Four reasons for X-ray inspection of surface mount devices
25 February 2015Manufacturing / Production Technology, Hardware & Services
Vision inspection systems can find visible defects on PCBs, but these systems can only check the surface for errors, not the hidden solder joints of components like BGAs and flip chips. X-ray inspection can provide critical verification of the integrity of hidden solder joints on surface-mount devices.
Figure 1. Solder ball shorts.
The following are four of the most common examples of faults that X-ray inspection is best suited to detecting.
1. Solder ball shorts
Solder ball shorts, or solder bridges, can be easily detected with an X-ray image, as shown in Figure 1.
2. Solder ball voids
Figure 2. BGA void image with auto void calculation.
Ball-void inspection is used for BGA/CSP inspection along with solder ball bridge inspection.
Modern X-ray inspection systems can perform auto ball-void calculations (Figure 2).
Figure 3. BGA void location.
Not only is the size of the BGA voiding area important, the location of the BGA void is also important (see Figure 3), especially if the voiding area is close to the PCB pad area, because there is a possibility that this voiding area could cause a micro-crack.
Figure 4. Solder ball open.
3. Solder ball open / micro cold solder
Solder ball attachment to the PCB pad is a critical inspection criterion. A high-resolution and high-magnification X-ray inspection system is required to detect a solder ball open defect. The X-ray image in Figure 4 shows a solder-ball open where the copper pad is separated below the solder ball.
Figure 5. Solder ball open caused by small solder ball.
3D CT can assist with clear visualisation of open patterns. Figure 5 shows a solder ball open caused by the solder ball being too small. The image on the left shows a Y-Z slice image, indicating that the solder ball is smaller than the other ones. The image on the right shows an X-Y slice, indicating that the PCB pad (dark area) is not surrounded by a solder ball (white edges).
Figure 6. Cold solder – optical image.
Micro cold-solder joints can also be visualised with 3D CT, as illustrated in Figures 6 and 7.
Figure 7. Cold solder – non-destructive 3D CT image.
4. Solder ball crack
Using oblique CT technology, a solder ball crack can be visualised. Figure 8 shows a 10 micron solder ball crack.
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