A CPU CHIP-ON-BOARD MODULE

A CPU chip-on-board module for low and midrange computers is described . The module consists of a CPU bare chip, 24 SRAM's packaged in SOJ pa ckages, and some decoupling capacitors. The module substrate is a prin ted circuit board (PCB) made of bismaleimide-triazine resin. The modul e (156 mm x 58 mm) consists of four signal metal layers and four power /ground metal layers. A square clearance hole (17 mm x 17 mm) for the CPU is formed in the central part of the PCB. A thermal spreading meta l is glued to the PCB from the rear side, covering the square hole, an d the CPU chip is die-bonded onto the metal plate. The thermal resista nce can be made smaller than 2-degrees-C/W with 0.4 nl/s of wind veloc ity. Numerical analysis of electrical characteristics of the module sh ows that it can reduce signal delay time from the CPU to cache memorie s by 10% c compared with that of a daughter board type module with the CPU packaged in a pin-grid array package. It is estimated that simult aneously switched noise can be reduced by 60% from that of the daughte r board type module.