My First Four-Layer PCB

After several two-layer boards I finally had a design that needed four layers: a high-speed STM32H7 board with DDR3 memory.

Layer stackup: Layer 1 (top) = signal, Layer 2 = ground plane, Layer 3 = power planes (3.3V, 1.8V, 1.2V), Layer 4 (bottom) = signal. This classic stackup gives excellent signal integrity — every signal trace has a reference plane within 0.2mm. Ground vias between the two signal layers provide return path continuity.

Cost comparison at JLCPCB: a 100x100mm four-layer board costs $8 for 5 pieces — only marginally more than two-layer. The design time savings from having dedicated power planes (no power trace routing, naturally good decoupling) paid for the cost difference immediately. I'll default to four layers for any board with more than one power rail.