Assessment of Flip Chip Interconnect Integrity using Scanning Acoustic Microscopy

This paper describes a non-destructive technique using 50MHz c-mode scanning acoustic microscopy (CSAM) to characterize thermally accelerated diffusion mechanisms that degrade flip chip solder interconnect integrity. Empirical data, based on studies over the past two years, has been gathered on two different solder systems (5Sn95Pb and 63Sn37Pb) before and after exposure to a 150C ambient for more than 1000 hours. (See Table I for a cross-reference of element symbols). The experimental data is supported by microstructural composition and structural analysis of the flip chip joint. The results draw a strong correlation between the CSAM results, analytical examinations, and electrical continuity of the flip chip joint. The technique is most suited for large screening experiments and determining first order survivability when only mechanical die are available.