Practical Guidance for X-ray CT Scanning Electronics.
X-ray CT is a powerful nondestructive inspection technique, but some electronics components can be sensitive to X-rays and other ionizing radiation. Passive electronic components like resistors, capacitors, inductors, and the actual PCBs themselves are unaffected by exposure to ionizing radiation, but flash memory units, IMUs, and accelerometers are all susceptible to total ionizing dose (TID), which is a measure of the cumulative amount of ionizing radiation they have received. TID can cause electronic threshold shifts, leakage current, timing changes and functional failures. The total dose threshold varies by device, so it is best to determine the dose threshold for a given device via direct testing. When scanning electronics, it’s important to understand TID to perform a scan that both achieves a given inspection while minimizing the risk of affecting the device’s performance.
Dose is dependent on multiple factors, including:
Dose rate is highest at high magnifications (smaller source to object distance) and at high source energy and lowest at low magnification (larger source to object distance) and low source energy. The charts below show absorption rates for silicon, the primary material in active electronic devices, and can be used to determine the rate of absorbed dose at different magnifications with different source energies.
Fig 1. Absorbed dose rate for electronics on 190 kV and 120 kV Neptunes.
The below table provides general guidance on TID thresholds for common electronic devices.
Type of Semiconductor Device | Total Ionizing Dose Threshold (krads) |
Linear | 2-50 |
Mixed Signal | 2-50 |
Flash Memory | 5-15 |
DRAM | 15-50 |
Microprocessors | 15-70 |
Fig. 2 X-ray Inspection Considerations for Surface Mounted Flash ICs. Infineon Technologies 001-98522 Rev. *C ref.
As can be seen from the table above, TID thresholds for many devices vary dramatically. While not always possible, the highest confidence method to assess the impact of X-rays on an electronic device is to find the TID limit experimentally. See this worked example to learn how to determine the TID threshold experimentally.
Device: Flash Drive
Scan Conditions:
Procedure:
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