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Elementary, Mr. Watson: Honey, I Shrunk the PCBs

In 1989, the family-friendly science fiction adventure film, “Honey, I Shrunk the Kids,” was released. This movie, with a grammatically incorrect title, follows the misadventures of inventor Wayne Szalinski, played by Rick Moranis, who accidentally shrinks his children and their friends down to a minuscule size with his experimental shrinking machine.

Through a series of unfortunate events, the children end up stranded in their backyard, and because of their size, it becomes a treacherous and gargantuan wilderness. As they try to navigate their way home, the kids encounter a series of larger-than-life obstacles. Things that generally would not be a problem now pose a huge challenge: the lawn turned into a vast jungle and everyday objects became life-threatening. They face menacing insects, unpredictable weather conditions, and are forced to sleep inside a LEGO brick.

As an industry, we live in our own version of “Honey, I Shrunk the Kids.” PCB designs are shrinking smaller and smaller with each design spin. Our industry demands the latest and greatest, where innovations coming off the line must be smaller and sleeker and have all the latest new functions, which, as we know, determines the fit and form. Miniaturization and integration are growing trend with electronics.

Manufacturers have pushed that trend to the very edge of the envelope; some would say they’ve pushed too far. One example is smartphones, which have become increasingly compact, resulting in smaller screen sizes and, consequently, smaller virtual keyboards. This is a problem for me, because I suffer from a common condition called Fat Finger Syndrome, better known as FFS. Many users with FFS have expressed frustration with the diminishing size of smartphone keyboards, making typing more challenging and prone to errors. The reduced surface area of the keyboard often leads to unintentional typos, making it difficult for people (such as myself) to type accurately.

Nowhere is the tinier tech trend happening faster than with wearables and medical devices. The future market size and revenue growth of such a wearable technology market is expected to experience significant growth. Statista said the wearable devices' market size was around $27 billion in 2020¹, and it is projected to reach over $74 billion by 2026. You see them everywhere: fitness trackers, smart watches, glasses, rings, jewelry, clothing, and even shoes with embedded sensors monitoring every feasible detail about your life. It's today's version of the mood ring. (The younger generation may have to Google that one.)

Such devices come with unique engineering challenges, but the bigger problem is that wearable devices collect and transmit personal data. This is all done wirelessly by uploading your health metrics, location information, and even personal habits into the cloud. There lies the risk that this data could be intercepted or misused, compromising an individual's privacy. These wearable devices are vulnerable to security breaches and hacking. If not properly secured, personal information or sensitive data stored on the device could be accessed by unauthorized individuals.

Design Challenges and Considerations
As we saw in “Honey, I Shrunk the Kids,” size matters; the same goes for our PCBs. Things that were not typically a concern with a larger PCB design become significant problems when you reduce the board size. It is the equivalence of the backyard becoming the vast jungle.

Serendipity refers to the occurrence of unexpected and fortunate events or discoveries by chance, often while searching for something unrelated. But a principle known as "designed serendipity" refers to the deliberate creation of conditions or environments that increase the likelihood of serendipitous discoveries or opportunities.

That, in its basic form, is a PCB. We are creating an environment where the forces of energy are controlled in a specific way. Over the years, I have changed how I look at PCB design. It's not just "connecting the dots." Instead, there is a fascinating interconnection of the various parts of the design. There’s an intricate balance between every part of the PCB, the FR-4, down to the grain on the copper. A change in one area impacts others differently. Like dominoes, the other areas are impacted when one is tipped over. Nothing has more of an impact than the size of the PCB. I want to walk through a scenario that explains what happens when we reduce the PCB size.

Form, Fit, and Function
As we know, wearable medical devices often need to be compact, lightweight, and comfortable. That requires designing PCBs that fit within the limited space available and conform to the shape of the wearable device.

Getting everything into a device requires using unique solutions and miniaturization techniques, much like the old joke about squeezing 10 pounds of "stuff" into a five-pound bag. First, just using smaller components like 1005s for your discretes will not cut it. You will need what I refer to as the "all of the above" approach. You will most likely use advanced packaging components, system-on-chip (SoC) integration, microcontrollers, sensors, integrated circuits, or even ultra HDI, giving more functionality in a smaller package. These components occupy less space on the PCB, allowing for a more compact design.

PCB Considerations
With wearable electronics, size matters, and the dominoes begin to fall. Using a conventional 0.062" PCB is probably out of the question, and FR-4 is not an option, strictly due to space requirements. This is why one of the fastest growing areas in the PCB industry is flex and rigid-flex. Flex and rigid-flex are often the only solution to meet the complexity of some of these devices. There is a direct correlation between the rise in wearable/medical devices and the increase in rigid-flex circuits. It’s not a matter of if you will ever do a flex design, but when.

We have seen that a smaller area means smaller components and overall PCB space; trace routing is our next challenge. Designers must use smaller trace widths and spacings to accommodate more routing channels, and inner layers for routing to maximize the routing density. That requires using microvias to create additional routing layers. With that, another domino falls, and smaller traces have higher resistance. That can lead to increased voltage drops and power losses, affecting signal quality and power delivery. This will introduce higher impedances, making controlled impedances more difficult.

Reducing the size of the PCB impacts the entire design: component sizes and routing impact the signal integrity and EMC/EMI. Power management is another consideration since these are battery-operated devices. Efficient power management is essential to maximize battery life while providing adequate power to the various components. That involves designing power-efficient circuits, implementing low-power modes, and optimizing the power supply network.

How small can we go? A Canadian company, Precision NanoSystems, is answering that question with the creation of nanotechnology directly out of another sci-fi movie, “Fantastic Voyage,” released in 1966. To save a scientist, a submarine is shrunken to microscopic size and injected into his bloodstream with a small crew. That is now nearly a reality, with nanotechnology that can navigate the human body—injecting medicine directly into a tumor, for example.

Honestly, where can this technology go? In my opinion, anywhere our imaginations will take it.

This column originally appeared in the July 2023 issue of Design007 Magazine.