Single-Sided Flex PCB

A single-sided flex PCB is a type of board. It has one layer of conductive material. This layer is on a flexible base material-polyimide (PI) or polyester (PET).

That layer could be made of copper or a metal-filled polymer. This would create circuitry on just one side. Because it is flexible, it is often used in tight spaces where lightweight and high flexibility are needed.

Flexible circuits, like single-sided flex circuits, can bend and flex. This makes them a great choice for dynamic applications.

They are ideal for wearables, medical devices, and automotive uses. Such circuits are commonly used where small size and resistance to movement are important. Their slim design allows for use in high-density connections. This is important for applications that need a compact and reliable link.

Single-Sided Flex PCB Stack-Up Example

A typical single-sided flexible PCB stack-up includes:

Coverlay (PI Film) – Encapsulates and insulates the circuit.
Adhesive – Binds copper to the film.
Copper Conductor (1 oz) – Transfers signals and power.
It consists of: Base Layer of Polyimide (25–50 μ m) – Core Flexible Substrate.

Overall Thickness: ~0.1mm to 0.3mm (+/-0.03mm – thickness varies primarily due to copper thickness and layer options).

Thermal Considerations:

Thin materials restrict thermal flow, making thermal management a challenge. In higher power applications, incorporating thicker copper or external heat-spreading films can improve performance. Consider this during flex circuit design, especially for power-intensive systems.

Structure of a Single-Sided Flex PCB vs Double-Sided Flex PCB

Single-Sided Flex PCB Structure:

Base Material (PI/PET): Ensures flexibility and insulation.
Copper Layer: Single layer of conductive traces for signal routing.
Adhesive (if applicable): Attaches the copper foil to the substrate. Solder
Mask: Also protects the copper from oxidation or physical damage.
Coverlay Film: Acts as insulation and mechanical protection.

Double-Sided Flex PCB Structure:

Two copper layers (top and bottom).
Plated Through Holes (PTH) enable interlayer connections.
Supports more complex layouts and higher circuit density.
Better suited for impedance control and signal integrity.

Note: The double-sided design allows for multi-level flex solutions. You can layer or bond layers for multi-level (redundant) interconnects.

Single-Sided Flex Circuit vs Single-Sided Rigid Circuit: The Differences

Feature	Single-Sided Flex PCB	Single-Sided Rigid PCB
Material	Polyimide or polyester film	FR4 or fiberglass
Flexibility	Highly bendable and twistable	Completely rigid
Weight	Extremely lightweight	Comparatively heavier
Heat Dissipation	Limited due to thin construction	Better heat management
Applications	Wearables, medical, foldable electronics	Consumer and industrial products
Durability	Resilient to vibration and movement	Can crack under physical stress
Controlled Impedances	Difficult to manage	Easier due to thicker layers
Cost	Higher due to specialized materials	Lower with conventional methods

Key Takeaway:
If your application requires flex circuit design for dynamic environments, the single-sided flex PCB is ideal. For applications requiring structural rigidity and high thermal resistance, rigid boards are preferable.

More information: Rigid PCB vs Flexible PCB: Which Wins for Your Applications?

When to Use Single-Layer Or Double-Sided Flexible PCB?

For a cost-effective, low complexity solution, single-sided flex circuits are often an ideal choice.
A double-sided flex PCB provides excellent route guidance and better electrical performance. It works well in high-density systems, such as industrial automation and medical devices.

Pro Tip Time: If signal routing and electromagnetic shielding are paramount, consider multi-layered flex designs.

How Thick is a Single Layer Flex PCB?

The overall thickness of a single-layer flex PCB varies based on several components:

Base: Typically 12.5-50 µm.
Copper Weight: 0.5 oz (17 µm) to 2 oz (70 µm).
Adhesive & Coverlay: That’s an additional 25-50 µm.
Overall Thickness: About 0.05 mm- 0.3 mm.

Performance Impact:

Thinner constructions allow greater flexibility but reduce thermal resistance.
Thicker copper increases current-carrying capacity but limits bending radius.

How to Make a Single-Layer Flex PCB?

Step-by-Step Manufacturing Process

Material Selection
Choose appropriate base film and copper foil based on flexibility, temperature requirements, and final application.
Circuit Patterning
- Apply photoresist and use UV light to define copper traces.
- Use etching or laser cutting for precise circuit definition.
Lamination
- Apply adhesive to bond copper to the base layer if necessary.
Coverlay Application
- Laminate polyimide film to encapsulate the circuit.
Solder Mask Printing
- Optional, but often used to prevent bridging and enhance reliability.
Electrical Testing & Visual Inspection
- Critical for ensuring performance and detecting shorts or open circuits.

Flex PCB Design Guidelines:

Avoid sharp corners to prevent stress fractures.
Use staggered trace routing for better flexibility.
Optimize trace width and spacing for signal integrity and controlled impedance.
Employ dynamic bend simulation in design to improve product longevity.

Applications of Single-Sided Flex PCBs

Single-layer flexible circuits are widely used in:

Wearable Electronics: Smartwatches, health monitors, smart glasses.
Medical Devices: Endoscopes, hearing aids, portable diagnostics.
Automotive Applications: Flexible lighting, in-dash sensors, and display modules.
Consumer Electronics: Foldable phones, digital cameras, Bluetooth earbuds.

Key Advantages:

Compact and lightweight – ideal for miniaturized electronics.
High reliability in movement-heavy applications.
Tailorable to unusual shapes and enclosures.
Additionally, it offers easier assembly compared to complex rigid-flex solutions.

These benefits make flexible printed circuit boards essential in today’s trend toward smaller, more mobile electronic devices.

Conclusion

Rigid-Flex Single Sided flexible PCBs are a great solution. They work well for simple connections and tight spaces. They can survive bending, fit into tight spaces, and provide steady electrical performance. Therefore, they are a top choice for many growing markets, such as wearables, automotive, and medical applications.

As materials and design tools get better, flex circuits will grow. So, this includes both single and multi-layer flex circuits. They will push the boundaries of today’s electronics design.