Ask the Experts
May 11, 2009

BGA Voids - Process Indicator or Reject

During X-Ray inspection after a recent production of 15 assemblies, each with 2 BGA components, we found one ball in one assembly having a greater than 25% void. IPC-7095 stated that there is no evidence or empirical data that indicates that voids within BGA balls will cause a failure. Can advise us whether we should classify this case as a process indicator or reject?

J. K.

Expert Panel Responses

You are correct that the IPC standard and other literature do not present a definitive answer on when BGA voids should be classified as solder joint failures. In fact, there is much data suggesting some voiding can actually improve BGA solder joint integrity as it provides beneficial compliance to the joint. I believe one has to look at a number of factors in order to make a determination. First, where is the void located? Typically the majority of voids will be at the interface between the solder sphere and the PCB pads. If the void is near the center of the pad it is not as likely to cause problems. If the void is near the edge, especially if it is in the fillet area, there is much greater concern. These voids are more likely to lead to crack propagation and latent failure. Second, which solder ball has the void? If the void is located on one of the spheres near the center of the array it will be subject to far less shear force under thermal load as a sphere near the edge of the array. Finally, and most importantly, how critical is the application? If the BGA is used in a high reliability application one should not take the risk. Applications such as aerospace, mission critical computing/ communication, or life support are not worth taking chances. 25% voiding is substantial. BGA rework is very reliable and has become cost effective. If you are not equipped to perform BGA rework there are many companies willing to help out. We would be happy to perform the service or help you identify a local company which can meet your needs.

Don Naugler
General Manager
VJ Technologies, Inc.
Don is the General Manager of VJ Technologies, Inc., a leading manufacturer of X-ray Inspection and Rework equipment for the electronics manufacturing industry. He has more than 20 years experience in development, manufacturing, and support of a wide range of capital equipment.
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