The same plastic BGA packages shown in Note #1011 were imaged using the THRU-Scan technique, which places a second transducer beneath the sample to collect ultrasound pulsed by the topside transducer. The resulting image shows internal defects at all depths within the sample.
Note the excellent transmission through most of the area in these BGA packages and the appearance of the solder bumps. Two of the packages (upper left and lower right) have significant areas where the molding compound is delaminated from the substrate. The package at lower left has a large “popcorn crack”. Popcorn cracks are typically caused by the expansion of retained humidity during the reflow process. |
