Modeling of viscoelastic effects on interfacial delamination in IC packages

In the analysis of plastic-encapsulated IC packages, the epoxy molding compound is often modeled as an elastic material. However, many polymers show some viscoelastic behaviour which causes its Young's modulus to be not only temperature-dependent but also time-dependent. This paper describes a study of the effect of viscoelasticity on interfacial delamination in IC packages. A finite element fracture mechanics technique was used. A small initial crack was assumed at the edge of the pad-encapsulant interface. Fracture mechanics parameters such as energy release rate and mode mixity were calculated for various processing conditions first assuming that the encapsulant was elastic, and then again assuming that the encapsulant was viscoelastic. For various thermal histories differences in the values of energy release rate and mode mixity were determined and compared. The results show substantial discrepancy between the temperature-dependent elastic model and the viscoelastic model, which indicates that the effects of viscoelasticity of the molding compound may not be negligible.

[1]  M. Yuen,et al.  Viscoelastic Analysis of IC package warpage , 1996 .

[2]  Andrew A. O. Tay,et al.  Predicting delamination in plastic IC packages and determining suitable mold compound properties , 1994 .

[3]  A.A.O. Tay,et al.  Mechanics of interfacial delamination under hygrothermal stresses during reflow soldering , 1997, Proceedings of the 1997 1st Electronic Packaging Technology Conference (Cat. No.97TH8307).

[4]  Y. Miyano,et al.  Thermoviscoelastic Analysis of Residual Stresses in a Thermosetting Resin/Metal Laminated Beam Caused by Cooling , 1988 .

[5]  Andrew A. O. Tay,et al.  Moisture-induced interfacial delamination growth in plastic IC packages during solder reflow , 1998, 1998 Proceedings. 48th Electronic Components and Technology Conference (Cat. No.98CH36206).

[6]  N. Huang,et al.  Initiation of crack growth in linearly viscoelastic materials , 1990 .

[7]  Andrew A. O. Tay,et al.  The impact of moisture diffusion during solder reflow on package reliability , 1999, 1999 Proceedings. 49th Electronic Components and Technology Conference (Cat. No.99CH36299).

[8]  I. Raju.  Calculation of strain-energy release rates with higher order and singular finite elements , 1987 .

[9]  K. Y. Sze,et al.  Cooling Rate Effect on Post Cure Stresses in Molded Plastic IC Packages , 1998 .

[10]  Richard Schapery.  Correspondence principles and a generalizedJ integral for large deformation and fracture analysis of viscoelastic media , 1984 .

[11]  Sheng Liu,et al.  Process Induced Stresses of a Flip-Chip Packaging by Sequential Processing Modeling Technique , 1998 .

[12]  G. Ravichandran,et al.  Interfacial crack propagation in a thin viscoelastic film bonded to an elastic substrate , 1994 .