Non destructive stress evaluation by Raman spectroscopy of flip chip thin die on organic substrate assembled by TCB

Non destructive Si die residual stress was investigated with Raman spectroscopy. The dies were assembled on the organic substrates by flip chip bonding technology. Two different thickness dies, which were 50 and 100 μm, were used. The measurement was implemented on the die backside. The die specimen was 12 mm × 12 mm size with 4576 columnar Cu bumps having Sn-Ag solder caps. Bump diameter, Cu height and solder cap thickness were 25, 15 and 25 μm, respectively. The pitches of the bumps in the peripheral and core areas were 80 and 200 μm, respectively. Those were bonded to the organic substrate with Cu pad by a thermal compression bonder with a pre applied adhesive of non conductive film. The substrate was 0.3 mm thick organic laminate of 1-2-1 structure with 0.2 mm thick core. The maximum bonding temperature was 250°C. 50 μm thick die assembled sample was used for the corner area backside residual stress non-destructive evaluation. The very corner end area had very low residual stress and 0.6 to 0.8 distant from the end showed compressive stress of 50 to 90 MPa at room temperature. The die center area backside residual stress measurement at room temperature was carried out with two specimens which were 50 and 100 μm thick dies bonded to the substrates. 16 points per die, which were aligned with 150 μm pitch of 4 × 4 grid, were measured. 100 μm thick die sample showed relatively higher tensile stress than 50 μm die one. It indicated that those sample dies' backsides had substantially tensile residual stress. Temperature dependence of the residual stress was also investigated with 50 μm thick die sample. 16 points were measured at -55, 21, 125 and 150°C. The stress values at 21°C were very small. It became larger compressive stress as the temperature increased. It also showed a relatively higher compressive stress at -55°C.