Overview
Reverse engineering printed circuit boards is generally regarded as a time-intensive and sometimes difficult process as the interconnect often vanishes beneath the surface of the board only to return to the surface at locations inaccessible to the tip of a continuity check. With marginal investment (and with the appropriate certifications) a dental-class X-ray sensor with a dental-class X-ray source can significantly reduce the time to decipher PCB interconnectivity. In this blog post, we delve into how this method can be extended beyond basic X-ray imaging and explore the potential of using this setup for a budget-friendly version of 3D X-ray tomography, accelerating the time to full reversal.
Introduction
In comparison to past decades, X-ray setups no longer require a significant financial investment. With dental offices opening and closing, the availability of X-ray sources on the used marketplaces (for example, Craigslist) is common, and a complete X-ray setup can be purchased for less than $1000, including the imagery software. A variety of safeguards ensure the safe operation of the machine in a standard lab environment. These include protective casing on portable and hand-held units, the use of lead aprons and shields during X-ray procedures, and adherence to radiation safety guidelines. These units are specifically designed to be easily transported into a dental office for patient convenience and safety.
Below is an example of a complete setup available for purchase on eBay for $642.39 (plus tax) that includes both the X-ray source as well as the sensor and software:
Armed with these materials, we can go after the real cavities of the reversing world: unknown printed circuit board interconnect. Our first take on the dental software (this one is called “XVSensor”) is that it is designed for dentists who really only understand teeth. The software is easy to use and understand for the most part. The interface presents picture slots for all the teeth:
After a capture is made, the program indexes to the next tooth and is ready for another read. The detail with the budget sensor is pretty impressive for its price:
This level of detail immediately provides incredibly useful information to someone trying to understand the connectivity of the target. The sensor is situated right behind the circuit board and it targets a relatively small area of about 1.5″ x 1″. Therefore, to achieve larger plan views of the board, a tiled acquisition approach must be implemented.
A Poor Man’s Tomography
The result in this example is a set of two images of a Bluetooth serial converter. While they look identical, there is a slightly different look angle. If you place them side by side and cross your eyes such that they overlap, you will register a 3D stereoscopic image. Go ahead. Cross those eyes!
The resulting information allows you to discern things like top and bottom board components and traces. It enables you to follow traces from the bottom of the board, through a via (a type of PCB electrical conduit), and to the top of the board (or to an inner metal layer).
This new representation of the X-ray images ultimately allows us a better and faster understanding of board interconnect. With a quick setup time, obtaining X-rays is simple, efficient, and illuminating! Enjoy these examples, and don’t forget to cross your eyes!
Examples
Waveshare USB to TTL converter
Logitech USB mouse interface
Jabra ear bud
Apple Airtag
Can you resolve the Bluetooth antenna beneath the primary circuit board?
USB-A to USB-C adapter
Power FET (Field-Effect Transistor)
Mostly metal.
Samsung Galaxy camera & speaker
FlirOne’s Lepton IR sensor
Microchip PolarFire 300T
Note inner-layer high-speed signal routing.
Flash chip
Ublox GPS module
Smartcard chip
Note that even with an extreme look-angle, a stereo image is difficult to resolve because the card is so thin.
Oceanus OCW-M700 solar-powered atomic time watch
2000s-era 4 GB SDCard
The surprisingly-empty 2010s-era 64 GB SDCARD
No joke! This YouTube video shows the dissection of this particular SDCard—it really is just a small board in a large plastic case.
