Adhesive products, such as adhesive films and adhesive sheets, are widely used not only for protective films used to for various semiconductor processes, such as dicing and backgrinding, but also for various industrial sheets, such as protective films, films for advertisement, cleaning sheets, reflective sheets, adhesive sheets for structures, photos and lane marking, optical adhesive products, adhesive products for electronic components, and medial patches or multi-layered laminate products.
Base films included in these adhesive films or adhesive sheets generally include plastic films, such as polyethylene terephthalate (PED), polyolefin, polyurethane, ethylene-vinyl acetate, polybutylene terephthalate, polypropylene, and polyethylene.
These plastic films may be prepared by melting various thermoplastic resins and applying the melted resins to T-shaped die, blotting-extruding or calendering. A film prepared by extruding or calendering has excellent productivity and is inexpensive.
However, according to these methods, improper foreign materials are introduced into the resin while forming a film, or insoluble ingredients exist, causing a high possibility of forming protrusions, so called fish eyes, on the film. Further, according to these methods, it is difficult to obtain uniform film thickness, and considerable differences in physical properties between vertical and horizontal directions of a film occur due to stress applied during a manufacturing process.
Thus, when a film prepared by conventional methods is applied to dicing or backgrinding, cracking or bending of a wafer is likely to occur due to non-uniform pressure. Further, various problems occur when such a film is applied to other uses.