Linked to the prior level, the impedance of any signals on L4 may have smaller deviations close to power rail splits on L3 More versatility and dependability: Double-sided PCB will come with the two the top layer and bottom layer, so You should utilize the bottom layer for a floor https://10-layer-2-order-hdi-mult83715.elbloglibre.com/31172497/aluminum-copper-based-pcb-an-overview