BGA X-Ray Inspection – An Incredibly Easy Method That Works For All

by Katy Radcliff Training Coordinator

BGA Inspection for both process development and for process troubleshooting is becoming more critical as BGA package implementation on modern PCBs has become commonplace. The distance between components, the ever-finer pitch of BGAs and the increasing complexity of PCB designs using BGAs has made the use of BGA x-ray inspection more of a necessity as opposed as a “nice to have” , process qualification only tool.

BGA x-ray inspection for the development and confirmation of the capability of the PCB assembly process has become a necessity. After properly profiling the assembly and sending boards through the reflow process the verification of ball collapse as well as proper wetting and shape of the solder joint is important. Ball collapse, while being able to determine in some board layouts, using manual visual inspection, is critical for determining that the profile has been used to collapse of the solder balls uniformly. These visual techniques are often impeded by nearby lying components. Only through the use of proper BGA inspection can all of the ball shapes be determined. Proper wetting of all of the solder balls can also be determined through the use of BGA x-ray inspection given that these solder joints are not inspectable through the used standard visual techniques. Finally, shape of the reflowed solder joint will help determine if all of the solder volume is on each pad. The BGA inspection image through the use of a trained eye as well as x-ray imaging capture software can be used to determine if the ball shape is consistent post reflow. This will allow a call to be made on the acceptability of each solder joint underneath the BGA.

Without BGA x-ray inspection, troubleshooting the PCB assembly process has become extremely difficult. There are numerous anomalies and defects that without BGA x-ray inspection are not possible. One of the areas where BGA inspection is mission critical in the area of device warpage and the subsequent screening for head-in-pillow, opens and shorts. Head-in-pillow or HIP defects occur when there is a lack of coalescing between the solder ball of the BGA and the solder paste which has been printed on the board. This result in an open or worse yet an intermittent connection of the device to the PCB meaning it could pass electrical tests but fail later as the assembly is out in the field going through power cycles and temperature cycles. A typical head in pillow defect, as indicated in the image below:

Irregular-shaped solder balls indicate process anomaly

Only through proper screening while performing a BGA x-ray inspection can such a defect be picked up in the manufacturing process. Opens will also be noticed during the inspection screening process. Short circuits can also be picked out through the BGA x-ray inspection screening process. These shorts can be caused by a variety of factors including but not limited to warped components, warped boards, and improper distribution of thermal mass in the PCB.