Effect of bump height on flip-chip joint reliability using ACA

Abstract

There are many parameters that influence the quality and reliability of flip-chip joints assembled using anisotropically conductive adhesives. In this study, the influence of bump height has been investigated. Electroless nickel/gold bumps of 4, 20, 40 and 70 /spl mu/m in height have been used. The chips have been assembled on FR-4 substrates using an anisotropically conductive adhesive and the samples have been subjected to temperature cycling from -40 to +125/spl deg/C. It has been concluded that the bump height is of importance for flip-chip joint quality and reliability. Theoretical calculations have been conducted to find the relationship between joint mechanical strength and bump height at various distances from the centre of the chip.