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36 The PCB Design Magazine • March 2016 bility under changing temperature conditions demand the additional increase in cost over stainless steel. Stainless steel and titanium sub- strates are usually used in HTCC designs, and not LTCC. The word "co-fired" means that the conduc- tors and the ceramic are all heated (fired) in an oven at the same time. LTCC is fired at a temper- ature of up to approximately 900°C and when in use these LTCC designs can operate in a design temperature range of up to 225°C. This is one of the main advantages over standard PCB designs which are usually restricted to operating tem- perature ranges that do not exceed 85°C. We have also mentioned HTCC hybrid de- signs, and as you might expect, HTCC stands for high-temperature co-fired ceramics. These designs get fired in ovens up to 1500°C and can support operating temperature ranges of up to 500°C. But these designs are also subjected to higher conductor resistance due to the different type of conductive inks required for the higher temperatures. HTCC designs also have other con - siderations such as the requirement of different methods of soldering components using different mixtures of metals due to the higher temperature environments. Because of these reasons, HTCC technology is used for hybrid designs only if the advantages it provides are truly required. There are other hybrid technology types be- sides LTCC and HTCC in use as well. Greentape technology is a blend of both FR-4 and LTCC technologies for high-precision designs. Green- tape stacks several thin ceramic substrates, each printed with only one conductor layer, and presses them into a layered package. This technology lends itself to RF and microwave designs for Bluetooth, radar and transceiver ap- plications. But as we said, for the purposes of this series we will focus primarily on the LTCC hybrid design in our efforts to introduce you to the basics of the hybrid design world. Unfortunately, just as we are getting started, we have reached the end of Part 1 of this se- ries. We've discussed the basic structure of a hy- brid design and talked about their benefits, but there's still so much more. I teased ink resistors with a promise of more information, and that is still to come. And we haven't even touched yet on things like software differences for hy- brid design applications, routing conductors, or designing dielectric areas, to mention just a few of the topics that still need to be covered. Therefore, I hope that next month you will look for Part 2 in this series on basic hybrid de- sign, and we will continue down this path of exploration. See you then. PCBDESIGN Tim Haag is customer support and training manager for Intercept Technology. the principles of hyBrid design, part 1 A group of researchers from the UK has demonstrat- ed the first practical laser that has been grown directly on a silicon substrate. It is believed the breakthrough could lead to ultra- fast communication between computer chips and elec- tronic systems and therefore transform a wide variety of sectors, from communications and healthcare to energy generation. The EPSRC-funded UK group, led by Cardiff Universi- ty and including researchers from UCL and the University of Sheffield, have presented their findings in the journal Nature Photonics. Silicon is the most widely used material for the fab- rication of electronic devices and is used to fabricate semiconductors, which are embedded into nearly every device and piece of technology that we use in our every- day lives, from smartphones and computers to satellite communications and GPS. Professor Peter Smowton, from the School of Phys- ics and Astronomy, said, "Realising electrically-pumped lasers based on Si substrates is a fundamental step to- wards silicon photonics. The precise outcomes of such a step are impossible to predict in their entirety, but it will clearly transform computing and the digital economy, revolutionise healthcare through patient monitoring, and provide a step-change in energy efficiency." Step Towards 'Holy Grail' of Silicon Photonics

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