Epoxy resins are used extensively to manufacture printed circuit boards. The most demanding use for these is in data processing equipment. The necessity for reproducible, well defined final properties requires stringent inspection of all starting materials, processes, and the final composite. Because epoxy is the component subject to the most variations, it, and the properties it imparts to the board, must be monitored throughout manufacture. Incoming inspection is critical because of the need to maintain constant processing parameters. Therefore, many tests are performed to measure physical and chemical properties and make any adjustment needed in the level of catalyst, solvent, etc. As the composite progresses, the emphasis switches to mostly physical properties that will define how the product will hold up in actual use. Any printed circuit board that does not meet the high standards is rejected.