Issue link: https://iconnect007.uberflip.com/i/721932
September 2016 • SMT Magazine 103 Plastic LGA 1156 I/O and Fine Pitch Package Assemblies Plastic LGA with 1156 I/O were subjected to C-SAM evaluation. Figure 17 shows images of this package. No defect anomaly was detected by C-SAM. Characterization was limited to the top section only. A number of other fine pitch plastic packages were also imaged. No defect anomaly was detected. Effect of 20 Solder Iron Touches at 700°F CGA 1752 I/O without heat sink and one fine pitch plastic BGA package assembly was subjected up to 20 solder iron touches at 700°F, each for about 5 seconds. C-SAM was performed at 5, 10, and 20 exposures. Figure 18 shows C- SAM images after twenty touch ups. No anom- DEFECT FEATURES DETECTED BY ACOUSTIC EMISSION aly was detectable for either package after 20 touches. Cross-sectional Characterization of LGA1517 The flip-chip ceramic LGA1517 package was cross-sectioned to verify the condition of solder bump solder joints and underfill integrity. This package was selected for X-sectioning since it clearly showed a large dark area on the periph- ery of the die with minor shadowing at the cen- ter of the die. Figure 19 shows the optical im- age of X-sectioned LGA package at lower and higher magnifications. Inspection of the X-sec- tioned samples did not reveal any separation in the periphery of the die, as revealed by the C- SAM images. The reason for this discrepancy is unknown. Conclusions The evaluations covered in this paper deal with inspection methods and comparison of in- spection results performed for advanced flip- chip column grid array, flip-chip ball grid, and a number of other fine pitch ball grid array and land grid array package assemblies. Visual in- spection using optical microscopy has been the traditional approach for acceptance/rejection of workmanship defects by quality assurance per- sonnel. Inspection of hidden elements in FC- CGA and FCBGA package assemblies requires using nondestructive inspection tools such as 2D/3D X-ray and, potentially, acoustic micro- scopic imaging. Limitations on using acoustic Figure 17: Optical (top) and representative C-SAM images for various PBGA and FPGA package assemblies. Figure 18: C-SAM images for FC-CGA 1752 I/O and FPBGA after 20 touches with a solder iron with 700°F tip temperature. No apparent changes were revealed.