Dry film is a polyester film coated with a polymer which is sensitive to ultraviolet light. A dry film comprises of cover sheet formed of flexible, but generally non-conforming material, giving the dry film shape while allowing it to be rolled into a reel. On one surface of the cover sheet is a thin layer of material known as a top coat which is soluble in the developer for the photoimageable composition. The photoimageable composition forms a layer over the other surface of the top coat. A removable sheet protects the photoimageable composition layer. The material which is used to form the top coat is selectively adherent to the photoimageable composition layer relative to its adherence to the cover sheet, whereby the cover sheet may be removed from the top coat and thereby leave the top coat as a protective covering for the layer of photoimageable composition.
It is a major advantage in a dry film for applying a primary imaging photoresist layer to a substrate that the relatively thick cover sheet be removed prior to imaging, thereby substantially improving the resolution of the imaging which may be achieved. Although, similar advantages of resolution are obtained, in fact, with a solder mask-forming dry film, resolution of image is of substantially less concern with solder masks than with primary photoresists.
According to the study “Asia Dry Film Industry Situation and Prospects Research report”, dry film is used in the development, manufacturing and distribution for wiring formation of printed circuit boards, including IC packages, rigid substrates and FPC. With the evolution in electronic circuits, the application of dry film has expanded to touch panels and precision metal machining. The exposed area of dry film, which is of negative type, is hardened. It is necessary for a user to control the stability of the film thickness of the liquid resist during coating. Controlling the film thickness with high accuracy is difficult due to its liquid state although it depends on the coating method. However, the thickness of the dry film does not change and there is no necessary for a user to control the resist thickness. Dry films can reduce environmental load compared with liquid resist due to waste liquid disposal.
Dry films can be applied to stainless steel, 42 alloy, invar alloy, copper, which are generally used for circuit formation. Variants of copper are electro-less copper, electrolytic copper, rolled copper foil, sputtered copper, and other types. Dry film is photosensitive to natural light and needs to be handled under a yellow lamp. When storing substrates with laminated dry film before exposure, it is recommended to shield it from light using a black polyethylene sheet.
Geographically, Asia dry film industry is spread across China, Japan, India, Korea, Saudi Arabia and other regions. Asia dry film industry is segmented into various product types such as thickness 20 m, thickness 21-29, thickness 30-39, and thickness 40m. The various applications in Asia dry film industry are PCB, semiconductor packaging and others. The leading players in Asia dry film industry are Hitachi Chemical (JP), Asahi Kasei (JP), Eternal (TW), KOLON Industries (KR), DuPont (US), Changchun Group (TW), Mitsubishi (JP), Elga Japan (IT), FIRST (CN) and EMS (US). Asia is witnessing an increasing demand in dry films industry sectors that is driving its demand. It was observed that there is a continuing demand due to modernization and industrialization. The development in various industries is bolstering the growth of dry films market. In Asia, Japan, India and China will witness a drastic growth in dry films market over the next few years.
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