The term IoT, or Internet of Things, refers to an infrastructure comprising several electronic devices connected to the Internet. Smart devices, remotely controllable by means of dedicated apps, represent only a small part of the IoT network. The ability to connect together smart sensors and traditional electronic devices has had a significant impact on various application fields, such as industry, agriculture, biomedical, transport and consumer electronics. The primary requirement that every IoT device must meet is definitely connectivity, achieved through wireless technologies such as Bluetooth, Wi-Fi and mobile network. As a result, the development of the hardware capable of supporting IoT functionality passes through a subtle but targeted change: connectivity, remote control and high energy efficiency are requirements that every IoT device shall meet.
The design of an IoT device requires proper evaluation and the right selection of three key factors: sensors, wireless connectivity and power management. The printed circuit board, which must be able to support the functionality offered by these components, requires a different design approach than the conventional one. The main aspects that affect the design of an IoT PCB are the following:
Wireless connectivity, common to every IoT device, implies obtaining the necessary certifications relating to the RF part. The most common certifications are FCC (in the United States), IC (in Canada) and CE (in Europe). Additionally, designers must consider standards related to intentionally and unintentionally emitted radiation and requirements for additional certifications such as PTCRB and WEEE. Obtaining certification is facilitated by the use of pre-certified RF modules, which can be integrated directly into the device, avoiding expensive certification processes.
The high demand for IoT solutions has led to an acceleration in the development of design tools for PCBs with AMS (Analog/Mixed Signal) signals, based on specific models, simulations and circuit analysis. Simulation is the phase in which the integrity of the connections is validated. Suitable software tools simulate the schematic of the circuit, considering different parameters such as operating point, time domain, frequency domain, Monte Carlo analysis, sensitivity, and worst-case scenarios. For wearable devices, special requirements such as size, power consumption and charging time need to be met.
One of the secrets to creating a successful PCB is to always consider, from the very beginning, the assembly and manufacturing phases. An example is provided by the wearables market: the very small space available for assembly has brought out the need for flexible PCBs that can flex and bend without breaking or compromising the functionality of the device. Also, industrial devices and equipment for assembly and material handling must withstand shocks, vibrations and other extreme operating conditions. In addition to flexible PCBs, another technical solution that can simplify the fabrication of an IoT PCB is the adoption of System-in-Package (SiP) technology. System-in-Packages allow to integrate increasingly complex analog, digital and RF systems on a single chip, with form factors very similar to those of traditional single chip solutions. Figure 2 shows an extremely compact SiP solution for the implementation of a Sigfox node with up-link and down-link functionalities. SiP components greatly simplify PCB design and manufacturing, with advantages also on costs. The SiP module in Figure 2 is certified, has an integrated antenna and does not require any external components.
Figure 2: A SiP module (source: ON Semiconductor)
IoT devices must be able to maintain constant connectivity with the network and with other nodes belonging to it. In industrial applications (IIoT and Industry 4.0), 24/7 operation is very common and, therefore, an uptime of 100% is incredibly important. Maintaining adequate and constant power levels at the PCB level is critical to maintaining operational capability and connectivity. This is also essential to extend battery life in portable devices and to ensure facility level efficiency. At each stage of the development of an IoT device, starting from the PCB design, it is necessary to verify the manufacturability of the product. A tool such as the DFT (Design for Test) is for example useful for verifying the testability of the PCB and for identifying any manufacturing defects in advance. Similarly, DFMA (Design for Manufacturing and Assembly) analysis allows the identification of PCB design problems that can be corrected before going into production.
For many classes of IoT devices, security also implies the adoption of measures to prevent PCB counterfeiting, an important aspect especially in metrology applications. With the growing demand for solutions to support IoT applications, PCB manufacturers are changing the way they design and validate their printed circuit boards. A very common method is to add coded identifiers (IDs) on each physical layer of the PCB. Each ID is cryptographically tied to that of the other layers, which means it is almost impossible to replicate it successfully. This technique is much more sophisticated and secure than the standard one, based on printing a simple barcode ID on the top face of the PCB.