This study proposes the design of a roll-to-roll system for flexible electronics that enables accurate and precise tension control. It analyzes the factors for change in the tension of a roll-to-roll system and develops a tension model for each section to successfully predict the tension that is applied to such a system, the sagging of film according to tension, and deformation due to residual stress. This series of modeling processes allow engineers to design a roll-to-roll system for flexible electronics. Both a velocity control method for the tension between in-feeder and out-feeder—where there is no change of roller radius—and torque control method for the tension in modules like the rewinder, where the roll radius changes, are proposed. A roll-to-roll system according to the proposed design procedure and tension control methods was manufactured and experimented on under various test conditions. The accuracy and precision of velocity control between the in-feeder and the out-feeder were 100.01% and 1.15%, respectively, whereas those of torque control between the out-feeder and the rewinder were 99.9% and 1.35%, respectively, both at one sigma. The experiments confirmed that the two proposed types of tension control methods were accurate and precise. The experimental result with a monitoring sensor showed that the modeling was valid and that an accurate roll-to-roll system minimizing tension reduction was built. This study successfully demonstrated roll-to-roll system design and control techniques that are applicable to various pieces of roll-to-roll process equipment.

This paper details the development of a novel flexure jointed precision parallel nano-positioning system in combination with piezo-electric stepping motor for the application of precise optics alignment. The characteristics of the developed system are evaluated in this paper by the simulation and experiments. Based on the precision piezo-electric stepping motor and flexure joints, a high precision motion is obtained. Results of this paper include that of a translation resolution of 15 nm and a rotational resolution of 0.14 arc sec being achieved. In addition, the piezo-electric stepping motors provide a power-off hold characteristic to the system. Meanwhile, the parallel structure provides the high dynamic bandwidth of the lowest resonant frequency of 396.1 Hz. The symmetric structure is advantageous for thermal variation. To increase the motion range of the system, all of flexure joints are designed specially and the coupled workspace of ±2 mm × ±2 mm × ±2 mm × ±2° × ±2° × ±2° is achieved. The overall size of the designed system is Φ350 mm × 120 mm.

One of the key challenges for adapting the roll-to-roll (R2R) process to flexible electronics production is to fulfill the tight registration requirements between layers. This study proposed a precise registration control for an R2R screen printing system based on a combination of registration error analysis, passive compensation, and active compensation. The registration error factors, such as film tension error, sintering error, reference alignment mark accuracy, screen printing error, and screen mask error, were evaluated. Meanwhile, with a refined correlation factor through the experiments, evaluation-based passive compensation was applied to the design layout for making a screen mask. Active compensation is based on combined control, which consists of the tension control and stage alignment control, reduces the registration error’s varying term. As a result of passive and active compensation for polyethylene terephthalate film, achieving a machine direction registration error of 0 ± 9 µ m ( σ ) and cross direction of 10 ± 4 µ m ( σ ) was possible. The proposed R2R system with registration control was capable of accurate and precise registration over several hundred prints and was suitable for manufacturing flexible electronic devices.

Hybrid copper bonding (HCB) technology has been introduced and evaluated to overcome a fine pitch limit and degradation in thermal properties in 3D semiconductor package structure. In this study, we successfully demonstrated 3D memory stacking package by HCB technology which integrated Cu-Cu diffusion bonding along with oxide bonding simultaneously. HCB process was developed and die-to-wafer (D2W) multi-stack structure was realized which shows excellent electrical and thermal properties. The flatness of the bonding surface was controlled by chemical mechanical polishing (CMP), and highly activated bonding surface desirable for HCB was obtained through optimization of plasma condition. The properties of the chip surface were measured in terms of oxide topography, Cu dishing height, surface hydrophilicity, hydroxyl group density, and adhesion force. Then package chips were stacked up to 12 levels by HCB method to demonstrate 12 stacked D2W package. In particular, we focused on eliminating oxide voids at the bonding interface since even a single void can deteriorate the functional properties of the whole stacked package. Oxide voids were classified into several categories on the basis of the causes, then the sources of the void were eliminated in advance to achieve void free HCB interfaces. Through the accomplishment of D2W HCB technology, it is expected to be applied to advanced 2.5D/3D packages for superior thermal and electrical performances.

The electrostatic spray deposition (ESD) is a method of coating thin films based on electrostatic atomization. This paper proposes a method of quantifying the transport of droplets using images of spray patterns measured by the vision system during the ESD process, and verifies by experiment the correlation between the quantified parameters for the dispersion shape of the spray and the thickness of the deposited thin film. When using the proposed method, the ESD process can be optimized simply by monitoring variations of the spray shapes caused by the process conditions. In addition, the proposed method can be applicable to the in-line monitoring method of the variation in the transport of droplets during the ESD process.