Reliability of palladium coated copper wire

Stephan, D.; Wulff, F.; Milke, E.

doi:10.1109/eptc.2010.5702660

Cited by 24 publications

(11 citation statements)

References 3 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.…”

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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“…Earlier studies [5] have shown that the first bond process responses of shear/area and ball diameter of PdCu and bare Cu wire are nearly the same for the same bonding parameters. However, the PdCu free-air ball is harder [4,8] and appears to cause more pad damage [5]. Peels, lifts and craters are more likely.…”

Section: Introductionmentioning

confidence: 99%

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

Qin

Clauberg

et al. 2011

2011 IEEE 61st Electronic Components and Technology Conference (ECTC)

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Wire bonding with bare Cu and Pd coated Cu (PdCu) wire have been adopted quickly as a mainstream packaging technology for high pin count and fine pitch devices. The differences between Au and Cu wire bonding are well understood as a result of extensive research. However, the differences between Cu and PdCu wire have not been investigated in as much detail. This paper is a result of collaborative work to study the wire bonding process using Cu wire and PdCu wire. 0.7 mil Cu and PdCu wires are used in the study with bonded ball diameter of about 33 µm. This is the leading edge of fine pitch Cu wire bonding. This study showed that Cu and PdCu wire can be bonded with similar 1st bond parameters, and the bonding results for these two wire types are similar. Process window test results with respect to the ultrasonic level and force level showed that shear, ball size and pad splash are very similar between Cu wire and PdCu wire. 1st bond pull strength is about 11% higher with PdCu wire indicating higher PdCu wire tensile strength. The after bake pull test results are very different between the two wires. PdCu wire has much higher pad peeling failure rate than Cu wire and the peeling showed up after 24 hour bake at 175ºC. The after bake pull strength is also much lower. The poor after bake results indicate that PdCu wire may need different bonding parameter settings than Cu wire. The effect of forming gas versus nitrogen should be examined as well. Second bond study showed the advantage of PdCu wire. The most significant difference is the tail pull strength. PdCu wire has 50% higher tail strength than Cu wire, indicating a more robust 2 nd bond process and less chance for short tails. A deeper understanding of these and other differences will assist in the proper selection between these wire types.High resolution transmission electron microscopy (HRTEM) with Energy Dispersive X-ray Spectrometer (EDX) studies show that the approximately 80 nm Pd coating dissolves into the Cu bulk during ball formation process, therefore, almost no Pd is present at the bond interface in the as-bonded state. However, Pd congregates and diffuses back to the bond interface, especially, a Pd-rich layer forms in the peripheral interface. The congregation of Pd near the bond interface appears to be detrimental to the bond strength, causing high peeling failure.

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“…The shear strength increased more than 30% after subjected to isothermal aging at 175°C for 336 hours, but subsequently remained unchanged up till 1008 hours, similar trend to the previous studies performed on Cu wire bonding. 13,14 The initial shear mode for both bare Cu and insulated Cu was through a Al bond pad. However, as the isothermal aging hours increased, the shear mode was through Cu ball bond.…”

Section: Ball Shear and Wire Pull Strengthmentioning

confidence: 99%

Characterisation of insulated Cu wire ball bonding

Leong

Yap

Khan³

et al. 2014

Materials Research Innovations

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Insulated Cu wire technology offers potential solutions for fine and ultra-fine pitch wire bonding as the insulator coating on the bare wire prevents wires shorting problem. Most previous works focused on insulated wire stitch bonding. This paper presents a comparison study between insulated Cu and bare Cu wire ball-bonding process characterisation in the standpoints of free air ball formation, Al splash, hardness, ball bond strength and intermetallic growth at the bond interface study. Spherical and clean free air ball was formed using lower electric flame off energy compared to bare Cu wire. The study shows that insulated Cu bonding demonstrated comparable equivalent ball bond strength to bare Cu wire bonding at T 0 and even after subjected to isothermal aging 175°C up to 1008 hours. Intermetallic formation was uniform at the bond interface for both wires. Insulated Cu wire demonstrates good bondability and reliability performance, suitable for fine pitch wire bonding in large-scale integration applications.

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Reliability of palladium coated copper wire

Cited by 24 publications

References 3 publications

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

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

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

Characterisation of insulated Cu wire ball bonding

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