As ball grid array (BGA) manufacturing grows in popularity, replacing many gull wing fine-pitch packaged components, the demand increases for inspection equipment which can verify and maintain solder joint integrity in BGA devices. This adds a step to the inspection process and increases manufacturing costs.

This month’s Demo/Lab article explores the different types of BGA inspection equipment and the applications of each. The article also discusses how to choose the right BGA inspection system to fit your application and reviews the cost vs. capability of each type of system.

Types of BGA inspection equipment
There are three non-destructive types of BGA inspection equipment used in electronics manufacturing today – 2-D X-ray, endoscopic, and 3-D X-ray. Each system has inspection capabilities that the others do not.

2-D X-ray
2-D X-ray transmission systems can generally show you many obvious defects such as bridging, voids, or missing balls. However, in many cases, it is hard to detect other common defects such as opens and insufficient or cold soldering. These types of defects require a high-powered system (100kv-165kv) with oblique view at highest magnification (OVHM) capability (Figure 2-1) and an experienced technician to detect. Standard 2-D X-ray inspection systems offer image resolution between 8 and 10 microns, while many advanced systems can achieve a resolution of less than 1 micron.

Endoscopes
As an alternate method to X-ray, endoscopic inspection technology (a form of optical inspection) can be used to locate defects such as opens, insufficient or unreflowed solder, lifted pads, and debris (Figure 2-2). However, it too has limitations when inspecting the center balls of a BGA component. While these types of systems are capable of seeing 10-15 rows in, it is difficult to make observations on the entire ball, as they are limited to viewing just the outer edge of the ball.

3-D X-ray
Then there is 3-D X-ray laminography or planar computed tomography (PCT) which combines the capabilities of 2-D X-ray and endoscopic technology with added features. These types of systems allow viewing of the BGA balls and joints in a 3-dimensional model. In addition, the inner structure of the ball can be inspected through the system’s ability to cross-section a view, creating sliced layers (Figure 2-3). This allows for a more detailed inspection of the solder joint connection and inner metallics. The disadvantages of X-ray laminography are its high cost, slow speed, and excessive capability. Much of what a 3-D X-ray inspection system can do is considered over-analysis, unnecessary to detect a common BGA defect. This is particularly evident in a production environment, where speed becomes a necessity. Return on investment is unlikely to be realized, as the 3-D X-ray system may not be used to its full potential.

Choosing the right BGA inspection system
2-D X-ray
Choosing the best BGA inspection system to fit your needs primarily depends on how detailed the analysis must be. If your business is an OEM (Original Equipment Manufacturer) or production environment, a standard 2-D OVHM system provides more than enough capability to view BGAs at several angles. Most of these systems also have software for void and ball calculation, which is a critical inspection parameter. In addition, the speed at which many of these systems can operate allows manufacturing lines to maintain a high throughput. The 2-D X-ray system has also proven to be an excellent analytical tool to inspect prototype and small production boards, as demonstrated at the EMPF with the Phoenix PCBA analyzer.

Endoscopes
An endoscopic system is much less expensive than X-ray and can prove to be a versatile inspection tool. By itself, an endoscope can provide clear captured images or video of your BGA process. However, when combined with 2-D X-ray, the endoscope can help locate defects (such as opens) that are commonly missed in X-ray inspection. This additional inspection tool allows technicians to further
analyze what has been located under X-ray. Endoscopes are meant for sample lot inspections in a production environment and provide additional analysis in prototyping.

3-D X-ray
3-D X-ray laminography systems are useful tools for more intricate processes and products. These systems are best suited for failure analysis and R&D projects that require more detailed information regarding the intermetallic layers of the BGA ball and solder joint. In addition, 3-D systems work best when used to evaluate internal structures of the BGA device. As a result, these systems will operate a lot slower and cost much more than 2-D X-ray systems.

BGA inspection equipment software capability
2-D X-ray
BGA inspection equipment software has come a long way, with increased analyzing and programming capabilities. This is evident in many advanced 2-D X-ray systems which allow for the measuring of voids, ball size, ball count, and distance calculations (Figures 2-4 and 2-5). An option called Computer Numeric Control (CNC) can be added to aid in automating the inspection process. This allows the user to create programs that perform sample manipulation and image processing. Additional test criteria that are programmable include presence of solder bridges, missing solder joints, deviating diameter of solder joints, insufficient wetting, tilted component, non-circular shape of solder joint, and solder joint opens.

Endoscopes
The software used to control many endoscopic systems requires more user input and less programming. The features available allow the user to perform a full-blown optical microscopy analysis on the BGA ball. This includes measuring, labeling, image processing, video recording, and presentation mode. A guided failure analysis database comparing many of the common BGA defects is available. The software also allows for importing and exporting of images, reports, spreadsheets, and database information. Some of the visual controls include contrast and color changes of many levels to retrieve the best image possible.

3-D X-ray
Software found in 3-D X-ray laminography systems has the capability of 2-D systems with the technology for 3-D image rendering. This is created by bringing multiple 2-D images through software computation while reconstructing it to show the depth dimension or Z-Axis. The user then has the ability to choose the height, geometric magnification, and resolution to be used for the model. The 3-D image can be moved in all directions to precisely reveal the BGA’s inner structure. The programming is simplified with a software-based “wizard,” which guides the user through the test process.

Conclusion
Any piece of BGA inspection equipment is only as good as its ability to meet the customer’s needs. The best rule of thumb in choosing the most compatible system is to know what each system offers, how it operates, and which type is considered best for your BGA manufacturing application.