redistribution layer (rdl)

Redistribution Layers (RDL) are thin-film metal interconnect layers that reroute electrical connections from fine-pitch die bond pads to larger-pitch package connections, enabling area-array I/O distribution and advanced packaging architectures. RDL uses semiconductor-like processing (photolithography, metal deposition, dielectric deposition) to create multiple layers of wiring on wafers or panels. Typical RDL has 2-5 metal layers with 2-10μm line width and spacing. RDL enables fan-out packaging where interconnects extend beyond the die area, allowing larger bump pitch for board assembly while maintaining fine pitch at the die. This eliminates the need for traditional substrates, reducing cost and thickness. RDL also enables heterogeneous integration by routing connections between multiple dies. Materials include copper for conductors and polyimide or polybenzoxazole for dielectrics. RDL processing can be done at wafer level (FOWLP) or panel level for higher throughput. Applications include mobile processors, RF modules, and sensors. RDL quality affects signal integrity, power delivery, and reliability. The technology enables thin, high-density packages critical for mobile and wearable devices.