Wearable electronics have showed their profound impact in military, sports, medical and other fields, but their large-scale applications are still limited due to high manufacturing costs. As an advanced micro-fabrication process, laser processing technology has the advantages of high speed, high flexibility, strong controllability, environmental protection and non-contact in preparing micro-nano structures of wearable electronics. In this paper, a 355 nm ultraviolet laser was used to pattern the copper foil pasted on the flexible substrate, and the interconnection electrodes and wires were constructed. A processing method of multi-parallel line laser cutting and high-speed laser scanning is proposed to separate and assist in peeling off excess copper foil. The process parameters are optimized. A stretchable 3 × 3 light-emitting diode (LED) array was prepared and its performance was tested. The results showed that the LED array can work normally under the conditions of folding, bending and stretching, and the stretch rate can reach more than 50%. A stretchable temperature measurement circuit that can be attached to a curved surface was further fabricated, which proves the feasibility of this process in the fabrication of small-scale flexible wearable electronic devices. Requiring no wet etching or masking process, the proposed process is an efficient, simple and low-cost method for the fabrication of stretchable circuits.

Capillary self-alignment technique can achieve highly accurate and fast alignment of micro components. Capillary self-alignment technique relies on the confinement of liquid droplets at receptor sites where hydrophobic–hydrophilic patterns are widely used. This paper reports a low-cost microsecond pulse laser micromachining method for fabrication of super hydrophilic–super hydrophobic grooves as receptor sites for capillary self-alignment of microfibers. We investigated the influence of major manufacturing parameters on groove sizes and wetting properties. The effects of the width (20 µm–100 µm) and depth (8 µm–36 µm) of the groove on the volume of water droplet contained inside the groove were also investigated. We show that by altering scanning speed, using a de-focused laser beam, we can modify the wetting properties of the microgrooves from 10° to 120° in terms of the contact angle. We demonstrated that different types of microfibers including natural and artificial microfibers can self-align to the size matching super hydrophilic–super hydrophobic microgrooves. The results show that super hydrophilic–super hydrophobic microgrooves have great potential in microfiber micromanipulation applications such as natural microfiber categorization, fiber-based microsensor construction, and fiber-enforced material development.

Microfibers are important components in the fabrication of fiber-reinforced materials, and the distribution and alignment of microfibers can affect the mechanical, electrical, and thermal properties of the fiber-reinforced materials. However, it remains a challenge to precisely align and distribute microfibers on a large scale at a high throughput. This paper reports a facile droplet-directed method to transport and self-align microfibers to micro trenches using droplets ejected from a non-contact dispenser. Employing super hydrophilic-super hydrophobic trenches with sizes matching the microfibers, the method can align and transport randomly dispersed fibers around trenches into the trenches as desired. We studied this alignment and transport mechanism and the results suggest that liquid volume is critical to allow the capillary force to be dominant leading to the success of the process. We demonstrated that microfibers having an aspect ratio of 200, a diameter of $15~\mu \text{m}$ and a length of 3 mm, can reliably self-align to super hydrophilic-super hydrophobic trenches and transport to the target location, achieving linear alignment accuracy of $0.5~\mu \text{m}$ and angular accuracy of 0.1°. The high accuracy and fast process of the proposed technique may greatly impact larger scale and high throughput construction of complex microstructures using microfibers. [2021-0108]