ICT Winter Seminar: Leading-edge Developments in Electronics Manufacturing

Estimated reading time: 6 minutes

Early fog made the journey challenging for those travelling from afar, but it lifted to reveal a clear blue sky over Hinckley, Leicestershire, which is actually closer to the exact geographical centre of England than the familiar Meriden venue, for the Institute of Circuit Technology winter seminar in December. An intriguing programme, focused on some leading-edge developments in electronics manufacturing, more than justified the effort to attend.

ICT Chair Mat Beadel welcomed delegates and introduced the first speaker, Jonathan Jones, process engineer with embedded-die packaging specialists RAM Innovations, who described the development of novel manufacturing technologies and the benefits of advanced embedded packaging for wide-band-gap semiconductors. 

Jones explained that RAM has established the capability to package multiple electronic components using PCB methodology, to produce circuits optimised for size, weight and power density, with a unique solution for high-current connect and thermal management. 

He demonstrated the benefits of RAM’s three-dimensional “heterogeneous integration” approach, with semiconductors and other components embedded within the printed circuit board. Compared with traditional two-dimensional surface-mounting of components, with limited opportunity for optimised placement resulting in longer routing of conductive paths and compromised symmetry, heterogeneous integration enables shorter conductive paths, improved matched impedance, lower parasitics, and higher efficiency.

In the specific example of wide-band-gap devices, which offers significant benefits at high switching frequencies compared with equivalent silicon-based power converters, embedding gives an opportunity to reduce the size of filter capacitors and inductors, consequently reducing overall system size, weight, and cost.

Embedding achieves tighter power loops and allows capacitors to be placed close to the die, whereas in conventional power converters these components are on the surface and connect with multiple wire bonds.

Jones discussed the robustness and reliability of embedded assemblies, with particular reference to the results of thermal cycling on die-base and die-top sinter and silver epoxy connections, where their superior properties compared with conventional assemblies are clearly demonstrated.

In high-power applications, embedded aluminium-nitride ceramic tiles ensure that the module is isolated whilst providing an excellent thermal path for efficient cooling.

Material selection for embedded applications is a critical consideration. Structural integrity is paramount; some challenges currently being addressed relate to material stability under thermal expansion and operational stress, and also to resin flow and encapsulation. Meticulous design-for-manufacture is fundamentally important.

During the transition between R&D and medium-volume production, panel size is being increased from 12” x 9” to 18” x 12”, with typically 40 modules per panel, and the emphasis is on maintaining the same consistency and yield as has been achieved on smaller panels. It is an advantage that RAM has its own PCB manufacturing facility, with all of its development work being carried out on production-scale machinery. Jones showed examples of equipment and products.

There has been commercial interest from the automotive industry, as an attractive means of cost-effective manufacture of power modules, eliminating the need for wire-bonding. Copper-metallised dies are necessary to enable direct connection to be made successfully, and there are presently a limited number of suppliers.

ICT council member Steve Driver introduced the second speaker, Dr. James Claypole, CEO and founder of Ail Arian in South Wales, with a presentation entitled “A silver lining for circular electronics,” pioneering a recycling approach that effectively creates a circular ecosystem for printed electronics. Claypole explained the derivation of the curious company name “Ail Arian” as a Welsh language term for recycled silver, although Google’s neural machine translation service informed me that it means “second money.” Whatever, the process he described was certainly the basis of a clever recycling concept for silver conductive inks.

Claypole began by reminding us that, of the 60 million tons of electronic waste generated last year, less than 20% was recycled. Indeed, in the case of printed electronics, less than 1% was recycled. Silver is the active component in many conductive inks; it is an expensive metal and its price continues to increase. So, the development of an efficient reclaim and recycling technique is well justified.

He reviewed the principal ingredients of a conductive ink: a resin consisting of solvent, polymers, and modifiers, and conductive particles that could be silver, gold, carbon, or an organic material.

Because silver is typically in the form of metallic micro-flakes, conventional processes for reclaiming it face a serious challenge in separating the metal from a dispersion of associated materials.

What if silver could be made magnetic? Claypole’s team of materials scientists has developed a method of forming a “shell” of silver on a ferrite core. Very fine particles of this silver-coated ferrite have been demonstrated to be an excellent conductive ingredient in ink for printed electronics. There is a significant cost saving against pure silver and very little effective conductivity has been sacrificed because of the phenomenon of “edge effect conduction.”

And the conductive particles are magnetic. Therefore, their recovery from end-of-life printed electronics, smart packaging, biosensors, biodegradable electronics, etc., is greatly simplified. Claypole showed a video comparing existing technology with Ail Arian’s alternative, using printed RFID tags as the example and demonstrating how easily not only the uncontaminated silver but also the uncontaminated substrate material can be recovered.

To close the loop, recovered silver has been reused to make new conductive inks and the first prints with 100% recycled conductive materials has been successfully achieved—a positive step toward the creation of circular electronics.

ICT technical director Emma Hudson introduced the final presentation, delivered by ICT vice chair Leigh Allinson, who discussed next-generation substrate materials. Typical applications included 5G infrastructure, electric vehicles, high-performance computing and aerospace, and the driving factors include lower loss and stable dielectric constant, higher performance, and thermal reliability, together with sustainability and cost reduction. From a development point of view, there is a need to “bridge the gap” between products based on standard glass-FR-4 and those with increased functionality, smaller form factors, and improved performance.

Not all the technology requirements can be met with glass-reinforced materials, and both the availability and the choice of ultra-thin glass fabrics are becoming limited by demand. So what glass-free alternative materials are available to support next-generation requirements?

Allinson described how his company’s background in thermal management technology, designed resin flow, and precise horizontal coating technology, combined with radio-frequency and microwave formulation technology, have enabled the development of a range of resin-coated-copper and resin-coated-foil bondply materials.

He went on to explain that resin-coated-copper bondply is an unreinforced adhesive system coated onto ultra-thin copper foil for use in high-performance and high-reliability multilayer PCB stackups. Similarly, resin-coated-foil bondply is an unreinforced adhesive system coated onto polyester film, offering design flexibility in high-performance multilayers.

He described the technology of the horizontal coating process, capable of precise thickness control down to 15 microns, and explained that, unlike traditional glass-reinforced prepregs, these glass-free materials eliminate micro-Dk variability from glass weave, ensuring signal integrity at high frequencies and in designs with extremely fine features. Typical resin chemistries are bismaleimide-triazine and halogen-free high-Tg epoxy and the resin-coated copper materials are particularly suitable for mSAP processing.

Summarising the benefits to PCB designers and manufacturers, he mentioned lower dielectric thickness, good adhesion with metal, better laser drilling, and better Dk skewness. He reviewed a long list of application examples, including “M+N” PCB stack-ups and embedded packages, concluding that these families of materials represent a leap in PCB bondply technology. The absence of glass reinforcement, combined with electrical precision and superior thermal management, result in properties that enable OEMs and manufacturers to build faster, cooler and more reliable electronics without adding manufacturing complexity.

An excellent seminar rounded off with a convivial buffet and pre-Christmas networking opportunity. Many thanks to the Institute of Circuit Technology and particularly to Emma Hudson for her efforts in organising another splendid event.