Packaging materials, thermally generated

Thermally Generated Volatile Compounds in Packaging Materials... 

The conditions under which the device is thermally characterized have to be clearly described. In fact, thermal resistance is made up of constant terms that are related to device and package materials and geometry in series with a number of variable terms. These terms are related to the heat paths from the package boundary to some point in the system that serves as the reference temperature and are determined by the method of mounting, the printed-wiring-board (PWB) if used, other heat generating components... 

The empirically generated field life prediction relationships that have been utilized for Pb-Sn solders are not automatically applicable to Pb-free solders. Solder joints as noted experience stresses due to thermal excursions, excessive electrical current, and also due to various mechanically applied loads. The tolerance or resistance and responses to stress as a result of these sources are typically different for Pb-free solders compared to the benchmark eutectic Sn-Pb solder. As noted, stresses in a solder joint can result due to a coefficient of thermal expansion (CTE) mismatch between package materials, but can also be due to temperature fluctuations caused by power transitions or environmental changes given the complexity of some modem microelectronic package structures and the environments they are placed in respectively. 

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