EMC & THERMAL MANAGEMENT FEATURE
SENSIBLE PCB DESIGN RULES FOR SMART DEVICES
In the rapidly expanding market that is IoT, devices must be designed with EMC in mind but not over-engineered. Here Ralf Brüning, product manager and senior consultant with Zukenat the Zuken EMC technology center in Paderborn/Germany offers advice and guidance
C
onsidered by many to be just as big as the dot-com boom, the Internet
of Things (IoT) is fast becoming an integral part of life, connecting as it does smart devices within an ever- expanding ‘information society’. For instance, in May, GSMA Intelligence, a business unit within GSMA (which represents the interests of mobile operators worldwide) predicted that by 2025 the global IoT market will be worth $1.1 trillion, of which 68% will come from platforms, applications and services. Of these, it is the applications and
services that seem to receive the most attention when the IoT market is discussed; certainly in the general media. This is rather bizarre, because it is the devices, with their PCBs and ICs, that are the bedrock of IoT. Moreover, the IoT market is also becoming renowned for its thin margins; and guess where those margins are to be found? Keeping costs low and hitting time to volume targets are twin imperatives for the OEMs of IoT devices but satisfying both is no easy feat. IoT design considerations are considerable. For instance, in wearables, size, weight, form factor and battery life are all important factors. In addition, new exotic materials (including flexible electronics and displays) are increasingly employed and many devices, particularly in medical, require new sensor types; to the extent that IoT is now recognised as one of the biggest drivers for sensor development. The operating environment is also a
consideration, and designs must factor in mechanical shock and vibration, moisture levels (from none/dry to submersion-in-water) and dust. There’s also the electromagnetic (EM) environment to consider. It presents considerable challenges and tends to be the one aspect of design with the most hidden costs.
THE INTERFERENCE OF THINGS The majority of IoT devices are wireless and many employ multiple comms protocols. Moreover, as new IoT must- have accessories and IoT-enabled white goods and office equipment become prevalent, the smart home, smart office and smart city may well experience IoT device congestion; higher number of devices vying for bandwidth; and with the Internet of Things will come the ‘Interference of Things’. In order to comply with general and,
increasingly, industry-specific regulations, IoT devices must be tested for radiated emissions and susceptibility. Creating an IoT requires a rich mix of design elements and disciplines including digital and analogue, electromechanical (e.g. actuation), mixed-signal transducers (sensors) and RF. From an EMC perspective, the entire IoT device needs to be considered, not just a single PCB in isolation. Indeed, a typical IoT devices is a 3D multi-board design problem, where some of the boards might be flexible (See Figure 1). However, many of the common-sense PCB design rules that serve us so well in the other industry sectors don’t necessarily apply to IoT. For instance, you’re not going to find a large loop
/ ELECTRONICS Figure 1:
Frequently used for interconnect purposes (as above) flex-boards will be used in wearable IoT devices and will carry increasingly complex components
antenna on a PCB that’s no larger than a postage stamp. Similarly, the (small) form-factors will give you little freedom when it comes to the placement and separation of components, or the luxury of shielded tracks. Instead there is greater emphasis
placed on good grounding practises and, if possible, the isolation of inputs (often from sensors). If space permits, filtering is beneficial for ensuring a proper and stable power supply and for preventing DC noise, and efficient bypassing and power distribution system optimisation are important too. Adherence to these ‘new’ rules should negate the need for additional components; i.e. ones needed for fixing EMI issues and which don’t contribute to the circuit’s ideal behaviour. Indeed, with smaller form-factors being the order of the day you’ll be fighting for every square millimetre anyway. Increasing the number of components (or board layers to combat EMI) can easily tip a project from good profits to lower (or worse) because of time delays and material costs. Also, the additional components will
almost certainly impact the overall power consumption (and could result in thermal issues) but you should be designing with low power in mind anyway. In this respect, most device manufactures provide recommendations for track impedances and most CAD tools can show predicted impedances.
BEARING IN MIND In conclusion, we’re in the relatively early stages of the IoT boom and devices (many of which will be battery powered) are having to operate in an increasingly EM noisy world. From an EMC perspective, you should
design with the following in mind: the entire device (not just a board or module); low power consumption; good signal and power integrity; crosstalk control; and compliance, especially if you involve RF transmitters in your IoT device.
Zuken
www.zuken.com T: 01454 207800
ELECTRONICS | JULY/AUGUST 2018 39
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68
