The Power of 2D and 3D Inspection

Ever been to see a doctor for an X-ray and a CT scan? This is a common process that builds a complete picture for diagnosis. In the electronics world we have similar x-ray techniques for non-destructive failure analysis. A quick 2D x-ray inspection provides a good insight into signs of defective connections, and a 3D CT scan can verify the problem with the added benefits of more data, building the complete picture ready for diagnosis.

BGA (Ball Grid Array) packages are a common device that is inspected non-destructively utilizing X-rays. Each solder joint is an individual electrical connection. A good solder joint will be reasonably circular in shape and the size of the joints should be reasonably consistent throughout the device array.

Figure 1 displays a diagram of several different defects that can occur during the BGA assembly reflow process.

2D X-ray inspection [https://youtu.be/jcHRBHPt6pA] is a great tool for quick analysis, and one type of analysis that can be easily performed is a ball diameter measurement. Looking at Figure 2 (left), you can see the ball in the middle is approximately 70 µm smaller in size compared to its neighbouring joints, highlighted with red outline. This is the first sign that there is a potential problem with this connection. The image next to it is a 2.5D oblique angle image of theses joints. This image builds our diagnosis further, as now we see another sign that this joint is not completely fused on one side. This is seen through a different greyscale displayed on the interface of this joint and is highlighted with a red arrow.

Figure 2. Left image displaying ball diameter measurements and right image showing 2.5D inspection of the solder joints.

Having identified strong signs there is potentially a defective connection, this can be verified further with a 3D CT scan [https://youtu.be/x4fNJGrIusA]. CT is a technique which captures several images from different angles, and then uses reconstruction algorithms to create a 3D model. The results of this can be seen below in figure 3. It can clearly be seen there is a difference in the ball shape highlighted with red arrows compared with surrounding balls. The image to the top right side shows the quality of ball wetting to the device interface. It is clearly seen that there is an interfacial difference compared to neighbouring joints (highlighted with red color).

Now that both 2D and 3D images have been analysed, there is enough data to build our complete picture and diagnose this BGA device. The solder joint is confirmed as ‘non-wet open’ and as a result this would have significant impact on its integrity, and ultimately the integrity of the BGA device and the product it ends up in.

So whether you are a doctor or are responsible for manufacturing quality, combining 2D and 3D X-ray images makes performing a diagnosis much easier.

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