Page 11

EDNE MAY 2014

The other primary challenge for the RTU is load switching. New generations of power semiconductors are emerging in response to the need for intelligent power management across an expanding range of applications, from Automotive through Renewable Energy Harvesting, Appliances, Solid State Lighting, and RF Power. All of these applications share the same objective- the efficient and economical management of power. Heavy, bulky electromechanical relays are being replaced by IGBT or MOSFET switches, and these same devices are also used for power control through pulse width modulation of IGBT or MOSFET power stages. The problems faced by peripheral crosspoints in Smart Grid systems are identical to those involving Digital Power – the need to carry and control loads up through 24 kVA. Power semiconductors packaged as surface mount devices are enabling significant form factor improvements Figure C. HSMtec Concept for power management and control systems, leading to a proliferation of package types such as those shown in Figure. B. In addition to the direct-drive capabilities provided by increasing voltage and current ratings, most of these bring lower assembly costs and improved assembly efficiencies through surface mounting. But, since they're power devices some fraction of that is transformed into thermal energy notwithstanding the improvements in junction efficiencies, and this has to go somewhere or the device will overheat. This is bad news for lifetime and reliability, because semiconductor lifetimes and failure rates are directly connected to temperature of the semiconductor junction. Most predictive models base the relationship between temperature and failure rate on the Arrhenius equation, where temperature can be used as a proportional multiplier. A firstorder solution of this relationship suggests that MTTF (mean time to failure) is reduced by half for every 10°C rise in junction temperature. The combination of surface mount packaging and compact assembly volume means that in most cases the heat can no longer go out to ambient through a heatsink. Surface mounted devices are intended to be small, and they lay flat on the board. So, at least for the first part of the journey, the only way out is down... into the board. Which means that the designer must now consider the need for low-resistance thermal pathways in addition to the well-known mounting and interconnection functions. The Solution The solutions which are emerging offer the potential for replacement of hardware and components formerly used to manage heat and power, and range from simply providing a metal base in the board for heat dissipation to sophisticated solutions combining thermal and power management with high density interconnect and formability. The term “Metal in the Board”, or “MiB” is coming into general use, because these solutions are not metal “core” or metal “base”. They are metal “in” the board. The manufacturing technologies and capabilities of MiB range from simple three-layer buildups commonly known as “Al-based” or “insulated metal substrate” to complex assemblies using a variety of techniques to provide low thermal and electrical resistance pathways in the board. In every case, the MiB component is providing additional functionality – thermal and/or power management. In the full version of this article, the author continues to explore practical examples of integrated measurement and Complete article, here switching designs using this technology. learn more Compensated Basic Board Mount Pressure Sensors EDN-Europe_277x93_FINAL.indd 1 3/31/2014 1:33:42 PM www.edn-europe.com EDN Europe | MAY 2014 11


EDNE MAY 2014
To see the actual publication please follow the link above