1. A substrate for a printed circuit board, comprising:a base film having an insulating property; and
a metal layer formed on at least one surface side of the base film,
wherein a plurality of fine particles are disposed between the base film and the metal layer so as to adhere to both the base film and the metal layer, and
the fine particles are formed of a metal the same as a main metal of the metal layer or formed of a metal compound of the main metal,
wherein the fine particles are formed of a metal oxide or a metal hydroxide, and have an average particle size of 0.1 nm or more and 20 nm or less.