The effects of rheological and wetting properties on underfill filler settling and flow voids in flip chip packages

As the bump diameter and bump pitch of flip chip packages get smaller, the underfill becomes more resistant to flow. Therefore, low viscosity underfills are used in the process to increase the throughput. Problems associated with low viscosity underfills include filler settling and flow induced voids due to fast edge flow. In this paper, we will discuss how the rheological properties can affect underfill filler settling and flow voids. The effects of yield stress of underfill on filler settling and the effects of shear thickening of underfill at large shear rates on flow voids of underfill were investigated. It was shown that the underfills with small fillers have shear-thickening viscosity and yield stress. The filler settling of underfills with yield stress was greatly reduced. A video underfill flow metrology with quartz die packages was developed for flow void observation. The correlation between underfill, substrate properties, and flow voids formation based on the video underfill flow measurement will be discussed.

[1]  Wenjun Chris Zhang,et al.  Influence of transient flow and solder bump resistance on underfill process , 2005, Microelectron. J..

[2]  N. Guydosh,et al.  Underflow process for direct-chip-attachment packaging , 1997, Proceedings. The First IEEE International Symposium on Polymeric Electronics Packaging, PEP '97 (Cat. No.97TH8268).

[3]  W. F. Schmidt,et al.  Flow properties of liquid underfill encapsulations and underfill process considerations , 1998, 1998 Proceedings. 48th Electronic Components and Technology Conference (Cat. No.98CH36206).

[4]  Jinlin Wang.  The effect of flux residue and substrate wettability on underfill flow process in flip chip packages , 2006, 56th Electronic Components and Technology Conference 2006.

[5]  P. Li,et al.  Underflow Process for Direct-Chip-Attachment Packaging , 1998 .

[6]  R. Chhabra,et al.  Bubbles, Drops, and Particles in Non-Newtonian Fluids , 2006 .

[7]  W. H. Leong,et al.  Underfill flow as viscous flow between parallel plates driven by capillary action , 1995 .

[8]  Sejin Han,et al.  Analysis of the flow of encapsulant during underfill encapsulation of flip-chips , 1997 .

[9]  D. J. Bergstrom,et al.  Recent advances in modeling the underfill process in flip-chip packaging , 2007, Microelectron. J..

[10]  D.J. Bergstrom,et al.  An analytical model for predicting the underfill flow characteristics in flip-chip encapsulation , 2005, IEEE Transactions on Advanced Packaging.

[11]  D. He,et al.  Methods of underfill flow voids detection and minimization in flip chip package , 2005, Proceedings Electronic Components and Technology, 2005. ECTC '05..

[12]  P. Fine,et al.  Flip chip underfill flow characteristics and prediction , 2000 .

[13]  E. W. Washburn.  The Dynamics of Capillary Flow , 1921 .

[14]  H. Barnes,et al.  An introduction to rheology , 1989 .

[15]  T. Togasaki,et al.  Resin flow characteristics of underfill encapsulant for flip-chip interconnection , 2003 .

[16]  W. T. Chen,et al.  A study of underfill dispensing process , 1999 .

[17]  Jinlin Wang.  Flow time measurements for underfills in flip-chip packaging , 2005 .

[18]  S. Newman.  Kinetics of wetting of surfaces by polymers; capillary flow , 1968 .

[19]  Wen-Bin Young,et al.  The effect of solder bump pitch on the underfill flow , 2002 .

[20]  Jinlin Wang,et al.  The effect of flow properties on filler settling of underfill in the flip chip package , 2004, 2004 Proceedings. 54th Electronic Components and Technology Conference (IEEE Cat. No.04CH37546).