What is Flex PCB Overmolding?

Flexible PCBs often used in environments that are far from ideal—continuous bending, vibration, moisture, or direct mechanical stress. In these cases, a standard flexible PCB structure is usually not enough.

That is where flex PCB overmolding becomes a practical and reliable solution.

Overmolding allows us to combine the flexibility of an flexible PCB with the protection of molded materials, creating a more robust and integrated product for our customers.

What Does Flex PCB Overmolding Mean in Real Production?

From a manufacturing perspective, flex PCB overmolding means placing a finished flexible circuit into a mold and injecting a selected material over specific areas of the board.

The areas that typically require overmolding include:

• Connector zones

• Solder joints and component areas

• Cable exits where strain relief is required

After molding, these areas are fully protected and mechanically reinforced, while the remaining part of the flexible PCB stays free to bend as designed.

Why use overmolding for flexible circuit boards?

Overmolding technology helps solve several common problems:

• Solder joint cracking due to vibration

• Conductor breakage at cable transition points

• Moisture ingress in outdoor or humid environments

• Excessive manual assembly and secondary fastening components

Through overmolding technology, protection and stress relief functions are directly integrated into the flexible circuit board structure.

Common Overmolding Materials

Material selection always depends on the application requirements.

• TPU for flexible and abrasion-resistant designs

• TPE for soft, elastic, and wearable applications

• Nylon (PA) for higher strength and temperature resistance

• Silicone for applications requiring long-term flexibility and thermal stability

All materials are evaluated for compatibility with PI-based flexible PCBs and copper circuitry.

Key Design Considerations

Overmolding is not just a molding process; it begins at the design stage of the flexible printed circuit board. In flexible PCB projects, the following points require close attention:

• Copper thickness and trace layout in high-stress areas

• Local reinforcement to prevent deformation during molding

• Adhesion between the molded material and the flexible PCB surface

• Component selection suitable for molding temperature and pressure

Early design coordination helps avoid delamination, warpage, or internal stress after molding.

Typical Applications

Flex PCB overmolding is widely used across different industries, including:

• Automotive sensors and control cables

• Medical and wearable electronic devices

• Consumer electronics with compact and flexible designs

• Industrial equipment requiring vibration and moisture resistance

In many of these applications, overmolding replaces traditional housings, tapes, or heat shrink solutions.

Overmolding Compared with Other Protection Methods

From our production experience, overmolding offers a good balance between protection, flexibility, and manufacturability:

• More durable than adhesive tapes or coatings

• More compact than external housings

• More consistent than manual assembly solutions

For medium to high-volume production, it also helps improve product consistency and reduce assembly steps.

Final Thoughts

Flex PCB overmolding is not always necessary, but when reliability and durability matter, it becomes a very effective option. By combining flexible PCB manufacturing with material selection and molding experience, Flex Plus help customers achieve designs that work reliably in real-world conditions.