The surface characteristics of under bump metallurgy (UBM) in electroless nickel immersion gold (ENIG) deposition

This paper discusses on the surface characteristics of each of the seven set-up process steps prior completion of under bump metallurgy (UBM) deposition. The Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM) techniques were used to obtain the surface roughness and morphology of each deposition process. The elemental analysis using Energy Disperse X-Ray (EDX) and precision micro-cross-section using Focus Ion Beam (FIB) was also used in this study. The first zincation process has high surface roughness but preserved surface morphology of initial thin-film surface. The second zincation provides the improved surface roughness due to the replacement aluminum layer with ion zinc in the solution. Smooth surfaces leads to better shear strength. However, second zincation will affect the Al thickness, hence excessive attacks on Al layer may cause reliability problem.

[1]  Jae-Ho Lee,et al.  A study on the nucleation behavior of zinc particles on aluminum substrate [flip-chip technology] , 2001, Advances in Electronic Materials and Packaging 2001 (Cat. No.01EX506).

[2]  Chun-Jen Chen,et al.  Electroless Ni-Cu-P barrier between Si/Ti/Al pad and Sn-Pb flip-chip solder bumps , 2001 .

[3]  John H. Lau,et al.  Electronics Manufacturing: with Lead-Free, Halogen-Free, and Conductive-Adhesive Materials , 2002 .

[4]  Philip Chan,et al.  Al surface morphology effect on flip-chip solder bump shear strength , 2004, Microelectron. Reliab..

[5]  Young-Ho Kim,et al.  Adhesion improvement of electroless plated Ni layer by ultrasonic agitation during zincating process , 2004 .

[6]  Paul Conway,et al.  Electroless nickel bumping of aluminum bondpads. I. Surface pretreatment and activation , 2002 .

[7]  M. van Kleef,et al.  The influence of Sn-Cu-Ni(Au) and Sn-Au intermetallic compounds on the solder joint reliability of flip chips on low temperature co-fired ceramic substrates , 2003, Microelectron. Reliab..

[8]  Andrew J. G. Strandjord,et al.  Interconnecting to aluminum- and copper-based semiconductors (electroless-nickel/gold for solder bumping and wire bonding) , 2002, Microelectron. Reliab..

[9]  Paul Conway,et al.  Electroless nickel bumping of aluminium bondpads. Part 1 - surface pre-treatment and activation , 2002 .

[10]  M. Kaufmann,et al.  Brittle interfacial fracture of PBGA packages soldered on electroless nickel/immersion gold , 1998, 1998 Proceedings. 48th Electronic Components and Technology Conference (Cat. No.98CH36206).

[11]  Kwang-Lung Lin,et al.  The morphologies and the chemical states of the multiple zincating deposits on Al pads of Si chips , 1996 .

[12]  H. Reichl,et al.  Approaches to flip chip technology using electroless nickel-gold bumps , 1995, Proceedings of 1995 Japan International Electronic Manufacturing Technology Symposium.

[13]  Herbert Reichl,et al.  Electroless deposition of bumps for TAB technology , 1990, 40th Conference Proceedings on Electronic Components and Technology.

[14]  Andreas Ostmann,et al.  The pretreatment of aluminum bondpads for electroless nickel bumping , 1993, Proceedings 1993 IEEE Multi-Chip Module Conference MCMC-93.

[15]  W.-C. Ng,et al.  The effects of immersion zincation to the electroless nickel under-bump materials in microelectronics packaging , 1998, Proceedings of 2nd Electronics Packaging Technology Conference (Cat. No.98EX235).