4-layer PCB stackup thickness: common builds, impedance tips, tolerances

Most 4-layer PCBs finish at 1.6 mm (63 mil), with common options at 0.8, 1.0, 1.2, 1.6, 2.0, and 2.4 mm.

Quick answer: common 4-layer thicknesses

0.8, 1.0, 1.2, 1.6, 2.0, and 2.4 mm are industry-standard finished thicknesses for rigid 4-layer FR-4 builds. 1.6 mm (63 mil) is by far the most used due to connector ecosystems and stiffness.

What determines the finished thickness?

• Core thickness (typically 0.4–1.3 mm for 4-layer)

• Prepreg ply type and count (e.g., 1080 ≈ 0.06 mm, 2113 ≈ 0.08 mm, 2116 ≈ 0.10 mm, 7628 ≈ 0.18–0.20 mm per ply after cure)

• Copper weight (0.5 oz ≈ 17 µm, 1 oz ≈ 35 µm, 2 oz ≈ 70 µm per layer)

• Outer copper plating (adds roughly 10–25 µm per side)

• Solder mask (≈10–20 µm per side)

All contributions are additive; copper and mask shift total thickness by only tens of microns.

Example 1.6 mm 4-layer builds you can copy

• General purpose (microstrip outer): L1 Sig (1 oz) | 0.18–0.20 mm prepreg (2116+1080) | L2 GND (1 oz) | 1.0 mm core | L3 PWR (1 oz) | 0.18–0.20 mm prepreg | L4 Sig (1 oz). Finishes ≈1.55–1.70 mm.

• High‑speed outer impedance: L1 Sig (0.5–1 oz) | 0.09–0.12 mm prepreg (2×1080) | L2 GND (1 oz) | 1.25–1.35 mm core | L3 PWR (1 oz) | 0.09–0.12 mm prepreg | L4 Sig (0.5–1 oz). Keeps L1‑L2 and L3‑L4 close for tight return paths.

• Thin 1.0 mm build: L1 Sig (0.5–1 oz) | 0.10–0.12 mm prepreg | L2 GND | 0.55–0.65 mm core | L3 PWR | 0.10–0.12 mm prepreg | L4 Sig. Finishes ≈0.95–1.05 mm.

• Compact 0.8 mm build: outer dielectric 0.08–0.10 mm, center core ≈0.45–0.50 mm, 0.5 oz copper common. Finishes ≈0.75–0.85 mm.

How thin or thick can I go?

Below ~0.6 mm, handling stiffness and warpage risk rise quickly; above ~2.4 mm, weight and drill aspect ratio constraints tend to dominate. Connector standoffs and enclosure slots often quantize choices to 1.0 or 1.6 mm.

How to hit 50 Ω and 90–100 Ω on 4-layer?

For outer-layer microstrip over FR‑4 (Er ≈3.7–4.1):

• 50 Ω, 0.5 oz copper: dielectric (L1–L2) ≈0.10 mm typically yields a 7–9 mil (0.18–0.23 mm) trace; at 0.15 mm dielectric, expect ~11–13 mil.

• 100 Ω differential, 0.5 oz: with 4/4 mil (0.10/0.10 mm) pair, target dielectric ≈0.08–0.10 mm; with 5/5 mil, ≈0.10–0.12 mm. Pair spacing strongly affects results.

For inner-layer stripline, required widths are narrower for the same impedance; use an impedance calculator with your exact Er and copper.

What tolerance should I expect?

Finished board thickness and individual dielectric thicknesses typically vary on the order of ±10% with FR‑4 glass styles. Impedance targets are usually held within ±10% when the stackup is locked and controlled.

Does copper weight change thickness much?

Changing from 0.5 oz to 1 oz adds ~18 µm per copper layer (≈36 µm total for two outers), plus 10–25 µm plating per side. That is only a few hundredths of a millimeter on the overall stack, but it can shift impedance and via aspect ratio.

Notes on stiffness, warpage, and connectors

Bending stiffness scales roughly with the cube of thickness (t³). Doubling thickness raises stiffness ~8×, which helps with large panels and press‑fit connectors but increases Z‑height and mass. Keep outer dielectrics thin (≈0.10 mm) for EMI control; place a solid ground on L2 to give outer traces short return paths.

Standards and services you can request

HyperPCB operates an ISO 9001:2015 certified quality management system (certificate CN-2023-Q1156, SGS, valid to June 2027). Boards can be built and inspected to IPC Class 2 or IPC Class 3 acceptance criteria. RoHS and REACH compliance is supported. Quotes are returned within 24 hours and DFM feedback within 1 business day.