Measurement of local two dimensional stress distribution in a flip chip structure by using strain sensor chips with 2-jum long piezoresistance gauges

Complicated local distribution of residual stress and strain occurs in flip-chip structures due to the difference in material properties such as the coefficients of thermal expansion and elastic modulus among metallic bumps, underfill material, the silicon chip and the substrate. The residual stress was measured using newly-developed strain sensor chips with 2-/im long piezoresistance gauges. As a result of three dimensional analyses and the experiment, it was found that the amplitude of the residual stress in the stacked chips reached about 300 MPa. In addition, both isotropic and anisotropic normal stress fields appeared locally on the chip surface depending on the bump alignment. The magnitude of the difference in the anisotropic residual normal stress reached 150 MPa.