High tech devices are packed with sensors and antennas. Sensors can include accelerometers, heart rate monitors, an altimeter and a microphone. Antennas include cellular, WiFi and satellite. Many of these components, by their nature, are highly sensitive and their outputs can be affected by localized noise and vibration generated within the device itself.
The piezoelectric effect, Lorentz forces and magnetostriction can all cause electronic components to vibrate. If these vibrations interact with a mechanical resonance of the printed circuit board (PCB), the entire board can vibrate. These vibrations are unlikely to be heard audibly, but they can cause interference with sensors and other sensitive electronic components in devices such as smartwatches, medical equipment, scientific instruments and precision manufacturing machinery.
In this blog post, we show how a coupled physics virtual twin can simulate electromagnetic, structural and vibro-acoustic effects and the cause-effect coupling that causes vibrational interference. With this detailed analysis, engineers can mitigate any vibrations with appropriate design changes.
What Causes Vibration in Electronic Components?
Oscillating signals are used widely in electronics, both in power supplies and in analog and digital signal transmission. There are commonly used components in electronics that are susceptible to vibration from these signals, due to several physical phenomena.
Normally, the vibrations are negligible. However, if the component is mounted on a PCB, the board can become a resonator, significantly amplifying the effect. The vibrations can be conducted to other components potentially adversely affecting their function.
Piezoelectric Effect
Multilayer ceramic capacitors (MLCCs) are used widely in electronic applications, including decoupling, filtering and timing and have many benefits including their size and reliability. MLCCs make use of materials that exhibit the piezoelectric effect. The piezoelectric effect is a phenomenon whereby certain materials generate an electric charge when subjected to mechanical stress. Conversely, these materials can also experience a mechanical deformation when subjected to an electric field. This can give rise to vibrations when an oscillating signal is applied.
Magnetostriction
Commonly seen in power supply electronics, a similar effect occurs inside magnetic materials such as the ferrite cores of inductors and transformers, due to a phenomenon called magnetostriction. When a material is magnetized, the dipoles rotate to align with the magnetic field. This produces a strain inside the material at the magnetic level and causes it to elongate. With an oscillating signal applied, this can cause vibration.
Lorentz Force
Another potential cause of vibration is the Lorentz force. Along with Maxwell’s equations, the Lorentz force is a fundamental part of electromagnetics. Often called the magnetic force, it is exploited in motors and generators where current carrying conductors in a magnetic field experience a force. The effect can be seen in electronic components such as inductors and coils in the presence of an oscillating signal. Again, this can give rise to unwanted vibration.
Why is Vibration Undesirable on PCBs?
Audible Noise
One issue caused by vibration is noise. If the vibration is in the audible frequency range, it can be perceived as a hum. The hum or buzzing from transformers is a common noise complaint caused by magnetostriction, for example. Generally, audible effects are more common in high powered electronics.
Electromagnetic Interference
Vibrations can also cause electromagnetic interference through an effect called “microphonics”. Microphones often make use of the Piezoelectric effect to covert vibrations into electrical signals. MLCCs can act like miniature microphones, converting vibrations into electrical signals. This is particularly noticeable in audio systems, producing unwanted buzzing noise in the sound output.
Sensor Interference
An increasing number of devices include high-precision sensors. These are commonly found in smartwatches and other wearable medical devices, in scientific instruments, and in high-precision manufacturing machinery – for example, in semiconductor production. Vibrations can interfere with the sensor, leading to noise in the output and limiting the sensor’s precision.
Strain and Cracking
Vibration also causes stresses inside materials. Over time, these can weaken the component and cause it to fail sooner. In particular, PCBs can crack around points of high stress, connectors can become loose, and soldered joints can fail.
Analyzing and Mitigating PCB Component Vibration with Simulation
To find solutions, engineers need to study component vibration and PCB resonance, with a view to minimizing interference and noise through careful design. Simulation can reveal vibration sources on a “virtual twin” of the device, allowing issues to be identified and resolved early in the development process. This means that problems can be found without the need to construct and test physical prototypes, accelerating the development process and reducing development costs.
Engineers can make use of a multi-physics workflow with the simulation tools from Dassault Systèmes SIMULIA on the 3DEXPERIENCE Platform. This provides an integrated environment bringing together several physics-based simulation tools in a shared environment.
Electromagnetic Simulation
The first step in the simulation workflow is to build a simulation model. PCB layouts from electronic design automation (EDA) tools are imported into SIMULIA CST Studio Suite, which can automatically extract a 3D simulation model. Users define the input signal for the system. Electromagnetic simulation then calculates the currents, fields and Lorentz forces within the component which can be easily visualized.
Structural Simulation
The 3D model and the associated fields are then be imported into SIMULIA Abaqus for structural simulation. Abaqus can model the piezoelectric properties of capacitors and the strain caused by magnetostriction and Lorentz forces. The resonant modes of the PCB structure can also be calculated. The vibration sources can then be used to drive the PCB resonances in a coupled simulation to calculate the spatial velocity field.
Vibroacoustic Simulation
The spatial velocity field is then exported into the vibroacoustic tool SIMULIA Wave6. This calculates the PCB vibration fields and the acoustic radiation pattern and probed sound pressure levels (SPL). With this, engineers can understand how vibrations couple into other sensors and what noise can be perceived.
Improving the Design
The simulation results allow PCB designers to identify potential issues and resolve them rapidly. Designers can compare the effect of different noise suppression products and component placement on the PCB. They can also identify potential failure points on PCB and optimize the PCB layout and size to withstand expected vibrational stresses in its intended operating environment. Proactively addressing potential issues like sensor failures, component loosening or solder joint fatigue before physical prototyping can improve device reliability.
If vibration issues are identified, engineers can use several methods to improve the PCB layout:
- Adjusting the locations of vibration sources and the victim sensors if possible, moving these sensitive components away from high-strain areas in PCB at resonance frequencies.
- Noise suppression components, such as rubber dampers, can also reduce vibration.
- Changing the fixing points and screws that hold the PCB in place.
- Adjust the size or shape of the PCB to remove resonances.
Conclusion
Vibration on PCBs can cause undesirable noise and interference between components. Simulation can reveal the sources of vibration and help designers to develop countermeasures. Understanding PCB vibration requires a combined physics approach, integrating electromagnetic, structural and vibroacoustic simulation methods into an electronic design automation (EDA) workflow. Dassault Systèmes SIMULIA tools offer a complete multiphysics workflow for PCB vibration analysis. Using simulation, PCB designers can identify issues and find solutions without the cost of constructing and testing a physical prototype. Using simulation accelerates PCB design and reduces the risk of problems emerging late in development or after release.
Interested in the latest in simulation? Looking for advice and best practices? Want to discuss simulation with fellow users and Dassault Systèmes experts? The SIMULIA Community is the place to find the latest resources for SIMULIA software and to collaborate with other users. The key that unlocks the door of innovative thinking and knowledge building, the SIMULIA Community provides you with the tools you need to expand your knowledge, whenever and wherever.
Stephen is an Advocacy Offer Marketing Specialist in Global Marketing.