Methods and apparatus for measuring the temperature of epoxy resin in an electronics package are provided herein. In some embodiments, apparatus for encapsulating an electronics package includes: a process chamber having a chamber body enclosing a processing volume; a substrate support having a support surface for receiving and supporting a substrate for forming an electronics package; and a temperature sensor to measure a temperature of an epoxy resin in an electronics package. The temperature sensor includes: an input apparatus including at least a light source disposed outside the chamber body to provide an excitation light energy to a portion of the epoxy resin; and an output apparatus including at least a signal analyzer disposed outside the chamber body to detect fluorescent light energy emitted by the portion of the epoxy resin and determine a temperature of the epoxy resin based on the excitation light energy and the fluorescent light energy.