PBGA Popcorn Cracks

Pictured

Time Domain Imaging (TDI)™
Utilizes an echo (amplitude & polarity) arrival ‘time’ as a reference, such as standard A-Scan, B-Scan and C-Mode type images.

PBGA Popcorn Cracks

PBGA Popcorn Crack, Through Transmission - Application Note 1012

PBGA Popcorn Cracks
Acoustic image of a large popcorn crack located on the bottom left BGA

Sample & Method

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.

Result

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.