Characteristics of current crowding in flip-chip solder bumps

Lai, Yi‐Shao; Kao, Chin-Li

doi:10.1016/j.microrel.2005.02.007

Cited by 51 publications

(37 citation statements)

References 8 publications

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“…We have determined that there is no current density convergence at the inner corner with the mesh density increase. The same result was demonstrated in paper [3] for a more complex conductor geometry. This numerical nonconvergence doesn't allow us to rely upon the results of the finite element method and requires an analytical analysis of the problem.…”

Section: Introductionsupporting

confidence: 83%

“…As a rule, it takes place at the vicinity of contacts or various inhomogeneities. Being localized in a small area, this increase may lead to overheating of a conductor and acceleration of electromigration processes [1][2][3]. It in turn may cause a failure in a chip.…”

Section: Introductionmentioning

confidence: 99%

“…On the one hand, a numerical algorithm cannot deal with the infinity, on the other hand, one doesn't know what value of the current density should be used instead of an infinite one. One way to cope with this problem is to average the current density over a finite volume near the singularity [3]. This method is very useful yet approximate; and it requires complex numerical investigations.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Elimination of Current Crowding Problem in Flat Conductors Bent at Arbitrary Angles

Gerasimenko¹,

Polyakov²,

Frolov³

2014

PIER Letters

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Abstract-This work is devoted to a theoretical investigation of the current crowding problem in flat conductors bent at arbitrary angles. Using conformal mapping techniques, we succeed in obtaining an analytical expression for current density distributions in such conductors. It is shown that the current density increases in a small vicinity of the corner and approaches to infinity at its top. In order to eliminate the infinity, the vertex is replaced by an arc of a circle with a small radius. The method has been developed for an arbitrary angle; several specific examples are considered.

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Section: Introductionsupporting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Elimination of Current Crowding Problem in Flat Conductors Bent at Arbitrary Angles

Gerasimenko¹,

Polyakov²,

Frolov³

2014

PIER Letters

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“…[4][5][6] A view of the microstructural evolution of EM is that very high current crowding occurs, causing a unique and fast EM failure in solder bumps. 7,8 Due to the current crowding effect, voids initiate first at the edge of solder joints. Propagation of voids then causes a nonuniform distribution of current density, and increased resistance around the voids induces further localized temperature rises, which in turn accelerate the formation of voids.…”

Section: Introductionmentioning

confidence: 99%

Resistance Changes in Eutectic Sn-Bi Solder Joints During Electromigration

Guo

Sun

et al. 2009

Journal of Elec Materi

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The resistance of electronic interconnects made with Sn-based solders experiences significant deterioration during service in high-performance electronic products. During electromigration damage, metal atoms/ions can migrate in the direction of electron flow. Accordingly, accumulation of metal atoms/ions at the anode interface can induce surface bulging. On the other hand, depletion of metal atoms/ions at the cathode interface can induce surface dimpling. In addition, the different a-rich and b-rich phases in a binary eutectic system were found to separate in the bulk region of eutectic Sn-Bi solder joints. Such atomic movement leads to complex interactions between the resistance changes of electronic solder joints during the different stages of electromigration. In order to clarify such scenarios, a LabVIEW Ò -controlled system was employed to quantitatively measure the instantaneous resistance values after an electric current was applied. This study investigated the effects of a high current density (10 4 A/cm 2 ) at two different ambient temperatures (25°C and 80°C) on the deterioration of resistance changes during the early stage of the electromigration process.

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“…Similar to Sn-Pb solder joints, the high current density induced by current crowding (e.g., Refs. [8][9][10][11] around the thin-film-stack underbump metallurgy (UBM) at the chip side has been identified as a crucial driving force responsible for the failure of these solder joints. [5][6][7] In response to this critical and general electromigration-induced failure in flip-chip solder joints, the thick Cu pillar UBM has been proposed to alleviate current crowding and consumption of UBM as well.…”

Section: Introductionmentioning

confidence: 99%

Electromigration Reliability and Morphologies of Cu Pillar Flip-Chip Solder Joints with Cu Substrate Pad Metallization

Lai

Chiu

Chen

2008

Journal of Elec Materi

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The Cu pillar is a thick underbump metallurgy (UBM) structure developed to alleviate current crowding in a flip-chip solder joint under operating conditions. We present in this work an examination of the electromigration reliability and morphologies of Cu pillar flip-chip solder joints formed by joining Ti/Cu/Ni UBM with largely elongated $62 lm Cu onto Cu substrate pad metallization using the Sn-3Ag-0.5Cu solder alloy. Three test conditions that controlled average current densities in solder joints and ambient temperatures were considered: 10 kA/cm 2 at 150°C, 10 kA/cm 2 at 160°C, and 15 kA/cm 2 at 125°C. Electromigration reliability of this particular solder joint turns out to be greatly enhanced compared to a conventional solder joint with a thinfilm-stack UBM. Cross-sectional examinations of solder joints upon failure indicate that cracks formed in (Cu,Ni) 6 Sn 5 or Cu 6 Sn 5 intermetallic compounds (IMCs) near the cathode side of the solder joint. Moreover, the $52-lm-thick Sn-Ag-Cu solder after long-term current stressing has turned into a combination of $80% Cu-Ni-Sn IMC and $20% Sn-rich phases, which appeared in the form of large aggregates that in general were distributed on the cathode side of the solder joint.

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Characteristics of current crowding in flip-chip solder bumps

Cited by 51 publications

References 8 publications

Elimination of Current Crowding Problem in Flat Conductors Bent at Arbitrary Angles

Elimination of Current Crowding Problem in Flat Conductors Bent at Arbitrary Angles

Resistance Changes in Eutectic Sn-Bi Solder Joints During Electromigration

Electromigration Reliability and Morphologies of Cu Pillar Flip-Chip Solder Joints with Cu Substrate Pad Metallization

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