Avionics PCB Manufacturing

Electronics That Fly

Avionics covers everything electronic in an aircraft: the flight control computers, the navigation and communication equipment, the radar and sensor systems, the displays in the cockpit and the monitoring systems that track the health of the airframe and the engines. Every one of those functions runs on circuit boards, and every one of them has to work in an environment where the temperature swings from the cold of altitude to the heat of a sun soaked apron, the vibration never stops and the consequences of failure are obvious.

The design of an avionics board is therefore shaped by reliability, weight and certification as much as by electrical function.

What the Board Does

Functionally the boards distribute power to sensitive systems, process digital and analog signals, move data between sensors, computers and displays, and implement the redundancy and fault tolerance that safety critical functions require. The flight control system may use several channels that compare their results, the navigation equipment combines inputs from several sources, and the monitoring system collects data from across the airframe.

That mix means an avionics board often has to be good at several things at once: a quiet analog front end for a sensor, controlled impedance routing for a data bus, and a power section that can tolerate transients.

Design Priorities

High reliability is the first requirement, expressed as a very low failure rate over a long service life. Thermal management follows, because the equipment is often installed in a bay where the airflow is limited and the ambient temperature can be high. Electromagnetic compatibility is the third, and it works in both directions: the board must not interfere with the aircraft’s communication and navigation systems, and it must not be disturbed by them.

Weight is the fourth, and it is a genuine engineering constraint rather than a preference. Every kilogram carried costs fuel over the life of the aircraft, which is why lightweight materials, thinner constructions and rigid flex assemblies that replace wiring harnesses are attractive even when they cost more. Our notes on PCB manufacturing describe the constructions involved.

Materials and Construction

High performance laminates are used, with high temperature capability for the boards that sit near engines or in poorly ventilated bays, and low loss material where the radio frequency or high speed data content requires it. The layer count is driven by the signal count and by the grounding requirement, and rigid flex construction is common because it saves weight, removes connectors and allows the electronics to be folded into an irregular space.

Conformal coating protects the assembly from moisture and contamination, and the mechanical design of the board has to account for the vibration environment, with connectors and heavy components secured rather than merely soldered.

Manufacturing Requirements

Fabrication follows the processes used for high reliability work: precision drilling and plating, controlled lamination, fine line imaging and a surface finish chosen for soldering reliability and corrosion resistance. Because the boards are often rigid flex, the flex to rigid transitions have to be laid out and manufactured so that the conductors do not fatigue, and the flexible sections have to be protected where they are exposed.

Inspection is comprehensive rather than sampled. Automated optical inspection, X-ray inspection of the joints that cannot be seen, impedance verification and a full electrical test are applied to every board, and the records are retained. Our PCBA testing group plans this coverage with the customer.

Certification and Traceability

Avionics work sits inside an aerospace quality system such as AS9100, layered on the IPC construction standards and, where the function is safety critical, on the airborne software and hardware development processes. Material and process traceability runs from the raw laminate to the finished unit, and any change to a qualified process requires assessment and revalidation before it is introduced.

This is what allows a part to remain in service for decades with confidence, and it is why the documentation is as much a deliverable as the hardware. Our notes on quality management describe the system in place.

Testing

Testing covers the electrical function, the environmental tolerance and the electromagnetic behaviour. Thermal cycling, vibration and humidity testing simulate the service environment, and functional testing at temperature verifies that the board still performs when it is hot or cold. For the equipment that has to demonstrate compliance with the aircraft’s electromagnetic requirements, the emission and immunity testing is carried out against the applicable standards.

Because the equipment may be repaired and returned to service, the test programme also has to support fault isolation, which affects the design of the test access and the built in test features.

Cost Structure

Avionics boards are expensive relative to industrial electronics because of the material, the construction, the small production volumes and the certification and documentation work. A straightforward prototype sits in the low hundreds of dollars per board, a board of moderate complexity costs several times that, and the most complex high reliability assemblies exceed that again.

Volume reduces the unit price, but avionics volumes are modest compared with consumer markets, so the fixed engineering and certification effort is spread over fewer units and remains a significant part of the cost. Reducing the layer count, simplifying the flex construction where the mechanical design allows and reusing qualified designs across programmes are the practical ways to control it.

Choosing a Supplier

The relevant criteria are the certifications the manufacturer holds, its experience with aerospace work, its ability to build rigid flex and multilayer constructions, and the stability of its supply chain over the long life of an aircraft programme. Because the parts may need to be produced for many years, the supplier’s continuity matters as much as its capability. Our PCB capabilities page sets out what is available.

Trends

There is also a strong pull towards consolidating functions onto fewer boards. Where a platform once had several separate units connected by wiring harnesses, it now tends to have integrated assemblies that combine the processing, the power and the interfaces on one rigid flex structure. That reduces weight and connector count, but it concentrates the thermal load and the reliability requirement in one place, so the design and the qualification effort rise even as the parts count falls.

The direction of the industry is towards smaller and lighter electronics, more rigid flex and flexible construction to save weight and volume, more integration of sensing, processing and communication so that systems can predict their own maintenance needs, and greater attention to the environmental footprint of the materials used.

FAQ

How is an avionics board different from an industrial board? It is designed for a wider environmental range, a much lower failure rate and the certification and traceability that aerospace programmes require.

How long does manufacturing take? Prototypes typically run a few weeks, with production scheduled according to the programme and the test requirements.

Which certifications apply? An AS9100 quality system, the IPC construction standards and, for safety critical functions, the applicable airborne hardware and software processes.

Does the board have to be customised for a platform? Usually, because the mechanical envelope, the connector arrangement and the environmental requirements are specific to the installation.

Conclusion

An avionics board is a high reliability assembly that also has to be light. Rigid flex construction, high performance laminate, disciplined thermal and electromagnetic design, redundancy where the function requires it and a certified, traceable manufacturing process are what allow the electronics to be trusted in the air for the life of the platform.