How do I relate dewpoint, relative humidity, and ppm of moisture?
Let’s begin with the definition of dew point that is the temperature to which the air would have to be cooled (at constant pressure and constant water vapor content) in order to reach saturation. In a finite or closed environment, such as a semiconductor package, we do not have the proper conditions that permit the definition of dew point to be valid. As we cool the package, both the internal pressure and the moisture content change. So perhaps dew point is not a relevant term when trying to describe the moisture content of a hermetically sealed semiconductor package. The measurement of moisture per the Mil-Std in a semiconductor package is expressed in per cent per unit volume (where 10,000 ppmv = 1.0%) following a specific measurement recipe. Measurements made following the same recipe can be compared. Other recipes (such as tests conducted at 37C for medical devices) only produce data which is relevant to themselves. When comparing moisture measurements made at different laboratorie
