This month we look at solder paste slump during preheating. It is important to know how much, if any, of the paste slumps like butter on a hot day during reflow. If solder paste does slump, it can lead to shorts, solder balls or solder beads, or cause variations in solder joint volume on selected joints. Variation in joint volume occurs when one joint acquires more solder from an adjacent joint during reflow due to the paste being linked. Testing of solder paste is well covered in IPC specifications, and equipment is available to test paste and record the results.
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