Analysis of Cu-wire pull and shear test failure modes under ageing cycles and finite element modelling of Si-crack propagation

Abstract In microelectronic packaging, wire bonding is the predominant method for making electrical connections. Copper is increasingly substituting gold as interconnection material since it is a much cheaper alternative and it also offers several physical advantages. Adequate and reliable mechanical integrity of the connection is usually checked by process controls based onto “wire pull” and “ball bond shear” tests. In this paper the two methods are compared in terms of sensitiveness in detecting a latent weakness of the bond-pad structure, either induced by inappropriate wire bonding process or cumulated during reliability ageing. The failure modes (in terms of frequency and maximum test load) observed at the ball bond interface have been investigated on two different batches of a same chip, obtained from different wire-bonding recipes and including both unstressed and aged units. Cross-sections of the samples, submitted to pull and shear both in destructive and non-destructive tests, have allowed us to investigate the relationship between the bond morphological characteristics (metal deformation and potential micro-damages induced by copper bonding) and the weak points for fracture propagation inside the bond-pad inner layers and the silicon substrate. Besides the experimental activities, fracture mechanics and the finite element method have been employed to model the pull and shear tests. The aims of the finite element modelling have been to predict the reduction of test maximum load in defective ball bonds and the crack growth angle adopting a mixed-mode criterion. Good results have been obtained by the numerical fracture analysis, which can then support the reliability characterization and mechanical improvement of the bond.

[1]  J. Dundurs,et al.  Discussion of Edge-Bonded Dissimilar Orthogonal Elastic Wedges under Normal and Shear Loading , 1969 .

[2]  G. Harman,et al.  The Microelectronic Wire Bond Pull Test-How to use It, How to Abuse It , 1978 .

[3]  P. Sharma.  Mechanics of materials. , 2010, Technology and health care : official journal of the European Society for Engineering and Medicine.

[4]  A. R. Daud,et al.  Cratering on thermosonic copper wire ball bonding , 2002 .

[5]  J. W. McPherson,et al.  Temperature-cycling acceleration factors for aluminium metallization failure in VLSI applications , 1990, 28th Annual Proceedings on Reliability Physics Symposium.

[6]  T. K. Hellen,et al.  The calculation of stress intensity factors for combined tensile and shear loading , 1975 .

[7]  K. Paik,et al.  Effects of Cu/Al intermetallic compound (IMC) on copper wire and aluminum pad bondability , 2003 .

[8]  Mauro Madia,et al.  Multiaxial fatigue and defect assessment of truck stabilisers , 2004 .

[9]  Yi-Shao Lai,et al.  Copper Wire Bonding , 2011, Microelectron. Reliab..

[10]  Saraswati,et al.  Characterisation of intermetallic growth in copper and gold ball bonds on aluminium metallization , 2004, Proceedings of 6th Electronics Packaging Technology Conference (EPTC 2004) (IEEE Cat. No.04EX971).

[11]  Chua Kok Yau,et al.  Oxidation study on as-bonded intermetallic of copper wire–aluminum bond pad metallization for electronic microchip , 2012 .

[12]  Michael Pecht,et al.  Copper Wire Bonding , 2013 .

[13]  John W. Hutchinson,et al.  Crack Paralleling an Interface Between Dissimilar Materials , 1987 .

[14]  G. Harman.  Wire Bonding in Microelectronics: Materials, Processes, Reliability, and Yield , 1997 .

[15]  J. Hutchinson,et al.  Kinking of A Crack Out of AN Interface , 1989 .

[16]  Y. Zhou,et al.  Reduction of ultrasonic pad stress and aluminum splash in copper ball bonding , 2011, Microelectron. Reliab..

[17]  Michael Mayer,et al.  Effect of electronic flame off parameters on copper bonding wire: Free-air ball deformability, heat affected zone length, heat affected zone breaking force , 2009 .

[18]  Jl Swedlow,et al.  Criteria for Growth of the Angled Crack , 1976 .

[19]  J. Dundurs.  Discussion: ``Edge-Bonded Dissimilar Orthogonal Elastic Wedges Under Normal and Shear Loading'' (Bogy, D. B., 1968, ASME J. Appl. Mech., 35, pp. 460-466) , 1969 .

[20]  H. K. Charles,et al.  The effect of high-temperature intermetallic growth on ball shear-induced cratering , 1989 .

[21]  Y. Zhou,et al.  Growth behavior of Cu/Al intermetallic compounds and cracks in copper ball bonds during isothermal aging , 2008, Microelectron. Reliab..

[22]  Z. Suo,et al.  Mixed mode cracking in layered materials , 1991 .

[23]  David B. Bogy,et al.  Edge-Bonded Dissimilar Orthogonal Elastic Wedges Under Normal and Shear Loading , 1968 .