Sales & Service to the PCB Industry
 
 
X-Ray Inspection - Technical Papers
 
 
 
The Three Steps of X-Ray Inspection
Acquire, Understand, Analyze

The more an engineer learns about BGA, the more likely he or she is to develop an appreciation of why these leadless components have become so widely used in electronics today. BGAs have contributed to the overall trend in technology today - increased performance for a lower price.

This trend has affected the entire industry, including both final product and the equipment used to manufacture it. A prime example is BGA inspection equipment: the cost of a real-time X-ray inspection system with full BGA capabilities is now less than £45,000.
 
 
The adoption of real-time X-ray inspection for BGAs was required to determine the solder bond integrity of the interconnects hidden under the surface of the component. For engineers and operators, the procedures involved in performing X-ray inspection can be broken down into three simple steps: image acquisition, image understanding and image analysis.
 
 
For image acquisition, a real-time X-ray inspection system is required. Whatever piece of equipment is selected, its sole purpose is to acquire an X-ray image of the assembly and project it onto a monitor for viewing. For this step, the X-ray source and X-ray camera are the critical features to consider. A high-sensitivity, high-resolution transmission X-ray camera, used in conjunction with an X-ray source designed to ensure long tube life, delivers the image clarity required for successful BGA inspection in the most cost-efficient manner.

Image understanding, the second step in the process, does require the engineer or operator to develop an understanding of what is being displayed in the X-ray image. Very often, people who are new to X-ray inspection have said, "Yes, I can see the image but I don't know what to look for."

As with any new procedure, some training is required to recognize when the X-ray image displays successful reflow, and when it displays a defect. Just as a radiologist examining a medical X-ray has to understand human anatomy in order to recognize pathology, an operator or engineer has to understand the reflow process in order to recognize a defect. Fortunately, BGA assemblies are much less complex than human anatomy.

There are a variety of ways to gain an understanding of what the BGA X-ray image is displaying. Many people have, in effect, trained themselves to recognize defects in a few days of on-the-job use, just as if they were learning a new computer program. A one-day training course with hands-on content is always recommended to impart the basics. One of the most effective ways to learn about the reflow process is to use the newly developed "X-ray movie," which demonstrates the reflow in action and can help identify the specific parameter that may be causing a defect.

The final step of analyzing the X-ray image, to know which solder bonds are acceptable and which are not, can now be done automatically, using software developed specifically for this purpose. Rather than having to measure individual solder bonds, users can use the software to obtain immediate information, in graphical or spreadsheet formats, identifying solder bonds that may be defective. They can also enter pass-fail criteria, eliminating the need to depend on human interpretation and intervention.

When implemented together, these three steps - image acquisition using a cost-effective system, easily-learned image interpretation and software-supported image analysis - enable engineers and operators to perform successful real-time X-ray inspection of BGA assemblies.