Signal processing board and image forming apparatus

A signal processing board comprising:

• a six-layer substrate in which six wiring layers are stacked;
• a first semiconductor element and a second semiconductor element arranged on an outer surface of a first layer of the six wiring layers;
• a plurality of signal transmission planes formed in the first layer, a third layer, a fourth layer, and a sixth layer of the six wiring layers and electrically connected to one or both of the first semiconductor element and the second semiconductor element;
• a first ground plane formed in a second layer of the six wiring layers and electrically connected to the first semiconductor element and the second semiconductor element;
• a first power supply plane formed in a fifth layer of the six wiring layers and electrically connected to the first semiconductor element;
• a second power supply plane formed in the fifth layer of the six wiring layers and electrically connected to the second semiconductor element;
• a second ground plane formed in the fifth layer of the six wiring layers and electrically connected to the first semiconductor element and the second semiconductor element;
• a first bypass capacitor arranged on an outer surface of the first layer or the sixth layer and electrically connected to the first power supply plane and the second ground plane;
• and
• a second bypass capacitor arranged on an outer surface of the first layer or the sixth layer and electrically connected to the second power supply plane and the second ground plane.