Is the resistance of very short copper wire in small signal circuit important?

The conduction band of printed circuit board is manufactured wide for reducing the gain error. That is why relatively wide conductive bands will be frequently applied in analog circuits. Nevertheless, many PCB designers prefer the minimum width ones to facilitate the placement of the signal lines. In all, it is very vital to calculate the resistance of the conductive band and analyze its effect for all possible problems.

Are there any problems among the capacitance composed by conductive band in too large width and the metal layer on the back of PCB?

The problem is very small. The capacitance formed by the conductive band of PCB is important and should always be estimated first. If this is not the case, it will not cause problems even if the wider conductive band forms a large capacitor. If problems appear, you can reduce the capacitance of the ground by removing a small piece of ground plane area. many PCB designers prefer the minimum width ones to facilitate the placement of the signal lines. In all, it is very vital to calculate the resistance of the conductive band and analyze its effect for all possible problems.