pcb circuit board handle vibration and shock
Whether in military equipment, cars, electronic instruments or consumer devices, a pcb circuit board is constantly exposed to vibrations and shock. These extreme forces are continuously imposed on the device as it is used and can result in failures, including electrical shorts and even explosions. The pcb circuit board must be designed to withstand such events without damage and this is a key factor for the success of the device.
This is especially important for devices that operate in harsh environments, such as those found on land, sea or air, as they are continuously subjected to mechanical stress and shocks, very wide thermal excursions and vibrations. The four main causes of pcb circuit board failure are electric shock, mechanical shock, vibration and thermal runaway. Two of these, mechanical shock and vibration, are largely avoidable with careful design and layout considerations.
Mechanical shock is caused by a sudden and irregular acceleration that induces a mechanical displacement of the pcb circuit board. The displacement can be either a bending or a twisting. This type of shock can cause failures such as mechanical flex, solder joint cracking, or even structural damage. To prevent this type of failure, it is recommended that the resonant frequency of the pcb circuit board be at least three times higher than the shock pulse frequency. To ensure this, the resonant frequency should be measured with a vibration analysis tool.
How do pcb circuit board handle vibration and shock?
Vibration fatigue is a common problem that can occur over long periods of time. The repeated exposure of the pcb to vibration can eventually lead to a loss of elasticity in the copper power and ground planes and weaken their ability to conduct signals. To protect soldered connections, it is essential to suppress vibration with damping at the fixation points of the pcb in the enclosure and use nyloc nuts to securely lock the pcb on the standoffs.
It is also important to consider the effects of vibration on component leads and solder joints. Using a vibration fatigue analysis tool can help to determine the natural frequency of the pcb and changes that can be made to it to reduce its resonant frequencies. A resonant frequency can be reduced by increasing the mass or stiffness of the pcb, a process called “mass tuning”, and by changing the excitation frequency.
PCBs that are used in harsh environments are often designed to meet very strict requirements and specifications. They must be small, light and have a high glass transition temperature (Tg). They are also likely to be encapsulated in plastic or have a conformal coating to protect them from dust and moisture. Considering all the environmental conditions and extremes they must withstand is challenging, and it’s crucial to understand what effects these factors can have on a PCB.
