Vacuum Web Coating - State of the Art and Potential for Electronics

Going flexible seems to be a major trend for a variety of electronic applications such as displays, printed circuit boards, solar cells, and solid-state lighting. Driving forces, which may often include the function of "flexibility," are the potential to build units with less thickness and with less weight or the ability for very-large-area applications. Last but not least, there is the need for a remarkable reduction of production costs, which can be fulfilled by changing the production process from sheet processing to roll to roll. The first vacuum web coater was built 70 years ago, and vacuum web coating is currently used for a wide variety of applications. In the packaging industry, aluminum coating is primarily used for barrier improvement of plastic substrates. Such coatings are deposited with an evaporation process in machines of up to 4-m coating widths on rolls up to 60 000-m length and at coating speeds of more than 16 m/s. For capacitor production, thin webs with thicknesses down to the submicrometer range are vacuum-coated with aluminum, silver, or zinc layers, and uncoated stripes or patterns are also needed. Vacuum-coated web-shaped substrates can also be used for antireflective, antistatic function in the front of monitors, as window films for cars and architectural applications or as front electrodes for touch panels as a few examples. Different coating tools such as evaporation, sputtering, plasma-enhanced chemical-vapor deposition (PECVD), as well as pretreatment tools and inline layer measurement systems are available. Many of the currently available tools and processes existing in the web coating industry may become useful for upcoming electronic applications, but special demands for these new applications, such as exact area tracking, zero defects, roll-to-roll masking, and reduced substrate temperature during coating, require further development of machine design and process technology. This paper will summarize the state of the art of vacuum w