February_EDFA_Digital

edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 23 NO. 1 8 The atmospheric pressure MIP decapsulation process exposes different layers of devices in sequence during the layer-by-layer decapsulation process. A newly developed software function also allows the setting of a different number of etch cycles for different areas on the sample, enabling all components to be exposed at the same time. All components inside the SIP will be preserved in excellent state for further analysis and testing (see Fig. 8). Passivecomponents,whichareeasilydamagedby conven- tional acid or plasma decapsulation methods (see Fig. 8, comparisonbetweenacidandMIPdecapsulation), arepre- served in their original state. The ability of the atmospheric pressureMIPmachine to perform localized decapsulation without using anymasking further increases the efficiency of the decapsulation process. APPLICATION EXAMPLE II: 2.5D PACKAGING [5] Another advanced package type that has recently been receiving industry attention is 2.5D packaging. Using the atmospheric pressure MIP process to remove underfill over or around 2.5D structures does not alter all othermaterials on the samples. Interposer interconnects, for example, are difficult to expose using conventional decapsulation methods as the laminate, chip bumps and microbumps would be attacked by wet chemicals (see Fig. 11). Fluorocarbon-based plasma etchers will attack the passivation, metal layers, and chip silicon. Contrary to that, the atmospheric pressure MIP is a highly selec- tive and isotropic process and can expose interposer interconnects while preserving all materials and original failures sites, allowing for subsequent, careful analysis. Microbumps can also be cleanly exposed either from the top down or in a cross-section (see Fig. 9), enabling analysis of defects further into the cross-section (see Fig. 10), while guaranteeing that no artifacts are induced by the sample preparation. APPLICATION EXAMPLE III: SILVER WIRE SD CARD The use of silver and silver-alloys as bond wire mate- rial has been investigated over the past years. Especially for certain applications such as flashmemory or dynamic randomaccessmemory (DRAM) stack-die, silver is a viable candidate to replace gold wire as an alternative low-cost bonding wire. Due to the chemical properties of silver, artifact-free decapsulation without inducing damage to the silver wires, is highly challenging. Substantial research into the cause of etching damage to silver wire has led to thedevelopment of ahydrogen-containingMIPdecapsula- tionprocess to achieve artifact-free decapsulationof silver wire bonded devices. For example, localized decapsulation using hydrogen- containing MIP can be used to expose top tier die, bottom tier die, Ag ball bonds, wire loop, and stitch bonds in a stacked die SD card (see Fig. 12). To evaluate the effect of plasma decapsulation on the SD card, data was stored on the card before decapsulation and evaluated after the decapsulation process. The pre-stored data on silver wire bonded stacked-die microSD card remained intact after decapsulation. Fig. 9 BeforeMIPprocessing,mechanical cross-sectionwas applied just before the microbumps are exposed. The entire cross-section face (> 10 mm) is brought to approximately this point. Fig. 10 SEM image of microbumps after MIP processing. Fig. 11 Optical images of pre and post MIP processing focusing on removing the overmold around the high- bandwidth memory (HBM) top chip stack and the underfill over the interposer and between the top chips. (a) Angled optical image of the HBM overmold and surrounding underfill. (b) Angled optical image of the HBM after MIP processing has removed the overmold and underfill.