DEVELOPMENT OF BIAXIALLY STRETCHED FILM FOR FLEXIBLE PRINTED-CIRCUIT BOARDS

A biaxially stretched film of BEK, a new engineering plastic with high heat resistance (T-g: 181 degrees C,;T-m: 364 degrees C) and chemical resistance, was developed as a base film for flexible printed circuit boards, Its heat shrinkage percentage at 260 degrees C and the coeffi cient of thermal expansion below T-g were decreased to below 0.1%, and 3.3 x 10(-5)/degrees C: respectively. The process of determining stre tching and heat setting conditions for film formation with a role stre tcher and a tenter is reported.