Phenolaldehyde resins particularly phenolformaldehyde resins are manufactured by replacing a proportion of the phenol content by a mixture of at least two different natural materials having a phenolic content. The uncured spacer body may include a curable material, and an activatable heat generating material mixed with the curable material. Further, a phase detector in communication with the first clock generator and the second clock generator is provided for receiving the first clock signal from the first clock generator and the second clock signal from the second clock generator, and outputting a phase difference signal that is capable of being used as a measure of an integrated circuit age.