Electromagnetic wave shielding sheet and printed wiring board
An electromagnetic wave shielding sheet according to the disclosure is configured by a protection layer, a metal layer, and a conductive adhesive layer. The metal layer has a plurality of openings, and an aperture ratio of the opening is 0.1%-20%. In addition, a tensile breaking strength of the electromagnetic wave shielding sheet is 10 N/20 mm-80 N/20 mm.
1. An electromagnetic wave shielding sheet, comprising:
a protection layer, a metal layer, and a conductive adhesive layer, wherein the metal layer has a plurality of openings, and an aperture ratio of the openings is 0.1%-20%; and
a tensile breaking strength is 10 N/20 mm-80 N/20 mm,
wherein an average value of a circularity factor of the openings of the metal layer obtained by an expression below is 0.5 or more,
circularity factor=(area×4π)/(perimeter) 2
herein, the perimeter is a length of an outer circumference when an image which is obtained by observing the metal layer by any one of an optical microscope, a laser microscope and an electron microscope is read, a plane of the opening becomes a direction perpendicular to an observation viewpoint, the opening capable of being entirely confirmed is extracted, and a extracted opening is projected two-dimensionally; and the area is a breadth of a region defined by the outer circumference when the extracted opening is projected two-dimensionally.
2. The electromagnetic wave shielding sheet according to claim 1 , wherein a thickness of the metal layer is 0.5 μm-5 μm.
3. The electromagnetic wave shielding sheet according to claim 2 , wherein
the conductive adhesive layer contains a thermosetting resin and a conductive filler, and
a content of the conductive filler in the conductive adhesive layer is 35 mass %-90 mass %.
4. The electromagnetic wave shielding sheet according to claim 1 , wherein
the conductive adhesive layer contains a thermosetting resin and a conductive filler, and
a content of the conductive filler in the conductive adhesive layer is 35 mass %-90 mass %.
5. A printed wiring board comprising the electromagnetic wave shielding sheet according to claim 1 , a cover coat layer, and a wiring board having signal wirings and an insulation base material.
6. The printed wiring board according to claim 5 , wherein
the signal wirings have signal circuits and ground circuits;
a via is arranged on the cover coat layer to expose the ground circuits; and
an area of the via is 0.008 mm 2 or more and 0.8 mm 2 or less.