Investigation of Delamination and Foaming by TMA-MS

Introduction

Thermomechanical analysis (TMA) measures the dimensional changes of a sample as a function of temperature. The online coupling of TMA with mass spectrometry (MS) allows the simultaneous measurement of decomposition gases and blowing or foaming agents and their effect on sample dimensions. For example, it is possible to investigate the delamination of printed circuit boards to determine the temperatures at which particular decomposition products are formed, or to follow the behavior of plastics on blowing or foaming.

TMA combined with a gas analyzer (MS or FTIR) allows the dimensional changes caused by decomposition processes to be rapidly investigated or foaming processes to be optimized. A METTLER TOLEDO STARe system TMA/SDTA840 was coupled to an Inficon Thermostar QMS300 mass spectrometer (mass range 1-300) by means of a heated capillary in much the same way as for the TGA-MS coupling [1].

Delamination and Decomposition of a Printed Circuit Board

Printed circuit boards (PCBs) are manufactured from woven fiberglass embedded in an epoxy resin matrix and are used as supports for electronic components. Disks (4 mm diameter and 1.683 mm thick) were prepared from the material and the expansion behavior of the samples measured using a ballpoint probe with a load of 0.05 N. The samples were first heated up to 100 °C to remove any “memory” effects, then cooled and heated from von 30 °C to 650 °C at 20 K/min under a protective atmosphere of nitrogen (10 ml/min).

The PCB sample measured exhibits a glass transition at 92 °C. This can be seen as a change in slope in the curve in Figure 1. The sudden dimensional change the z-direction at temperatures above 320 °C indicates that the sample begins to delaminate.

This process was followed simultaneously with MS by measuring the intensities of the m/z 79 and 94 fragment ions. Theses m/z values are characteristic of bromine and methyl bromide, i.e. decomposition products of tetrabromobisphenol A (TBBA, flame-retardant). Reaction products containing bromine can even be detected immediately after the glass transition. The rapid increase in the formation of bromine-containing decomposition products above 330 °C also indicates the reason for the delamination process.

Expansion Behavior of a Polymer Powder

Plastic granules containing a dissolved gas or a chemical blowing agent exhibit unique properties when exposed to heat. The increase in the vapor pressure of the blowing agent and the softening of the polymer result in a large increase in volume in the temperature range 80 °C to 190 °C. The increase in volume can be easily measured with TMA.

Summary

The application possibilities of an online combination of a thermomechanical analyzer and a mass spectrometer (TMA-MS) were demonstrated by using the system to measure a printed circuit board and an expandable copolymer. Changes in the dimensions of the sample were correlated with the release of gaseous substances. Qualitative information on the composition of the samples was obtained by mass spectrometry. TMA-MS is an excellent technique to investigate the influence of temperature on sudden changes in volume and the reasons for such changes.

_{Investigation of Delamination and Foaming by TMA-MS | Thermal Analysis Application No. UC 157 | Application published in METTLER TOLEDO Thermal Analysis UserCom 15}