CT of Fuse failure mechanisms
Introduction
Fuses are used in most electronics to limit damage to electronics in the case of short-circuits that would otherwise overload a circuit with high current and cause damage. They are primarily made up of a wire, surrounded by insulated material to protective measure. Knowing the failure mechanism is essential in designing fuses which reliably blow to at their current rating.
Because most fuses are opaque and cannot be opened without interfering with the morphology, computational tomography (CT) scanning was employed to see the failure mode – which takes hundreds of X-ray radiographs as the sample is rotating and reconstructs them so they can be modelled and analysed.
Experimental
To look inside the fuse, a Nikon XT H 160i CT scanner was used to scan around the fuse using 100kV X-rays, 200uA beam current, 0.25mm copper filter was used to prevent overexposure of the X-ray detector and provides good contrast between elements inside the sample. Due to the field of view scanned a 20μm voxel size was yielded.
Fig 1: X-ray radiographs of the fuse from side at 90° and 45° from the side view.
Results
The CT scan was then reconstructed and then analysed in 3D analysis software (Dragonfly 3D World). Using AI Deep Learning, the fuse can be separated from the bulk surrounding material and then processed to make it appear better visually.
Fig 2: AI segmented slice with the fuse and metal casing in orange & insulation material in green.
As shown in figure 2, there are two wire elements in the fuse, one of which has been completely failed and the other is partly failed. In the figure 1 radiograph, the shape of the fuse also shows narrow points which will be areas of higher localised heating and therefore will melt first. The melted fuse particles travels ~1.5mm before being stopped by the insulation material as can be seen in figure 3. The AI segmentation does a reasonable job at segmenting the individual grains of the insulation material but not with perfect accuracy due to the densely packed nature of the insulation material.
Fig 3: Segmented fuse with annotated edge to edge distances of the failed component.
Summary
CT analysis is a useful tool to capture the internal structure of a material to view the failure mode without disturbing the structure through traditional sample preparation methods. Specifically for fuses, CT can be used to test different failure mode conditions, having high throughput allows for repeatable, and accurate data to inform iterative design methods.
Acknowledgement
Melvin Chan