Date: Dec. 2019
It is well-known that there bound to be friction problems by repeatedly plugging and unplugging of charging cables and USB. So, it is interesting to investigate the details about these cables. We take Lightning connector as an example to show you MSS analysis capability.
Figure a is a photo of the Lightning connector for analysis. Figures b & c, the image is gradually enlarged by the optical microscope (OM), and the enlarged area is indicated by the red square.
Through the OM, you can clearly observe the surface wear profile of the gold finger. Is it much worse than comparing to the naked eye?
Figure 1.Sample for analysis: Lightning connector appearance, OM (a-c) and SEM (d-f) images.
Analysis Methods Employ
Method 1: Analyzing structures of interest by SEM.
Figure 2. Tilted angle SEM images. From the zoom-in image (right-hand side), the surface near the scratch is slightly concave.
Method 2: Analyzing structures of interest by 3D laser confocal microscopy.
Figure 3.Surface morphology scanned by 3D laser confocal microscopy. Similar to the Taiwan altimeter shown in the right-hand side, height distribution can be clearly seen.
The height distribution, along the red dotted line, is shown in the lower figure. It clearly shows the most critical position of the wear, marked by the blue arrow, on the gold finger. Through this technique, we can understand the surface condition.
Figure 4. Surface morphology (upper) and cross-section line profile (lower), along the red dotted line, taken by 3D laser confocal microscopy. You can observe the surface height distribution.
After the non-destructive analysis we introduced above, now we start with the destructive methods to understand the structures of interest underneath. Imagining cutting a birthday cake (see figure), you can see its whole cross-section.
Figure 5. Cake cross-section schematic diagram
Method 3: Preparing cross-section sample by cross-section Polisher (CP)
The most critical position of the wear on the gold finger has been confirmed by SEM (Fig. a) and 3D laser confocal microscopy (Fig. b). It is eager to understand what structure is hidden underneath.
With the help of CP, cross-section cut can be prepared. The red dotted line in Fig. a is the place to be cut, and Figs. c-e are SEM images with different magnifications.
Figure 6. SEM (Fig. a) and 3D laser confocal microscopy (Fig. b) images. Figures c-e are cross-section SEM images. The cutting direction is marked by the red dotted line.
Beside microstructure observation shown above, MSS can do more. With the help of energy dispersive spectrometer (EDS) installed in SEMs, chemical composition can be determined. One of examples is shown in the images below: Different elemental distribution in the area of interest can be clearly resolved.
Figure 7. SEM/EDS analysis on the area shown in the SEM image (upper-left), elements of each layer of the sample can be determined.
With a closer view of the cross-section sample, surprisingly, more interfaces can be observed in the upper Ni layer with MSS special stain technique.In order to meet manufacture standard, it is crucial to have the thickness of each metal layer. This information plays a decisive role in products’ quality, such as durability, electrical conductivity, .. etc.
Figure 8. Comparison before and after MSS special stain technique.
Figure 9. Based on the EDS results, only one layer of Ni is determined between Au and Cu layers. From the current SEM image, however, two layers of Ni with different contrast, Ni-P and Ni, are observed, indicating two different processing perimeters.
Now we focus on the underlying copper (Cu) layer to observe its grain details. Traditional analysis, I-beam imaging on the grains, the Cu grains can be investigated up to a magnification of 54 KX (Fig. a). At higher magnifications, however, ion beam could damage structures of observation. MSS delivers a special E-beam imaging technique (Figs. b-e) can drastically improve the quality of imaging on Cu grains, even up to a magnification of 350 KX, where crystal micron-scale precipitates (red arrows in Fig. 11) can be clearly observed.
Figure 10. I-Beam (a) vs E-Beam (b-e) imaging
Do you know what analysis help us to understand the elements present in the sample? YES!!! That is SEM/EDS!!!
Figure 11. SEM / EDS analysis on the residual particles in the process (marked by the red arrows). It clearly shows that these particles contain Ni and Si.
The above introduced methods and techniques are important for electronic related industries, such as gold fingers or PCBs, which can ensure that the set specifications of products from manufacturing to final products are correctly conformed. Therefore, the MSS team has indirectly made a patron saint of commodity quality for general consumer products.