Study on the correlation of flip-chip reliability with mechanical properties of no-flow underfill materials

This paper investigates the correlation of thermo-mechanical reliability of no-flow flip-chip packages with the mechanical properties of the involved no-flow underfill materials. Fracture toughness (K_IC) and fatigue property of the cured no-flow underfill materials are two possible factors that may be important in determining the collapse-controlled chip connection (C4) joint reliability. Seven no-flow underfill materials are formulated. Each should have at least one material property noticeably different from the others, so that a spectrum of any interested material property can be obtained. The interested material properties include heat distortion temperature (TMA Tg measured by thermomechanical analyzer), coefficient of thermal expansion (CTE), modulus, die shear strength, K_IC, and fatigue. The measurement of K_IC is conducted using single edge notch bending (SENB) specimens. The specimens for fatigue testing are in dog-bone shape as described in ASTM D638M. The obtained S-N (Stress-Fatigue Life) curve is used as the measurement of the material fatigue property. The interested responses that we want to collect include the number of cycles under -55°C to 125°C air to air thermal cycling test and -55°C to 125°C liquid to liquid thermal shock test, and the failure mode of the C4 joint and cured underfill material