Growth of CuAl intermetallic compounds in Cu and Cu(Pd) wire bonding

Lu, Ying-Yu; Wang, Y. W.; Appelt, Bernd K.; Lai, Yi‐Shao; Kao, C. R.

doi:10.1109/ectc.2011.5898706

Cited by 36 publications

(12 citation statements)

References 30 publications

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“…[5] The other paper verified Cu 9 Al 4 /Cu 3 Al 2 /CuAl/CuAl 2 with various HTSL conditions. [6] With PCT/H3TRB, in case with failure afterwards, Cu 9 Al 4 /CuAl/CuAl 2 were detected before reliability test while in case without failure afterwards only CuAl/CuAl 2 were detected before reliability test and Cu 9 Al 4 was not detected. [7] After PCT, failed ball bond showed 1)crack, 2) Cu, Al oxide, Cl, 3) CuAl.…”

Section: Introductionmentioning

confidence: 89%

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: Introductionmentioning

confidence: 89%

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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“…The interfacial behavior between Cu wire and Al pad of the first bonding has been investigated in details. [8] [9] The use of the Pd-plated Cu wire will also increase the process windows of stitch bonding. [8] [10] However, compared with the ball bonding, the stitch bonding is weaker the reliability issue can be significant.…”

Section: Introductionmentioning

confidence: 99%

Study on interface of Pd-plated Cu wire stitch bonding

Liu

Wang²,

Cong³

et al. 2011

2011 International Symposium on Advanced Packaging Materials (APM)

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Cu wire is the alternative material to the Au wire in many aspects, such as better electrical and thermal conductivity, higher mechanical strength and its lower cost for the high volume manufacture. Due to the surface oxidation of the Cu wire, the Pdplated Cu wire (Pd-Cu wire) has been adopted quickly in many fine pitch and high density package devices. Cu wire bonding has been well understood in recent years, while Pd-Cu wire is still under intense investigation. Here we present a study on the interface of the stitch bonding by TEM analysis.Our experiments were performed on 1 mil (~25um) Pd-Cu wire bonding with Ag plated leadframes under the 5% Hydrogen forming gases. The Pd coating thickness of the Cu wire was about 100nm, while the thickness of the lead-frame's Ag coating was about 6um. The leadframes were subjected to pre-heating treatments at 200 in normal, 5 minutes extended and 20 minutes extended condition, total 3 samples, in order to investigate whether it will form oxide material on surface of the lead-frames and degenerate the bondability. The research tried to understand the underlying microscopic mechanism of the stitch bonding interface by means of micro-topography and elements distribution analysis. The samples for TEM examination were prepared by specific manual grinding followed by FIB micro-machining.No oxide layer or Oxygen gathering region was found at the interfaces of three samples by TEM topography. The results indicated that the existing Pd coating at the Cu wire surface was able to prevent Cu from being oxidized, and the surface of the lead-frames also showed no oxygen gathering. A thin "dark" Pd layer at the interface of three samples between copper and silver layers was observed by TEM with EDX, and the peak value of the Pd at the interface was about 40 atomic %. The thickness of the Pd layer was about 30nm which was much thinner than the original coating thickness. It indicated Pd coating has been seriously deformed during the bonding process. Each element (Cu, Pd, and Ag) at the interface had low interdiffusion rates under the pre-heating temperature (200 ) from the analysis of the abrupt elements distribution curves. It was observed that the content of the Cu in Ag coating was varying for the three samples. When the pre-heated time of the lead-frame increased at 200 , the content of the Cu in Ag coatings increased from 10% to 20% and then to 30%. The details of Pd layer microstructure and topography need further investigation with improved analytical means.

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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%