Tombstoning is just waiting to happen with this SMT component. As can be guessed, Pad 1 is going to generate way more heat than Pad 2 when passed through a wave soldering oven. Pad 2 on the right is connected to a wide trace and ground plane, whereas Pad 1 is attached to a thinner trace. Check out the image below which shows an SMT component connected with two different trace widths. HereвЂ™s a quick example to show how tombstoning might occur in a practical design.

ThereвЂ™s also the varying sizes of pads themselves, with SMT pads having their own set of tolerances that are often ignored but can affect the accuracy of solder applications.

Solder paste being applied to your board in a non-uniform application across all of your pads which can lead to wetting beginning and ending at different times.

The temperature of the reflow oven being uneven, which can cause the solder to begin and finalize its wetting process at different times on your PCB layout.

Some of the most common causes of a tombstoning issue on a PCB can include: As you can imagine, identifying exactly what caused this uneven wetting can be quite the detective work as there are so many variables in play during a typical wave reflow process. Of course, the wet pad ends up winning, pulling up the other pin still in the process of wetting, and the entire component gets tilted on its side, looking like a tombstone. Like when the solder on one pad completes its wetting process before the other, which results in one side of a component solidifying while the other is still in process, and so begins the game of tug-o-war. But you run into a problem when the wetting process of solder is unbalanced. In an ideal process, the solder will attach itself to both pads and complete its wetting process at the same time on both ends. Take a simple SMD resistor as an example, which has two pads.

Wetting is an ideal situation when the solder is applied to your board has reached an ideal fluid state and can attach properly to a component lead or pad.ДЄ healthy solder joint with a smooth surface and 40-70 degree wetting angles. To understand what causes tombstoning, you first have to understand what вЂњwettingвЂќ means to describe a process of attaching components to a bare board with solder. And when you put these two variables together, youвЂ™ve got a recipe for tombstoning to occur. There has also been a greater increase in high temperature, lead-free solders to meet RoHS regulations. There has been a significant decrease in the size and mass of components being used in PCB layouts. Tombstoning is still plaguing manufacturers around the world, sending PCB layouts to an early grave when a component rises off a pad. But as these vapor technologies declined in use, manufacturers and designers assumed that tombstoning issues would cease to exist. In the early days of PCB manufacturing, tombstoning was an issue related to the process of vapor phase reflow technologies. ThereвЂ™s going to be some post-soldering rework done by your manufacturer, and youвЂ™ll likely be sending more money their way to correct the issue.

While the angle of a lifted tombstone component can vary, it all means the same thing. As your component stands on end like itвЂ™s rising from the dead, it ends up looking like a tombstone in the graveyard of what is now a defunct PCB design with an open circuit.ДЄn SMD component tombstoning after the wave soldering process. In the case of a PCB design, tombstoning is typically a surface mount passive component, like a resistor or a capacitor, that partially lifts from a pad on one end. Tombstoning In a NutshellДЄs the name suggests, tombstoning resembles those large, sometimes slanted slabs of granite that youвЂ™ll find at a cemetery. So letвЂ™s dispel once and for all what tombstoning is, and what you as a PCB designer can do to prevent it at design time. While a bunch of articles on the web point the fingers of blame at manufacturers for tombstoning issues, the truth is you also have a part to play as well. And since the beginning of PCB manufacturing, tombstoning has been and continues to be an issue. Tombstoning is just one of many issues that can occur during the soldering process when all of your components get attached to a bare board.

What the heck is tombstoning youвЂ™ll ask, and why are you calling me about it? And then youвЂ™ll probably sit there with a puzzled look on your face. One day you might get a call or an email from your manufacturer saying that you have an issue with tombstoning on your PCB. What Is Tombstoning On a PCB, and How Can You Prevent It?

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