn solder is reflowed on Ni/Cu substrates and is aged at 503 K. The formation of IMCs and their composition is characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Diffusion coefficients and diffusion distances of Zn, Ni and Sn in the liquid state during reflow and ageing are theoretically calculated. Both experimental and theoretical behaviours for Ni and Zn diffusions are compared. Findings Calculations show a linear increment in the liquid-state diffusion coefficients of Ni, Zn and Sn in the solder matrix with a rise in temperature, but they remained constant during ageing. However, diffusion distances increased slowly with temperature but manifold with ageing time. The experimental results revealed segregation of Zn and Ni at the interface in the as-reflow aged specimens. The Zn was concentrated at the solder–substrate interface and it reacted with Ni diffusing from the substrate to form Ni-Sn-Zn IMCs. The rapid diffusion of Zn and Ni with the increase in ageing time increased their atomic concentrations in the IMCs against the reduction in Sn concentration owing to a comparatively slower diffusion. Originality/value The novelty of the paper is the detailed study of theoretical diffusion of Zn, Sn and Ni in the liquid state during reflow ageing of Sn-Zn above its melting points on a Ni/Cu substrate. This is compared with values obtained experimentally and related to the mechanisms of IMC formation.

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Size effect on interface reaction of Sn–xCu/Cu solder joints during multiple reflows

Huang

Shang

et al. 2019

J Mater Sci: Mater Electron

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At present, electronic products are developing in the direction of miniaturization and integration, which leads to the downsizing of solder bump in the packaging process. Moreover, micro solder bumps often require undergoing multiple reflow processes due to the improvement of packaging technology, which has a great influence on interface reaction. Hence, it is necessary to study the effects of solder composition, bump size and reflow cycle on interfacial reaction between solder alloys and Cu substrates. In this experiment, Sn-xCu (x=0, 0.7, 2.0 wt.%) alloys with diameter of 200μm, 500μm, and 800μm were soldered to Cu substrates at 250°C for 1 min, and then reflowed 20 cycles totally. The size effect of micro solder joints on the growth of IMC after multiple reflows was analyzed. At the same time, the impact of Cu concentration inside the bulk solder on the interfacial reaction during multiple reflows was explored. This experiment finds that the diameter of IMC grains increases with the decrease of solder ball diameter after one reflow cycle, and a significant size effect occurs in Sn/Cu solder bump. As the number of reflow cycle increases, the size effect on interface reaction is more pronounced. The most direct kinetic factor of this phenomenon is that the average Cu concentration in the small-sized solder ball rises faster than the others. When the number of reflow cycle reach to 9 times, the lateral growth rate of IMC grains begins to surpass the longitudinal growth rate, and the morphology of IMC grains becomes flat. This phenomenon is especially evident in the small-sized solder ball. Moreover, the addition of Cu element in solder promotes ripening reaction resulting in the lateral growth of IMC. Cu6Sn5 micro particles appearing at the Sn/Cu, Sn-0.7Cu/Cu interface hinder the grain boundary motion and inhibit the lateral annexation of IMC grains, thereby suppressing the lateral growth of IMC.

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Geometric size effect on IMC growth and elements diffusion in Cu/Sn/Cu solder joints

Cited by 8 publications

References 15 publications

The effect of vacancy on the interfacial diffusion in Cu/Sn lead-free solder joints

The effect of vacancy on the interfacial diffusion in Cu/Sn lead-free solder joints

Diffusion of elements during reflow ageing of Sn-Zn solder in liquid state on Ni/Cu substrate – theoretical and experimental study

Size effect on interface reaction of Sn–xCu/Cu solder joints during multiple reflows

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