Abstract: A multi layer printed circuit interconnection system together with pillars for mounting integrated circuit components is progressively formed layer by layer by successive sequences for each layer, involving using a photo resist to produce a pattern of apertures defining circuit tracks and the pillar positions, depositing metal to form the tracks and the pillars and replacing the remainder of the resist with insulation material. Openings co-operating with the pillars, for the circuit elements are produced during formation of the outermost insulation layer of the circuit system.The circuit elements are mounted on the pillars and the connections between the elements and the printed circuit system are formed by using a further one of said sequences.