Experimental characterization of rolled annealed copper film used in flexible printed circuit boards: Identification of the elastic-plastic and low-cycle fatigue behaviors

• Published in: Microelectronics and reliability Vol. 115; p. 113976
• Main Authors: Girard, Gautier, Martiny, Marion, Mercier, Sébastien
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2020; Elsevier
• Subjects: Copper film; Elastic-plastic behavior; Electronics; Engineering Sciences; Kinematic hardening; Low-cycle fatigue; Mechanical tests; Mechanics; Mechanics of materials; Printed circuit boards; Printed circuit boards; Mechanical tests; Elastic-plastic behavior; Kinematic hardening; Copper film; Low-cycle fatigue
• ISSN: 0026-2714; 1872-941X
• DOI: 10.1016/j.microrel.2020.113976

The elastic-plastic and low-cycle fatigue behaviors of copper films are studied experimentally and identified for further simulation works. A rolled annealed copper grade is considered here, as it is often used in flexible printed circuit boards for its mechanical resistance to high elongations. During operation, the printed circuit board (PCB) will undergo various loadings, whether purely mechanical or environmental. These loadings can lead to the fracture of copper and thus to the disconnection of the electrical signal in the PCB. Copper has a low yield stress, so it undergoes easily plastic deformation. In the present work, a predominant kinematic hardening has been observed experimentally and modeled with the combined hardening model of Lemaitre-Chaboche. The fatigue behavior has been identified on cyclic loadings at different strain amplitudes. A Coffin-Manson model has been adopted to reproduce experimental data. Identified behaviors have been introduced in a numerical simulation of a flexible PCB under cyclic bending/reverse bending, in order to estimate its mechanical reliability. •Cyclic tension-compression response of rolled-annealed copper foil is captured•Kinematic hardening of copper is identified and modeled by a Chaboche approach•An original setup is developed to study the low-cycle fatigue of a copper foil•A low-cycle fatigue model is identified from tests with various strain amplitudes•The lifetime of a flexible PCB under cyclic folding is assessed via a FE simulation