Tombstoning (Manhattan Effect): Causes, Detection and Prevention

Tombstoning, also called the Manhattan effect or drawbridging, is a reflow defect in which a small two-terminal chip component, usually a resistor or capacitor, lifts off one pad and stands up on its other end. The raised termination has no solder connection, so the circuit is open even though the part appears to be on the board.

What causes tombstoning?

Tombstoning happens when the solder at one end of a chip melts and wets before the solder at the other end. The surface tension of the molten side pulls on its termination, and on a light part such as an 0402 or 0201 chip (imperial sizes), that pull is enough to rotate the component upright. Anything that makes the two ends unequal can start it:

• Solder paste: unequal paste volume on the two pads, or a deposit offset so one termination sits in more paste than the other.
• Stencil: asymmetric apertures, or a partly clogged aperture that starves one pad.
• Reflow profile: a fast ramp through the melting point, so one end reaches liquidus well before the other, and no soak to even out board temperatures.
• Placement: an X or Y offset toward one pad, or low placement force that leaves the part sitting on top of the paste instead of seated in it.
• Component and pad design: one pad tied to a large copper plane without thermal relief, a via in one pad only, unequal pad sizes, or a pad gap too wide for the termination length. Poor solderability on one termination has the same effect.

Tombstoning is closely related to component shift and skew: the same imbalance that stands a chip on end often just drags it sideways instead.

How is tombstoning detected?

Manual inspection finds a fully raised 0603 easily, but a partly lifted 0201 is hard to see without magnification.

SPI cannot see a tombstone, but it measures the most common cause: a volume or area imbalance between the two pads of a chip. Tracking pad-to-pad balance on small passives is one of the most useful SPI checks for this defect.

2D AOI sees a standing chip as a change in body footprint, a bare pad on one end and an unusual reflection from the upright termination. A part lifted only a few degrees is harder to judge from a top-down image. 3D AOI measures height, so a raised end becomes a measured step rather than an inference from shading. AXI is rarely needed, since tombstones are visible from above.

In DaoAI's inspection coverage, tombstoning is part of item 02, Placement, Orientation & Polarity, alongside billboarding (a chip resting on its side) and X/Y offset. AI auto-programming includes tombstoning among the component checks it generates from one golden board, so small passives are covered without teaching each package by hand. On DaoAI's 3D machines, item 04 also measures component height and detects lifted or tilted bodies.

How to prevent tombstoning

Tombstoning is a balance problem: both ends of the chip need the same paste, heat and timing. If it repeats at the same designators, look at pad design and profile first.

Some lines see more tombstoning on very small chips in nitrogen reflow, because wetting is faster and less forgiving of imbalance. If the defect appeared after a change to nitrogen, test the profile in both atmospheres.

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FAQ

Why is tombstoning called the Manhattan effect?

A board with many chips standing on end looks like a skyline of tall buildings, which gave the defect the name Manhattan effect. It is also called drawbridging, because the part lifts like a drawbridge from one end.

Which components are most prone to tombstoning?

Small, light two-terminal chips such as 0402, 0201 and 01005 resistors and capacitors are most prone. Their low mass means surface tension at one termination can easily outweigh the part.

What is the difference between tombstoning and billboarding?

A tombstoned chip stands upright on one end, with one termination off its pad. A billboarded chip lies on its long side, so both terminations may be soldered but the part is rotated 90° onto its edge.

Can AOI detect a partially lifted chip?

2D AOI detects it once the lift changes the image enough, such as exposing bare pad or changing the body outline. 3D AOI measures the height difference between the two ends directly, which makes small lifts easier to confirm.