PCB Tombstone: Understanding, Prevention and Effects on PCB

What is PCB Tombstone?

Common occurrence issues on surface-mount technology are PCB tombstone, which impacts not only device functionality but also manufacturing efficiency. In this discussion, we analyze what leads down the path depending on what caused PCB tombstone and how to prevent it so your production will rollout smoothly and your electronic devices will be more reliable.

Other Terms for PCB Tombstone

PCB tombstone also has some other names. All of these terms refer to the same problem.

• Manhattan Effect
• Stonehenge Effect
• Crocodile Effect
• Drawbridge Effect

Causes of PCB Tombstone

• Imbalance in Solder Paste Volume

It’s when you put solder on the pad in an uneven manner and it gets reflowed that you get the imbalance. This is one side of the component is made to have more solder than the other. As it heats and cools the extra solder pulls harder on one side, it is a little extra solder. This exercise leads to an uneven force that lifts and causes the component to stand up. To prevent this the solder paste should have the same amount on all of the pads. The consistent paste is achieved by the use of a properly designed stencil.

• Component Placement Challenges

Placing components slightly off center can cause big problems when soldering. If parts aren’t aligned properly, they heat and cool unequally. That imbalance can cause one side that is stuck, while the other side is able to lift. Tombstoning is initiated even by small placement errors. Placement is critical and regular calibration of a pick and place machine can help prevent this problem.

• Thermal Gradient Variations

Sections of the board can become hotter than others during reflow, therefore causing our components to lift from the board. Some parts expand and contract unevenly more quickly than others. Such mismatch of forces can result in components tilting or tombstoning. This risk reduces when the heat is distributed evenly in the reflow oven. This can be fixed with proper thermal profiling of the board.

• Material Properties and Surface Tension

But the physical properties of the solder paste — its viscosity and stickiness — determine how well parts will stay in place. The metrics will vary if the solder can’t properly connect the component to the pad, so if these properties are uneven then things may be rough. It can also leave weak joints or lifting during reflow. This prevents problem by choosing the right solder paste and making sure it is consistently delivered.

• Surface Finish and Pad Design

How solder sticks is largely due to the type of finish on the PCB pads. Weak connections can be caused by poor surface finishes or bad pad design. It increases the possibility of components lifting during the soldering. Soldering reliability can improve using finishes like ENIG or HASL and pads can be designed correctly.

• Component Geometry and Size

The reflow behavior of components is influenced by shape and size. In components that are unevenly shaped or have large dimensions, heat may be uneven. This can cause a pad to lift one side. A design that helps to reduce the risk of tombstoning is to build with components that have a balanced design.

• Board Warpage and Flatness

Warped or uneven board can cause lots of soldering problems. How solder paste distributes and how heat is applied is influenced by warpage. Once these parts are heated in that environment they will start to expand and lift, which would cause inconsistency when soldering. Flat and well made boards give us even soldering conditions and eliminates tombstoning.

• Incorrect PNP Placement or Bad Stencils

Components placed incorrectly by the pick and place machine will not solder properly. Parts that are misaligned might be able to make weak connections or cause tombstoning. The bad stencils add to that problem too because that also leads to uneven solder paste. Once these factors are established proper maintenance and regularization of machines and stencils should help in avoiding these problems.

• Bad Reflow Oven Regulation

If the oven is not properly cared for, the solder can not be evenly heated. When the temperature isn’t consistent, this happens. Uneven heating of parts may occur causing parts to also lift during reflow. Correct thermal profile and keeping the oven calibrated will make sure that you get consistent soldering.

• Asymmetric Pads or Paste

If one has more solder or larger of the pads, it isn’t balanced. During soldering, the component will tilt and stand up. By applying equal solder paste, and matching pad sizes, this problem is solved. To develop symmetry is largely dependent on proper design / stencil use.

