Vibration fatigue in PCBs.
The importance of reliability in mission-critical applications.
How finite element vibration analysis can improve reliability.
PCB failures due to vibrations and shock loading make up about 20% of all PCB failures
Printed circuit boards (PCBs) are inevitable in any electronic equipment. Initially, through-hole soldered electronic components were utilized to fabricate circuits. However, conventional through-hole PCB design consumed a lot of space. The need for compact designs paved the way to a new technology called surface-mount technology.
The emergence of surface-mount device-based PCBs (SMD PCBs) reduced manufacturing costs, miniaturized electronic assemblies, and ensured effective space utilization. However, both through-hole type PCBs and SMD PCBs are equally subjected to vibration and shock loading, which are reasons for device failure. To predict the chances of PCB failure from vibration or shock loading, finite element vibration analysis is used. This analysis technique helps designers predict a PCB’s response to vibrations, improving the reliability of the board.
Vibration Fatigue in PCBs
The possible causes of failure in printed circuit boards include component failure, poor connection, short circuits, electric shocks, thermal runaway, mechanical shocks, and vibrations. Failures due to vibrations and shock loading make up about 20% of all PCB failures. Mechanical vibrations result in PCB failure of two forms:
- Solder joints are subjected to vibration fatigue.
- Mechanical deformation and bending of the board due to vibrations lead to solder damage and component lead damage.
The board solder joints and the components soldered to them undergo stress under vibration. The vibration imparts excessive dynamic loading on the PCB and the components soldered to it. The vibration stress leads to loss of contact or disconnection from the circuit due to stiffness and stretching. Over time, the vibration stresses on a PCB result in premature failure, decreasing the reliability of the board.
PCB Reliability and Mission-Critical Applications
For mission-critical applications such as space launch vehicles, aerospace or avionics systems, defense systems, and military electronic circuits, it is important for PCBs to be 100% reliable. PCB failures due to vibrations cannot be allowed in such critical applications. For this reason, designers try to predict the PCB’s response to various vibrations and gauge its reliability before placing it in mission-critical systems.
Finite element vibration analysis can be used to predict the behavior or mechanical deformations as well as chances of breaks (open circuit) and makes (short circuit) in a PCB due to vibration stress or fatigue. This analysis method is useful in getting an accurate understanding of a PCB response when subjected to random vibrations.
Finite Element Vibration Analysis
Finite element vibration analysis is a powerful type of analysis that helps PCB designers understand the interactive effects of boundary conditions, support positions, component location, component layout, component terminal types, terminal lead height, input force, and its direction on the vibration-induced stress and fatigue experienced on solder joints, components, and other sections of a PCB. The designer can acquire design guidelines from the finite element vibration analysis results and can iterate the design until minimum vibration stress is experienced by the PCB.
Finite element vibration analysis can be used to predict the natural frequency of the PCB. Minimum vibration fatigue is established in the board when the natural frequency does not coincide with the system frequency. With the help of finite element vibration analysis, the designer can vary the layout and designs until there is a sufficient buffer between the natural frequency of the PCB and the system frequency. Using finite element vibration analysis, the mechanical movement due to vibration and its associated modal shapes can be simulated. The effect of boundary conditions, lumped mass, material characteristics, material thickness, etc. in counteracting the vibrations subjected on a PCB can be analyzed.
Finite element vibration analysis is a powerful tool that can help designers investigate the vibration characteristics of a PCB and create more reliable and optimized circuit designs. And, this analysis method eliminates the need for costly vibration tests on hardware prototypes in mission-critical applications.
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