1. What is the relative humidity inside my package?

The relative humidity of air is the percentage of moisture contained in the air relative to the fully saturated state of the air and is a function of both pressure and temperature.

For a finite volume (such as a semiconductor package) we can look up the low temperature, saturated steam tables in the Handbook of Physics and Chemistry and determine the vapor pressure of water at a given temperature. However, finding information on the equilibrium characteristics of the environment may prove difficult. It is possible, for example, to have a closed environment maintain 100% RH over a wide temperature and pressure range and yet never have a liquid condensate present. The materials used in modern semiconductor devices can include epoxies, polyamides, desiccants, adhesives, and other materials which can take up or release water and maintain equilibrium with the closed environment over a broad range of pressures and temperatures. The concept of relative humidity is difficult to apply to a closed system.

2. 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 laboratories, it is essential that the recipe for calibration is considered as well as the recipe for measurement.

3. Why is my package full of water?

When a manufacturer offends the Moisture Gods, bedlam is sure to follow. The Pernicka Corporation has been in constant negotiation with the Moisture Gods over the past 40 years and has developed numerous approaches to quelling their anger. We provide consulting services to try to help appease the Moisture Gods and allow a manufacturer to produce dry packages.

4. How can I convert percent per unit volume to ppm?

1.0% per unit volume = 10,000 ppmv.

5. How accurate is my data?

At Pernicka Corporation our mass spectrometers are checked daily to ensure that the following accuracy for standard analytical procedures, traceable to NIST, is routinely maintained: