Issue link: https://iconnect007.uberflip.com/i/721932
98 SMT Magazine • September 2016 • Cross-sectional examinations were per- formed for the LGA 1517 I/O to correlate the C-SAM images with optical microscopy images. To achieve the highest results with limit- ed funding, this investigation examined only packages as individual or test vehicles built pre- viously, either used samples "as assembled" or were already subjected to thermal cycling con- ditions. Ideally, new test vehicles with induc- ing known defects should add additional val- ues when additional funds become available. The purpose of using such a mix of packages and assemblies was to initially determine the benefits of C-SAM and to determine its poten- tial limitations, especially for FCBGA and FC- CGA. Detailed information on package includ- ing internal configuration, optical photomicro- graphs, X-ray and as well C-SAM images using a range of transducers are also presented. Two fa- cilities one external and one internal were used for the C-SAM evaluation. The outside facili- ty had extensive equipment capability with an experienced operator, whereas the internal C- SAM equipment had a lower capability with a less experienced operator. Results are presented. Plastic LGA132 Figure 6 compares an optical photomicro- graph image of a plastic LGA package assem- bly with 132 lands and their X-ray and C-SAM images. The C-SAM image was taken using a very low frequency transducer of 5 MHz in or- der enable deeper acoustic wave penetration into the package for comparison to its X-ray images. The C-SAM image shows a few key in- ternal chips similar to X-ray, but several oth- er details are missing. The X-ray shows greater details of internal package configuration, in- cluding solder on land pads and land shape (e.g., a square land on the top left). Layering image is impossible with the 2D X-ray, but it can be performed by the C-SAM technique. Figure 7 shows C-SAM layering images using a 25 MHz transducer. It clearly shows different interfaces in package assembly from the top to the bottom. Flip-Chip BGA1704 with Heat Sink The cross-sectional photomicrograph from a FCBGA1704, which was previously subjected to a number of thermal cycles, is shown in Fig- ure 8. It is apparent that the back of the flip-chip die is covered by a heat sink that extended over the edge of the die, covering the flip-chip area. The only feature that could be revealed through C-SAM evaluation was the bonding condition of the thermal interface material (TIM). No in- Figure 6: Comparison images by optical microscopy (top), by X-ray (bottom left) and by C-SAM from the LGA 132 I/O assembly. Figure 7: C-SAM layering images taken from the top to the internal LGA package assembly. DEFECT FEATURES DETECTED BY ACOUSTIC EMISSION