Demand for smaller, higher performance electronic equipment is increasing, and subsequently, high-density wiring and a reduction in attenuation of high-speed signals are required for packaging substrates. To manage this demand for high-density wiring, a semi-additive method has been adopted to enable the manufacture of 60 μm pitch wiring. In the conventional semi-additive method, however, a process of roughing the surface of the insulating layer with chemicals is required, thus limiting the insulating layer. The attenuation of high-speed signals is, on the whole, rather extensive in such insulating layers. Therefore, we have developed a new semi-additive method applicable to wiring of 40 μm pitch or less has been developed, in which ultra-thin copper foil (1 to 3 μm), the surface roughness of which is Rz < 1.0 μm, is used as a feeder layer. Figure 1 shows the schematic diagram of a new fine-line formation system.
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