Delamination/cracking of low-k dielectrics for Cu interconnects and underfill epoxy have significantly limited the reliability of 3D packaging. We present diagnosing adhesion and cohesion with fracture mechanics testing. Post deposition UV cure depth profiles of low-k thin films were successfully tailored to have maximum interfacial fracture energy. Environmentally-assisted crack growth rate and diffusion in low-k thin films were shown sensitive to process solution chemistry. Graded hybrid adhesion layers between a Si chip and underfill were shown to prevent the interfacial failure of underfill and result in the dramatic increase of fracture energy.