On the outside, drones appear to be very basic, yet internally, they are a cramped combination of power, sensors, radios, and high-speed processors. Each gram counts, each connector a risk and each vibration may cause a field failure to what seemed like a good design.
This is the reason why a multilayer rigid flex pcb, FastTurn PCB strategy has become the flight controller, camera gimbal and mini size payload board of choice by more drone teams. It offers high wiring density, reduced interconnects, and routing cleaner on the same footprint, and retains the design rugged enough to fly in the real world.
I have been doing some electronics work and the drone was flying well on a bench, and it would begin to drop packets or re-boot in the middle of the air as the motors revved up. The problem itself, in almost every case, was the PCB layout and the interconnect choices.
The grounding plan, right multilayer stack-up and design of flexible interconnect can save weeks of debugging in future.
The use of multilayer PCBs to design drones is warranted.
Why drones benefit from multilayer PCBs
An IMU, barometer, GPS, magnetometer, ESC signals, video processing and a high-frequency radio connection are all features of a modern drone. Placing that on a 2-layer board usually requires long traces, untidy ground returns, and a dense routing around noise generators.
This is addressed in multi-layered PCBs by adding extra planes and routing layers to allow signals to be short and controlled. Having 4-10+ layers you are able to maintain a solid ground plane beneath sensitive signals, isolate power rails and minimize electromagnetic interference (EMI).
That is important in drones since loud power stages and motors are located near sensitive sensor lines.
Mechanical strength is also enhanced by a structurally sound multi-layered board. Drones shake, drop, and experience thermal changes. Additional layers may imply increased rigidity and more level platform of fine-pitch parts.
What is changing in drone packaging with rigid-flex?
Rigid-flex consists of hard FR-4 parts and soft polyimide parts in a single circuit. The flex region takes the place of ribbon cables or board-to-board connectors.
This is a big deal in drones.
Fewer connector failures
Connectors fail first. They are subject to vibration loosening, corrosion and they increase the time of assembly. Rigid-flex eliminates the use of several connector points, improving reliability.
Lower weight
Weight drops. With flex interconnects, very large cables and connector housings can be substituted.
Easier 3D packaging
3D packaging becomes easier. Rigid-flex assembly folding is used to fit curved frame work, gimbal housings with tight fit stops, and stacked electronics bays.
A multilayer rigid flex PCB build would be the easiest engineering decision to make, where high reliability and small size is desired.
Common rigid-flex drone applications
Rigid-flex drone applications are common in the following applications.
Flight controller stacks
Flight controller and sensor module in a stacked design, with the flex connections being the minimum height boards.
Camera gimbals
Gimbal camera systems where repeating motion will enjoy the flex which is made to bend.
Mini FPV builds
Electronics folded in mini FPV drones with space constraints, where connectors are problematic at times.
Multilayer rigid-flex vs standard rigid multilayer
A flexible multilayer PCB-board is typically less expensive and easier to produce. Rigid boards can work well provided that your drone has a lot of internal space and you can work with powerful connectors.
Rigid-flex is more expensive per unit, but it can save overall cost in the system since you can fewer assembly steps, less wiring errors and connector troubleshooting. The cost argument in my case goes the other way considering warranty returns and the amount of time wasted in tracking faults that are vibration related.
Key comparison points
Reliability: Rigid-flex normally prevails due to decreased connector points.
Serviceability: Rigid boards are possibly easier to replace, whereas rigid-flex is more internalized.
Weight and space: Rigid-flex tends to win, particularly in the small drones.
Initial PCB price: The usual price of standard rigid multilayer is lower.
Design considerations for drone-grade multilayer PCBs
Signal integrity and clean grounding
Drones carry high-speed digital signals, high-frequency radio frequency as well as power with noisiness in the same small board. A stack-up enables assigning of clean reference planes.
Shorten high-speed signals, have ground planes next to signal planes, and do not split ground under sensitive traces. A robust return path would tend to cure any mystery glitch that only occurs when throttle is applied.
Power integrity and noise control in motors
Power lines are injected with noise by motors and ESCs. Where feasible, use dedicated power planes, add local decoupling around all key ICs and isolate noisy power areas around sensors.
Layout does not simply consist of the ability to fit the parts; it deals with managing the flows of current.
Vibration and mechanical reinforcement
Selecting mounting points is important, and heavy components should not be mounted on a thin section. The designs with rigid-flex will keep control bend radius with copper not in the bend-region unless it is made to flex.
A crumpled tail that is bent unnaturally will not last long.
Thermal management
Small drones can trap heat. Internal copper planes, thermal vias, and intelligent component placement can be used on multilayer boards to conduct heat. That prevents stabilization of processors and minimizes sensor drift.
The significance of FastTurn in the construction and development of drones
Drone hardware changes fast. You mock, try, fix and repeat. The difference between time shipping and seasonal miss is fast-turn manufacturing.
Planning the FastTurn PCB workflow
When designing a multilayer rigid flex pcb, manufacturing should be considered on day one. That implies stack-up notes that are clear, trace/space rules that are realistic, controlled impedance where necessary, and complete fabrication drawings.
Insert test points and outline inspection and electrical test expectations early. In high-turn constructions, small omissions cause huge delays.
Another useful point to remember is that the quickest prototypes are those which do not attract questions. Unless the factory must make the guess, you lose time.
Conclusion
In conclusion, it is possible to say that the choice in favor of a smartest PCB regarding the drones of the modern era is the best solution.
Electronics are fragile to drones. They require lightweight designs, clean signals and vibration resistance. FastTurn PCB strategy uses a multilayer rigid flex pcb to put more functionality in a smaller area and reduce connector failures and performance enhancement.
When your drone has tight packaging, assemblies, or high frequency radios; it is common to upgrade to rigid-flex to make it a bit more stable and easier to put up.
In case of a doubt, reason like a pilot: reliability is better than almost working. Right multilayer and rigid-flex solution is able to transform a delicate prototype into a product which can withstand actual flights.
FAQs
What is the simple definition of a multilayer rigid-flex PCB?
It is a single board that has rigid board and flexible board, which is constructed in many layers of copper. The components are contained in the rigid areas and the flex areas are used to connect sections without cables or connectors.
Is it necessary to have multilayer PCBs or is 2-layer adequate?
Basic drone designs may be built around 2-layer boards, although numerous designs today exploit 4 or more layers to provide enhanced grounding, cleaner power and reduced EMI. This normally enhances stability and minimizes random failures.
Is rigid-flex exclusively high end drones?
Not always. This is typical of high-quality drones, but it is also reasonable with small drones when there is not much space or when the connectors wear out due to vibration. Value is based on your packaging and reliability objectives.
What are the causes of rigid-flex failures in drones?
The most frequent reasons are bending the flex excessively, introducing copper or vias into bend sections without appropriate regulations, and recurrent stress at the point where the flex joins the solid space.
The majority of problems can be avoided by good bend-radius planning and correct stack-up rules.
Which is better to select rigid multilayer or multilayer rigid-flex?
When there is space, maximum movement and connectors can easily reach, rigid multilayer can be a solid option.
Multilayer rigid-flex is generally the more engineering-friendly choice when you need smaller folding dimensions, reduction in the number of connector, or greater vibration insensitivity.
