Characterization of BGA solder joints using X-ray imaging

X-ray inspection is generally used to detect shorts under area array components. But x-ray images can also provide a valuable insight into the quality of joint formation of the arrays. We have been able to show that the relative sizes of the balls in x-ray images before and after reflow can reliably detect the following defects :

• No reflow / insufficient reflow
• Blocked stencil aperture
• Insufficient paste deposit

The actual diameter of the ellipsoid formed after reflow under an area array component provides  valuable information for solder joint quality assessment. A typical example :

In conjunction with visual inspection methods and other X-ray signature identifiers , the method developed in this investigation  provides indicators for process development and serve as a tool for solder joint quality evaluation during production. The proposed process can be implemented using an entry level X-ray machine.

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