My customer feedback they found one board with cold solder on the BGA ball.I looked at the picture,the ball looks very shining but I dont think that is a cold solder.What is the method can be used to confirm the colde solder beside cross sectioning the component.
Comments are: * A good looking solder ball does not necessarily mean that you have a good solder connection between the ball and the pad. We've all seen a bright and shiney solder ball on the floor, but that doesn't mean there's a good metalurgical bond between the floor and the ball. * You probably can see the poor solder connection that your customer sees with Scanning Acoustic Microscopy (SAM) and avoid distructive techniques. [Pity, we do enjoy those distructive techniques.] Your local university probaly has a SAM machine and a technician to assist in your analysis.