Flexible printed circuits capable of transmitting electrical and optical signals

What is this patent about?

’985 is related to the field of flexible printed circuits (FPCs) and high-speed signal transmission. Specifically, it addresses the need for interconnects that can handle both traditional electrical signals and high-bandwidth optical data within a single, pliable substrate. This is particularly relevant for modern electronic packaging where space is limited and electromagnetic interference must be managed alongside optical fiber integration.

The underlying idea behind ’985 is to integrate optical fibers directly into the structural layers of a flexible circuit board by physically nesting them within the electrical pathways. Rather than treating optical and electrical paths as separate entities, the invention uses the conductive layers and plated sidewalls to form a coaxial-like enclosure around individual optical waveguides. This dual-purpose architecture allows the circuit to utilize the same spatial footprint for both types of signal transmission.

The claims of ’985 focus on a flexible printed circuit structure where a plurality of optical waveguides are embedded within an adhesive layer sandwiched between two primary building blocks. Each building block consists of a dielectric layer and a conductive substrate. The independent claim specifically requires that certain conductors are configured to enclose an optical waveguide by electrically connecting the first substrate layer to the second substrate layer through the use of metal coatings.

In practice, this is achieved by laminating the optical fibers between two flexible copper-clad laminates. After the fibers are secured in the adhesive core, channels are created—typically via laser ablation—that extend through the layers to reach the opposing conductive planes. These channels are then plated with metal to create vertical conductive walls. When combined with the horizontal copper planes, these plated walls form a conductive cage that surrounds the fiber optic core.

This approach differs from prior solutions that simply bonded fiber ribbons to the surface of a PCB or routed them through separate dedicated layers. By utilizing plated-through channels to bridge the top and bottom substrate layers around the fiber, the invention creates a robust, integrated conduit. This design not only protects the delicate glass or plastic waveguides but also allows the surrounding metal structure to serve as an electrical conductor or shield while the interior carries optical data.