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There are several types of Ball Grid Array (BGA) inspection systems on the market today. These Tech Tips are for optical inspection systems which use endoscope or bore-scope technologies with a backlighting system. These systems use an adjustable magnification collar which allows a technician to focus on a joint that is located a few rows into the BGA.

1. Know the distance required between components to accommodate the size of the scope head. This area is commonly known as the “keep out” area. This is important because some system heads need more area than others to inspect a BGA. Choose one that can be used on all of your boards. In some machines, a typical “keep out” area is 1.5mm x 5mm. Others are smaller or larger, depending on the manufacturer.

2. Another area to pay attention to is the “stand off” height. This is the distance between the circuit board and the scope head. It is critical to get a good view of the board before the pad alignment process begins.

3. Measuring software is common for most units. Make certain that your machine is calibrated for accuracy before beginning any job. When calibrating a system, you will be required to enter a known value, which is commonly provided by the manufacturer. If the manufacturer does not supply a calibration block, you can use a penny or other known value or scale. In most cases, it is important to recognize and maintain magnification so that the measurements are as accurate as possible. If the magnification changes, so may the measurement values.

4. If you need references, use the system database or defect library. This helps to ensure that defects are detected and provides a high quality image for comparison. Some more comprehensive system libraries also provide a corrective action list, as well as online libraries. Most systems allow customized entry of user images into the defect library, along with corrective actions for a specific manufacturing process.

5. Important defects to keep in mind while performing a visual inspection include:

a. Rough, dull, or porous surface
b. Surface deformities like holes, streaks, scaling, and ridges
c. Micro-cracking
d. De-lamination or fractures
e. Discoloration
f. Micro-balling or solder splash
g. Excess flux residue
h. Dross inclusions

Figures 4-1 through 4-12 show images of some common and not-so-common defects found during BGA inspections.

6. When performing an inspection, you may need to measure the “stand off” height to tell if there was any package or board warping. Make sure to measure the distance from the joint to the board interface and from the joint to the component interface.

7. When inspecting joints in the center of the package, remember to adjust the backlighting to allow for a clear image of the joint’s silhouette. This will allow you to detect opens and shorts more effectively.

Please contact the EMPF Helpline at (610) 362-1320 with any questions regarding your BGA optical inspection process.