Semiconductor Manufacturing Handbook, Second Edition by Hwaiyu Geng

Author:Hwaiyu Geng [Geng, Hwaiyu]
Language: eng
Format: azw3
Publisher: McGraw-Hill Education
Published: 2017-10-06T04:00:00+00:00

24.3 MANUFACTURING TECHNOLOGY FOR FLEXIBLE CIRCUITS

The manufacture of flexible circuits is related with the initial design flexibility and in combinations of manufacturing stages for the basic types of circuit constructions. In the manufacturing of flexible circuits, some processing steps are in a high degree of similarity with the traditional manufacture of rigid boards. However, considering the large-scale production of the flexible circuits, the amenability of flexible circuits to roll-to-roll (R2R) processing makes it significantly different with that of rigid circuits.

Roll-to-roll processing, also referred as web processing, is the process of creating electronic devices on a roll of flexible plastic or metal foil. At present, this R2R processing has been widely applied in the fabrications of large-area electronics, such as solar cells, flexible screen or display, etc., which is in urgent need of cost reduction. In other active electronic circuit manufacturing, a large number of patterning steps is required by the additive processes of directly printing the active materials, shadow masking, or subtractive patterning by photolithography. All of these techniques can be adapted to web processing.33 However, facing the demand for the miniaturization of feature size in electronic devices, the roll-to-roll photolithography and etching tools are not capable of 2 mm resolution and overlay registration. In that case, the innovations in equipment and process design, and system integration are the next important research goals of R2R processing for the flexible circuit manufacturing.

Besides, there are several special fabrication methods of flexible devices in the laboratory. Screen printing is a high-throughput process, which could be compatible with R2R processing. In fact, many crucial materials used in the fabrication of flexible circuits could be printed, such as metallic paste, organic conductors and insulators, and so on.

In order to avoid the mechanical damage during the fabrication process, a transfer technology has been developed by separating the flexible circuits from the silicon-based substrate. As shown in Fig. 24.3, the flexible substrate such as PI can be deposited on the Si-based substrate followed by a standard curing process. Then the traditional manufacturing processes of rigid boards can be applied on this composite substrate to form the electronic circuits. Finally, the flexible circuits could be separated from the Si-based substrate by mechanical stripping or chemical corrosion method. The whole fabrication process is conducted on the Si-based substrate, which helps to be compatible with conventional CMOS processes.

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