Microstructure evolution in Cu pillar/eutectic SnPb solder system during isothermal annealing

A technique has been developed to facilitate analysis of the microstructural evolution of solder bumps after current stressing. Eutectic SnPb solders were connected to under-bump metallization (UBM) of Ti/Cr-Cu/Cu and pad metallization of Cu/Ni/Au. It was found that the Cu6Sn5 compounds on the cathode/chip side dissolved after the current stressing by 5 × 103 A/cm2 at 150 °C for 218 h. However, on the anode/chip side, they were transformed into (Nix,Cu1-x)3Sn4 in the center region of the UBM, and they were converted into (Cuy,Ni1-y)6Sn5 on the periphery of the UBM. For both cathode/substrate and anode/substrate ends, (Cuy,Ni1-y)6Sn5 compounds were transformed into (Nix,Cu1-x)3Sn4. In addition, the bumps failed at cathode/chip end due to serious damage of the UBM and the Al pad. A failure mechanism induced by electromigration is proposed in this paper.

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Dominant Migration Element in Electrochemical Migration of Eutectic SnPb Solder Alloy

56th Electronic Components and Technology Conference 2006 ◽

10.1109/ectc.2006.1645714 ◽

2006 ◽

Cited By ~ 1

Author(s):

Shin-Bok Lee ◽

Ja-Young Jung ◽

Young-Ran Yoo ◽

Young-Bae Park ◽

Young-Sik Kim ◽

...

Keyword(s):

Solder Alloy ◽

Electrochemical Migration ◽

Snpb Solder ◽

Eutectic Snpb

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Measurement of impact toughness of eutectic SnPb and SnAgCu solder joints in ball grid array by mini-impact tester

Journal of Materials Research ◽

10.1557/jmr.2008.0186 ◽

2008 ◽

Vol 23 (5) ◽

pp. 1482-1487 ◽

Cited By ~ 9

Author(s):

Yuhuan Xu ◽

Shengquan Ou ◽

K.N. Tu ◽

Kejun Zeng ◽

Rajiv Dunne

Keyword(s):

Impact Toughness ◽

High Speed ◽

Solder Joints ◽

Ball Grid Array ◽

Snagcu Solder ◽

Snpb Solder ◽

Impact Tester ◽

Pull Tests ◽

The Impact ◽

Eutectic Snpb

The most frequent cause of failure for wireless, handheld, and portable consumer electronic products is an accidental drop to the ground. The impact may cause interfacial fracture of ball-grid-array solder joints. Existing metrology, such as ball shear and ball pull tests, cannot characterize the impact-induced high speed fracture failure. In this study, a mini-impact tester was utilized to measure the impact toughness and to characterize the impact reliability of both eutectic SnPb and SnAgCu solder joints. The annealing effect at 150 °C on the impact toughness was investigated, and the fractured surfaces were examined. The impact toughness of SnAgCu solder joints with the plating of electroless Ni/immersion Au (ENIG) became worse after annealing, decreasing from 10 or 11 mJ to 7 mJ. On the other hand, an improvement of the impact toughness of eutectic SnPb solder joints with ENIG was recorded after annealing, increasing from 6 or 10 to 15 mJ. Annealing has softened the bulk SnPb solder so that more plastic deformation can occur to absorb the impact energy.

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Interfacial reaction and wetting behavior in eutectic SnPb solder on Ni/Ti thin films and Ni foils

Journal of Applied Physics ◽

10.1063/1.371751 ◽

1999 ◽

Vol 86 (12) ◽

pp. 6746-6751 ◽

Cited By ~ 123

Author(s):

P. G. Kim ◽

J. W. Jang ◽

T. Y. Lee ◽

K. N. Tu

Keyword(s):

Thin Films ◽

Interfacial Reaction ◽

Wetting Behavior ◽

Snpb Solder ◽

Eutectic Snpb

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Effect of Solder Thickness on Electromigration Behavior in Eutectic SnPb Solder Reaction Couples

Journal of Materials Engineering and Performance ◽

10.1007/s11665-009-9519-2 ◽

2009 ◽

Vol 19 (5) ◽

pp. 616-622 ◽

Cited By ~ 1

Author(s):

Guangchen Xu ◽

Fu Guo ◽

Zhidong Xia ◽

Yongping Lei ◽

Yaowu Shi ◽

...

Keyword(s):

Snpb Solder ◽

Solder Reaction ◽

Eutectic Snpb

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Interfacial stability of eutectic SnPb solder and composite 60Pb40Sn solder on Cu/Ni(V)/Ti under-bump metallization

Journal of Materials Research ◽

10.1557/jmr.2007.0083 ◽

2007 ◽

Vol 22 (3) ◽

pp. 735-741 ◽

Cited By ~ 10

Author(s):

Albert T. Wu ◽

F. Hua

Keyword(s):

