One question that I often hear from customers is; “Once out of the refrigerator, how long do I have to wait to allow my solder paste and/or flux to reach room temperature in order to use it?”
It is indeed very important for solder pastes and fluxes to be at ambient temperature (approximately 23oC) in order for them to exhibit optimal performance, as the rheology of these materials will differ in a refrigerated state. Additionally, "cool" materials condense atmospheric moisture onto their surfaces (like a glass of cold water in the humid summer air). This condensed moisture is an unwanted ingredient in high quality soldering.
In order to quantify the amount of time necessary for these materials to reach room temperature, we refrigerated both solder paste and flux in 6oz cartridges. We then recorded the time it took to reach room temperature by placing thermocouple leads in the center of the materials through small holes that were drilled in the containers.
The following is a graph of the time versus temperature of warming both paste and flux:
For the testing above, the ambient temperature was approximately 22-24oC. The flux required approximately 2.5 hours to reach room temperature, whereas the solder paste required approximately 2 hours. It would be expected that the solder paste would reach room temperature faster than flux alone, as the metal content of the paste increases the thermal conductivity of the material.
Of course, your particular conditions (refrigerator temperature, container size and shape, ambient temperature, etc.) will make your situation somewhat different.
For questions regarding the proper handling and storage procedures for solder materials, please contact Askus@indium.com.