On the FO-WLP line, RDL stability starts at bake. A 1°C swing during photoresist soft bake or encapsulant cure will pull linewidth, invite voids, and kill wafers that already cleared lithography. We built the fan-out wafer level packaging heater to keep thermal behavior honest, shift after shift. Here is the technical heart of it. The unit leans on short-wave infrared with a quartz-halogen emitter array, so it ramps fast to setpoint without overshoot. Across the full 300 mm field, wafer-level uniformity holds ±0.1°C at typical soft bake temperatures (90–120°C) and hard bake setpoints (100–150°C). Cleanroom Class 1–100 compatibility comes from 316L stainless construction, PVDF insulators, and zero particle generation verified by in-situ particle monitoring. The controller keeps the temperature loop closed in real time, holding repeatability within ±0.2°C lot-to-lot and day-to-day. FO-WLP stacks run on a tight thermal budget. This heater protects that budget by staying on spec, even under 7×24 operation. Expect zero unplanned downtime in continuous production, with MTBF exceeding 10,000 hours. The upshot: fewer reworks, stable critical dimension control, and cycle time you can count on. Energy draw stays lean thanks to low thermal mass and efficient emitter coupling, so operating cost drops without sacrificing temperature accuracy. Installation comes down to matched tool interfaces and verified exhaust routing to maintain cleanroom pressure differentials. You get peak performance when the heater aligns within ±1 mm of the target chuck and the cooling path stays clear of debris. Plan on a one-day integration window, then a short qualification run to lock your recipe in.