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Designing PCBs for harsh environments means understanding the various conditions they will likely be exposed to – extremes of humidity, temperature, shock, vibration and other conditions that can impact their reliability and performance.
These extreme environments can include aerospace and defence, military and industrial settings. Various things need to be considered when it comes to PCB assembly in these circumstances.
What are considered harsh environments?
Electronics may not perform as well in harsh environments, but despite this, there’s usually no choice other than to use them. This means the PCBs may be exposed for long periods to conditions that impair their reliability.
A harsh environment is one where there are extreme temperatures, where heat causes a risk of the components overheating, or cold makes the joints freeze, become brittle or fail altogether.
Humidity and moisture don’t mix well with electronics and can cause corrosion and short circuits. Dust is also a hazard, as it can gather on the PCB, leading to overheating and ultimately short-circuiting.
Stresses, vibrations and shocks can loosen components, damaging the joints and causing the circuits to fail.
When PCBs are in contact with solvents, chemicals, gases and other hazardous substances, this can corrode the components quickly, while electromagnetic radiation can impair performance.
Electrical overloads caused by power surges lead to voltage spikes, excessive electrical currents and other connected events, causing complete circuit failure.
Aerospace PCB applications
The aerospace industry poses various unique challenges for businesses providing PCB assembly services.
The printed circuit boards are exposed to particularly harsh environments and will be subject to temperature changes at high altitudes. The temperature surrounding an aircraft can also change quickly, so the PCBs need to be able to survive these fluctuations.
Thermal stress that leads to the loosening of components and damaged joints must be avoided at all costs, as it could endanger the safety of the aircraft and its occupants.
In addition, vibrations are continuous on aircraft, especially on take-off and landing, or during periods of turbulent weather. Manufacturers use stiffeners to ensure the circuit boards are more resistant to vibration.
Aircraft also suffer exposure to ionising radiation, leading to the PCB components degrading and impaired performance. Manufacturers use radiation-hardened components to stop this dangerous problem from occurring.
Their weight and size are kept to a minimum, so miniaturisation space saving techniques are used, including multi-layer boards.
While reliability is important in every industry, it is particularly crucial in the aerospace industry, as PCB failure at height could be a catastrophe – circuit boards used in the sector have backup systems to improve reliability.
Military PCB applications
The military and defence industry presents its own demands for PCB design.
Military operations on land, in the air and at sea can suffer vibrations and shock, and radio frequency and electromagnetic interference are commonplace. This is due to the radar, sonar and other communication equipment.
All PCBs must withstand electronic warfare and continue to be reliable to protect data in the military and defence industry. The circuit boards’ longevity and durability are crucial, as the lives of the personnel using the equipment on operations depends on it.
In addition, military PCBs must be light and small, yet still able to maintain power and efficiency. To achieve this, miniaturisation techniques including multi-layer boards are used to ensure optimum efficiency.
Oil and gas PCB applications
The energy industry requires PCBs in several different sectors, including oil and gas. This leads to varied challenges for printed circuit board manufacturers.
The boards can be subject to high currents and voltages, so they require specific insulation distances, trace widths and components that have the necessary dielectric strength.
They can also be exposed to intense heat, so are designed to withstand this by being manufactured with thermally conductive materials and techniques to manage heat efficiently.
The energy industry uses complex heavy machinery, which generates electromagnetic interference and electrical noise. The PCBs must be designed with ground planes, filters and other shielding techniques to make sure they are reliable.
PCBs manufactured for harsh environments must be compliant with stringent quality standards, such as AS9100 – a standardised quality management system that the aerospace industry uses. The European Association of Aerospace Industries and the Society of Automotive Engineers released the regulation jointly in 1999 to ensure the highest standards would be met.