Reactions between Sn–Ag–Cu lead‐free solders and the Au/Ni surface finish in advanced electronic packages

Shiau, L.C.; Ho, Cheng–En; Kao, C. R.

doi:10.1108/09540910210444692

Cited by 106 publications

(74 citation statements)

References 11 publications

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“…It is interesting to note that the quaternary (Cu 1-p-q Au q Ni p ) 6 Sn 5 IMC was well adhered to the Ni when the solder contained 0.75 wt.% Cu but was detached from the Ni when the solder contained 0.5 wt.% Cu. Laurila et al 19 obtained results that were consistent with those of Ho et al 5 and Shiau et al 18 Both Stepniak 20,21 and Zhang et al 17 found that the addition of Au increased the degradation rate of a standard multilayer thin-film UBM composed of Al, Ni(V), and Cu (Al/Ni(V)/Cu). In fact Stepniak reported that the addition of Au counteracts the reduction in the Ni-solder reaction rate that V-doping is know to provide in an Au-free environment.…”

Section: Introductionsupporting

confidence: 73%

“…However, when the Pb-Sn solder was doped with 0.5 wt.% Cu, no ternary (Au 1-x Ni x )Sn 4 IMC particles were found in the solder but rather Au was incorporated in the form of a quaternary (Cu 1-p-q Au q Ni p ) 6 Sn 5 phase at the Ni-solder interface. Shiau et al 18 found binary Ni 3 Sn 4 IMC at the Ni solder-interface when Cu was not present in the Sn-Ag solder and quaternary (Cu 1-p-q Au q Ni p ) 6 Sn 5 IMC at the Ni-solder interface when 0.75 wt.% Cu was present in the Sn-Ag solder. For 0.5 wt.% Cu in Sn-Ag solder the solder-Ni interface was composed of a mixture of binary Ni 3 Sn 4 IMC and quaternary (Cu 1-p-q Au q Ni p ) 6 Sn 5 IMC.…”

Section: Introductionmentioning

confidence: 98%

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Stability of Flip-Chip Interconnects Assembled with Al/Ni(V)/Cu-UBM and Eutectic Pb-Sn Solder During Exposure to High-Temperature Storage

Osenbach¹,

Amin

Bachman³

et al. 2008

Journal of Elec Materi

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The thermal stability of flip-chip solder joints made with trilayer Al/Ni(V)/Cu underbump metalization (UBM) and eutectic Pb-Sn solder connected to substrates with either electroless Ni(P)-immersion gold (ENIG) or Pb-Sn solder on Cu pad (Cu-SOP) surface finish was determined. The ENIG devices degraded more than 50 times faster than the Cu-SOP devices. Microstructural characterization of these joints using scanning and transmission electron microscopy and ion beam microscopy showed that electrical degradation of the ENIG devices was a direct result of the conversion of the as-deposited Ni(V) barrier UBM layer into a porous fine-grained V 3 Sn-intermetallic compound (IMC). This conversion was driven by the Au layer in the ENIG surface finish. No such conversion was observed for the devices assembled on Cu-SOP surface finish substrates. A resistance degradation model is proposed. The model captures changes from a combination of phenomena including increased (1) intrinsic resistivity, (2) porosity, and (3) electron scattering at grain boundaries and surfaces. Finally, the results from this study were compared with results found in a number of published electromigration studies. This comparison indicates that degradation during current stressing in the Pb-Sn bump/ENIG system is in part due to current-crowding-induced Joule heating and the thermal gradients that result from localized Joule heating.

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Section: Introductionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 98%

Stability of Flip-Chip Interconnects Assembled with Al/Ni(V)/Cu-UBM and Eutectic Pb-Sn Solder During Exposure to High-Temperature Storage

Osenbach¹,

Amin

Bachman³

et al. 2008

Journal of Elec Materi

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“…8 This strong sensitivity is similar to the Cu concentration sensitivity in the reaction between SnAgCu solders and Ni substrates. [10][11][12][13][14] However, note that the above Zn concentration sensitivity was established in bulk reactions where the supply of Zn was large. In other words, the Zn concentration remained almost constant.…”

Section: Introductionmentioning

confidence: 94%

Analysis and Experimental Verification of the Volume Effect in the Reaction Between Zn-Doped Solders and Cu

Yang

Wang

Chang

et al. 2008

Journal of Elec Materi

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The volume effect in the reaction between Zn-doped solders and Cu is reported and explained in this article. Zn-doped solders with two different volumes, bulk solder baths (6 g) and small solder balls (10 mg), were reacted with Cu substrates. It was found that the reaction at the interface depended not only on the Zn concentration but also on the volume of the solder. For the bulk solder reaction the Zn concentration stayed nearly constant, whereas in the small solder joint case the Zn concentration changed substantially with the reaction time. This was because the Zn concentration during reaction was different for different solder volumes when the volume effect became important. For bulk solder baths, when the Zn content was 0.5 wt.%, the reaction product was a Cu 6 Sn 5 -based compound. As the Zn content increased to 2 wt.%, the reaction product switched to a Cu 5 Zn 8 -based compound. When the Zn content was 1.0 wt.%, Cu 6 Sn 5 and CuZn formed simultaneously. When the solder volume became smaller, the Zn concentration was no longer constant, and the phase equilibrium at the interface changed with time. It was shown that the shifting of the equilibrium at the interface caused the massive spalling of CuZn.

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“…14 The driving force for the migration of AuSn 4 is for this compound to seek Ni so that this binary compound becomes a Ni-saturated (Au 1Àx Ni x )Sn 4 . 9 In the high-Sn system, such as pure tin, 14 or the eutectic SnAg, 11,12,[19][20][21][22] AuSn 4 seems to have a much lesser tendency to migrate back to the interface. It was even claimed that Au embrittlement was no longer a problem for high-Sn solders.…”

Section: Introductionmentioning

confidence: 99%

Kinetics of AuSn4 migration in lead-free solders

Chang

Yang

et al. 2006

J. Electron. Mater.

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The relatively fast diffusion of Au atoms in eutectic PbSn matrix is considered one of the contributing factors to the Au embrittlement problem. In this study, we further investigated the Au embrittlement problem in high-Sn solders. Experimentally, Sn3.5Ag (wt.%) spheres with 500-mm diameter were soldered over the Au/Ni soldering pads. It was found that some of the AuSn 4 needles that formed after reflow inside the solder migrated back to the solder/pad interface during thermal aging. However, the migration kinetics in high-Sn solders was slower compared to that in eutectic PbSn. The difference in migration kinetics of AuSn 4 in eutectic PbSn and SnAg was ascribed to the difference in the magnitudes of the Au flux and the Ni flux. In eutectic PbSn, the Au flux was much greater than that of the Ni flux, and the Au and Ni flux were in the same order of magnitude in eutectic SnAg. The relative magnitude of the Au and Ni flux changed in eutectic PbSn and SnAg because the homologous temperatures of PbSn and SnAg were different.

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Reactions between Sn–Ag–Cu lead‐free solders and the Au/Ni surface finish in advanced electronic packages

Cited by 106 publications

References 11 publications

Stability of Flip-Chip Interconnects Assembled with Al/Ni(V)/Cu-UBM and Eutectic Pb-Sn Solder During Exposure to High-Temperature Storage

Stability of Flip-Chip Interconnects Assembled with Al/Ni(V)/Cu-UBM and Eutectic Pb-Sn Solder During Exposure to High-Temperature Storage

Analysis and Experimental Verification of the Volume Effect in the Reaction Between Zn-Doped Solders and Cu

Kinetics of AuSn4 migration in lead-free solders

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