Macro-micro modelling of moisture induced stresses in an ACF flip chip assembly

Purpose - This paper discusses the use of modelling techniques to predict the reliability of an anisotropic conductive film (ACF) flip chip in a humid environment. The purpose of this modelling work is to understand the role that moisture plays in the failure of ACF flip chips. 
Design/methodology/approach - A 3D macro-micro finite element modelling technique was used to determine the moisture diffusion and moisture-induced stresses inside the ACF flip chip. 
Findings - The results show that the ACF layer in the flip chip can be expected to be fully saturated with moisture after 3 h at 121°C, 100%RH, 2 atm test conditions. The swelling effect of the adhesive due to this moisture absorption causes predominately tensile stress at the interface between the adhesive and the metallization, which could cause a decrease in the contact area, and therefore an increase in the contact resistance. 
Originality/value - This paper introduces a macro-micro modelling technique which enables more detailed 3D modelling analysis of an ACF flip chip than previously.