NOVELTY - The method involves preparing colloidal solution (S10). The colloidal solution is included with opal structure of polymer particle. Polymer resin is dispersed into organic solvent by a polymer resin dispersion part for forming the opal structure of the polymer particle of a coating layer (S20). Colloidal solution is coated (S30) on a material part. The opal structure of the polymer particle is rescued (S40) by dispersing membranous polymers resin. The polymer particle is dissolved (S50) by using organic solvent. The membranous polymers resin is cross-linked with an inverse opal structure.    USE - Method for manufacturing a porous base material of an electrode assembly of an electrochemical device (all claimed). Can also be used for an electric vehicle, a mobile phone, a camcorder and a notebook computer.    ADVANTAGE - The method enables performing manufacturing process of the inverse opal structure and a separation film according to size of a pore without performing fluoric acid treatment so as to improve porosity, ion conductivity and gas permeability of the separation film and environment-friendly effect and preventing harmful phenomenon of a human body.    DETAILED DESCRIPTION - The inverse opal structure is made high thermal resistance plastic engineering resin that comprises polysulfone, polyethersulfone, polyether imide, polyphenylene liquor poid, polyetheretherketone (PEEK) (RTM: Colorless organic polymer thermoplastic), polyarylate and polyamideimide and polyimide. The membranous polymers resin is made of styrene - butadiene rubber, polybutadiene rubber, nitrile rubber, acryl rubber, fluorine group rubber, PVC, polystyrene, polystyrene, polymethyl methacrylate, acrylonitrile-butadiene-styrene, polyvinylidene fluoride, polyvinylpluoride, PTFE, polyvinylacetate and vinyl acetate-ethylene copolymer. INDEPENDENT CLAIMS are also included for the following:    (1) a porous base material    (2) a electrode assembly    (3) a electrochemical device.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow diagram illustrating a method for manufacturing a separation film.'(Drawing includes non-English language text)'    Step for preparing colloidal solution (S10)    Step for dispersing polymer resin into organic solvent by polymer resin dispersion part (S20)    Step for coating colloidal solution on material part (S30)    Step for rescuing opal structure of polymer particle (S40)    Step for dissolving polymer particle (S50)