The term "thermal mass" is often used interchangeably with "thermal capacitance" and "thermal inertia". It is important during transient conditions, when something happens to make component temperatures change (change in external temperature or pressure, for example). Components with more thermal mass will change less rapidly than those with very little thermal mass. The thermal mass (usually thermal capacitance in textbooks) is used to determine the thermal time constant of the component. The formula time constant = thermal resistance x thermal capacitance gives the time necessary to complete about 63% of the change from the initial temperature to the final temperature. I hope this is the information you wanted. You may E-mail me at [log in to unmask] if I can be of further assistance. Bruce Smith Smiths Industries Hi, How do people claim the existence of thermal mass issue? Say if I have a PWA with large and small components. Do I measure the surface temperature of those components and relate the issue to the temperature discrepancy? OR do I measure the temperature underneath the lead (or even the bottom of the components)? Thank you very much. Regards, Victor *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To unsubscribe from this list at any time, send a message to: * * [log in to unmask] with <subject: unsubscribe> and no text. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************