Secure PC Board Design ⚙️

Building a secure printed circuit board for your IoT Devices

April 5, 2022

PC Boards are the most foundational building block of today’s modern electronic devices. These vary in size and complexity, from the single-layer board that opens your garage door to the 60 layers found in high-density, high-speed circuit boards that operate supercomputers.

Different electronic components such as diodes, resistors, and capacitors are then mounted to the PC board to communicate and create the desired function.

PC Boards were developed in the early 20th century but had a continued escalated development in technology since then. This advancement paralleled the widespread adoption of technology and the semiconductor packaging technology that enabled the creation of smaller and more efficient electronics.

When talking about the security of these boards, we underline two ideas. On one side, the hardware and how the different elements communicate, is it readable, encrypted directly on the chip ? We look at the protocols used and what the user can see from the outside by looking at the hardware. On the other, we talk about the software, how things are programmed, and if this exhibits a particular error or flawed process.

What are Printed Circuit Boards for?

Nowadays circuit boards are everywhere, they offer a small and lightweight design. Their reliability and ease of maintenance make them perfectly suited for integration in complex systems. As these boards are mass-produced, they become highly cost-effective.

In the medical field, these circuit boards power imaging systems and radiation equipment. As these boards become more compact, engineers have the opportunity to create transportable devices for remote areas and implement very small cameras for nonintrusive procedures. The space has in part been responsible for the development of flexible PC Boards that decrease the size of complex medical devices even further.

Aerospace is another large benefactor as these boards power flights control, and safety systems. As satellites and drones come to market, the need for even more advanced tech keeps growing.

The military sector uses a lot of equipment and circuit boards, they power modern weapons, electronic systems, and all the mobile vehicles involved.

Note that in all of these three domains, security is of major importance, all of these devices could be manipulated to create devastating effects. Aerospace and the military also require sturdy boards that can withstand pressure and temperature changes as well as vibration, this directly impacts the security requirements of the board and have to be addressed in construction.

How do you build a PC Board?

When building a PC Board, keep in mind it is highly probable that your circuit will fall into the hands of an attacker. He will try and reverse engineer it to understand the internals of your circuit board and where its design flaws are. With this in mind, you should make it as difficult as possible to reverse engineer your board.

Some known techniques consist in using uncommon chips, scratching off the top of chips to obscure them, and using silicone solutions to harden designs, this makes it much harder to take your board apart.

All of these are great, nonetheless, as hackers develop more advanced methods, it’s the hardware engineer’s job to match these advancements and develop his own.

Let’s look at other important elements:

Remove any unnecessary test points

As you remove test points, it makes it much harder for traces to be probed by an outsider, this prevents someone from knowing where the point-to-point connections are. If these cannot be removed, consider using a copper-filled pad as opposed to a through-hole pad, this will obscure the connections and further increase the opacity of your design.

Hide critical traces in inner PCB layers

To make sure your critical traces are not compromised, consider sandwiching them between two solid copper layers, this will prevent them from being visible from the outside.

Use buried or blind vias wherever possible

So as to alleviate some of the routing density, you could try to of the methods available to you. Buried vias connect two or more inner layers, but no outer layers and therefore are invisible from either side of the board. Buried vias avoid the top and bottom layers and offer a similar benefit. Both of these methods reduce an attacker’s potential entries.

Try and use advanced packages, like Ball Grid Array (BGA) and Chip-on-Board (COB)

This part does require more means but provides increased security that can be worth it if security is a priority concern to you. Advanced packaging limits the visibility of your connections to strictly X-ray vision. Since all die connections will be located under the device packaging, an attacker will have a hard time manipulating, attacking, or probing your circuit. This does come to a high cost as solder points have to be verified through X-ray vision.

As our society continues to demand connected devices, it will become increasingly relevant to understand and initiate more advanced security measures. This article lists a few methods to help make your system more opaque with the idea that an attacker will have a harder time reverse engineering your PC board. Security however isn’t a fixed set of requirements, hackers evolve very quickly and often develop attacks based on the architecture they have in front of them. Be mindful of what your vulnerabilities are and don’t be afraid to implement redundant systems if security is your focus.

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