Lifecycle Failure
Cyclic stress that causes the copper barrel in a circuit board to crack over time identifies a common reliability risk. Plated through hole fatigue happens because the copper and the board resin expand at different rates during temperature changes. This movement puts a tensile load on the copper wall that eventually leads to a fracture.
Stress Mechanics
Boards experience these thermal cycles every time the device is turned on or off. The resin expands much more in the vertical direction than the copper does, stretching the barrel like a spring. Over many cycles, the metal undergoes plastic deformation and eventually fails.
Most cracks occur at the center of the barrel or at the interface with the internal copper pads. The thickness of the plating and the properties of the laminate material determine how many cycles the hole can survive. Thicker copper and materials with a lower coefficient of thermal expansion improve the durability of the connection.
Design Mitigations
Engineers select materials with high glass transition temperatures to limit the amount of expansion. Adding more copper to the barrel or using larger pads can also extend the life of the hole. These choices are verified through accelerated thermal cycling tests.
