Humidity and condensation can negatively affect the reliability, longevity, and performance of electronic test equipment.
What are Humidity and Condensation?
Humidity is the presence of water vapor in the air. It is commonly described in terms of:
- Relative humidity, the amount of water vapor in the air as a percentage of the total amount that could be held at its current temperature.
- Warm air can hold far more moisture than cold air meaning that the relative humidity of cold air would be far higher than warm air if their absolute humidity levels were equal.
- Relative humidity is the parameter most often used to describe atmospheric conditions inside and outside of buildings.
- Absolute humidity, the mass of water vapor in a volume of air
- Dew point, the temperature of the air at which water begins to form on surfaces.
These three measures are effectively not dependent upon air pressure (elevation).
Condensation is the liquid water that forms on surfaces. It can take the form of droplets or a thin layer of water molecules across the surface and in micropores onto a material (circuit boards and components).
Effects of Humidity and Condensation on Electronics
Humidity can affect electronic equipment in several ways:
- Absorbed moisture can cause changes in the properties of printed circuit board materials.
- DC impedance of insulating material between traces can be reduced.
- It will affect transmission line parameters (e.g., phasing and timing) as permittivity changes.
- Swelling of board material can change critical distances between layers.
- Absorbed moisture can affect the properties and reliability of unsealed components and plastic parts.
- Moisture adsorbed from humid air can be attracted by surfaces of circuit boards and components, hydrolyzing contaminants and creating corrosive or reactive conditions.
- Liquid water can enable the growth of conductive dendrites between traces and across component leads.
- Liquid can cause surface contaminants (e.g., dust, chemicals, pollution deposit) to become conductive or corrosive.
- Condensation can absorb into the material and change its structure (printed circuit board delamination or swelling).
- A thin film of condensation, which is pure water saturated with oxygen, is very corrosive on susceptible surfaces.
The Psychrometric Chart and Facility Design and Management
The Psychrometric Chart depicts the typical parameters (moisture content and temperature) used to describe moist air. The specified operating region shown below is typical of many Keysight products. Keysight products will meet performance specifications at the extremes of the specified region but extended operation at those extremes is not recommended. The recommended operating region describes the conditions for maximum product longevity.
Designing and Managing Facilities for Heating, Ventilation, and Air Conditioning (HVAC)
- Facility designers use the psychrometric chart to manage temperature and humidity for
- Human comfort
- Dust and pollution control
- Prevention of mold and bacteria growth
- Limits of equipment performance specifications
- They also are concerned with control of pollution and dust inside the facility
1) IEC 61010-1 (Safety Requirements for Electrical Equipment for Measurement, Control and Laboratory Use – Part 1: General Requirements); UL 61010-1 and EN 61010-1
2) International Union of Pure and Applied Chemistry, Division of Physical Chemistry, Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II (1971)
3) R A Francis, “Humidity and Dew Point: Their Effect on Corrosion and Coatings”, ACA Annual Conference, November 2002, Adelaide, Paper 016
4) HP Technical White Paper, “Applying 2011 ASHRAE data center guidelines to HP ProLiant-based facilities”.
5) Thermal Guidelines for Data Processing Environments, 4th Ed. (2015)
6) Dayton ASHRAE Psychrometric Calculator
ASHRAE Dayton Chapter, Dayton, Ohio, USA
By John Bishop, Product Regulatory Engineer, Keysight Technologies, Inc.
and Bill Pritchard, Quality Engineer, Keysight Technologies, Inc.