Sacrificial Layer ◽

Under Bump Metallization ◽

Worst Case ◽

Die Attach ◽

Snpb Solder ◽

Cu Film ◽

Kirkendall Voids ◽

The Stability ◽

Cu Thin Film ◽

Eutectic Snpb

Eutectic SnPb solder has been widely used in packaging for several decades. The stability of the interface between solder and under-bump metallization (UBM) is an important issue that has led to many studies. Even though Ni atoms dissolve much slower into SnPb solder than Cu, the intermetallic compound, Ni3Sn4, which forms when eutectic SnPb solder reacts with Ni(V)/Ti UBM, is not stable on Ti layer, creates V-rich zone, and causes spalling. To prevent the phenomenon, and the resulting reduction of mechanical reliability in solder joints, we propose the addition of a layer of Cu thin film to serve as a sacrificial layer. Both eutectic SnPb solder and composite solder (high-Pb solder with eutectic SnPb solder) were studied in severe reflow conditions to simulate the worst case of die attach and later reflow process. Cu film first was consumed completely to form a compound. Due to lower interfacial energy between Cu6Sn5 and Ni(V), the interface was stable and no spalling occurred. However, the same thickness of Cu was insufficient to prevent Ni from diffusing into solder or compound. Not only diffusion of Ni atoms was observed; Sn atoms also diffused into the Ni(V) layer. The Sn–Ni reaction caused the interface between the compound and Ni(V) to retreat into the Ni(V) layer. The compound was not stable at the interface, and spalling could be seen. Due to the interdiffusion of Ni and Sn, many Kirkendall voids were also observed at both side of the interface.

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Microstructure-electromigration correlation in a thin stripe of eutectic SnPb solder stressed between Cu electrodes

Applied Physics Letters ◽

10.1063/1.124276 ◽

1999 ◽

Vol 75 (1) ◽

pp. 58-60 ◽

Cited By ~ 145

Author(s):

C. Y. Liu ◽

Chih Chen ◽

C. N. Liao ◽

K. N. Tu

Keyword(s):

Snpb Solder ◽

Eutectic Snpb

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Wetting Behaviors of Sn-Based Solders on Cu and Pd Surfaces

MRS Proceedings ◽

10.1557/proc-390-183 ◽

1995 ◽

Vol 390 ◽

Cited By ~ 1

Author(s):

H. K. Kim ◽

Y. Wang ◽

A. Maheshwari ◽

K. N. Tu

Keyword(s):

Surface Morphology ◽

Classical Model ◽

Layered Compound ◽

Quasi Equilibrium ◽

Compound Formation ◽

Snpb Solder ◽

Wetting Behaviors ◽

Pure Sn ◽

Compound Surface ◽

Eutectic Snpb

ABSTRACTWe have studied the surface morphology and wetting reaction of eutectic SnBi, eutectic SnPb, and pure Sn on Cu and Pd surfaces. In the case of Pd, the reactions were so fast that no quasi-equilibrium wetting angle could be measured. The compound formation has changed not only the interfaces but also the surfaces. Due to the formation of a reaction band outside the solder cap, the SnPb solder is no longer wetting the Cu surface but rather the Cu-Sn compound surface. In the wetting interface between eutectic SnPb and Cu, the morphology of the scallop-like Cu-Sn compound grains shows that we may not apply the classical model of layered compound growth to analyze the rate of soldering reactions.

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Morphology of wetting reaction of eutectic SnPb solder on Au foils

Journal of Applied Physics ◽

10.1063/1.363336 ◽

1996 ◽

Vol 80 (7) ◽

pp. 3822-3827 ◽

Cited By ~ 67

Author(s):

P. G. Kim ◽

K. N. Tu

Keyword(s):

Snpb Solder ◽

Eutectic Snpb

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Cross interactions on interfacial compound formation of solder bumps and metallization layers during reflow

Journal of Materials Research ◽

10.1557/jmr.2004.0478 ◽

2004 ◽

Vol 19 (12) ◽

pp. 3654-3664 ◽

Cited By ~ 23

Author(s):

T.L. Shao ◽

T.S. Chen ◽

Y.M. Huang ◽

Chih Chen

Keyword(s):

Flip Chip ◽

Driving Forces ◽

The Other ◽

Compound Formation ◽

Bump Height ◽

Performance Requirements ◽

Substrate Side ◽

Solder Bumps ◽

Snpb Solder ◽

Eutectic Snpb

While the dimension of solder bumps keeps shrinking to meet higher performance requirements, the formation of interfacial compounds may be affected more profoundly by the other side of metallization layer due to a smaller bump height. In this study, cross interactions on the formation of intermetallic compounds (IMCs) were investigated in eutectic SnPb, SnAg3.5, SnAg3.8Cu0.7, and SnSb5 solders jointed to Cu/Cr–Cu/Ti on the chip side and Au/Ni metallization on the substrate side. It is found that the Cu atoms on the chip side diffused to the substrate side to form (Cux,Ni1−x)6Sn5 or (Niy,Cu1−y)3Sn4 for the four solders during the reflow for joining flip chip packages. For the SnPb solder, Au atoms were observed on the chip side after the reflow, yet few Ni atoms were detected on the chip side. In addition, for SnAg3.5 and SnSn5 solders, the Ni atoms on the substrate side migrated to the chip side during the reflow to change binary Cu6Sn5 into ternary (Cux,Ni1−x)6Sn5 IMCs, in which the Ni weighed approximately 21%. Furthermore, it is intriguing that no Ni atoms were detected on the chip side of the SnAg3.8Cu0.7 joint. The possible driving forces responsible for the diffusion of Au, Ni, and Cu atoms are discussed in this paper.

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