Printed Circuit Boards Rugged for Harsh Environments
Some electronic products must operate in harsh environments, such as salt spray or blowing sand or extreme temperature and terrain. This requires the electronics board to be rugged, so that it can perform as normal in these conditions. Printed circuit boards are the central component of any electronics board product, so it’s essential that they function as intended in these types of conditions.
To ensure a PCB can handle the rigors of a harsh environment, it’s important to consider the physical design, materials and testing requirements. To begin with, a ruggedized PCB should be made out of a material that is resistant to temperature fluctuations, moisture ingress and chemical exposure. It should also be designed to withstand vibrations, mechanical stress and shocks. Finally, a PCB should be tested under harsh conditions to simulate the actual environment it will be operating in.
Harsh environment PCBs are used in applications where the PCB and components must withstand extreme temperatures, moisture ingress, dust, chemicals, corrosive elements, electromagnetic radiation and voltage/current transients. These conditions are commonly found in automotive, industrial or aerospace applications.
How to Make Printed Circuit Boards Rugged for Harsh Environments
Moisture and humidity can cause electrical malfunctions like signal attenuation or even short circuits. Corrosive substances can rapidly deteriorate components and PCBs, while electromagnetic radiation can interfere with the performance of electronic devices. In addition, power surges and electrostatic discharges can completely destroy a PCB.
The most common choice for a PCB in harsh environments is FR-4, which has a dielectric composite structure that contains a polyester resin, fiberglass and sometimes other fillers. However, the quality of FR-4 can vary considerably, and small nonhomogeneities like uneven distribution of fiberglass or filler in the laminate, thickness variations, bubbles in the epoxy matrix and variations in the dielectric constant can cause problems in a harsh environment. For example, the high compressive forces of a harsh environment can affect the operation of ICs, especially memory chips that have to correct flipped bits caused by upset events. To combat this, IC designers for a harsh-environment application may physically distribute memory cells on the die so that logically adjacent bits are not exposed to the same upset event.
Another issue that can be difficult to overcome is latch-up, which occurs when the logical state of a memory cell becomes corrupted due to high levels of radiation, heat or temperature. To counter this, IC designers for harsh-environment applications will often re-calibrate the device at regular intervals and strategically place CMOS ICs in locations that have minimal exposure to electromagnetic radiation. In addition, ICs that must dissipate large amounts of heat will need to be placed in areas of the board with sufficient thermal conductivity and will benefit from an epoxy-packaged leaded version instead of a surface mount part for improved reliability.
The connectors on a PCB that are designed for harsh environments must meet a number of requirements, including IP (ingress protection) ratings, wire sealing, contacts, ampacity and corrosion resistance. Generally, the best connectors for harsh-environment use are ones that feature a threaded coupling method. Various designs are available, from D-subminiature and micro-miniature to push-pull and latch lock.
