THE USE OF A SIMULTANEOUS TGA DSC FT-IR SYSTEM AS A PROBLEM-SOLVING TOOL

Thermal analysis (TA) of complex samples has been greatly assisted by the coupling of Fourier transform-infrared spectroscopy (FT-IR) analysis to the TA experiment. Evolved gas analysis has been very successful in combined TGA/FT-IR experiments, whereas during a combined differential scanning calorimetry (DSC)/FT-IR experiment, the FT-IR analysis has generally been directed at the sample itself. By combining a simultaneous TGA/DSC instrument with FT-IR evolved gas analysis (STA/IR), we are now able to obtain three sets of complementary information on the same sample in one experiment. An STA/IR study of a sample of zinc stearate was made to demonstrate the operation of the instrument. This demonstrated that the sensitivity of the FT-IR analysis was greater than that of the TG analysis, as a small amount of water vapour was released during the sample melt, even though no weight loss was measured at the same time. Practical applications of this instrument combination include the detailed examination of various formulations of solder paste and an epoxy-based encapsulant. Solder pastes from three vendors were shown to contain different organic species, and to lose these organics at different rates under different atmospheric conditions, to give varying residual levels of organics. The encapsulant samples were shown to contain different, albeit very low, levels of an ester species, which may explain their different physical behaviour.