Integrated Process-Aging Modeling Methodology for Flip Chip on Flex Interconnections With Nonconductive Adhesives

Abstract

This paper presents a comprehensive methodology to model the static temperature-humidity (TH) aging test (85 C/85%RH over 1000 h) of flip chip on flex interconnections with nonconductive adhesives (NCAs). NCAs, being a special form of conductive adhesives, are chosen, as they allow bringing the pitch further down. The methodology combines experimental techniques for material characterization, finite element modeling (FEM), and model validation. A NCA has been characterized using several techniques. The thermomechanical properties and the moisture absorption properties were obtained for the NCA. A temperature dependent viscoelastic constitutive model was also obtained for the NCA. The viscoelastic model was defined by the Prony series expansion. The shift factor was approximated by the Williams-Landel-Ferry (WLF) equation. Finite element modeling has been performed to analyze the flip chip interconnects on flex with the NCA under process condition and reliability aging conditions. The viscoelastic constitutive relation has been used to model the NCA in aging modeling. An integrated process-aging modeling methodology has been developed to combine the thermo-mechanical stress and hygro-mechanical stress, followed by stress relaxation analysis. To verify the finite element models, static TH aging tests (85 C/85%RH) were also performed. The contact resistance was monitored with high measuring resolution during the accelerated test. The simulation results are in good agreement with the experimental results. The approach developed in this paper can be used to provide guidelines with respect to adhesive material properties, assembly process parameters to achieve good reliability performance.Index Terms-Finite element modeling (FEM), flex substrate, flip chip, moisture absorption properties, nonconductive adhesives, static temperature-humidity (TH) aging test, viscoelasticity.

Thermal–mechanical optimization of a novel nanocomposite-film typed flip chip technology

“…Among the existing packaging technologies, the adhesive-based FC technologies (see, e.g., [1][2][3][4][5][6][7]) can be an engaging option for very fine-pitch interconnection. However, existing technologies, such as the particle-based anisotropic conductive film/adhesive (ACF/A) technology (e.g., [1,2]), consist of certain technical limitation, especially when I/O pitch is less than 40 lm or even down to 30 lm.…”

“…It is however found that there presents some technical challenges in achieving a high aspect-ratio pillar structure using a standard photolithography technique, and in addition, those metal posts or flakes are not structurally compliant. Note that the lack of structural compliance of the metal posts or flakes would potentially result in reliability issue at an elevated temperature, just as the conventional nonconductive film/paste (NCF/P) technology (e.g., [5][6][7]). …”

Hygro-Thermal Warpages of COG Package With Nonconductive Paste Adhesive

“…The use of a low-stress ACF associated with appropriately heating the glass substrate during bonding, proposed in [6], can reduce the warpage and improve the reliability of the COG packages. Application of NCP bonding to flip chip on flex was studied and a power formulation for addressing the electrical contact resistance in terms of contact bump pressure has been proposed [7]. The nonlinear FEM models were proposed for studying the effects of process parameters on bump contact stresses in the COG package with UV-cured NCP [8].…”