How Thick is a FPC and What is the Standard FPCB Thickness?

PCB designers often rely on common "standards" when working with flex PCB, leaning toward certain thicknesses that balance cost and performance. While there’s no strict rule for how thick a FPC board must be, industry trends have settled on a few preferred ranges to keep manufacturing simple and affordable.

The thickness of your FPCB isn’t just about flexibility—it directly impacts the board’s electrical performance, durability, and where it can be used.

Typical FPCB Thickness

Most flex PCBs fall between 0.7 mm and 6.4 mm, but the sweet spot for many applications is around 0.062 inches (1.57 mm). Here’s how layer count affects FPCB thickness:

• Single-layer flex PCB: ~0.1 mm

• 2-layer flex PCB: ~0.32 mm

• 4-layer flex PCB: ~0.42 mm

Naturally, more layers mean a thicker board. But thickness isn’t just about layer count—several key factors influence the final measurement.

What Determines FPCB Thickness?

1. Application & Space Constraints

Flex PCBs are meant to be thin, but some designs need extra thickness for strength. Thicker boards handle stress better but take up more space—a trade-off in tight electronics like wearables or medical devices.

2. Copper Thickness

Copper carries the current, and its thickness affects both performance and board thickness. Standard copper weights:

0.5 oz (17.5 µm) – Thinner, good for fine traces

1 oz (35 µm) – Most common

2 oz (70 µm) – Thicker, handles more power

Thicker copper means a sturdier (but less flexible) board, and higher cost due to processing challenges.

3. Layer Count

More layers = thicker board. Simple 2-6 layer designs stay within standard thicknesses, but once you go beyond 8 layers, things get tricky. If your design doesn’t need extra layers, keeping them to a minimum helps maintain flexibility.

4. Materials Matter

The base material (usually polyimide) and protective layers (coverlay) add to the thickness. Common options:

• Polyimide substrate: 12.5–50 µm

• Coverlay: Adds ~25–50 µm

• Stiffeners (if used): Can significantly increase thickness

  

5. Trace Width & Signal Type

High-power signals? Wider traces and thicker copper are needed, increasing overall thickness.

HDI (high-density) designs? These use ultra-thin traces and microvias, allowing for thinner boards.

What is the Thickness Tolerance of a Flex PCB?

The thickness of FPCB also needs to take into account the thickness tolerance - that is, the allowable deviation from the specified thickness. Thickness tolerance can affect the performance of the circuit board, especially in applications where space constraints or mechanical properties are critical.

Typically, the thickness tolerance for a flex PCB can range from ±10% to ±20%, depending on:

• Material type (polyimide, adhesive, copper foil)

• Number of layers

• Manufacturing capabilities of the Flex PCB supplier

For example, an FPCB specified at 0.20 mm thick may have an actual thickness ranging from 0.18 to 0.22 mm. To ensure optimal performance, especially in fine-pitch connectors or tight enclosures, it's essential to confirm the manufacturer’s tolerances during the design phase.

High-precision applications may require tighter tolerances, and in such cases, manufacturers can offer custom stack-up controls and advanced lamination techniques to reduce variation.

Final Takeaway

There’s no one-size-fits-all answer—your FPCB’s thickness depends on:

✔ How much does it need to bend

✔ Power requirements

✔ Layer count

✔ Space constraints

Need an ultra-thin build for your portable electronic device? Or something a little thicker for rugged industrial equipment? Contact us to tailor a stackup to your needs.