Characteristic and formation mechanism of matt surface of double-rolled copper foil

Abstract

Copper foils for flexible printed circuit boards were prepared by double rolling, and the matt surface of double-rolled copper foil was characterized by atomic force microscope, scanning electron microscope, 3D optical interferometer, optical microscope and surface profiler. The morphology characteristics of matt surface were studied, and the formation mechanism of matt surface was discussed. The results showed that the matt surface of the double-rolled copper foil presented rough and relatively homogeneous morphology, and the morphologies of upper and lower matt surfaces were practically coincident. As the copper strips just entered into the deforming zone, the roughening of laminated surface occurred, but the roughness was relatively small. When the copper strips passed through the neutral plane, the roughness of the laminated surface increased significantly. In the backward slip zone, the initial micro-dimples between the two laminated surfaces were connected in the rolling direction, which led to the formation of larger and airtight dimples; when the copper strips moved toward the neutral plane and entered into the forward slip zone, the pressure of fluid in the airtight dimples increased rapidly, which enhanced the depths of the dimples; meanwhile, the depression corrugations with certain depth and larger width were formed on the laminated surface because of the dimple connection in the width direction. The copper foils with thickness of 36–54μm were fabricated by double rolling, and the Rz value of their matt surfaces was 1.0–1.3μm, which meet the requirements for directly using as adhesive surface of resin substrate, and therefore multiple roughening treatments during the traditional production process of flexible printed circuit board might be omitted. The formation mechanism of the matt surface of double-rolled copper foil proposed on the basis of the metal flow and deformation mechanics theory could explain the representative characteristics of the length direction of corrugations on matt surface being perpendicular to the rolling direction, several corrugations within a grain on the matt surface and the coincident morphologies of the upper and lower matt surfaces.