What is Response to Pause in Solder Paste?

During the PCB Assembly process, SMT lines often need to be stopped to replenish components in the pick and place machines or fix a faulty machine. During this pause, the solder paste being used can stiffen. The stiffening causes inconsistencies in the volume of the solder being deposited on the board. Large volume variations in solder during the printing process are not wanted and can lead to defects like shorts or opens. This is not a desirable property of solder paste. The time the solder paste takes to stiffen is called Response to Pause (RTP).

Good solder paste should have low RTP value. Response-to-pause (RTP) is measured by the difference in volume of solder paste deposition as a function of number of prints and pause time.