interconnects

Interconnects are the physical pathways that link components within an electronic system. They encompass copper traces on printed circuit boards, vias in multilayer substrates, and packaging interconnects such as wire bonds or solder bumps that attach integrated circuits to their packages. In high-speed systems, interconnects may also include cables and fiber-optic links that carry signals between subsystems.

Interconnects operate at multiple levels. On silicon, metal interconnects form the back-end-of-line network that routes signals and power between transistors. In packaging, interconnects connect chips to substrates or to each other. In PCBs, copper traces and vias route signals between components and layers. Optical interconnects are increasingly used for long-distance or high-bandwidth links in data centers and telecommunication networks.

Design considerations focus on signal integrity and reliability. Parasitics from resistance, capacitance, and inductance affect timing and bandwidth. Crosstalk, impedance matching, and controlled dielectric environments are managed through layout practices and material choices. Electromigration, thermal expansion, fatigue, and mechanical stresses influence longevity of solder joints, bonds, and vias.

Materials and manufacturing have evolved with technology. Copper is standard for conductors, with dielectrics chosen to minimize capacitance. Solder, wire bonds, copper pillars, and flip-chip bumps provide the interfaces between devices and packages. Manufacturing processes include lithography, plating, etching, and chemical-mechanical planarization, as well as reliability testing and screening.

Emerging trends include 3D integration and through-silicon vias (TSVs) that stack chips to reduce interconnect length, and advanced packaging techniques such as fan-out wafer-level packaging. Optical interconnects and silicon photonics are used to overcome electrical limits at very high speeds. Ongoing research addresses materials, reliability, and cost to sustain scaling.