Stack-up
A PCB stack-up is the cross-sectional arrangement of copper layers, dielectric materials, and bonding films that make up a multilayer board. It defines layer thickness, copper weight, dielectric properties, and is critical for impedance control, signal integrity, and manufacturability.
What it is
For a single or double-sided board, the stack-up is trivial: a single core with copper on one or both sides. For multilayer boards, the stack-up becomes a stack of cores (cured laminate with copper) bonded together by prepreg (uncured B-stage resin) under heat and pressure. A typical 4-layer board uses one core in the middle with prepreg between it and the outer copper foils.
A complete stack-up specifies the order and thickness of every layer, the copper weight on each layer (typically 18 µm / 0.5 oz, 35 µm / 1 oz, or 70 µm / 2 oz — European specifications usually quote µm directly), the dielectric material and thickness between layers, and any blind or buried via structures. For controlled-impedance designs, the stack-up also defines the trace width and spacing required to achieve target impedances on signal layers.
Most fabricators publish standard stack-ups for 2, 4, 6, and 8 layers using common FR-4 thicknesses. Using a standard stack-up is faster to quote, cheaper to build, and avoids material lead time. Custom stack-ups are necessary for unusual layer counts, controlled-impedance designs with specific targets, or mixed-material boards (e.g. FR-4 plus Rogers).
When it matters
Stack-up choice affects manufacturability, cost, lead time, and signal integrity. Choosing a non-standard stack-up — for example, requesting an unusual prepreg thickness for impedance control — can add days to lead time and require minimum order quantities to justify material setup. Conversely, specifying the wrong stack-up for a high-speed design can cause signal integrity failures that are only discovered after assembly. For any design with controlled-impedance requirements or high-speed digital interfaces, the stack-up should be specified explicitly with impedance targets, not left to fabricator default.
At Nordic PCB
For standard 2, 4, 6, and 8-layer boards, our certified suppliers use established stack-ups with documented impedance targets — request these by specifying layer count and dielectric requirements. For custom stack-ups including controlled impedance, mixed materials, or unusual layer counts, our DFM review verifies manufacturability and we return a stack-up diagram with the quote for your approval before production.
Related terms
- FR-4
FR-4 is a flame-retardant woven glass-reinforced epoxy laminate. It is the default base material for most rigid PCBs, balancing mechanical strength, electrical insulation, thermal performance, and cost. Variants exist for high-Tg, halogen-free, and high-speed applications.
- Multilayer PCB
A multilayer PCB has more than two copper layers separated by dielectric material and bonded together under heat and pressure. Common configurations are 4, 6, 8, 10, and 12 layers. Multilayer designs enable higher routing density, dedicated power and ground planes, and better signal integrity for complex circuits.
- Impedance control
Impedance control is the practice of specifying and manufacturing PCB traces so their characteristic impedance meets a precise target — typically 50 Ω single-ended or 100 Ω differential. Required for high-speed digital, RF, and signal integrity-critical designs, it depends on trace width, dielectric thickness, copper weight, and material properties.
- Copper weight
Copper weight is the thickness of copper foil on each PCB layer, specified in µm or ounces per square foot. Common weights are 18 µm (0.5 oz), 35 µm (1 oz), and 70 µm (2 oz). Heavier copper carries more current and dissipates more heat but limits minimum trace width.
- DFM
DFM (Design for Manufacturability) is a structured review of your PCB design against a fabricator's process limits — trace widths, drill sizes, annular rings, solder mask clearances, and stack-up choices — to catch issues before tooling starts. A good DFM review prevents rework, scrap, and missed delivery dates.