Mechanical reliability and characterization techniques of flexible printed electronic devices - A research review: characterization techniques, bending reliability investigations, and durability improvement techniques

At present, the flourishing and diverse field of flexible electronics is under intense development for a broad range of potential device applications. The device-flexibility conditions largely differ according to its wide range of applications. Various characterization techniques are applied to evaluate the flexibility or strain tolerance of flexible electronic devices. A variety of information regarding the mechanical reliability of the materials or devices is revealed from these characterization techniques. Understanding the basic mechanics of flexible devices and their mechanical characterizations with the developing form factors of these materials and devices are very important for the future of this field. After understanding the basic mechanics of flexible devices under various deformation conditions, the aim of this literature review-based thesis was to focus on different types of mechanical characterization techniques to comprehend the strain tolerance and bending reliabilities of a broad variety of flexible printed electronic devices including their durability improvement techniques. In this thesis, at first, the fundamental mechanics of flexible devices under different deformation conditions were described. Following this, various mechanical characterization techniques, such as bending, stretching, rolling, shear/twisting deformations, adhesion, cohesion, scratching, impact resistance, and crumple compression were discussed in detail to assess the strain-tolerance of flexible printed electronic devices. After that, the review was implicated in analyzing the cyclic bending reliability of printed devices that were fabricated with various polymer thick film pastes. The lifetimes of test specimens differed with different silver pastes. Then the study was endured by analyzing the torsional reliability and lifetime of the printed conductors, which revealed that the torsional bending causes wear-out type failures with a significant impact on reliability on the length-to-width ratio of the printed samples. The investigation was concluded by discussing some pertinent durability improvement techniques for potential flexible printed electronic devices as the future scopes