Impact of palladium to the interfacial behavior of palladium coated copper wire on aluminium pad metallization during high temperature storage

Stephan, D.; Chew, Effie; Yeung, Johnny; Milke, E.

doi:10.1109/eptc.2011.6184434

Cited by 10 publications

(11 citation statements)

References 8 publications

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“…Considering actual time length of humidity reliability test, Pd is absolute barrier layer to prevent Cu and Al diffusion and then no diffusion means no easily-corroded Cu rich IMC creation. The other experimental results showed thinner IMC growth with Cu-Pd wire than Cu wire [4,10] and more Pd at the surface of FAB showed less growth of Cu/Al IMC [14], which are consistent with our simulation results. Although these experimental IMC growth measurements was done at 175degC HTSL condition, this Pd barrier effect for Cu an Al diffusion should be still valid even at higher temperature.…”

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

confidence: 95%

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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: 95%

“…[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. We explored four different possibilities.…”

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

confidence: 99%

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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“…It has a longer shelf life compared to bare copper wire due to the noble metal coating and is perceived to have better bond reliability under humid conditions [4,9]. Numerous studies on interfacial reaction and IMC formation between Cu and Al bond pads have been carried out [4][5][6][7][8][9][10][11]. It was reported that the IMC phases identified in the Cu/Al bond interface are typically CuAl 2 , CuAl and Cu 9 Al 4 ; the latter two IMCs are mostly found after thermal treatment [10].…”

Section: Introductionmentioning

confidence: 99%

“…However, copper wire is readily oxidized in air and requires the use of forming gas during the ball bonding process [3]. The corrosion susceptibility of Cu wire in humidity reliability tests such as the pressure cooker test (PCT), and the highly accelerated temperature and humidity stress test (HAST), is also a concern and has been widely studied [4][5][6][7]. Copper wire bonds were` reported to have poor reliability performance under PCT and HAST due to the interaction of moisture with chlorine from epoxy mold compounds (EMC) that attack copper in the first bond [8][9].…”

Section: Introductionmentioning

confidence: 99%

“…In the past few years, palladium-coated copper wire (Pd-Cu) has been used as an alternative to bonding with bare Cu wire. It has a longer shelf life compared to bare copper wire due to the noble metal coating and is perceived to have better bond reliability under humid conditions [4,9]. Numerous studies on interfacial reaction and IMC formation between Cu and Al bond pads have been carried out [4][5][6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

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Evaluation of the corrosion performance of Cu-Al intermetallic compounds and the effect of Pd addition

Lim

Neo

Yauw

et al. 2015

2015 IEEE 17th Electronics Packaging and Technology Conference (EPTC)

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Copper wire has become a mainstream bonding material in fine-pitch applications due to the rising cost of gold wire. In recent years, palladium-coated copper (Pd-Cu) wire is being increasingly used to overcome some constraints posed by pure Cu wire. During wire bonding with aluminum bond pads, different intermetallic compound (IMC) phases that have been identified at the bond interface are typically CuAl 2 , CuAl and Cu 9 Al 4 . Copper wire bonds were reported to fail humidity reliability tests and Cu 9 Al 4 was observed to be the corroded IMC layer. However, the corrosion susceptibility of the individual IMCs has not been investigated. There has also been conflicting results on the effect of palladium on the reliability of copper wire bonds reported in literature. This paper compares the corrosion performance of the three types of Cu-Al IMCs in a chloride medium by employing electrochemical potentiodynamic polarization. A comparison was made with pure Cu and Al. The effect of Pd on the IMC corrosion performance was also studied. Among the three CuAl IMCs, Cu 9 Al 4 was observed to have the largest corrosion rate followed by CuAl 2 and CuAl. For the metals, Cu was observed to have the lowest corrosion rate and Al is the most easily corroded. The addition of a few percent of Pd slightly improves the corrosion resistance of the metals and IMCs.

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