TECHNICAL FIELD

The present disclosure relates to a cover film for a flexible printed circuit board and a flexible printed circuit board. The present application is based on and claims priority to Japanese Patent Application No. 2018-072403, filed on Apr. 4, 2018, the entire contents of the Japanese Patent Application being hereby incorporated herein by reference.

BACKGROUND ART

In recent years, along with the reduction in size and weight of electronic devices, electronic components, such as planar coil elements, have been reduced in size by a configuration using a conductive pattern and mounted on a flexible printed circuit board.

Such electronic components mounted on a flexible printed circuit board are covered and protected, for example, by a coverlay (see, for example, Japanese Laid-open Patent Publication No. 2008-205125). The coverlay is composed of a thin adhesive layer that is layered on a conductive pattern and a resin layer that is layered on the adhesive layer to cover the conductive pattern. The adhesive layer and the resin layer are flexible and adhere to the conductive pattern so that the electronic components are covered and protected mainly by the resin layer.

PRIOR ART DOCUMENT

Patent Document

[Patent Document 1] Japanese Laid-open Patent Publication No. 2008-205125

SUMMARY OF THE INVENTION

According to one aspect of the present disclosure, a cover film for a flexible printed circuit board includes: an adhesive layer; and a protective layer that is layered on a surface of the adhesive layer, wherein a lamination temperature range in which a ratio of a viscosity of the protective layer to a viscosity of the adhesive layer is five times or more is present within a temperature range of 50° C. or more and 150° C. or less.

