What are PCBs?
A printed circuit board is a thin sheet of insulating material that provides mechanical structure and electrical connectivity to electronic device components. PCBs are utilised in devices of varying shapes and sizesâwith single-layer, dual-layer, and multi-layer configurations to suit various levels of design complexity.
Common Problems with PCBs
PCBs are commonplace, and itâs of course hard to imagine designing electric circuits without them. However (alongside the obvious problem of extended usage), failures can result from many issues, including poor design, component failure, ageing, and manufacturing defects.
Letâs take a look at such issues and how to resolve them.
Conductive traces that link components on a printed circuit board. Image courtesy of Pixabay.
Faulty design is a leading cause of issues that engineers face while working with PCBs. Challenges can arise when a design does not match the intended board layout, system model, or schematic.
To prevent electrical issues in PCBs, engineers must adopt best practice design techniques alongside software tools for greater precision. Some essential tips for proper PCB design include:
Proper Component Placement
Placing components onto a PCB is critical and requires strategic planning. One of the most efficient ways to address errors during routing is to orient components in the same direction. Engineers can also use CAD tools to map placement locations.
Conductive traces between components on the board must be kept as short as possible. For complex circuits that utilise multi-layered PCBs, a proper routing strategy may involve using both vertical and horizontal traces with advanced routing techniques.
When working with high-voltage PCBs, designers should ensure adequate clearance and creepage spacing, to prevent issues such as electric arcs and short-circuits.
Keeping Conductive Tracings Separate
Keeping analogue and digital traces separate on a PCB can help minimise electromagnetic interference. In RF circuits, this is critical for preserving signal integrity.
When the traces are situated too close to each other, capacitive coupling is induced between the analogue and digital signals that try to âtalkâ to each other. Ground planes for the control and power supply should have adequate clearance, moreover.
Component failure due to short-circuits, electric arcs, and/or overheating can damage the conductive paths on a PCB. Physical damage to circuit boards can cause open-circuit conditions that prevent current flow, and/or it can cause the bridging of terminals between components, which leads to further damage still.
These issues can arise when there is overcurrent or surge voltage in the system, which can each cause a rapid rise in the temperature.
Additionally, component failure can occur when components are used above their rated maximum operating values, or under adverse ambient temperature conditions.
To prevent component failures on PCBs, engineers should integrate overcurrent protection devices, such as fast-acting fuses in electric circuits that are exposed to overload or surges. These components will open the circuit fast enough to protect sensitive components from damage, and also prevent overheating of the conductive traces (which can cause the board to melt in places).
An engineer's first-person view when soldering a component onto a printed circuit board. Image courtesy of Pixabay.
With prolonged use, all PCBs will fail for several reasons. The damaging effects of heating and high voltages on ageing PCBs can reduce the conductivity of the copper tracings. Conductive traces having visible cracks or voids (or perhaps simply a âdullâ look) may indicate problems in the conductivity of the copper or silver material.
Also, vibrations from using the device in unstable environments can impact the integrity of the soldered joints over time. To prevent PCB failure due to ageing, the engineer should perform a physical inspection of the circuit board to identify several issues, such as weak joints, unstable components, or dislodged solder. Components found to be compromised should be reseated or re-soldered where applicable (see below image).
Thanks to precision manufacturing, high-quality PCBs are in fact commonplace. However, some PCBs can develop mechanical or electrical faults due to manufacturing defects.
When the PCB is bare (i.e it has no components integrated into it), engineers can test for resistance or induced capacitance using the flying probe or universal grid techniques. A high resistance value indicates defective conductors, while a high capacitance reading indicates short-circuit or open-circuit conditions.