Printed wiring board unit, auxiliary substrate for hierarchical mounting, and electronic apparatus

摘要

A rectangular frame-like auxiliary substrate for hierarchical mounting 14 is mounted so as to surround a semiconductor component 15 mounted on a printed wiring board 11, and another semiconductor component 16 is mounted above the semiconductor component 15, being supported on the auxiliary substrate for hierarchical mounting 14 with terminals of the semiconductor component 16 being connected thereto. The auxiliary substrate for hierarchical mounting 14 has wiring patterns 35a and through holes 34a, and includes a power supply layer 32 and a ground layer 33 inside thereof with printed wiring board pads on a lower surface of the auxiliary substrate for hierarchical mounting 14 being more dispersed than component pads 23a on an upper surface of the auxiliary substrate for hierarchical mounting 14. Therefore, a gap space 41 between each adjacent ones of pads 40a on the printed wiring board 11 which gap space 41 corresponds to the semiconductor component 16 is widened so that a wiring pattern 43 extending outward on the printed wiring board from a pad 21a connected to the semiconductor component 15 passes through the gap space 41 without difficulty.