Quick-Turn Flexible Circuit Overmolding and Lens Integration

The Device

Blood oxygen sensing platform for reliable tissue oxygen levels in peripheral arterial disease.

The Challenge

The application required a flexible reader consisting of LEDs and a photomultiplier flexible enough to conform to an on-the-skin application on the leg or arm. The reader had to minimize light leakage and maintain cleanability. Minnetronix designed a flex circuit with floating LED pads and slots. In addition, a process was developed that demonstrated lens molding and overmolding capabilities by leveraging 3D printed molds and flexible thermoplastic materials. This allowed for fast and economical fabrication of prototype molded feasibility sample assemblies.

How Minnetronix Added Value

  • Clear Lenses: A complex mold flow was required to optically isolate the sensors from the emitters. Applying Design for Manufacturing principles to the flex circuit, the Minnetronix team added features to allow the polymer to flow from the back side to create discrete lens elements that were optically isolated from each other while mechanically interlocking the flex circuit. This also effectively created a substrate layer for further overmolding.
  • 3D Printed Molds: Minnetronix leveraged 3D printing and a small tonnage press to quickly iterate low-cost tooling for development and improvement of the mold performance.
  • Flex Overmold: The overmold allowed the clear lenses to show through – like windows – with no delaminations or seams where bioburden could accumulate. The Minnetronix team demonstrated the superior adhesion of thermoplastic elastomers (TPE) as compared to a Liquid Silicone Rubber fabrication method.
Technology

Optical Systems

Prototype components and 3D printed mold

Prototype components and 3D printed mold

3D printed mold and low tonnage press

3D printed mold and low tonnage press