Craig, Here's my understanding: On a local level, an increase in temperature results in a decrease in relative humidity. On the global level, the moisture content is constant. Some assumptions include the ability of the oven to maintain the conditions, a fixed pressure, and moisture penetration within the board. Calculations require use of vapor pressure tables (one source, CRC Handbook). Based on your conditions, I calculate a local relative humidity of 5.1% Hope this helps, Glenn Ref: 1) http://www.usatoday.com/weather/whumcalc.htm 2) CRC Handbook of Chemistry and Physics 3) Accelerated Testing Handbook, Peck and Trapp Craig Hillman <[log in to unmask]> Wrote: | | An environmental question: | | I have a board operating in a 30C, 70%RH environment. The board | is operating at 85C. How do I determine the humidity level at the | board? | | 1. Is the moisture concentration and the RH lower than ambient | because of evaporation? | 2. Is the moisture concentration the same and the RH lower because | of a higher temperature (and thus higher solubility limit)? | 3. Is the moisture concentration and the RH higher than ambient | because the higher temperature results in a higher solubility limit? | | Thanks in advance, | Craig ############################################################## TechNet Mail List provided as a free service by IPC using LISTSERV 1.8c ############################################################## To subscribe/unsubscribe, send a message to [log in to unmask] with following text in the body: To subscribe: SUBSCRIBE TECHNET <your full name> To unsubscribe: SIGNOFF TECHNET ############################################################## Please visit IPC web site (http://www.ipc.org/html/forum.htm) for additional information. If you need assistance - contact Gayatri Sardeshpande at [log in to unmask] or 847-509-9700 ext.5365 ##############################################################