Conditioning the paste at 40°C for 1 month is an accelerated aging test. It is designed to see if there would be any change in paste performance should it be exposed to elevated temperatures for a brief period, such as in the case of ground shipping conditions in very warm climates. No change in solderability was observed after paste conditioning. Examples illustrated here in the photo are 0.5 mm pitch BGA devices and 0402 resistors. Also, no change in reflow performance was observed. Solder joints after reflow are shiny and smooth.