{"id":17849,"date":"2017-06-26T08:00:48","date_gmt":"2017-06-26T15:00:48","guid":{"rendered":"http:\/\/www.autodesk.com\/products\/eagle\/blog\/?p=1243"},"modified":"2023-09-25T13:30:16","modified_gmt":"2023-09-25T20:30:16","slug":"what-is-pcb-tombstoning","status":"publish","type":"post","link":"https:\/\/www.autodesk.com\/products\/fusion-360\/blog\/what-is-pcb-tombstoning\/","title":{"rendered":"What Is PCB Tombstoning?"},"content":{"rendered":"

What Is Tombstoning On a PCB, and How Can You Prevent It?<\/span><\/h1>\n\n\n

One day you might get a call or an email from your manufacturer saying that you have an issue with tombstoning on your PCB. And then you\u2019ll probably sit there with a puzzled look on your face. What the heck is tombstoning you\u2019ll ask, and why are you calling me about it? <\/span><\/p>\n\n\n\n

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. And since the beginning of PCB manufacturing, tombstoning has been and continues to be an issue. 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. So let\u2019s dispel once and for all what tombstoning is, and what you as a PCB designer can do to prevent it at design time.<\/p>\n\n\n

Tombstoning In a Nutshell<\/h2>\n\n\n

As the name suggests, tombstoning resembles those large, sometimes slanted slabs of granite that you\u2019ll find at a cemetery. 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. As your component stands on end like it’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.<\/span><\/p>\n\n\n\n

\"smd-component-tombstoning\"\/
An SMD component tombstoning after the wave soldering process. (Image source<\/a>)<\/em><\/figcaption><\/figure>\n\n\n\n

While the angle of a lifted tombstone component can vary, it all means the same thing. There\u2019s going to be some post-soldering rework done by your manufacturer, and you\u2019ll likely be sending more money their way to correct the issue. In the early days of PCB manufacturing, tombstoning was an issue related to the process of <\/span>vapor phase reflow technologies<\/span><\/a>. But as these vapor technologies declined in use, manufacturers and designers assumed that tombstoning issues would cease to exist. But they were wrong.<\/span><\/p>\n\n\n\n

Tombstoning is still plaguing manufacturers around the world, sending PCB layouts to an early grave when a component rises off a pad. But why the return?<\/span><\/p>\n\n\n\n

\n

Size<\/b>. There has been a significant decrease in the size and mass of components being used in PCB layouts.<\/span><\/p>\n\n\n\n

+ New Regulations<\/b>. There has also been a greater increase in high temperature, lead-free solders to meet RoHS regulations. <\/span><\/p>\n\n\n\n

= Issues<\/b>. And when you put these two variables together, you\u2019ve got a recipe for tombstoning to occur.<\/span><\/p>\n<\/blockquote>\n\n\n

Causes of Tombstoning<\/h2>\n\n\n

To understand what causes tombstoning, you first have to understand what \u201cwetting\u201d means to describe a process of attaching components to a bare board with solder. 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.<\/span><\/p>\n\n\n\n

\"perfect-solder-joint\"\/
A healthy solder joint with a smooth surface and 40-70 degree wetting angles. (Image source<\/a>)<\/em><\/figcaption><\/figure>\n\n\n\n

Take a simple SMD resistor as an example, which has two pads. In an ideal process, the solder will attach itself to both pads and complete its wetting process at the same time on both ends. No tombstoning issues here. But you run into a problem when the wetting process of solder is unbalanced. 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.<\/span><\/p>\n\n\n\n

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. 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. Some of the most common causes of a tombstoning issue on a PCB can include:<\/span><\/p>\n\n\n\n