How do you prevent tombstoning of SMD chips?
Tombstoning lifts small SMD chips upright during reflow soldering. This guide explains the unequal wetting forces behind it and shows how to adjust pad design, paste volume and the reflow profile to prevent it reliably.
View soldering guidesWhat causes the tombstone effect?
Tombstoning (also called the Manhattan or drawbridge effect) occurs when the two terminations of a two-pin SMD component melt at different times. The surface tension of the first molten solder pulls the part upward, the opposite pad lifts off the board and the chip stands up vertically like a tombstone.
The root cause is always an unbalanced wetting force: one pad becomes liquid while the other is still pasty. Small, light chip components in sizes 0402, 0201 and 01005 are most at risk because their low mass barely counteracts the tipping moment.
- Unequal thermal mass of the pads, for example a large copper plane on only one terminal.
- Different paste volume or offset placement on the two pads.
- Too fast a temperature ramp, so the pads do not reach liquidus together.
- Contaminated or unevenly wettable component terminations.
How do pad and stencil design help?
Symmetry is the most important countermeasure. Both pads must be thermally identical and receive the same volume of solder. The land pattern per IPC-7351 provides proven pad geometries for every component size as a starting point.
If a trace or copper plane connects to only one pad, that pad acts as a heat sink and melts later. Attach wide copper areas through thermal reliefs so that both terminals reach liquidus at the same rate.
What roles do paste volume and reflow profile play?
Too much paste increases surface tension and the tipping moment, too little causes incomplete wetting. The key is an even, side-balanced deposit and a reflow profile that brings both pads over liquidus almost simultaneously.
A moderate ramp of about 1 to 3 K/s and a sufficient soak of 60 to 120 s at around 150 to 200 °C even out temperature differences across the assembly. For lead-free SAC305 solder the peak is typically 235 to 245 °C, with 45 to 90 s time above liquidus (217 °C).
- Match stencil thickness and aperture to the size, often 0.10 to 0.12 mm foil for 0201.
- Check placement accuracy; the target is a centred chip with no more than ±0.05 mm offset.
- Nitrogen reflow can improve wetting but, with an aggressive profile, increases floating.
- Verify the reflow profile with a thermal profiling run on the real assembly.
Frequently asked questions
Which components are most prone to tombstoning?
Mostly small two-terminal chips such as resistors and capacitors in sizes 0402, 0201 and 01005. Their low mass can barely counteract the tipping moment of the surface tension.
Does less solder paste help against tombstoning?
A slightly reduced but side-balanced paste volume lowers the tipping moment. More important than the absolute amount is that both pads receive exactly the same volume of paste.
What should the reflow profile look like?
A moderate ramp of 1 to 3 K/s and a sufficient soak zone even out temperature differences so both terminals melt almost simultaneously. The peak should be no higher than necessary.
Is tombstoning more common with lead-free solder?
Yes, lead-free SAC305 has a higher liquidus (217 °C) and different wetting kinetics, so timing differences at melting have a stronger effect. A carefully tuned profile is therefore even more important.
A reflow process free of tombstoning?
We supply solder paste, stencils and reflow accessories for reliable SMD soldering, matched to fine sizes down to 01005.
Standards based
Land pattern guidance per IPC-7351.
Profile know-how
Reflow profiles tuned for lead-free solder.
Process safe
Materials for reproducible results.
Expert advice
Soldering specialists help you choose.