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In Figure 1, two chip components have shorted together during reflow soldering. In an ideal world on a perfect production process this may not occur, but designs should be robust to withstand the real world of manufacture. The defect shown could occur due to general placement errors, or due to movement during reflow soldering.

Figure 1: The component on the left was the result of either a placement error or movement during reflow soldering.

Solder shorts as shown in Figure 2 occur during reflow soldering for a number of reasons, the most common being too much solder paste, or more correctly, too much metal. When examining reflow problems, consider other causes as well, such as poor solderability of the leads or pads not allowing solder to wet as far as on previous occasions. Movement of the component during reflow due to poor control of convection rates or vibration in the conveyor can also be a culprit.

A common cause is incorrect reflow profiles causing shorting. If you try watching a part reflow, you will often see shorts forming initially as the paste slumps on fine pitch parts. In the liquid state, shorts will break as wetting occurs, when the solder is being stretched between the two pins. If the board assembly starts to cool at that point, a short will remain in place, hence it may be a profile issue.

Figure 2: The short shown here may be caused be an incorrect reflow profile.

Chip Leaching	Component Cracking	Cracked Joint	Crystallized Joints	Failure to Reflow
Joint Failure	Joint Voiding	Lifted Component	Open Joints	PCB Measelling
Plastic Coplanarity	Plastic Softening	Poor Pad Wetting	Poor Solderability & Wetting	Solder Beading
Solder Short	Solder Wicking