Ways to raise the signal transmission velocity of printed circuit boards (PCBs) are discussed. A low dielectric constant laminate (dielectric constant=3.7) for the PCBs, which has almost the same thermal stability and flame retardancy as a polyimide one, was produced by a maleimide-styryl resin synthesis based on a molecular design technique in combination with optimum reinforcement. A high-aspect-ratio, fine-pattern formation process was established by pattern copper plating. The signal line width is 70 mu m and its thickness is 65 mu m. A high-aspect-ratio, fine through-hole formation process was derived by optimization of the drilling conditions. Using these technologies, a high-density, multilayer printed circuit board (MPB), 730*534 mm in size with 46 layers, was developed. This high-performance MPB was applied in the HITAC M-880, the newest and largest mainframe computer manufactured by Hitachi.
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