As aerospace and defence platforms become smaller, lighter and more sophisticated, engineers are being asked to deliver greater performance from increasingly constrained spaces. Hybrid microelectronics can provide a highly integrated solution, says Richard Smith, Chief Engineer at TT Electronics.
When space is limited, every component matters. When weight is critical, every gram matters. And when electronics have to operate reliably in extreme environments for decades, every design decision matters.
This is the challenge facing engineers developing the next generation of aerospace and defence platforms. Systems need to deliver more functionality and higher power density, while becoming smaller and lighter. At the same time, they must withstand demanding conditions including extreme temperatures, vibration, mechanical stress and, in some applications, radiation.
Traditional printed circuit board assemblies can struggle to meet these competing requirements. Increasingly, engineers are therefore looking towards hybrid microelectronics - highly integrated, application-specific packaging solutions that can deliver maximum performance from a much smaller package.
Hybrid microelectronics have evolved significantly from simple component integration into sophisticated system-in-package solutions. The fundamental principle is to remove unnecessary layers of packaging and integrate the electronics as efficiently as possible.
In a conventional surface-mount assembly, semiconductor devices are individually packaged so that they can withstand the PCB assembly process. With hybrid microelectronics, engineers can instead work with bare semiconductor die, passive components and ceramic substrates to create a package specifically designed around the application.
This bespoke approach can deliver significant benefits in size, weight and performance, while also allowing the package to be engineered for the environmental conditions in which it will operate. For aerospace and defence applications, where available space can be extremely limited and reliability is critical, this flexibility can be particularly valuable.
Hybrid microelectronics are typically suited to low- to medium-volume applications where performance and reliability are more important than achieving the lowest possible unit cost. The design priority can vary considerably from one application to another.
For an aircraft or spacecraft, reducing weight may be the primary objective. In a compact defence system, the challenge might be fitting the electronics into an unusually shaped or space-constrained enclosure. Elsewhere, engineers may need to maximise power output from a very small footprint, creating significant thermal-management challenges.
This is where a bespoke hybrid approach can come into its own. Rather than adapting the application around the limitations of a standard package, engineers can develop the electronics around the specific requirements of the platform. However, achieving this requires specialist knowledge across multiple disciplines, from semiconductor and materials selection through to packaging, thermal management, manufacturing and reliability testing.
For system suppliers, electronics are often only one part of a much larger and highly complex aerospace or defence platform. Working with a specialist hybrid microelectronics partner can therefore provide access to expertise that may not be available in-house.
The process typically begins with the customer and electronics specialist working together to establish the key requirements. These can include:
Electrical and performance requirements
Size, weight and power constraints
Environmental conditions
Applicable regulatory and industry standards
Production volumes and expected lifecycle
Technology and obsolescence considerations
Once these requirements are understood, the detailed design process can begin. The relationship can be highly collaborative, with the electronics specialist effectively operating as an extension of the customer's engineering team, or it can follow a more traditional subcontracting model.
Whatever the approach, the objective is to develop a solution that is not only technically optimised, but also fully qualified and suitable for long-term production.
For mission-critical aerospace and defence electronics, reliability cannot be added at the end of the development process. It needs to be considered from the outset. Material selection, thermal performance, package construction, assembly techniques and environmental protection all contribute to the reliability of the finished product.
Extensive testing and qualification can then be used to demonstrate performance under demanding conditions. Testing may include electrical testing under operational loads, temperature cycling and high-g centrifuge testing to simulate the mechanical stresses experienced during launch or flight.
For sealed packages, hermetic seal integrity testing can help ensure that moisture cannot enter the package and cause degradation over an extended operating life. For particularly critical applications, qualification may also involve destructive testing, where selected components from production batches are deliberately tested to destruction in order to demonstrate the reliability of the remaining units.
The result is a rigorous process designed to give system suppliers confidence that the electronics will perform when they are needed most.
Reliability is only part of the challenge. Aerospace and defence platforms can remain operational for decades, so engineers also need to consider how technology will evolve over the lifetime of the programme. This makes future-proofing an important part of the hybrid microelectronics design process.
Aerospace and defence are understandably cautious when adopting new technologies. Emerging approaches need to be proven before they can be incorporated into mission-critical systems. However, innovation in other industries can provide valuable opportunities.
Technologies developed for sectors such as automotive and telecommunications can be evaluated, refined and qualified for use in high-reliability aerospace and defence applications. This can allow system suppliers to benefit from advances in materials, packaging, power management and integration while maintaining the levels of reliability their platforms demand.
Several areas of development are likely to shape the next generation of hybrid microelectronics.
Advanced materials are one. Engineers are continuing to explore ceramic substrates and other materials that can provide improved thermal and mechanical performance.
Power density and thermal management are also becoming increasingly important. As more power is delivered from smaller packages, innovative approaches to heat dissipation will be required. Advanced cooling structures and technologies such as vapour chambers could provide new options for managing heat within highly constrained designs.
Another key consideration is coefficient of thermal expansion (CTE) matching. Selecting materials with compatible thermal expansion characteristics can help minimise mechanical stresses as the package experiences repeated temperature changes, reducing the risk of cracking and supporting long-term reliability.
Finally, there is a continued drive towards greater functional integration. Combining analogue, digital, RF and power electronics within a single package could further reduce size and weight while improving overall system performance.
These developments could see hybrid microelectronics play an increasingly important role across a broad range of applications.
Aircraft electrification is increasing the demand for lightweight, compact electronics, while modern avionics and flight-control systems require highly reliable electronics within increasingly constrained platforms. In defence, high-power systems need to deliver greater capability without adding unnecessary size and weight.
Space applications present another significant opportunity. Satellite power and communications modules need to operate reliably for long periods, often without the possibility of maintenance, creating demand for compact, highly reliable and, where required, radiation-tolerant electronics.
Across all these applications, the underlying challenge remains the same: how do you deliver more capability from less space, while maintaining the reliability demanded by a mission-critical platform? Hybrid microelectronics provide one answer.
The technology itself is only part of the solution. Delivering a successful hybrid microelectronics programme requires expertise across the entire product lifecycle - from initial design and materials selection through to prototyping, qualification and volume production.
TT Electronics provides design-led, advanced electronics technologies for performance-critical applications in specialised markets, supporting customers throughout this lifecycle. Its hybrid microelectronics capabilities include turnkey circuit layout and packaging design based on customers' electrical schematics, performance requirements and environmental conditions, alongside design and manufacture in compliance with MIL-PRF-38534 Class H.
The technology portfolio includes hermetic and non-hermetic packaging, multilayer thick-film printing on ceramic substrates including alumina (Al₂O₃) and aluminium nitride (AlN), high- and low-temperature co-fired ceramic (HTCC and LTCC), thin-film technologies, surface-mount assembly, bare die and wire bonding, mixed SMT and chip-and-wire solutions, pressured sintering, hi-rel QFN and CGA technologies.
By bringing these capabilities together, TT Electronics can support customers from initial development through to testing, qualification and production - helping optimise designs, accelerate time to market and build long-term reliability into the finished product.
As aerospace and defence platforms continue to become smaller, lighter and more capable, the electronics inside them will face ever greater demands. Hybrid microelectronics offer engineers a way to meet those demands - combining miniaturisation, performance, thermal management and high reliability in a package designed specifically for the application.
For the most demanding environments, that could make hybrid microelectronics an increasingly important technology for the next generation of aerospace and defence systems.