• Package Profile

Height of a component has bearing over its stability during soldering. The stronger forces come because taller components have more surface to grab with solder. They can cause part to lift unevenly. This risk can be lowered and improving soldering reliability with thinner components.

How to Prevent PCB Tombstone

• Optimized Stencil Design

Even solder paste application is guaranteed with a good stencil design. Solder paste that’s spread evenly doesn’t allow for imbalances that can lift parts. Accuracy can be improved. You just have to use stencils of consistent aperture size. It will decrease tombstoning from occurring during the reflow.

• Precision Component Placement

With accurate placement, components are placed in the right place. Uneven soldering can occur even for small misplacements. Use calibrated machines for a better precision. Tombstoning is less likely if placed carefully.

• Thermal Profile Fine-Tuning

It’s important that the temperature profile of the reflow oven is adjusted. Soldering without parts lifting is an outcome of balanced heating. Be sure all the stages (heating, soaking and cooling) are well adjusted. The risk of tombstoning is lessened by consistent temperatures.

• Simultaneous Welding at Both Ends

By soldering both ends of a component at the same time, lifting during assembly isn’t a problem. Incorrect solder melting can cause one side to tilt. Simultaneous welding ensures that weld tension is balanced by the pull from solder tension. With this method components are stable while getting soldered.

• Reasonable Pad Design

Good soldering requires that the pads be of equal size and have equal spacing. Uneven solder paste application results from uneven pads. So keep pads lengths and widths the same to avoid imbalances. Promoting steady connections requires the right pad design.

How Can PCB Tombstone Affect the PCB and PCB Manufacturing?

• Electrical Connection Loss

Tombstoning can interrupt electrical connection on your PCB. It occurs when a component is lifted and no longer in contact with the pad. An open connection is the one that will not work properly. Signals can be interrupted or not carried at all. This can make your PCB unusable. I consider this a big failure because it impacts overall performance.

• Circuit Discontinuity

As a consequence of tombstoning — the flow of electricity is interrupted. A break in the circuit is caused even by one lifted component. It leaves a gap that won’t allow for the board to work. Cutting a link in a chain is like it—disrupts the whole system. You can’t get the results you desire from the circuit.

• Component Misalignment

Components are ultimately brought into unintended positions because of tombstoning. This can be interpreted in the sense that the two ends of the component don’t connect up to the PCB pads properly. These components are misaligned. This could result from weak electrical connections or perhaps with a short circuit. But more importantly, they cause performance problems and ultimately cause device failures.

• Unstable Connections

A connection is unstable if only one side of a component has been soldered. It’s possible for the component to wobble or even lift even more over time. Under vibration or stress this weak solder could fail. On a PCB with unstable connections, the reliability is a lot lower. Use causes the same issues to occur with the board.

• Device Failure

Complete device failure is possible if tombstoning occurs. The device stops working if there is an only one disturbed connection. The signals don’t flow properly simply because broken circuits are broken. That kind of malfunction can bring the product down altogether. Both manufacturers and users will be affected from that one.

• Increased Rework Costs

Fixing tombstoning is going to require time and effort. In order to fix that problem, you need to hire a skilled worker. That’s a big raising of production costs. It also adversely affects the time, and makes it less efficient. The more tombstone defects you have, the more expensive the repair and rework costs.

• Reduced Reliability

Tombstoning makes your PCB less reliable. It may fail during use, because of faulty or unstable connections. It can lower user trust, and satisfaction from your company. This impacts your product quality and PCB product reputation.

Effective Solutions for PCB Tombstone

• Reflow Profile Optimization

To prevent tombstoning, you can adjust the reflow soldering process. For simple chopping and mixing tasks, like that, tweaking the temperature and timing makes a big difference. By matching your reflow profile to your components, you get an even heating. It has good effect on forming the strong solder joint and the reduction of defects. Reflow settings are optimized to allow you to keep your assembly process smooth and reliable.

