This post is the third in a series about how to read CT scans, in collaboration with Lumafield (which provided our awesome CT scanner) and No Starch Press (which contributed all the cool cross-section images from the book Open Circuits).
When people tour the iFixit office in San Luis Obispo, we always like to show off our CT scanner. “A CT scanner?” people say, “Like, in the hospital?” Exactly, yes. Sometimes they still think we’re joking. “Why on earth do you need a CT scanner?”
The answer: CT scans are a secret weapon for repair information. They help us figure out how stuff ticks before we turn a single screw. And in this series, we’re helping you see what we see in Computed Axial Tomography images.
In Part 1, we ran through the basics of what a CT scanner is, how it works, and how it can be invaluable for teardowns and repairs. In Part 2, we took a closer look at a few components and talked about how they worked.
In the final part of this series, we’re going to take a macro-level look at some common structures that can be identified in CT scans. While component-level identification helps us locate potential failure points inside a device, the big-picture view helps us understand how a device is put together (and how it might be taken apart).
Artifacts, Density, and Magnets
One of the first things you might notice in some CT scans is noise: The picture may not be equally clear in all places. But don’t discount these as a problem necessarily, because these artifacts sometimes can be informative in their own right.
An X-ray source will emit both high and low energy radiation, the energy being determined by the photonic radiation wavelength and frequency. Dense materials tend to absorb the low energy X-rays, allowing the higher energy photons to pass through which creates a “beam hardening” effect in the form of streaks in the final image.
A similar type of artifacting in the form of a cloudy fuzziness can be observed around dense materials. This is also beam hardening, but thanks to various post processing methods, those streaks have been reduced to a fuzzy blob.
Whenever you see this type of artifacting you can be fairly confident that you’re looking at a change in material density. Steel, copper, and titanium are all examples of high-density materials, as are neodymium magnets. Spotting a fuzzy cloud on the surface of any resolved CT image is a sure-fire way of quickly locating these magnets in a scan.
Traces & Vias
A trace is a sliver of copper wire etched into a PCB. These conductive pathways connect different components (like processors, memory chips, and sensors) by directing current where it needs to go. When visualized with an X-ray or CT of high enough resolution, they appear as snaking lines of various thickness separated by a void. That void is the lower-density non-conductive material separating the copper traces from each other.
Modern electronics aren’t limited to a single-layer PCB. Instead, they rely on multi-layered boards stacked like a high-tech sandwich. A via (which is actually an acronym, short for “vertical interconnect access”) is a tiny hole, often filled with conductive material, that allows electrical signals to travel between layers.
PCB Antennas
On a PCB, copper isn’t just used as a wire. Among its very many uses, a copper trace of sufficient thickness and length can be used as an extremely compact and low-profile antenna. The tell tale signs of a PCB antenna are usually thick straight traces of differing length that terminate on one end without connecting to anything. They’re usually placed in close proximity to each other, ideally clear of any other electronics around them to avoid interference.
Different trace lengths enable communication over different frequencies. In this Xbox controller, we can see a dual-band 2.4GHz and 5 Ghz antenna used for WiFi and Bluetooth communication. Note the inclusion of a second monopole 2.4 GHz antenna on the left; this is added to increase signal diversity and increase reception.
AA Batteries
AA batteries come in a few different flavors, and their internal structures tell you a lot about how they work. In CT scans of an alkaline AA, you can clearly see a nail-like rod in the center, which is the brass collector pin that transfers the battery’s internal energy to the device it powers. The collector pin is surrounded by a lower-density zinc paste (the anode) which is hemmed in by a dense manganese dioxide cathode outer shell. All of this is wrapped tightly into a metal cylinder. Alkaline batteries are built to be simple and sturdy, but they’re made for one-time use only.
The internals of NiMH (Nickel-metal Hydride) and lithium-ion AAs share some similarities with each other. Instead of layers, they use a rolled-up sandwich of materials to store and move energy more efficiently, often referred to as a “jelly roll.” NiMH batteries use a relatively safe water-based electrolyte and are built to last through hundreds of recharges. NiMH batteries share electrical properties that are closer to what you’d get with an alkaline battery.
Lithium AAs come in two types: non-rechargeable versions that cram in as much power as possible, and rechargeable versions that include tiny circuits and charging ports but make the battery safe to use again and again. Rechargeable lithium-ion AAs like the one in this CT can only be charged using the USB-C port near the positive terminal. The circuitry connected to the USB-C port is designed to keep the chemistry inside the battery stable and safe.
Why You Can’t Recharge a Non-Rechargeable Lithium Battery
Don’t try recharging a lithium battery that wasn’t made for it. It could be dangerous. Lithium metal anodes in non-rechargeable batteries are highly reactive and form dendrites if recharged, leading to short circuits and potential thermal runaway. The electrolyte and separator in non-rechargeables are not designed to handle repeated ion movement, meaning they degrade after discharge. Rechargeable lithium batteries use materials that allow for stable cycling without permanent damage.
Lithium-Ion Batteries
Lithium-ion and lithium polymer batteries are closely related, but their internal structures set them apart. Most lithium-ion batteries use a hard metal casing and a tightly wound jelly roll of thin layers—like a Swiss roll—made of energy-storing materials and separators soaked in a flammable liquid electrolyte. This design packs a lot of energy into a small space, making it ideal for phones, laptops, and power tools, but it also requires built-in protection circuits to prevent overheating or fires.
Lithium polymer batteries, or LiPo for short, use the same basic chemistry but swap the rigid metal case for a flexible pouch and often use a gel-like electrolyte instead of a liquid. That gives them more freedom in shape and size—perfect for slim devices like tablets or drones. Internally, they often still use a flat version of the jelly roll, but the soft outer shell makes them more vulnerable to punctures or swelling over time. So while both battery types offer high performance, LiPo trades a bit of toughness for flexibility.
Weld Marks vs Solder Joints
Micro-welding is quite common in electronics, specifically when connecting lithium ion cells in series or parallel. It’s also common to see battery tabs micro-welded to the anode and cathode of the battery, which in turn is soldered to the PCB.
When reading X-rays and CTs, a sure way of identifying whether a battery tab is soldered or welded is to look for the telltale signs of welding. The absence of weld marks is probably a strong indicator of the presence of solder, assuming some other novel means of securing the battery hasn’t been employed.
Why It Matters
By now, you’ve hopefully started seeing the value of CTs the way we do: not just as a fancy way to peek inside your gadgets, but as a powerful tool for understanding how they tick—and what might make them tock. From magnetic fuzz to copper spaghetti, the internal world of electronics is weird, beautiful, and surprisingly readable once you know what to look for.
For you, this might just be the beginning. Whether you’re a seasoned engineer, a curious student, or someone who’s just cracked open their first remote, CT can help you become a better fixer. Every scan you explore builds that mental library of “I’ve seen that before.” And the more we learn to read these invisible layers, the better we can design, repair, and teach the next generation to keep in working condition the things we rely on every day. So go forth and scroll, slice, and zoom. We’re giving you the tools; it’s up to you to use them.
Thanks again to our friends at Lumafield and No Starch Press for making this collaboration possible and a special thanks to the authors of Open Circuits for their inspiring photography.
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