Wire bonding of Cu and Pd coated Cu wire: Bondability, reliability, and IMC formation

Qin, Ivy; Xu, Huining; Clauberg, Horst; Cathcart, Ray; Acoff, Viola L.; Chylak, Bob; Huynh, Cuong

doi:10.1109/ectc.2011.5898707

Cited by 35 publications

(16 citation statements)

References 6 publications

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“…In addition, another paper showed concentrated Pd at the peripheral area of the bonds reduced IMC growth comparing to the central area of the bonds with Pd coated Cu wire at 175degC HTSL condition. [11] This also matches with our simulation results. On the other hand, NiPd or NiPdAu plating could be used on Al pad for Cu wire.…”

Section: Case 2 Pd Is Only At Surface Case 2-1 Pd Could Behave Barrsupporting

confidence: 93%

“…[1,4,8,10,11,12,13] The Pd distribution in FAB could be decided by Pd-Cu type from different wire supplier and bonding condition. [12,14,15] The mechanism of Pd-Cu wire humidity reliability improvement over bare Cu wire needs to discussed case by case.…”

Section: Fig 10 Hast Results Comparison Between Cu and Pd-cumentioning

confidence: 99%

“…For Case 2-1, Cl ion diffusion coefficient in Pd is 4.76x10 -17 m 2 /s. Assuming Pd thickness is 80nm [11] and Cl ion moves towards one direction without random walk, the needed time for Cl ion to penetrate Pd layer is 67sec. On the other hand, we also calculated Cl ion diffusion coefficient in Cu 3 Al 2 resulting in 3.94x10 -15 m 2 /s.…”

Section: Case 2 Pd Is Only At Surface Case 2-1 Pd Could Behave Barrmentioning

confidence: 99%

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Cu wire and Pd-Cu wire package reliability and molding compounds

Abe

Kang

Yamamoto

et al. 2012

2012 IEEE 62nd Electronic Components and Technology Conference

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Cu wire is drastically replacing Au wire due to surge of Au price. However, Cu wire package has poorer humidity reliability than Au wire package. Although Pd coated Cu wire package could show better humidity reliability than Cu wire, it is still worse than Au. Enough information regarding failure mechanism was not available. For failure analysis, x-section has been widely used to identify the Cu/Al IMC after failure. However, the x-section is the results of corrosion reaction and doesn't show the IMC status before corrosion. Therefore, the failure mechanism could not be estimated precisely. We used chemical model simulation to predict what kinds of IMC could be created after wire bonding, then which IMC could be corroded more easily during HAST. The Desorption energy was used to estimate reactivity between specified Cu/Al IMC and chlorine ion. The simulation suggested that the formation of Cu rich and Cu poor Cu/Al IMC and the Cu rich IMC was estimated to be corroded by chlorine ion. These chemical model simulations are the effective way to have fundamental understanding of the mechanism of Cu/Al IMC corrosion. Furthermore, chemical model simulation for Pd coated Cu wire was done to explore the effect of Pd existence and distribution of Pd in Cu/Al IMC. Dispersed Pd contributed to create new IMC of Cu/Al/Pd instead of easily corroded Cu rich Cu/Al IMC. Cu and Al diffusion and also Cl ion diffusion were inhibited by Pd at surface. Even Cl ion catching effect by Pd is also discussed.To improve humidity reliability performance with Cu wire, we developed new ion trapper using chemical model simulation technique. Developed molding compounds with the ion trapper showed significant improvement at bias HAST with Cu wire, which was even better than conventional Cu wire compatible molding compounds. IntroductionOne of the concerns to use Cu wire has been failure during humidity reliability test such as PCT, unbias HAST and bias HAST. [1,2] Failure mode of humidity reliability test was open with observed corroded layer and crack. We also confirmed that open failure at positive pad at bias HAST.[3] Conventional Br contained molding compound showed worse HAST results. However, even green molding compound showed HAST failure. We explored the factors of humidity reliability failure for Cu wire packages. As a result, extracted chlorine ion from molding compounds turned to be major factor while pH of extracted water turned to be minor factor through bias HAST. We also examined impact of wire bonding strength, bias and reliability condition.

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Section: Case 2 Pd Is Only At Surface Case 2-1 Pd Could Behave Barrsupporting

confidence: 93%

Section: Fig 10 Hast Results Comparison Between Cu and Pd-cumentioning

confidence: 99%

Section: Case 2 Pd Is Only At Surface Case 2-1 Pd Could Behave Barrmentioning

confidence: 99%

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Cu wire and Pd-Cu wire package reliability and molding compounds

Abe

Kang

Yamamoto

et al. 2012

2012 IEEE 62nd Electronic Components and Technology Conference

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“…During the free-air ball forming process, Pd would dissolve into Cu instead of staying on the ball surface. During aging, Pd tends to diffuse and segregate to the bonding interface, which appears to degrade the bond strength [17,18]. It seems that Cu wire bonding technique is still in the developing stage.…”

Section: Introductionmentioning

confidence: 99%

A solid-state bonding technique of large copper wires for high power devices operating at high temperature

Lee

2015

J Mater Sci: Mater Electron

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Solid-state processes of bonding 1 mm copper (Cu) wires on Cu substrates and silicon (Si) chips, respectively, were developed. To overcome Cu oxidation issue, the bonding surface on the wire was plated a silver (Ag) layer. An annealing step followed to make the Ag layer much easier to deform and conform to the Cu or Si bonding surfaces. The bonding process was performed at 300°C with 6.89 MPa. Wire-bond cross sections were studied using optical and electron microscopy, respectively. The images obtained exhibit nearly perfect Ag-Cu bonding interface. For wire-bonds made on Cu substrate, in-plane (shear) pull test measured a breaking of force 20.7-23.7 kg, comparable to the 22.5 kg breaking force of the Cu wire itself. Breaking forces on vertical (peel) pull test are about one-half of in-plane pull test results. For wire-bonds made on Si chip, breaking forces are about 80 % of those made on Cu substrate. Fracture modes were evaluated in details. 90 % of the wire-bonds broke with three modes mixed together: near Cu-Ag plating interface, inside Ag layer, and Ag-Cu bonding interface. Thus, the bonding interface is as strong as other regions of the wirebond. This solid-state wire bonding process is expected to have valuable applications in high power and high temperature devices and modules where the wire-bonds have to stand alone without protection due to lack of high temperature molding compound and reinforcing materials.

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“…Previous studies had been carried out to understand the intermetallic phase formed with Pd coated copper wire bonded on aluminium pad and subjected to high temperature aging. There were reports on Pd forming Cu-Al-Pd phase after PCT test [1,6] while others found Pd did not form the compound but rather, diffused back into Cu to form Pd rich phase [7,8].…”

Section: Introductionmentioning

confidence: 99%