• Skilled Manual Rework

Skilled technicians can fix it manually if tombstoning occurs. Carefully, they put components back on their place. They then spend time and use exact soldering to repair those connections. This hands-on solution makes sure that your PCB works as needed. Isolated defects can be fixed with manual rework, and that is a practical way to protect overall quality.

• Continuous Process Refinement

Tombstoning can be avoided by simply regularly improving your assembly process. There is the technique to review, the equipment to update and train your team. Small changes to your process will mean big things. Low defects, high quality is achieved by consistent evaluation. Keeping a culture of improvement will help keep your production dependable in over time.

• Automated Optical Inspection (AOI) Systems

The addition of AOI to your assembly line can find problems early. Using cameras, these systems quickly identify and find missing aligned components. You can identify problems before it negatively impacts your final product. It is time saving and reduces the chance of producing a defect. The AOI system is a smart tool to keep production standards at a high level.

• Material and Process Optimization

With any is this important to choose the right materials for your assembly. Help suppliers develop solder pastes and fluxes that fit your requirements. Better materials help with how the solder sticks and flows. This prevents tombstoning while soldering. Your boards are kept reliable by optimized materials and processes.

How to Avoid Tombstoning of Small SMD Components?

A few key things to check for in order to avoid tombstoning on small SMD components is to make sure your two pads on the components have the same copper balance. It allows for both sides to heat up at the same time. Next is to make the solder paste applied on both sides equally. Uneven paste will cause imbalances, so called tombstoning. Also make sure that the component is right in the middle of the pads. While small shifts can lead to problems with placement. Next, control the reflow profile carefully to avoid sudden temperature changes that will cause heat affected area which will result in no expansion equal on the whole.

More FAQs About PCB Tombstone 

• Does Tombstoning Always Need to Be Fixed?

When the connections are good sufficient, some tombstoning defects doesn’t actually need fixing. If both pads still have a solid solder joint on the component, the component may work. But a tilted component can bring future issues. Before deciding to leave it as is, however, it’s important to assess the long term reliability.

• What Percentage of Tombstones Is Acceptable?

In the realm of consumer electronics, less than 1% tombstoning may be acceptable. A small amount of tombstoning won’t typically impact performance for low risk products. But in high stakes industries such as aerospace and automotive zero tombstones is the only considered rate. These applications are critically reliant on reliability.

• How Does Adhesive Help Mitigate Tombstoning?

The component can be held down with a small amount of adhesive on only one side. With this it stays flat and doesn’t lift in reflow. Balancing the forces working on the component is what adhesive does. For more delicate components, those that tend to tombstone, this is especially useful.

• What Angle Do Tombstoned Components Lift To?

Typical tombstoned components lift at angles between 1 and 45 degrees. How uneven you’ve deposited the solder paste depends on the angle. The idea is that if the component is further parallel to the board, it probably had less solder paste under it. Angle of lift indicates the severity of the tombstone.

• Does Higher or Lower Solder Paste Deposition Help Avoid Tombstoning?

Lower solder paste deposits may help to prevent tombstoning. Soldering causes one side of a component to lift, known as tombstoning. In the event that the paste is too thick, the component rises above the solder. This imbalance between the pads too tilts the component. This thinner paste layer helps to keep the component flat.

• How Do You Know If You Have a Tombstoning Problem?

Lifting of components off at odd angles are indicators of tombstoning. Alternatively, you can check with X-ray inspection as well to know if there is a less amount of solder on one side. Running the component connections will prove if they are intermittent. The sooner you catch it, the less damage will be done.

Conclusion

In this blog, we have given where we covered key issues related to PCB tombstone and how it affects your device’s performance. We recognize this challenge, and at PCBMay, we are prepared to deal with it. We take care of everything from precise solder paste deposition, to well-designed stencils and the throughout reflow profile management. PCBMay is trusted by us to solve tombstoning problems and to offer you high quality, reliable PCBs.