Definition
Tombstoning, also called the Manhattan effect or drawbridge effect, is a surface-mount soldering defect in which a small two-terminal component lifts off one pad during reflow and stands upright, anchored by solder at only one end. It almost exclusively afflicts tiny passives such as 0402 and 0201 resistors and capacitors, which are light enough for surface tension to overpower.
Why it happens
The root cause is an imbalance in the wetting forces acting on the two terminals. When solder paste at one end reaches its melting point and begins to wet before the paste at the other end, the surface tension of the molten solder pulls the component toward the wetted side. If that pull exceeds the weight of the part, it rotates the component up onto its end. Common contributors are asymmetric pad design, uneven thermal mass (for example one pad tied to a large copper plane), inconsistent paste deposition, and steep thermal gradients across a densely populated board.
Relevance to ASIC repair
On Bitcoin mining hashboards, tombstoning is more often seen during hot-air rework than original manufacture. Reflowing a stubborn chip or replacing nearby passives can disturb a neighboring component and stand it up if heat is applied unevenly. Even, controlled heating and a balanced thermal approach are the practical defenses. Diagnosing it visually is straightforward once you know the signature: a part perched vertically with one terminal in the air.
Tombstoning is fundamentally a heating-uniformity problem, which is why a board preheater and a measured reflow profile matter so much. Once a part has tombstoned it is functionally an open circuit, verifiable with a multimeter.
In Simple Terms
Tombstoning, also called the Manhattan effect or drawbridge effect, is a surface-mount soldering defect in which a small two-terminal component lifts off one pad during…