Dr. Jolyon Browne asked about the elemental composition and the density of
the board material of a typical PCB.

Perhaps the following passage from an article by Wu et al. (1993) in the 
IBM Journal of Research and Development helps:
  "The first epoxy, a Ciba-Geigy FR-4 resin (Tg ~125C), consists of a
   mixture of brominated diglycidyl ether of bis-phenol A and an 
   epoxidized cresol novolac with dicyandiamide as the hardener. 
   The second epoxy, a Ciba-Geigy resin (Tg ~175C) with higher Tg
   (called 'high-Tg' in the remainder of the paper), consists of an
   epoxidized cresol novolac and tetrabromobisphenol A hardener 
   with 2 methyl imidazole catalyst." 

Wu et al. give the density of the first as 1350 kg/m^3, and the second 
as 1550 kg/m^3, with E glass having a density of 2540 kg/m^3.

These densities seem a little high to me, I have seen in the literature 
values for FR-4 ranging from 220 kg/m^3 [Barker et al., p. 150]  
to 1800 kg/m^3 for FR-4 and copper planes [Mahaney, p. 613]


Cheers,  
	Andy



References:

Barker, D., Pecht, M., Dasgupta, A., Naqvi, "Transient Thermal 
Stress Analysis of a Plated Through Hole Subjected
to Wave Soldering," Journal of Electronic Packaging, 
Vol. 113, No. 2, 1991, pp.149-155.

Mahaney, H. V., "Thermal modeling of the infrared reflow process for 
Solder Ball Connect (SBC)" IBM Journal of Research and 
Development, Vol. 37, No. 5, September 1993, pp 609-619.

Wu, T. Y., Guo, Y., Chen, W. T., "Thermal-mechanical strain 
characterization for Printed Wiring Boards," IBM Journal of 
Research and Development, Vol. 37, No. 5, September 1993,
pp.621-634.

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