A: These are very different properties and need to be considered individually. Glass Transition Temperature (Tg) is related to molecular free volume. A resin system exhibits changes in physical properties, such as an increase in the rate of Z direction expansion. Because Z-direction expansion impacts plated through hole reliability in PWB fab and subsequent assembly processes TMA is often used to characterize Tg. On the other hand, Decomposition Temperature (Td) is that temperature at which chemical bonds in the resin system actually start to break, resulting in emission of gaseous components. Weight loss measured by TGA is the standard method of determining Td. For your application you may want to try a High Tg multifunctional epoxy system such as Arlon's 45N (Tg 170oC, Td 295oC. For very high layer count builds a higher Tg material such as polyimide might be desirable, especially if PTH reliability is critical. Arlon's 35N polyimide (Tg 250oC, Td 361oC) with a total Z expansion from room temperature to 250oC of only 1.1% is an optimal material for high temp process and end use application. Newer products such as Arlon's 210oC Tg 11N, a chemically modified epoxy system originally designed for the Burn-In industry may also be of interest. For additional information about Arlon solutions to with you temperature or stability problems, contact your Arlon sales or technical service representative or call Arlon directly at (909) 987-9533.
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