The present invention provides an electrolytic 
copper foil. The electrolytic 
copper foil is an electrolytic 
copper foil in which roughened particles are formed on the roughened surface (M surface) of the electrolytic 
copper foil. It is characterized in that the 
average size of the roughened particles is  0.1~1.0μm.  The present invention provides an electrolytic 
copper foil and a manufacturing method thereof. The properties of the electrolytic 
copper foil are not deteriorated, the roughening treatment layer on the copper foil can be improved, and the 
bonding strength between the copper foil and the resin substrate can be improved; especially  , Compared with general-purpose 
epoxy resin-based substrates (FR‑4, etc.), peeling can be achieved when using a combination of a substrate for 
semiconductor packaging or a 
liquid crystal polymer substrate that generally has low adhesion to copper foil and an electrolytic copper foil.  Stronger electrolytic copper foil.  An object of the present invention is to provide an electrolytic copper foil useful as an electrolytic copper foil used as a negative 
electrode material for a printed wiring board or a battery (LiB, etc.).