Intermetallic phase transformations in Au–Al wire bonds

Xu, Huining; Liu, C.; Silberschmidt, Vadim V.; Pramana, Stevin S.; White, Timothy John; Chen, Zhong; Acoff, Viola L.

doi:10.1016/j.intermet.2011.07.003

Cited by 48 publications

(15 citation statements)

References 29 publications

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“…Especially, the uniform distribution of the Au and Al elements in the intermediate metal compound layers demonstrated uniform inter-atomic diffusion at the bond interface, although individual microvoids were sometimes found at the bond interfaces. The EDS analysis revealed an Au to Al atomic ratio of more than 4.8, indicating that the formed IMCs were likely to be Au 4 Al or a combination with Au 8 Al 3 , which is in agreement with the resulting IMCs of previous work where Au-Al wire bonds underwent a similar thermal process at 250 • C [49]. In addition, the exposed Au-Al IMCs have a tan color after shear testing ( Fig.…”

Section: B Inspection Of Bond Interfacessupporting

confidence: 89%

Wafer-Level Vacuum Sealing by Transfer Bonding of Silicon Caps for Small Footprint and Ultra-Thin MEMS Packages

Wang

Bleiker

Edinger

et al. 2019

J. Microelectromech. Syst.

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Vacuum and hermetic packaging is a critical requirement for optimal performance of many micro-electromechanical systems (MEMS), vacuum electronics, and quantum devices. However, existing packaging solutions are either elaborate to implement or rely on bulky caps and footprint-consuming seals. Here, we address this problem by demonstrating a waferlevel vacuum packaging method featuring transfer bonding of 25-µm-thin silicon (Si) caps that are transferred from a 100-mm-diameter silicon-on-insulator (SOI) wafer to a cavity wafer to seal the cavities by gold-aluminum (Au-Al) thermocompression bonding at a low temperature of 250 • C. The resulting wafer-scale sealing yields after wafer dicing are 98% and 100% with sealing rings as narrow as 6 and 9 µm, respectively. Despite the small sealing footprint, the Si caps with 9-µm-wide sealing rings demonstrate a high mean shear strength of 127 MPa. The vacuum levels in the getter-free sealed cavities are measured by residual gas analysis to be as low as 1.3 mbar, based on which a leak rate smaller than 2.8 × 10 −14 mbarL/s is derived. We also show that the thickness of the Si caps can be reduced to 6 µm by post-transfer etching while still maintaining excellent hermeticity. The demonstrated ultra-thin packages can potentially be placed in between the solder bumps in flip-chip interfaces, thereby avoiding the need of through-capvias in conventional MEMS packages. [2018-0257] Index Terms-Vacuum, hermetic, packaging, sealing, MEMS, ultra-thin package, small footprint, transfer bonding, 3D integration, flip chip, aluminum, gold, thermo-compression bonding. I. INTRODUCTION V ACUUM packaging is a process for encapsulating a device (e.g. a MEMS or nano-electro-mechanical system (NEMS) device) in a vacuum environment and maintaining the internal vacuum level using hermetic seals. It enables functionality and long-term reliability of various MEMS devices, such as inertial sensors, pressure sensors and infrared detectors, but typically also constitutes a significant part of their cost in high-volume production [1], [2]. As a general trend,

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Section: B Inspection Of Bond Interfacessupporting

confidence: 89%

Wafer-Level Vacuum Sealing by Transfer Bonding of Silicon Caps for Small Footprint and Ultra-Thin MEMS Packages

Wang

Bleiker

Edinger

et al. 2019

J. Microelectromech. Syst.

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“…Copper wire bonding appears to be the alternate materials, and various engineering studies on copper wire deployment have been reported [2,3]. The Au-Al intermetallic compound (IMC) growth is widely characterized and analyzed [4][5][6]. Zulkifli MN et al [7] suggested new approaches: examining the effect of individual phase and surroundings on the strengthening produced by the Au-Al intermetallic compound, combiningmore susceptible to moisture corrosion compared to gold ball bonds and undergoes different corrosion mechanisms in microelectronic packaging [11,12].…”

