PCB Stackup Explained — Layers, Materials, Return Currents, Microstrip vs Stripline | KiCad Advanced

The stackup is the first decision in any PCB layout — and one of the most consequential. It determines trace impedance, return path geometry, layer assignment, and whether your high-speed signals will behave. Change it mid-layout and you restart. Get it wrong and no amount of careful routing fixes it. This lecture builds the mental model: what a stackup is, what FR4 actually does to your signals, how ground planes control return currents, the difference between microstrip and stripline, why odd layer counts warp boards, and the five factors that determine the right layer count for a given design. It also covers the decision made in this course — why the Smart USB Thumb Drive started as a two-layer design and why it was switched to four layers. 🎓 Course: KiCad Advanced — BGA, Signal Integrity, and High-Speed Layout Full enrollment and course details: https://connect.techexplorations.com/... This course takes you through the complete design of a Smart USB Thumb Drive — from schematic to manufactured PCB — using KiCad. You'll work with BGA packaging, USB differential pairs, eMMC length matching, and ideal diode power management on a real, orderable board. In this video A conceptual primer on PCB stackups, covering materials, layer types, transmission line geometry, and layer count selection. Impedance calculation is a separate topic covered in the next lecture — the goal here is to build the understanding that makes the maths meaningful when you get there. Timestamps 00:00 Introduction — the stackup must be defined before a single trace is placed 01:07 What a PCB stackup is — layer sequence, types, and thickness 01:32 Core vs prepreg — materials, lamination, and why the distinction matters 02:44 FR4 dielectric properties — dielectric constant (Dk), dissipation factor (Df), and their limits 05:09 Three layer roles — signal layer, ground plane, power plane 05:51 Ground planes — return paths, impedance reference, EMI shielding, and thermal spreading 06:32 Power planes — voltage distribution and when they can serve as a secondary reference 07:23 Return current at high frequencies — path of least impedance, loop area, and why ground planes are essential 09:35 Microstrip vs stripline — outer layer vs inner layer transmission lines, trade-offs for EMI and debug access 11:43 Why stackups require even layer counts — lamination physics and board warping 13:48 Choosing layer count — signal speed, component density, power rails, EMI, and cost 16:27 The project decision — why the Smart USB Thumb Drive started as a two-layer design 17:44 Why the design switched to four layers — routing complexity and engineering trade-offs 18:32 Six rules to carry into every stackup decision Tech Explorations creates practical electronics and PCB design courses for engineers, makers, and educators. More courses at techexplorations.com.