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Conventional electronic circuits are made up of electronic components assembled on either rigid substrates like FR4 and ceramic or on flexible substrates based on polymers such as polyimide, PET and PEN foils. The latter type of substrates offers considerable improvements in freedom of motion over its rigid complement although the deformations are still pretty limited due to the inability of common electronic materials, such as metals, to cope with the corresponding deformation. Moreover, the assembly of rigid electronic components can often reduce the circuit’s ability to bend. The current trend towards increased component density on substrates makes the final assembly even less flexible. However, electronic circuits which can fully conform and easily fit in the arbitrary curved surface topologies are of keen interest in various areas of applications. Aside from flexibility, a certain degree of stretching is required for the three-dimensional shaping of electronic systems. Hence, deformability will offer electronics a number of additional features like bendability, conformability shaping and lightweight. Three-dimensional shaped electronics can be obtained either by multi-time (dynamic or elastic) or one time (static, permanent) stretching. In this paper an introduction on deformable and conformable electronics is outlined highlighting the different existing approaches. Some examples of flexible and stretchable electronic applications will be provided in various fields. [ABSTRACT FROM AUTHOR]

Getting output of multiple chips within the volume of a single chip is the driving force behind development of this novel 3D integration technology, which has a broad range of industrial and medical electronic applications. This goal is achieved in a two-step approach. Initially, thinned dies are embedded in a polyimide interposer with a fine-pitch metal fanout, resulting in ultrathin chip packages (UTCPs). Next these UTCPs are stacked by lamination. Step height at the chip edge of these UTCPs is the major reason of die cracking during the lamination. This paper contains an approach to solve this issue by the introduction of an additional layer of interposer, which makes it flat at the chip edge and thus the whole package is named as flat-UTCP. In addition to that, randomness in nonfunctional package positions per panel reduces the overall yield of the whole process up to a certain extent. A detailed analysis on these two issues to improve the process yield is presented in this paper. 3D-stacked memory module composed of four electrically erasable programmable read-only memory dies was processed and tested to demonstrate this new concept for enhancing the fabrication yield. [ABSTRACT FROM PUBLISHER]

In order to increase the functionality of electronic devices, while reducing the overall size and weight of the electronic chip packages, electronic chip packages can be combined into a 3-D assembly. In this field, we present a technology for stacking multiple chip packages, resulting in total volume almost equal to that of a single bare die. The technology is based on batch-processed ultrathin chip packages (UTCPs) with a fine pitch metal fan-out. Package-on-package technology enables stacking of UTCPs by vacuum lamination, followed by through-hole interconnection technology for making contacts to the metal fan-out of the embedded UTCPs within the stack. The individual chip packages can be tested before stacking. [ABSTRACT FROM AUTHOR]

The development and mechanical characterization of a novel technology for stretchable electronics is presented, which can be used for the realization of wearable textile electronics and biomedical implants. The stretchable devices consist of rigid or flexible component islands interconnected with stretchable meander-shaped copper conductors embedded in a stretchable polymer, polydemethylsiloxane. The technology uses standard printed circuit board manufacturing steps and liquid injection molding techniques to achieve a robust and reliable product. The conductors in the device are designed to accommodate strains up to 10–15%. Spin-on photo-definable polyimide as mechanical support for the stretchable interconnects and the functional flexible islands are introduced. By use of polyimide, the reliability of the stretchable interconnects, the straight interconnects on the flexible islands and the transitions between the stretchable and nonstretchable parts are improved. Long-term endurance behavior of the stretchable interconnects is studied by cyclic elongation at strain ranges of up to 20% while monitoring the electrical connectivity. It's shown that the lifetime of the polyimide supported interconnects is at least two times better compared to the nonsupported. [ABSTRACT FROM AUTHOR]

The article presents research on n-type metal oxide thin-film transistors (TFTs) in flexible active-matrix organic light-emitting diode (AMOLED) displays. It discusses the performance of solution-based oxide n-type TFTs on low-voltage complementary circuitry on flexible polyimide foil. It explores the significance of the hybrid complementary technology on AMOLED displays.

Assembly of thinned die has become common practice to meet the demand for smaller and lighter electronic products. One way to achieve this goal is to embed the thinned die into two dielectric films, which results in a flexible ultrathin chip package (UTCP). This paper describes a new UTCP process flow with microvia formation by standard UV lithography through photosensitive polyimide (PSPI). Such microvia-formation method proved to be more reliable than laser drilling techniques and simpler than a dry etching process. Since the used PSPI is self-priming, a thin layer of potassium chloride was introduced as a release layer. In the end, the polyimide encapsulation of the thinned die can be released from the carrier substrate and becomes a flexible chip package with a total thickness of around 50 \mum. Daisy-chain test dies were encapsulated inside spin-coated polyimide films. Excellent chip-to-package interconnection was demonstrated by electrical daisy chain and contact resistance measurements. Bending tests and thermal cycling tests were also performed on the daisy-chain test vehicles. Desired flexibility and reliability of UTCPs was observed. [ABSTRACT FROM PUBLISHER]

This paper discusses the optimization of a stretchable electrical interconnection between integrated circuits in terms of stretchability and fatigue lifetime. The interconnection is based on Cu stripes embedded in a polyimide-enhanced (PI-enhanced) layer. Design-of-experiment (DOE) methods and finite-element modeling were used to obtain an optimal design and to define design guidelines, concerning both stripe and layer dimensions and material selection. Stretchable interconnects with a PI-enhanced layer were fabricated based on the optimized design parameters and tested. In situ experimental observations did validate the optimal design. Statistical analysis indicated that the PI width plays the most important role among the different design parameters. By increasing the PI width, the plastic strain in the Cu stripes is reduced, and thus, the stretchability and fatigue lifetime of the system is increased. The experimental results demonstrate that the PI-enhanced stretchable interconnect enables elongations up to 250% without Cu rupture. This maximum elongation is two times larger than the one in samples without PI enhancement refid="ref1"/ . Moreover, the fatigue life at 30% elongation is 470 times higher refid="ref2" . [ABSTRACT FROM PUBLISHER]

Flexible materials, today, are being used already as base substrates for electronic assembly. A lot of mounted components could be integrated in flexible polyimide (PI) substrates. Very interesting advantages of integrating components into the flex are compactness and enhanced flexibility; not only the interconnection but also the components themselves can be mechanically flexible. This paper describes a PI-based embedding technology for integrating very thin silicon chips in between two spin-on PI layers, the ultra-thin chip package (UTCP). This paper discusses the different process steps in the UTCP production and also presents the interconnection test results realized with this technology. [ABSTRACT FROM AUTHOR]

Abstract: Tactile sensors are often used on irregular or moving surfaces, for example as artificial skin on a robotic hand or inside a prosthetic socket. In addition to tactile sensors able to detect pressure, there is also a need to detect shear stress, associated with slippage or friction. Therefore, this paper demonstrates a technology for fabricating unobtrusive flexible tactile shear sensors using a thin and mechanically strong polyimide substrate. The operation of the sensor is based on the changing optical coupling between a Vertical-Cavity Surface-Emitting Laser (VCSEL) and photodiode. Since this sensor is based on an optical principle, it is less susceptible to environmental influences and electromagnetic interference (EMI). Furthermore, a new design of this sensor was developed and tested to enable the detection of both shear force magnitude and direction (two axis sensor). [Copyright &y& Elsevier]