Section: Introductionmentioning

confidence: 99%

Extended reliability of gold and copper ball bonds in microelectronic packaging

Gan

Francis²,

Chan³

et al. 2013

Gold Bull

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Wire bonding is the predominant mode of interconnection in microelectronic packaging. Gold wire bonding has been refined again and again to retain control of interconnect technology due to its ease of workability and years of reliability data. Copper (Cu) wire bonding is well known for its advantages such as cost-effectiveness and better electrical conductivity in microelectronic packaging. However, extended reliabilities of Cu wire bonding are still unknown as of now. Extended reliabilities of Au and Pd-coated Cu (Cu) ball bonds are useful technical information for Au and Cu wire deployment in microelectronic packaging. This paper discusses the influence of wire type and mold compound effect on the package reliability and after several component reliability stress tests. Failure analysis has been conducted to identify its associated failure mechanisms after the package conditions for Au and Cu ball bonds. Extended reliabilities of both wire types are investigated after unbiased HAST (UHAST), temperature cycling (TC), and high-temperature storage life test (HTSL) at 150, 175, and 200°C aging temperatures. Weibull plots have been plotted for each reliability stress. Obviously, Au ball bond is found with longer time to failure in unbiased HAST stress compared to Cu ball bonds for both mold compounds. Cu wire exhibits equivalent package and or better reliability margin compared to Au ball bonds in TC and HTSL tests. Failure mechanisms of UHAST and TC have been proposed, and its mean time to failure (t 50 ), characteristic life (t 63.2 , η), and shape parameter (ß) have been discussed in this paper. Feasibility of silver (Ag) wire bonding deployment in microelectronic packaging is discussed at the last section in this paper.

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“…10, and have a high Al-content composition of Au:Al = 41.2:58.8. Xu et al [22], [23] reported Au 4 Al and AuAl 2 intermetallic particles with sizes of 0.15-0.3 µm encapsulated remnant alumina at the Au wire/Al pads interfaces after prolonged annealing treatment. They explained the observations of Au 4 Al and AuAl 2 intermetallic particles inserted with alumina cores as follows: The aluminum oxide film on the Al pads broke during the thermocompressive process of wire bonding and became a discontinuous remnant between continuous Au 4 Al and AuAl 2 films prior to annealing.…”

Section: Resultsmentioning

confidence: 99%

Formation and Growth of Intermetallics in an Annealing-Twinned Ag-8Au-3Pd Wire Bonding Package During Reliability Tests

Chuang

Chang

Chuang

et al. 2013

IEEE Trans. Compon., Packag. Manufact. Technol.

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Wire bonding on Al pad packages with an innovative annealing twinned Ag-8Au-3Pd alloy wire results in a sufficient interfacial intermetallic layer at the initial as-bonded stage, while its growth during the further temperature cycling test and pressure cooker test is very slow. Even after prolonged high-temperature storage at 150°C for 500 h, the thickness of its intermetallics is only around 1.7 µm. In contrast, a very thin CuAl 2 intermetallic layer appears at the interface of the Pdcoated Cu wire bonded package, and a thick layer of Au 8 Al 3 intermetallic compounds forms in the Au wire package, which grows to a thickness of around 4.0 µm after high-temperature storage at 150°C for 500 h. Energy dispersive X-ray spectrometry analyses indicate that AgAl 2 , Au 8 Al 3 , and CuAl 2 are the main intermetallic phases formed in the packages bonded with Ag8Au-3Pd, and Au and Pd-coated Cu wires, respectively. However, an additional Pd-containing Ag 2 Al layer found at the AgAl 2 /Al interface of Ag-8Au-3Pd wire bonded package can interrupt its intermetallic reaction, and the annealing twins can further slow the intermetallic growth.Index Terms-Ag-8Au-3Pd alloy wire, annealing twins, intermetallic compounds, wire bonding.

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Intermetallic phase transformations in Au–Al wire bonds

Cited by 48 publications

References 29 publications

Wafer-Level Vacuum Sealing by Transfer Bonding of Silicon Caps for Small Footprint and Ultra-Thin MEMS Packages

Wafer-Level Vacuum Sealing by Transfer Bonding of Silicon Caps for Small Footprint and Ultra-Thin MEMS Packages

Extended reliability of gold and copper ball bonds in microelectronic packaging

Formation and Growth of Intermetallics in an Annealing-Twinned Ag-8Au-3Pd Wire Bonding Package During Reliability Tests

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