Issue link: https://iconnect007.uberflip.com/i/721932
104 SMT Magazine • September 2016 emission for solder joint assemblies are yet to be fully established. AE and X-ray are complementary tech- niques that are frequently found in the same laboratories, but they reveal different features. X-ray detects features based on differential at- tenuation of the X-ray energy, whereas AE de- tects features based on materials changes. The practical result is that AE is orders of magnitude more sensitive for detecting air-gap defects such as voids, delaminations and cracks. C-mode scanning acoustic microscopy was evaluated for advanced electronic packaging assemblies, par- ticularly FC-CGA and FCBGA. Inspection evalu- ations revealed the following results. • Visual inspection by optical microscopy is ideal for detecting exposed features such as dewetting, microcracks, cold, and disturbed sol- der joint. • Visual inspection is possible for periphery columns in CGA and balls in BGA, but is diffi- cult for joints in a plastic land grid array due to a lower gap height. A 2D X-ray revealed many internal features of the LGA package including chips and solder joints. • Layering C-SAM using a low frequency transducer revealed many features of the plastic LGA package assembly detected by X-ray; how- ever, the features were less clear and it did not reveal package and board interfaces or solder joint conditions. • It was revealed that C-SAM could only show the quality of heat-sink thermal interface bonding materials of the FC-CGA 1752 I/O. Heat sink is part of the package and is attached with adhesive on top of the flip-chip die, hence, it hindered penetration by acoustic emission signal into bumps and adhesive interfaces. • C-SAM revealed the flip-chip bumps and underfill conditions of the FC-CGA package af- ter shearing off its heat sink. • The C-SAM revealed an edge delamina- tion for FC-CGA 1517 I/O assembly since it had DEFECT FEATURES DETECTED BY ACOUSTIC EMISSION Figure 19: Optical image of a microsection of FC-CGA 1517 assembly (SN016), showing images for die and underfill.