“The temptation to over-specify laminates can be great, but this ‘sledgehammer to crack a walnut’ approach can result in a lot of additional cost going into the PCB unnecessarily. Good design along with astute laminate selection will result in a robust and economic solution.”—Martin Cotton.

This month on the Signal Integrity Journal, we are taking a closer look at the new materials options for enhanced SI or PI performance. I recently asked Martin Cotton, director of OEM technology for the Ventec International Group, how his company saw the new materials opportunities for designers.Ventec designs and manufactures copper clad laminates and prepreg bonding materials used for printed circuit board (PCB) applications. Cotton is founding member of the ICDA and the IPC Designers Council, a member of the IPC Executive Board, sits on the IEC steering committee and is a published presenter and regular speaker at industry events.

Signal Integrity Journal (SIJ): What are some of the latest materials being used for PCBs that can improve signal integrity? Why?
Cotton: The issue of signal integrity, as it relates to PCB laminates, has two factors: one is insertion loss and the second is resistance. I believe future trends will look more at the resistance of traces. The aim is to lower the Df (Dissipation Factor) to enable faster data rates. Laminate manufacturers have always developed IP focused upon the chemistry and composition of laminates to do this. Raising and lowering the Dk (Dielectric Constant) of the material relates more to geometry and some of the latest materials have a Dk as low as three and Df as low as 002, which makes for very fast signal speeds.

However, it is very important not to underestimate the importance of design in improving signal integrity. The temptation to over specify laminates can be great, but this “sledgehammer to crack a walnut” approach can result in a lot of additional cost going into the PCB unnecessarily. Good design along with astute laminate selection will result in a robust and economic solution.

At Ventec, as well as supporting good design we also prioritize the manufacturability of the PCB to achieve the right solution for signal speed and integrity. A holistic approach that strikes the right balance, and uses design to enable incremental improvement, is the key to success and not wasting money.

SIJ: How do you characterize your materials?
Cotton: Ventec materials are characterized and specified in terms of quality, reliability and performance and in accordance with industry standards such as AS9100 Rev C, TS16949, etc. Reliability characterisation is by measuring Conductive anodic filament (CAF), plus thermal reliability testing using Interconnect Stress Test (IST) and other tests.

SIJ: What performance problems can be solved with materials?
Cotton: Performance problems are more accurately and better solved with good design. You can solve issues by over specifying material, but that will add cost that is hard to later remove.  Signal integrity and data rate are the key performance indicators that need to be measured and analyzed and while most design houses know the theory of designing with this in mind, less than half really have the experience and practical skills to get the right design and avoid putting too much overhead in the material selection. Talented, experienced designers will have a handful of tricks they can use to get the best solution. Experience is valuable here, and we are moving into a blend of art and science.

The key issues we are seeking to improve are speed, skew and jitter. And while these are related to Dk and Df, they are also related to trace width, bringing us back to the importance of good design. If you put a copper trace over a high resin portion of a laminate it exhibits a different Dk to a lower resin content path. This is why spread glass or square glass is used, to help amortize or mitigate skew.

Another issue that comes in is the thermal capabilities of the laminate. Increasing thermal performance can impact Dk and Df, so holistic design and laminate selection is required so neither performance measure is allowed to excessively impact the other.

SIJ: Do your customers understand how material properties affect performance? Do you need to train your customers/how do you do that?
Cotton: In our OEM group we deal largely with design engineers and PCB designers, but we also speak to the reliability engineers and the people that liaise directly with the PCB manufacturers. They each have different priorities. The PCB manufacturers are looking for materials that are easier to use and fit a stable tried and tested supply chain, whereas the OEM will have priorities that impact upon their design and their commercial imperatives.

Most of those up and down the supply chain understand, but with varied objectives it is not always a harmonious selection process. It also varies in different geographies where the desire to prioritize cost over quality or performance can impact upon selection.

We have our OEM team to educate and bring these varied ideals together. My design and manufacturing background, combined with Ventec’s laminate knowledge has allowed me to see what each side sees. I spend most of my time listening to the various voices and helping all the parties to create the right solution. As well as through articles like this, we do this at seminars, events and one-on-one discussions.

SIJ: What tools do you use for simulation and characterization?
Cotton: There are simulation tools, but we don’t use too many of them. We do use vector network analysis tools to get insertion loss data, and we use tools from Polar Instruments (http://www.polarinstruments.com/index.html) which reflects what the PCB manufacturers have. There are some known standards and measurement tools that we work with, but the key is always in dialogue. Decisions are holistic and while simulation provides data, it doesn’t provide the whole story, which needs to consider design, build, and the commercial imperatives that relate to the product. We do work with Polar, for example, to make sure all our materials data is available on their simulation products.

SIJ: What’s next for materials as it relates to SI/PI? Ultra thin laminates? 3D printing? How can current materials science R&D help? What is your company doing in these new areas?
Cotton: Thin and ultra thin laminates, with and without reinforcement are being more widely considered and used. Materials science has moved on leaps and bounds in the last decade or so. What you can do now wasn’t previously possible, so we are seeing more and more materials becoming available.

Signal integrity and, indeed, thermal performance demands are increasing, particularly for mil/aero and automotive applications where miniaturization and density of components are pushing the boundaries of PCB design. Ventec’s Tec-speed (see figure) materials and our strategic roadmap of new innovative additions to the range, provide the technological innovation, high performance and quality demanded by our customers.

We have a test lab and a development group, and in the OEM team we are working with clients to develop unique solutions while constantly sharing our vision with them on the future demands their products will bring. Our job is to be the conduit between demand and supply, letting both sides know what’s needed and what’s possible. As well as this, we work closely with academia and various groups and associations.

Figure 1: Ventec's tec-speed brand includes a range of products in high speed/low loss PCB material technology.

Janine Love is a Contributing Editor to Signal Integrity Journal.