Most solder pastes state that they can only be run at certain humidities, for the water soluables that I have used in the past, it is 40-60% Below 40% the paste starts to dry out, above 60% it starts to absorb moisture and becomes really soupy. As you have already seen, you can run the paste outside the stated conditions for a short period of time, but it will start to change over time. Some advanced screen printers have an airconditioning unit in them to help prolong stencil life of the paste. Humidity control is very important for the solder paste process!!! Your question brings up something else. You stated that you are at 14% humidity ---------------DANGER WILL ROBINSON!!!!!!!!!!!---------------- Running at 14% humidity level increases the ESD problems. The suggested humidity for an electronics facility is 40-60%. Low humidity increases the ESD concerns, high humidity could create moisture absorbtion problems in components. ------------- Original Text From: C=US/A=INTERNET/DDA=ID/TechNet-request(a)ipc.ipc.org, on 2/20/97 7:51 AM: Hello, We are having problems with our paste tack time not lasting as long this time of year. We are running at 14% humidity now, normal is about 40% to 50%. We are using a water soluble paste, 90% metal content, with a quoted tack time of 6 hours on stencil, and 6 hours on board. We are seeing problems after 3 to 4 hours. Does anyone have experience to say this is normal for the humidity, or ideas as to what we could be doing wrong.(I know of plenty myself, but still would appreciate more). Thanks Steve Quinn Heurikon Corp *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * *************************************************************************** *************************************************************************** * TechNet mail list is provided as a service by IPC using SmartList v3.05 * *************************************************************************** * To subscribe/unsubscribe send a message <to: [log in to unmask]> * * with <subject: subscribe/unsubscribe> and no text in the body. * *************************************************************************** * If you are having a problem with the IPC TechNet forum please contact * * Dmitriy Sklyar at 847-509-9700 ext. 311 or email at [log in to unmask] * ***************************************************************************