Method for manufacturing a composite member from a porous substrate by selectively infiltrating conductive material into the substrate to form via and wiring regions

A method for manufacturing a composite member comprising a porous substrate, non-interfacial conductive portions which are formed on the opposite surfaces of the porous substrate and where a conductive material is filled but not piercing the entire thickness of the porous substrate, and an interfacial conductive portion which is electrically connected with said non-interfacial conductive portions and where a conductive material is filled piercing through the entire thickness of the porous substrate;

• said method comprising:
• disposing masks on respective of the opposite surfaces of said porous substrate, said masks each comprising a first light-transmitting region for exposing a first region of said porous substrate and a second light-transmitting region for exposing a second region on the opposite surfaces of said porous substrate, said second light-transmitting region comprising an aggregation of fine patterns, an average transmittance of said second light-transmitting region being not more than 50% of an average transmittance of said first light-transmitting region, and each of said masks aligned based on the position of said first light-transmitting region of each of said masks;
• exposing said first region and said second region to an exposure beam through each of said masks, an average size of voids of said porous substrate being, as expressed by a radius of gyration, {fraction (1/20)} to 10 times a wavelength of said exposure beam;
• and
• forming said interfacial conductive portion and non-interfacial conductive portion by infiltrating a conductive material into said first region and said second region respectively.