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March 2014 • The PCB Magazine 67 Df values and have moved into more expansive options of spread weaves and copper smooth- ness offerings, as well as leveraging new sup- plier sources for lower Dk/Df glass types. All these changes have enabled new class within a class, a spate of mid-Dk/Df materials measurably above the traditional ones but still situated below the cost and performance abso- lutes of the ultra-premium low-Dk/Df class. The traditional mid-Dk/Df materials were showing some good use in the 5–10 Gbps space, but run- ning short of really supporting the upper end of that range, forcing some designs into over-spec- ifying of materials until these new issues started appearing. The new mid-Dk/Df+ class is target- ing use as fast as 12.5 Gbps depending on trace widths and routing lengths. This in turn has put pressure on the low-Dk/Df class of materials to either reduce their cost as-is or create better per- formance versions to satisfy the ramping devel- opment of 20–25 Gbps and faster designs. Not surprisingly, both actions are taking place now. Low-Dk/Df Class Laminates To better understand the low-Dk/Df class of materials, we define them as having Dk values at or below 3.7 and Df ratings at or below 0.005. A number of the mid-Dk/Df materials can eas- ily make this Dk range if enhanced with low- Dk glass, but not while also in the range of Df. These two values together then define a distinct class. The present standard bearers are Panason- ic's Megtron-6 and, to a lesser extent, the Rog- ers 4000 series of ceramic hydrocarbons. But there are more players today and many more in the queue and coming. The thermal-mechanical behavior of these materials is always important as they are often relegated to very complex, HDI designs and so must be able to endure multiple lamination cycles at lead-free temperatures, which is quite challenging; it is very difficult for laminators to concoct complex molecules that deliver very high electrical performance while remaining mechanically stable and robust. All the materi- als of this class have proprietary resin formula- tions, so it is not possible for us to know their entire makeup, although at the farthest end, most have measurable content of PTFE (e.g., Rogers Duroids, Taconic, etc.). Cost always plays a big part in any product design, so the PTFE-laden materials are still lim- ited players, although we're seeing some very large platform boards experimenting with PT- FE-based laminates for the sake of mitigating attenuation over traces on the order of about a meter. But these are 25+ Gbps R&D designs and not what is being built regularly today. Product in the 8–12.5 Gbps space has given Megtron-6 much of its market. Targeted transmission rates have been increasing toward 20–25+Gbps, thus driving the need for even lower-loss materials, most preferably ones that do not have the high cost and processing challenges of PTFEs. A number of these have been introduced in recent quarters and are under evaluation. Performance claims are just that, always war- ranting independent testing and measurement. We are especially interested in seeing how any high-end materials behave, as testing clicks through frequencies of, 5, 10, 12.5 GHz or more and how well they survive the rigors of modern HDI fabrication and assembly processes. Also, former background testing is often front and center today, with requirements of CAF, insula- tion resistance and the like being demand items and significant filters of acceptance for a num- ber of OEM industries. Overall, as a fabricator, we are very encour- aged to see such a huge flurry of new and prom- ising laminates entering the market and are op- timistic laminators will continue providing an- swers to our most pressing needs and demands of signal integrity and speed. PCB This article originally appeared in the Sep- tember 2013 issue of The PCB Design Magazine. LAMINATE MATERIAL SELECTION FOR TODAY'S PCBS continues steve iketani is the manager of strategic technology development for the pcB operations division of sanmina-sci. Brian nelson is manager of new product introduction for pcB fabri- cation operations at sanmina-sci.