Flexible interconnects are one of the key elements in realizing next‐generation flexible electronics. While wire bonding interconnection materials are being deployed and discussed widely, adhesives to support flip‐chip and surface‐mount interconnections are less commonly used and reported. A polyurethane (PU)‐based electrically conductive adhesive (ECA) is developed to meet all the requirements of flexible interconnects, including an ultralow bulk resistivity of ≈1.0 × 10−5 Ω cm that is maintained during bending, rolling, and compressing, good adhesion to various flexible substrates, and facile processing. The PU‐ECA enables various interconnection techniques in flexible and printed electronics: it can serve as a die‐attach material for flip‐chip, as vertical interconnect access (VIA)‐filling and polymer bump materials for 3D integration, and as a conductive paste for wearable radio‐frequency devices.

No abstract

No abstract

Poly(methyl methacrylate) tensile bars were prepared containing nearly spherical polytetrafluoroethylene particles in concentrations from one to a thousand particles per gauge length of the bars. Particle diameters varied from 0.0035 to 0.018 in. Exhaustive tensile tests were performed at sufficiently high strain rate to assure brittle fracture and the results analyzed statistically by the theory of extreme values as proposed by Epstein. The results suggested that the polytetrafluoroethylene particles themselves did not act as flaws, but that they intensified the stress field on natural flaws which acted as the origin of fracture. Assuming a Laplace distribution as the underlying distribution of tensile strength (not to be confused with observed distribution of tensile strengths) gave predicted fracture statistics in good agreement with experiment.

The effects of different shapes of silver; particles, flakes and dendrites on the electrical property of polydimethyl siloxane (PDMS)-based electrically conductive adhesives (ECA) under mechanical deformation are investigated. It is found that the high aspect ratio of silver dendrites helps to construct more conduction pathways in the ECAs compared with silver particles and flakes, therefore reducing the percolation threshold. Stretching made the bulk resistivity of spherical silver filled ECA increase exponentially, which is in good agreement with the classical piezoresistive models. On contrast, the resistivity of silver flakes filled ECAs did not change within 100% strain and up to 500 cycles of stretching/releasing tests. For silver dendrites, the resistivity decreased when stretching and increased slightly afterwards, resulting in an almost invariant value within 60% elongation. However, removing the external strain did not havethe resistance value recover back to the original level. IntroductionModern consumer electronics are striving for increased functionality and reduced form factor. Stretchable radiofrequency (RF) electronics are gaining popularity as a result of their increased functionality, impossible within the confines of rigid, planar substrates. However, the field of stretchable RF electronics is still in its infancy. Similarly to other emerging electronic technologies, new materials and new processing methods are the two driving forces for the development of stretchable RF electronics.There are currently two general approaches to the fabrication of stretchable RF electronics. The first one utilizes conventional rigid materials (such as silicon), but elegantly designed wavy or arc-shaped structures are capable of accommodating applied strains of 100% or more [1][2][3][4][5][6][7]. The second approach is to maintain the conventional layout, but embed stretchable or flowable conductive materials into a sheath, including conductive polymers [8,9], conductive polymer composites [10-12] and liquid metal alloys [13,14] as stretchable conduction lines.For RF electronics, the second approach is usually preferred because of the simplicity in circuit design and fabrication. However, this approach imposes stringent requirements for the conductive materials. These requirements include the following: 1) The material must have a very high electrical conductivity to achieve high-efficiency RF devices. 0[9]; 2) The material needs to be highly elastic for tunable resonant frequency [14] and still maintain a similar electrical conductivity. By stretching the antenna, the length is increased, leading to a decrease in resonant frequency. To gain a wide window of tunable resonant frequency, both the