PCBs Lighten the Loads for Commercial UAVs

Drones or unmanned aerial vehicles (UAVs) are typically associated with military users, although a growing number of applications are being found for UAVs in commercial, industrial, and even medical markets. Commercial users await approval from key government agencies, such as the U. S. Federal Aviation Administration, for properly authorized use of drones in non-military applications, but interest in non-military use of drones is growing rapidly, as the number of commercial drones with different sensor payload packages is growing, for help with everything from herding and counting cattle on farms to inspecting the structural integrity of commercial buildings. The differences in commercial and industrial applications for UAVs from battlefield electronic warfare (EW), reconnaissance, and surveillance missions for the military are apparent. But how do commercial UAVs differ from military UAVs for the electronic payload circuit designer who must choose the optimum printed-circuit-board (PCB) material for that mission?

The nature of a UAV’s application will determine the sensors required in its payload. The functionality and performance needed to best complete the application will help establish guidelines for the minimum requirements of the circuit materials that support a drone’s payload. Commercial drones are available in a wide range of sizes and with a wide range of sensor packages for many applications. Present and future applications for commercial UAVs include building and power-line inspections, farming, public safety, search and rescue (SAR), mapping and surveying, retail package delivery, weather forecasting, unmanned drone taxi services, and warehouse inventory management. Sensors include light detection and ranging (LIDAR), radar, infrared (IR) thermal imaging, visible-light cameras, and magnetometers.

Electronic circuits for military drones are expected to have higher reliability than similar circuits for commercial drones. While commercial drones may be specified for typical flight time of about one-half hour for a battery charge, a military UAV must provide a flight time closer to one hour for a battery charge, to support extended missions with longer ranges. Normally a larger battery would be part of the solution for longer flight time, but the added weight does not help with a commercial drone’s logistics and cost nor with a military drone’s compliance with reduced size, weight, and power (SWaP) goals. The military trend for reduced SWaP in electronic systems such as UAVs is sure to be adopted for commercial markets where cost and competition are major issues. For example, more efficient power-supply circuitry aided by automatic power detection and making use of low-loss circuit materials can contribute to longer UAV flight times without need for a larger battery.

High-Flying Circuits

Circuit materials for UAV payloads, whether the drones serve military or commercial applications, must support current trends for miniaturization even as the circuits become more densely populated with increasing number of functions. Circuit laminates must support integrated circuits (ICs) that may contain a suite of sensors or system-on-chip (SoC) devices that are chips with multiple components, active devices, and passive devices, or system-in-package (SiP) devices that can contain a complete subsystem, such as a receiver, within a surface-mount-technology (SMT) package. The leads on these SiP housings can be high in number and very closely spaced, requiring a circuit laminate capable of providing high-isolation interconnections to the package pins even when they are extremely close and in packages measuring only 5 × 5 mm.

Low loss is essential for circuit materials for both military and commercial UAVs, although the environmental requirements for commercial PCBs, such as for operating temperature range and relative humidity (RH), are less stringent for commercial UAV circuits than for military UAV circuits. The standard operating temperature range for military electronic circuits and components, for example, is -55 to +125°C compared to a temperature range of 0 to +70°C for commercial circuits and components. Reliability testing by means of extended temperature and elevated RH is usually performed within environmental chambers. Still, although commercial products are designed and manufactured for less severe operating environments than military products, commercial products are often tested according to military-grade test standards for temperature and humidity, such as MIL-STD-883, MIL-STD-810, and MIL-STD-202.

Because both commercial and military UAVs feature such densely packed electronic payloads with multiple sensors, and they must save as much board space and weight as possible, mixed-signal circuit design approaches are often adopted for UAV payloads, using multiple circuit materials best suited to the different circuit partitions (analog, digital, power) within the payload. Ideal circuit materials are those that can provide sufficient isolation between closely spaced circuit traces for optimal signal integrity even with different types of signals, speeds, frequencies, and power levels. In addition, both commercial and military UAVs are reaching to the millimeter-wave frequency range for enough frequency bandwidth to support the instantaneous communication of massive amounts of sensor data from a drone to a control station. UAV payload circuit materials must have the qualities needed for consistent, reliable performance at frequencies ever increasing into the millimeter-wave range (30 to 300 GHz).

As reported in previous blog on LEOS, several circuit materials from the Isola Group and our Asia Pacific division, such as Tachyon® 100G, I-Tera® MT40, and Astra® MT77, are well suited for high-frequency and HSD circuits. Tachyon® 100G can be used for circuits at digital speeds to 100 Gb/s and faster while Astra® MT77 is a low-loss foundation for high-frequency signals through W-band millimeter-wave frequencies (75 to 110 GHz). Astra® MT77 maintains a Dk of 3.00 across a wide operating temperature range of -40 to +125°C to serve both military and commercial UAV circuits. It is a very low-loss material, even for millimeter-wave signals. And it is process compatible with lower-cost FR-4 materials to simplify manufacturing of multiple-signal circuit assemblies based on multiple circuit materials. And for commercial drones in competitive marketplaces, a little bit of FR-4 may go a long way, especially for lower-frequency and power circuitry.

14 February 2023