Fine Pitch (150/spl mu/m) Pb-Free Flip-Chip Bumping and Packaging

Nicholls, Lou; Darveaux, Robert; Hansen, B.J.; Carey, C.; Aoki, Toyohiro; Akimoto, Takeshi; Chang, Jason J.

doi:10.1109/ectc.2006.1645636

Cited by 3 publications

(3 citation statements)

References 5 publications

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Section: Introductionmentioning

confidence: 99%

“…Since the EM driving force follows a power of the current density, reducing current density has one of the focal points for research. The introduction of thick UBM (under bump metallurgy) significantly reduced or eliminated current crowding [8][9], thus extending the current-carrying capability of Pb-free interconnect.Temperature is another important factor in the EM process, represented by the exponential factor in Black's Law. Due to the low melting temperature of Pb-free solders, the effect of temperature is particularly pronounced.…”

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confidence: 99%

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Effect of Joule heating on electromigration reliability of Pb-free interconnect

Wright

McVicker

et al. 2012

2012 IEEE 62nd Electronic Components and Technology Conference

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Temperature and current are two major parameters that impact electromigration reliability. Due to the large current used in the accelerated electromigration test, the Joule selfheating associated with the stress current can be significant. The paper presents a study of electromigration fails in Pb-free interconnect from the point of view of localized Joule heating. The Joule heating effect in two types of packages, a fully assembled flip chip module with standard C4s and a silicon to silicon assembly with microbumps, is considered. A thermal FEM model is used as a guide to interpret the experimental observations. IntroductionAs the EU and RoHS deadline on Pb-free solders draws close, the reported reliability of Sn based Pb-free solders has improved significantly. Advances in interconnect structure, materials and process have not only improved mechanical integrity of the large chip organic package, but also increased current carrying capability of Pb-free interconnects by more than an order of magnitude over the past decade [1-2]. Electromigration (EM) and thermal migration mechanisms of Pb-free solder have been proposed and studied [3-7], providing insight for further improvements. Since the EM driving force follows a power of the current density, reducing current density has one of the focal points for research. The introduction of thick UBM (under bump metallurgy) significantly reduced or eliminated current crowding [8][9], thus extending the current-carrying capability of Pb-free interconnect.Temperature is another important factor in the EM process, represented by the exponential factor in Black's Law. Due to the low melting temperature of Pb-free solders, the effect of temperature is particularly pronounced. Joule heating due to current crowding has been modeled and observed by IR microscopy [10][11]. Thermal migration due to temperature gradients within the solder joint has also been studied [12][13]. Although it is commonly accepted that the voids caused by mass transport, driven by electron wind, are the source for EM failure, the mechanism that leads to accumulation of voids which in turn leads to catastrophic failure has not been established. If the resistance change is mainly due to void formation, the voiding area needs to be over 90% of the conduction area before the change in resistance becomes observable. In this paper, an example of the correlation between measured resistance changes and bump temperature is shown. The EM test results from two types of test vehicles are compared, and the relationship between Joule heating, heat removal rate, and ultimate EM-induced failure is discussed. A thermal finite element model (FEM) model is used as a guide to interpret the experiments observations. An electro-thermal model will be onsidered in a separate study.

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Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

Effect of Joule heating on electromigration reliability of Pb-free interconnect

Wright

McVicker

et al. 2012

2012 IEEE 62nd Electronic Components and Technology Conference

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“…As flip chip packaging structures move from Pb-bearing solders to Pb-free solders, as influenced by Europe Union (EU) RoHS regulations, the reliability issues related to Pbfree solder have attracted a lot of attention in the microelectronics industry [1][2]. Electromigration (EM) in C4 interconnections has resurfaced because of the demand for finer pitch interconnections with higher current densities as well as unique Sn alloy properties.…”

Section: Introductionmentioning

confidence: 99%

Electromigration in Pb-free solders

Shih

Lauro

2008

2008 International Conference on Electronic Packaging Technology &Amp; High Density Packaging

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Electromigration (EM)-induced damage in lead-free solders strongly depend on the Sn grain orientation in the Pbfree solder joint. Significant damage can develop at a very early stage when the c-axis of a Sn-grain is oriented close to the current direction. Rapid dissolution of both intermetallic compounds (IMC) and under-bump metallurgy (UBM) that led to significant cavitations at interface is caused by fast diffusion of Cu and Ni through the Sn crystal along the caxis. On the other hand, when the c-axis of a Sn grain is not aligned with the current direction, cavitations at solder-IMC interface are formed mostly due to Sn-self diffusion which is correlated with failures at a much longer stress time. This is a direct proof of the highly anisotropic diffusion behavior of Cu and Ni in Sn, reported by Turnbull and Huntington many years ago. The stable Ag 3 Sn network and cyclic twinning in SnAg solder contributed to the better EM performance of Sn1.8Ag compared to that of Sn0.7Cu solder. The ranking of the three surface finishes, from best to worst, is Ni(P)/Cu, Ni(P)/Au, and Cu, when electrons are entering from the tested surfaces. A Ni barrier layer is needed to retard the electromigration damage. However, the addition of Cu at an optimized level to the Sn-Ag solder drastically improved the electromigration performance.

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Comparison of electromigration performance for Pb-free solders and surface finishes with Ni UBM

Lauro

Shih

et al. 2008

2008 58th Electronic Components and Technology Conference

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Fine Pitch (150/spl mu/m) Pb-Free Flip-Chip Bumping and Packaging

Cited by 3 publications

References 5 publications

Effect of Joule heating on electromigration reliability of Pb-free interconnect

Effect of Joule heating on electromigration reliability of Pb-free interconnect

Electromigration in Pb-free solders

Comparison of electromigration performance for Pb-free solders and surface finishes with Ni UBM

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