If one termination reflows and wets before the other, surface movement is generated either rotational or vertical. The different solderability of each termination has also be shown to cause lifting.

The use of vapour phase reflow is more likely to cause movement than convection due to the fluid movement on the board surface.

The example shown on the left is lifted because of the thick solder mask, during reflow it acted like a fulcrum lifting the part just above the pad surface.

The defect on the right, is often referred to as tombstoning, draw bridging or Manhattan skyline, particularly if there are many parts all standing vertically.

The defect is caused by uneven wetting where one termination solders before the second causing the surface tension of the solder to pull the device in one direction.

It can be exaggerated by the amount of paste on small parts, 0805 chips and below or incorrect pad sizes increasing movement during reflow.

Solder paste under components can cause the parts to lift before both terminations have soldered.

In this case the same causes attributed to solder beading apply; it is only the end results which are different.

Tombstone failures are also attributed to lead-free solder paste & blind vias.