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A Study on the Relationship of Processing Conditions, Microstructure and Properties of Copper Wirebond in Microelectronic Connections
Başlık:
A Study on the Relationship of Processing Conditions, Microstructure and Properties of Copper Wirebond in Microelectronic Connections
Yazar:
Liu, Dong, author.
ISBN:
9780438130869
Yazar Ek Girişi:
Fiziksel Tanımlama:
1 electronic resource (188 pages)
Genel Not:
Source: Masters Abstracts International, Volume: 57-06M(E).
Advisors: Jingshen Wu.
Özet:
Wire bonding is one of the dominant microelectronic connection technologies, which provides electrical connection between integrated circuits and external leads. A solid free air ball (FAB), which is fabricated by melting a part of bonding wire in electronic flame-off (EFO) process, is thermosonically bonded on the aluminum bonding pad at a high bonding temperature. Because of interdiffusion, intermetallic compounds (IMCs) form spontaneously at the bonding interface and play a critical role on the ball bonding strength. In recent years, the utilization of copper bonding wire to replace the traditional gold bonding wire brings new challenges into this field. The relationship of processing conditions, microstructure and properties of copper wirebond is therefore investigated in this thesis work.
First of all, although FABs with same diameter are fabricated using different EFO settings, same FAB hardness is measured. After thermosonical bonding on the aluminum pads, different bonding heights indicate these FABs have different resistance to the plastic deformation. Microstructure investigation demonstrates that different FAB properties are attributed to the competition between grain size hardening and texture hardening. During the FAB fabrication, thermal conduction along the bonding wire results in the formation of heat affected zone (HAZ) connected to the FAB. Different EFO settings are selected in order to obtain straight wire samples with different HAZ length. HAZ boundary is defined based on the microstructure evolution and hardness variation along the bonding wire. A novel deflection test was established to accurately measure the HAZ Young's modulus. Because of HAZ formation, Young's modulus drops significantly from 149 GPa in fresh copper wire to only 110 GPa. Although different HAZ lengths are measured, HAZ Young's modulus does not show notable difference.
Then, Cu-Al interfacial IMC corrosion in an accelerated humidity test is investigated. Although selective IMC corrosion was reported to be the feature of corroded bonding interface, basic mechanisms behind the selective corrosion are still not fully understood. After isothermal aging, Al2Cu, Cu3Al2 and Cu9Al4 phases are identified at the Cu-Al bonding interface. Selective IMC corrosion (or selective IMC dealloying) is closely relating to the chloride. Transmission electron microscopy (TEM) reveals the selective IMC dealloying process. When Cu3Al 2 and Cu9Al4 are continually attacked by chloride, a mushroom-shaped corrosion product, with dealloyed copper head and IMC stem, is undercut from the corroded IMC matrix. The dealloyed copper nano-grain is mounted by the amorphous Al(OH)3. A bilayer nanostructure, consisting of Al2O3 and aluminum, forms on the Al 2Cu surface and renders Al2Cu phase immune to the chloride-induced corrosion. In addition, IMC stress corrosion and high chloride concentration around corroded IMC surfaces make the corroded IMC region in a wedge shape.
Finally, an investigation on interfacial IMC corrosion is further conducted for palladium-coated copper (PCC) wirebond, since nano-scale palladium coating is believed to improve the corrosion resistant of interfacial IMCs. At the thermally aged interface, only Cu9Al4 and Cu3Al 2 are confirmed to be Pd-containing IMCs. Inert diffusion behavior of palladium renders the co-existence of Pd-containing and Pd-absent Cu-Al IMCs, which are separated by the original ball bonding interface. A Pd-rich Cu-Al IMC (approximately 43 atom % Pd) is found in the annealed Cu-Pd-Al thin film diffusion couple, and identified as the Cu3Al2 solid solubility. Pd-containing Cu-Al IMCs are also attacked by the chloride in a similar manner of Cu-Al IMC dealloying: a mushroom protuberance, consisting of Pd-containing copper solid solution as "head" and Pd-containing IMC as "stem", is undercut by the attach of chloride in a humid condition. Based on this study, it is speculated that the palladium coating cannot make the interfacial intermetallics completely immune to the chloride-induced corrosion in the humidity test.
Notlar:
School code: 1223
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Yer Numarası | Demirbaş Numarası | Shelf Location | Lokasyon / Statüsü / İade Tarihi |
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