Case Study: Successful Implementation of FPC with Silicone Overmolding in Wearables

In the rapidly evolving landscape of wearable technology, the demand for compact, durable, and highly reliable electronic components has never been greater. As industry leaders seek innovative solutions to enhance device performance and user comfort, the integration of Flexible Printed Circuits (FPC) with silicone overmolding has emerged as a groundbreaking approach. This comprehensive case study explores the design, engineering, manufacturing, and validation processes that led to a successful deployment of this technology in real-world wearable devices, setting new standards for performance, durability, and user experience.

Flexible Printed Circuits (FPC) are thin, lightweight, and highly adaptable circuit boards that provide electrical connectivity in constrained spaces. Their inherent flexibility makes them ideal for wearables, where form factor and comfort are paramount. However, FPCs are vulnerable to mechanical stress, environmental factors, and wear over time, posing significant challenges in long-term reliability.

Silicone overmolding addresses these issues by encapsulating the FPC with a durable, elastic, and biocompatible material. This process protects the delicate circuitry from moisture, dust, mechanical impact, and chemical exposure, while maintaining flexibility and user comfort. Together, FPC and silicone overmolding form a robust integration that enhances device lifespan and performance.

Designing wearable electronics involves navigating complex challenges such as:

FPC with silicone overmolding directly addresses these challenges through:

Thin, flexible circuitry that conforms to body contours

Encapsulation that prevents mechanical damage and environmental ingress

Elastomeric properties that absorb shocks and mechanical stresses

Compatibility with mass production techniques for scalability

This synergy results in wearable devices that are more reliable, longer-lasting, and more comfortable for users.

Flexible Printed Circuits (FPC) Materials

The core of the design involves selecting high-performance substrates such as polyimide or PET, which provide excellent thermal stability, mechanical flexibility, and electrical insulation. Conductive traces are typically made of copper, with protective coatings like gold plating to ensure corrosion resistance.

Silicone Overmolding Materials

The overmolding process employs medical-grade silicone elastomers such as RTV silicones or liquid silicone rubber (LSR). These materials are chosen for their biocompatibility, elasticity, UV and chemical resistance, and ability to withstand repeated flexing without cracking or delaminating.

Engineering Considerations

Adhesion:

Surface treatments like plasma cleaning and adhesion promoters ensure a strong bond between the silicone and FPC surface.

Thickness Optimization:

Silicone layers are optimized to balance protection and flexibility.

Thermal Management:

Materials are selected to dissipate heat, preventing damage during operation.

Prototyping

Initial prototypes involve lamination of circuit layers, component placement, and test runs of silicone overmolding. Advanced CAD/CAM software ensures precise alignment and mold design.

Mass Production

The manufacturing workflow includes:

FPC fabrication via photo-etching or laser cutting

Component assembly using pick-and-place machines

Silicone overmolding executed through mold injection or casting, ensuring uniform coverage and consistent thickness

Curing under controlled conditions to achieve desired mechanical properties

Quality control involving visual inspection, electrical testing, and environmental stress screening

Continuity and insulation resistance tests

Thermal cycling to simulate real-world temperature variations

Vibration and mechanical flexing to assess circuit integrity

Environmental Resistance Tests

Water ingress protection via IP testing standards

Chemical resistance testing against common substances encountered during wear

UV exposure testing to evaluate material degradation

Durability and Long-Term Reliability

Repeated flex tests simulating daily wear motions

Aging tests to predict long-term performance

Biocompatibility assessments for skin contact safety

A leading global wearable brand partnered with SiliconePlus to develop a custom FPC silicone-overmolded wristband for their next-generation health monitoring device. The goal was to achieve a balance between compact electronic integration, durability, and all-day comfort for users.

SiliconePlus engineered a precision-molded silicone wristband incorporating an ultra-thin flexible printed circuit (FPC) with integrated sensors and Bluetooth communication modules.

The liquid silicone rubber (LSR) overmolding process provided complete encapsulation — ensuring waterproofing, shock absorption, and a skin-friendly contact surface ideal for long-term wear.

Superior comfort: The medical-grade silicone surface offered a soft, breathable, and flexible fit, improving the overall user experience.

Scalability: The LSR injection process developed by SiliconePlus enabled high-volume manufacturing with tight dimensional control and consistent electrical reliability.

After extensive performance and user testing, the SiliconePlus solution achieved zero device failures over 12 months of continuous use.

Customer feedback confirmed greater comfort, improved reliability, and enhanced aesthetic quality, validating the integration of FPC with silicone overmolding as a leading approach in the wearable technology industry.

The trajectory of wearable device development points toward:

Advanced material innovations:

Development of self-healing silicones and conductive elastomers for self-repairing circuits

Integration of sensors within silicone encapsulation for more compact designs

Smart encapsulation technologies that monitor device health and predict failures

Sustainable manufacturing practices incorporating biodegradable materials and recyclable components

The ongoing evolution promises more resilient, comfortable, and intelligent wearables, with FPC and silicone overmolding at the forefront of this transformation.