Solder Tombstoning Issues During Reflow
FCT Field Application Engineer Tony Lentz
discusses tombstoning causes and solutions.
Nothing kills a PCB quite like tombstoning.
It’s a familiar foe for most manufacturers in the industry, especially as form factors continue to shrink.
Tombstoning happens when small components, such as chips, flip up during the reflow process. Tombstoning is also sometimes called “billboarding” (when the chip flips on its side instead), “the drawbridge effect,” “the Stonehenge effect,” and “the Manhattan effect.”
Tombstoning is linked to thermal differences from the pad at one end of the component to the other. One pad reflows before the other creating a force which can pull up the component causing a tombstone.
What causes tombstoning, and why is it a problem?
Tombstoning is a huge problem because it creates a disconnection on the PCB. It can be caused by various factors, including:
- Thermal inequalities between solder joints, where one solder joint warms up faster than the other and melts first. This creates a force that pulls the component and flips it into a tombstone condition.
- Ground plane circuit board designs, where one end sits on a ground plane and one end sits on a normal pad.
- Solder paste that isn’t applied evenly, or with too much paste on the ends.
- Pad designs that incorporate pads that are too large for the chip component.
Experiencing tombstoning issues? Need help solving a solder problem?
Give our engineers a call to talk things through and find a solution.
How to Prevent Tombstoning
There are a variety of solutions you can try to minimize tombstoning. Of course, every application is different, and you won’t always be able to apply all of these. You’ll have to take stock of your project and the trade-offs required.
1. Go with an anti-tombstoning solder paste.
Since we make solder pastes, this is one we’ve thought about a lot here at FCT Solder!
Anti-tombstoning solder pastes work by using a mixture of solder alloys with a wider melting range, which helps both ends of the components melt over the same time period.
Our anti-tombstoning pastes not only reduce the chances of tombstoning and skewing but also reduce the potential for solder voiding, too.
2. Mix up your reflow profile.
Try modifying the reflow profile to equalize temperature variations across the affected component. A longer soak time can help even heating from end to end of a component, as can reducing the ramp rate.
3. Modify the stencil design.
Take a look at your stencil design, especially for the trouble component, and try to equalize the solder paste deposit in that area. Move the paste deposit away from the ends (and towards the middle) or the component.
Resources to Help with Tombstoning
See our technical data sheet for more help with tombstoning and insight into which FCT Solder products can help solve the problem.