Growth behavior of Cu/Al intermetallic compounds and cracks in copper ball bonds during isothermal aging

Hang, Chunjin; Wang, Chunqing; Mayer, Michael; Tian, Yanhong; Zhou, Yunhong; Wang, H.H.

doi:10.1016/j.microrel.2007.06.008

Cited by 220 publications

(126 citation statements)

References 19 publications

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“…Significantly, the temperature was measured at the center of the nugget, whereas the local melting occurred at its periphery. The copper matrix underwent greater plastic deformation and stress at the periphery of the nugget [25]. The frictional energy intensity at the periphery of the welding region was always maximum [26].…”

Section: Microstructure Evolutionmentioning

confidence: 97%

Effects of Vibration Amplitude on Microstructure Evolution and Mechanical Strength of Ultrasonic Spot Welded Cu/Al Joints

Liu

Biao

Yang

2017

Metals

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Abstract:The effects of vibration amplitude on the interface reaction and mechanical strength of the Cu/Al joints were systematically investigated in ultrasonic spot welding (USW) experiments. The appropriate vibration amplitude (22.5 µm) was beneficial for obtaining a sound joint. The formation of the continuous intermetallic compounds (IMC) layer accelerated with a higher vibration amplitude. The lap shear tensile strength of the Cu/Al joints decreased when the thickness of the intermetallic layer was greater than 1 µm at various amplitudes. With the increase in welding time, a crack occurred in the copper side owing to the occurrence of the eutectic reaction, α-Al + θ → L, at the periphery of the nugget. The remarkable decline of ultrasonic power curves occurred at various amplitude levels upon the formation of a crack in the copper side.

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Section: Microstructure Evolutionmentioning

confidence: 97%

Effects of Vibration Amplitude on Microstructure Evolution and Mechanical Strength of Ultrasonic Spot Welded Cu/Al Joints

Liu

Biao

Yang

2017

Metals

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“…Fig. 10 shows an example from a recently published review of ball bonding materials science [13] and examples of similar squeeze out can be seen in as-bonded copper ball bonded packages in industry and in recent literature such as the study by Hang et al [14].…”

Section: The Ball Bonding Processmentioning

confidence: 79%

“…There was no pattern to the cratering after ageing. More recently, Hang et al [14] have found cracking of Cu-Al intermetallics after high temperature storage of encapsulated copper ball bonds at 250°C.…”

Section: Reliability Studies 2003 To Presentmentioning

confidence: 99%

What is the future of bonding wire? Will copper entirely replace gold?

Breach¹

2010

Gold Bull

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Thermosonic ball bonding is a major interconnect process in microelectronics packaging and is positioned to remain one of the key process technologies available to package designers in the near future. However, the main wire material used in fine pitch (FP) and ultra-fine pitch (UFP) ball bonding is gold and with significant increases in gold price, gold ball bonding has become a more costly process that has a considerable economic effect on the assembly of packages used in consumer electronics. An alternative wire material to gold is copper, which is much cheaper and has several technical benefits including better electrical conductivity and has been widely used in discrete and power devices with wire diameters typically larger than 30μm in diameter for many years. However, copper wire behaves quite differently than gold due to its different physical properties, some of which are beneficial and others detrimental to bonding performance. In this article, we briefly review some of the advantages and difficulties with using copper wire advanced packaging and explain why copper cannot replace gold in many applications and why gold offers significant benefits.

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“…However, the price of Au is increasing and copper (Cu) has been investigated as the most suitable alternative because of its lower cost, slower intermetallic growth on aluminum (Al) pads, and higher thermal conductivity. [1][2][3][4] The growth rate of Cu/Al IMCs are around 10% of that for Au/Al IMCs during annealing from 150°C to 300°C. This is attributed to two reasons; one is the larger size of Cu atoms (atomic radii 0.128 nm) which show a larger misfit with Al (0.143 nm), comparing with Au atoms (0.144 nm) and the other is lower electronegativity of Cu than Au.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Formation and Growth Behavior of Cu/Al Intermetallic Compounds during Isothermal Aging

Mokhtari

Kim

Nishikawa

et al. 2014

Transactions of The Japan Institute of Electronics Packaging

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Wire bonding is a key technique for electrical interconnections between integrated circuit (IC) and the metal frame or printed circuit board (PCB). One of the most common wire bonding system is bonding of the Au wire to Al metallization, however, Cu wire is being considered as replacement for Au wire due to surge of Au price. This research focuses on the formation and growth behavior of Cu/Al intermetallic compounds (IMCs). In order to investigate IMC growth after 30, 60 and 120 min of aging at 270, 300 and 330°C, cross-section of Al, Cu and Cu/Al IMCs were examined by scanning electron microscopy (SEM). The results showed that the consumption of the Al layer is more rapid than that of Cu layer, and that after 120 min at 330°C the Al layer is entirely consumed. The formation of three distinct Cu/Al IMC layers was observed. Scanning transmission electron microscopy (STEM)/energy-dispersive X-ray spectroscopy (EDS) was used to identify the three IMC layers formed at the interface. In addition, the IMC compositions were identified by selected-area diffraction pattern (SAD). These were CuAl, Cu 3 Al 2 and Cu 9 Al 4 . Also, the activation energies of Cu/Al IMC growth were obtained from an Arrhenius plot.

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Growth behavior of Cu/Al intermetallic compounds and cracks in copper ball bonds during isothermal aging

Cited by 220 publications

References 19 publications

Effects of Vibration Amplitude on Microstructure Evolution and Mechanical Strength of Ultrasonic Spot Welded Cu/Al Joints

Effects of Vibration Amplitude on Microstructure Evolution and Mechanical Strength of Ultrasonic Spot Welded Cu/Al Joints

What is the future of bonding wire? Will copper entirely replace gold?

Investigation of Formation and Growth Behavior of Cu/Al Intermetallic Compounds during Isothermal Aging

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