SSW researchers are leveraging non-destructive methods, such as Micro-CT, to analyze and image sensitive electronics. In the case study below, we used Micro-CT X-ray analyses to image integrated circuit (IC) micro-electro mechanical system (MEMS) chips that were mounted on a printed circuit board (PCB).
MEMS chips are tiny mechanical sensors and actuators that are commonly used in many modern-day products. In fact, their use keeps increasing with time:
Aviation and defence industries have strict quality control and only certified parts can be used. But what happens if an IC becomes obsolete and there are no certified components for a direct replacement?
Sometimes replacement ICs can be found from small shops (or ebay!), but they have absolutely no certifications, and ultimately, the internal dies of these suspect parts need to be compared to certified parts to check for compatibility. Typically, to certify old ICs, the internal die is revealed by etching away the outer plastic casing (using nitric and sulfuric acid) in a process called “decapping”. This obviously destroys the limited chips that are available, and is where micro-CT is beneficial. Micro-CT is a non-destructive technique that won’t damage the limited parts!
Here’s the board that was supplied to us (on the left), and what the board looks like as a Micro-CT X-ray radiometric projection image (on the right):
Specifically, this is the chip we’re investigating in detail (all we can see is the plastic black cap and not the IC inside):
But with the magic of X-rays we can now see everything under the black cap in this 2D radiometric projection:
Using post-processing software, if you adjust things correctly, then you can “see” the silicon die in the middle of the chip, which has the sensors and actuators on it, as shown in this processed 2D X-ray tomography slice:
These chips utilize something called a 3D-IC packaging, where the ICs are stacked on top of each other, which we can see when we put together a 3D X-ray tomography (note the top and bottom to it, along with the copper traces of the PCB):
Not only can this data be used to compare compatibility, but can also be used to backwards engineer parts. We can also use Micro-CT for fault finding with the bonding wires, or check solder points, all non-destructively.