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

Abstract

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.

Softened Microstructure and Properties of 12 μm Thick Rolled Copper Foil

“…Excellent bending resistance performance is one of the most important properties of the rolled copper foil, which is also the premise of wide application [ 26 ]. During the deformation process, the grain size, grain orientation, dislocation configuration and dislocation density of the copper foil will change with the deformation rate [ 27 , 28 ].…”

Temperature-Dependent Sheet Resistance and Surface Characterization of Thin Copper Films Bonded to FR4 Composite under Mechanical Vibrations

“…In an early work, Vinci and coworkers studied the effects of texture, thickness, and the passivation layer on the thermomechanical properties of thin copper films sputtered on a Si substrate [11]. Comparing mechanistic models with the measured properties, they found that oriented grains increased the stress between 15% and 22% in a thermal cycle compared with random orientations and, interestingly, passivation with silicon nitride induced a significant reduction in stress relaxation (~30%) at temperatures above 250 • C. Other studies have reported the mechanical properties of flexible [12][13][14][15] and rigid [16][17][18][19] copper films deposited on a variety of substrates to better understand their failure risk and durability [20,21]. For example, Park et al [15] found that the elastic limit and ultimate tensile strength of Sn-coated Cu thin films, like those used in tape carrier packages, were 10 times and 2.5 times higher than those of copper bulk material, respectively.…”

Probing the Electronic Properties of Cu and CuO Thin Films via XANES utilizing Powder XRD System

“…Copper (Cu) in its metallic state is a great electrical conductor but its conductivity changes with the presence of oxidation state, due to Ohmic-Schottky transition. Metallic Cu has been known for a long time in the electrical industries for its extensive application opportunities due to its great conducting abilities, e.g usage in printed circuit board (PCB) [5], and recently, in advance study of flexible circuit boards (FCB) [6]. Meanwhile ceramic Copper Oxides (CuXOX), like tenorites (CuO) is widely used in the wide range of applications like p-type semiconductors [7], and recently have been gaining interest for its potential application in the recent development of thin film solar cells [8].…”