Issue link: https://iconnect007.uberflip.com/i/721932
September 2016 • SMT Magazine 99 Figure 8: C-SAM image for plastic FC-BGA 1704 I/O assembly showing the heat sink interface, which hindered further penetration of signals. Figure 9: C-SAM image for FC-CGA 1752 I/O assembly showing heat sink interface, which hinders further penetration of singals. formation regarding underfill or solder bump condition below the TIM could be revealed due to this interface interference with the layers of interest. Hence, the heat sink hindered C-SAM evaluation. Flip-Chip CGA1752 with Heat Sink The schematic drawing of FC-CGA1752 is illustrated in Figure 9. It is apparent that this package has an additonal heat sink that over- shadows the flip-chip die, explaining the C- SAM signal interference with the TIM interface. Due to the TIM inteference, no layering imag- ing was possible. The heat sink restricted the C- SAM evaluation. Flip-Chip LGA1517/CGA without Heat Sink This ceramic LGA package was ideal for re- vealing the integrity of the flip-die, since its heat sink was yet to be attached. Two styples of LGAs with 1517 I/Os were evaluated; one as a package and the other as an assembly. Irrespec- tive of the package being alone or in an assem- bly, there was no heat sink and the back of the flip-chip die was exposed. There was no C-SAM signal interference due to the TIM as it wase the case for CGA 1752 I/O. The first interface was between the die and solder bump and underfill. The second was between substrate and the land pads or solder joints of columns. Figures 10 to 12 show three C-SAM images taken with three different transducers with increasing frequen- cies of 25-, 100-, and 230-MHz. It is apparent that as frequecy increases the granuality of the C-SAM image increases due to increase in spa- tial resolution. The details of the flip-chip solder bumps became apparent at a higher frequency. There is a dark region, which is surrounding the DEFECT FEATURES DETECTED BY ACOUSTIC EMISSION