Signal-integrity challenges are becoming more pressing across all frequencies, and materials technologies are evolving in response.
As the IoT gathers pace, keeping people – and, increasingly, things – connected involves shifting huge quantities of data. Handling the volume and speed imposes immense engineering challenges in all the various elements: handsets, IoT gateways, telco core networks. Even today’s cars are part of this high-performance information infrastructure, as manufacturers want to position value-added services like infotainment and e-call emergency care. And as the data get aggregated at various points into the network core, economics means they’re viewed as a commodity. The more that can be moved in a given time, the lower the cost per bit.
Maximizing the performance of data-handling equipment – whether it’s a smartphone, in-vehicle infotainment system, or carrier-class network switch – requires attention to all aspects of the design. In addition to key components like processors, converters and line drivers, elements like connectors and cables come under scrutiny, and all the way through to board-level design issues that affect signal integrity. Signal integrity challenges used to be mainly the concern of engineers working in esoteric areas like radar, but this is no longer true. Today, the demand for communication equipment to respond instantly to everything people want to do forces engineers to design for signal integrity in even the most mundane applications.
Engineers starting out on a new design already have some knowledge of approaches that have worked before, and those that for some reason or other have not. This is the baseline starting point, and there are always industry gurus and seminars for advice. The next step is to start combining that knowledge with specific product requirements. Then, they have to start looking at the unknowns, and this can often include the behavior of materials like the PCB substrate and metallization. There may be some experience within the organization, and other knowledge can come from specialists in the supply chain. It all adds up to a large body of information that needs to be brought together before the design team starts making decisions.
The way materials are selected and used can help create products that really stand out against the competition by offering great performance and value. At a high level, choosing low-loss materials can ensure you meet signal-integrity targets, but can add cost to the end-product. On the other hand, if the design know-how is there, it may be possible to meet the same targets with a lower-cost material and remove the burden of those extra dollars from the BoM.
Typically, engineers will look at dissipation factor as their key parameter determining the impact the substrate material will have on signal integrity. It’s not the only relevant metric, however. At Ventec, we see the dielectric constant, or Dk, as having a large impact on the mechanical and electrical properties of the printed circuit board. For example, it can determine the overall Z height of the PCB, and this can affect the overall enclosure size and whether the electronic assembly will allow the finished product to meet the specified dimensions. Simply put, both the dissipation factor and the Dk describe the substrate’s energy-release properties, and the mathematics bears this out. The importance of the Dk, however, is often neglected.
As markets are changing, signal-integrity challenges are becoming more pressing across all frequency ranges, and materials technologies are evolving in response. At Ventec, for example, we are developing new materials with ultra-low Dk to address the most stringent demands, and we are working with connector suppliers, PCB fabricators and OEMs to assess its performance within the system as a whole. This type of industry collaboration is important. Working in isolation is not an option because we need to fully understand the practical nuances of using these new types of materials. With the help of partners, we are studying the effects of ultra-low-Dk materials on electrical performance and signal integrity very closely, including the impact on antenna effects, such as through the barrels of plated holes or connector pins.
Product designers should also consider the effect their choice of materials has on system reliability. As a specialized material supplier, we can go some way toward providing reliability information through our own testing. However, OEMs need to work with their suppliers individually to collect important data that are specific to their product design, usually with support from external test houses. The automotive sector is one obvious area that demands intense focus on reliability and testing, and telcos, for their part, tend to place very high-reliability demands on their chosen materials.
Looking ahead, the thermal effects of high signal frequencies are also coming under consideration. As higher signal frequencies are used, extra heat is generated inside the PCB, and this moves toward the edges of the board through planes and other conductors. This happens differently in the z axis, compared to x-y, and we are looking closely at the behavior here to come up with materials to help deal with these issues. Insulated metal substrate (IMS) has some promising possibilities, and new materials in development give eight to nine times the thermal transfer capability of ordinary FR-4. The automotive and telco sectors, again, could be key beneficiaries of the enhanced thermal performance, combined with rigidity, this new class of substrates can offer.
As engineers come under increasing pressure to keep raising the performance of successive generations of products and systems, materials selection becomes a more important and more interesting part of the system-design mix. It’s no longer “just a substrate.” Taking the time to look at what’s available and talk with suppliers to gain extra knowledge about how to apply the materials will pay greater dividends as markets for high-speed digital communication systems continue to march forward.
Martin Cotton is director OEM technology at Ventec International Group (ventec-group.com); This email address is being protected from spambots. You need JavaScript enabled to view it..
