Four reasons for X-ray inspection of surface mount devices

25 February 2015 Manufacturing / 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.

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

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).

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.

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.

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).

Micro cold-solder joints can also be visualised with 3D CT, as illustrated in Figures 6 and 7.

4. Solder ball crack

Using oblique CT technology, a solder ball crack can be visualised. Figure 8 shows a 10 micron solder ball crack.

For more information contact Igmar Grewar, Quamba Technologies, +27 (0)83 417 4294, [email protected], www.quamba.co.za

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