How process optimisation takes mmWave innovations from the drawing board to production at scale
By Laurence Scullion, Director of Production Engineering, Filtronic
As many communications applications move into mmWave frequencies to access greater bandwidth and data capacity – the challenge of designing and manufacturing modules to transmit, receive and condition signals increases significantly. The ability to design modules for manufacturability is critical, and process optimisation is key to achieving repeatability and scalability in production.
When you’re manufacturing modules for mmWave frequencies, the slightest mechanical, electrical or production variations can have significant impacts on performance. Any tolerance deviations are amplified at these frequencies, due to the intricate interplay of multiple components within the module.
The mechanical and electrical design challenges at mmWave are well recognised, from tolerance alignment, material selection (CTE matching), connector interfaces and enclosure sealing to transmission line geometries and electromagnetic simulation. What is perhaps less well understood is the challenge of bringing these designs to fruition in the manufacturing plant, taking complex, intricate module designs from the drawing board into consistent and efficient production at scale.
Bridging the gap from design to production
This ‘process optimisation’ is often the unseen element in the design-to-manufacturing process, but is critical in bringing advanced new systems to the market. In practical terms, it involves detailed process engineering to optimise every element of module production, from epoxy dispensing and placement automation to fixture alignment, inspection and measurement.
With our vertical integration of design, manufacturing and testing, Filtronic has established a leading position as a design-for-manufacturability specialist. Crucially, our ability to use process engineering to bridge the gap between design and scalable manufacturing, spanning Technology Readiness Levels (TRL) 6 to 9, has enabled us to deliver innovative new products at mmWave using the latest semiconductor technologies.
Revolutionising GaN-based power amplifiers
These capabilities have proved key to revolutionising the development of power amplifiers for higher mmWave frequencies, using gallium nitride (GaN) MMICs to achieve considerable power and efficiency gains.
GaN has become increasingly important as a semiconductor compound in recent years, delivering significantly improved power density and efficiency at mmWave, and unlocking the size, weight and power (SWAP) gains that are critically important for many space, defence, and aerospace applications. But GaN brings with it new complexities for design, manufacturing and operation. One acute problem associated with developing smaller modules with greater power density is managing and dissipating heat within the module. This calls for advanced packaging solutions.
Packaging challenges for high-power modules
The successful use of GaN in power amplifiers for mmWave applications relies on optimising the module packaging. The key challenges associated with packaging for GaN power amplifiers are:
- Thermal dissipation – managing high heat within the device at high power levels. GaN chip junction temperatures can reach 300°C.
- Reliability – ensuring reliable high-frequency operation in extreme environments. This requires radiation-hardened and defence-compliant devices.
- Scalability – moving from prototype laboratory models to mass production. This demands repeatable assembly and alignment techniques.
- Sovereign control – achieving security and supply chain assurances against a backdrop of limited UK supply chains for high-reliability packaging.
- High-frequency performance (30GHz+) – achieving the required performance given the technical limitations on die-attach options and interconnections at mmWave.
Plotting a path to optimal packaging
Filtronic is addressing these challenges by exploring a variety of advanced packaging methodologies for GaN-based mmWave power amplifiers. Our rigorous approach to process optimisation means we have devised and tested multiple solutions, enabling us to deploy the right techniques to solve the challenges of specific applications in different sectors. The options we have explored to overcome specific packaging challenges include:
- Advanced materials and die-attach options
We have created innovative thermal interfaces using die-attach materials such as sintered silver (Ag) to provide high thermal conductivity (~250 W/m·K), reliable void-free bonding and low-temperature sintering (<300°C). Eutectic gold-tin (AuSn) is another die-attach option, providing high reliability and proven performance in defence and space applications.
- Next-generation substrates and interconnects
Copper-tungsten (CuW) or copper-moly (CuMo) substrates are a close match to the CTE of GaN, reducing thermal stresses and enhancing mechanical robustness. Aluminium nitride (AlN) substrates also offer high thermal conductivity combined with electrical insulation for heat dissipation and heat soaking. To optimise precision-engineered interconnects we use wire bonding to minimise losses.
- Hermetic packaging
To achieve airtight and moisture-tight packaging, we have used low-loss, high-Q ceramic or metal-based packaging, as well as advanced new 3D plastic packaging for GaN devices.
Introducing the Prometheus V-band power amplifier
We have applied all of our process engineering and design-for-manufacturability expertise to develop an advanced new solid-state power amplifier (SSPA) for V-band (49-52GHz), using GaN MMICs. The new Prometheus SSPA is a complete, integrated platform, combining GaN semiconductor technology with our proven Cerus 32 SSPAs, packaged and ready for deployment in high-frequency applications. These amplifiers are to be plugged into ground communication systems for outdoor and indoor configurations and intended for harsh environment such as space or defence installations.
Prometheus incorporates the optimum combination of materials and advanced packaging techniques to maximise the power and efficiency benefits of GaN. Engineered for performance, resilience and long-term reliability in challenging environments, Prometheus answers the need for improved signal amplification and enhanced linear power at mmWave.
The development of Prometheus is a result of the focused work of our recently opened system development hub in Cambridge, combined with our growing GaN expertise and the alignment of our design teams with our precision manufacturing operations. It is a testament to our proficiency in the art of optimising processes to deliver complex mmWave systems consistently at scale.
If you’re looking to increase manufacturing yields for mmWave devices or improve system reliability in the field, we’d be delighted to talk to you about process optimisation. Please contact a member of our team on +44 (0)1740 618 800 or visit our website to find out more.
You can find out more about Prometheus here and explore our Cerus range of SSPAs here.
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