Abstract
Mechanical properties under uniaxial and equi-biaxial tensions are examined for electronic copper foils and sheets ranging from 5 μm to 1 mm in thickness. A hydraulic microbulge test applicable to very thin metal foils is proposed for the equi-biaxial tension, and its validity is confirmed by computer simulation based on the Bassani yield function. The yield stresses in both the uniaxial and equi-biaxial tensions are dependent on the grain size, but not on thickness. The conventional yield criteria are shown to be applicable to very thin foils as well as to sheets with usual thickness. However, the fracture behavior varies according to the thickness, and the limit strain and ductility become markedly low for very thin foils.
