A crushing apparatus is provided for crushing a printed circuit board on which electronic components are mounted into pieces of a size ranging from a few to ten centimeters square and separating some of the components and sheathed wires from the printed circuit board. A face of a CDC, which is an expansion board to be connected to the mother board of a computer system is covered by an insulating sheet. In an hydrocarbon solvent or under bulk conditions, at a polymerization temperature in a range of \u221220-120\xb0 C. The reduction of components results in significant reduction in insertion loss and signal degradation. First polishing, in which the metal film is removed, is performed by supplying a first CMP slurry containing metal ions. The inventive heat protective layers can be used with or without intermediate layers on the surface of temperature-exposed components.