What Does it Mean When Components Tombstone?

“Tombstoning” is a phenomenon that can occur with surface mount electronic components during the Reflow Soldering process in PCB Assembly. When a component tombstones, one end lifts up vertically from the solder pad while the other end remains attached. The component ends up standing on end like a tombstone in a graveyard, hence the name.

Tombstoning is a defect that results in an open solder joint and a non-functional circuit board. It can be difficult to detect visually and often requires x-ray inspection to identify. Rework is usually required to correct tombstoned components by reflowing the solder to reattach the lifted end.

Some common component types prone to tombstoning include:

Component	Package
Resistors	0201, 0402, 0603
Capacitors	0201, 0402, 0603
Inductors	0402, 0603
Diodes	SOD-123

What Causes Components to Tombstone?

There are several factors that can contribute to tombstoning of surface mount components:

Uneven Heating

If one solder pad heats up and reflows before the other, the surface tension of the molten solder can pull the component up into a vertical tombstoned position. Causes of uneven heating include:

• Density of surrounding copper – more copper retains more heat
• Component orientation – perpendicular to direction of board travel through oven
• Proximity to larger components that shadow smaller ones

Solder Paste Issues

Using too much or too little solder paste can increase tombstoning risk. Too little solder may not provide sufficient surface tension to hold the component down on both pads. Too much solder, especially on smaller pads, has more surface tension to lift the component.

Other solder paste problems like poor registration, smearing, or inconsistent deposition can also cause imbalanced forces.

Component Geometry

Smaller, lightweight 2-terminal components like 0201 chip resistors and capacitors are most susceptible to tombstoning. There is less surface area on the component terminations in contact with the solder to anchor it down.

Components where the terminations are offset or not an equal distance from the center of mass are also at higher risk. The imbalance can allow one end to lift easier.

Board Conditions

Any warping or sagging of the circuit board during reflow can angle components and make it easier for one end to pull away from the pad. This is more likely to happen with thinner boards.

Contamination or oxidation on the component pads can interfere with solder wetting and result in a weaker joint on one end. Bent or non-coplanar leads that don’t sit flat also promote tombstoning.

How to Prevent Components from Tombstoning

Fortunately, there are many steps that can be taken in the design, component selection, and assembly process to minimize tombstoning:

PCB Design

• Maintain equal thermal mass of copper on both component pads
• Avoid unequal distances of pads to plane layers or thermal relief connections
• Route traces symmetrically off pads when possible
• Use larger pad sizes for smaller components
• Follow component manufacturer’s land pattern recommendations
• Panelize boards to promote consistent flatness

Component Selection

• Use slightly heavier/larger components when possible (0603 vs 0402)
• Choose components with flat, symmetrical terminations
• Avoid components with unequal termination offsets
• Consider alternative packages like molded/square tantalum capacitors

Solder Paste & Stencils

• Optimize paste deposition volume for component size
• Use type 4 or 5 paste for small chip components
• Reduce stencil aperture size and/or thickness for less paste
• Ensure proper gasketing and registration during paste printing
• Inspect prints frequently for defects or inconsistency

Placement & Reflow

• Align placement to account for any known offsets or asymmetry
• Decrease placement pressure to avoid disturbing paste deposits
• Optimize oven profile to achieve even heating across board
• Reduce ramp rate and increase soak time in reflow profile
• Minimize board vibration or jarring during transfer to oven
• Monitor and control oven temperature and conveyor speed

FAQ on Component Tombstoning

What is the main cause of tombstoning?

The primary cause of tombstoning is uneven heating and reflow of solder joints on opposite ends of a component. If one end melts and forms a fillet before the other, the surface tension of the liquid solder can pull the component up vertically.

Are some components more likely to tombstone than others?

Yes, smaller lightweight 2-terminal chip components like 0201 and 0402 resistors and capacitors are most prone to tombstoning. The less contact area between component termination and solder pad, the easier it is for the part to stand up on one end. Components with unequal termination offsets are also at higher risk.

Does solder paste have an effect on tombstoning?

Definitely – applying too much or too little solder paste can increase the likelihood of tombstoning. Too much solder, especially on small terminations, means more surface tension to potentially lift the part. Too little solder may not anchor the component securely to the pads. The solder particle size, alloy, and print quality also play a role.

How can you detect tombstoned components?

Tombstoned components can be difficult to see during visual inspection, especially for small chip sizes. The lifted end may only be separated from the pad by a few mils. Often x-ray inspection is needed to conclusively identify components that have tombstoned and resulted in open solder joints. Electrical test will catch any opens in the final assembled boards.

What has to be done to fix tombstoned components?

Tombstoned components have to be reworked by reheating and reflowing the solder joint to reattach the lifted termination back down to the pad. This is usually done with a targeted hot air rework station or soldering iron. Care must be taken not to damage the component or laminate. In some cases, the defective part may need to be removed and replaced entirely.

I hope you found this in-depth article on component tombstoning informative and helpful! Let me know if you have any other questions.