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edfas.org 5 ELECTRONIC DEV ICE FA I LURE ANALYSIS | VOLUME 23 NO . 2 a significant number of design and process details that improve overall die performance. However, the security assessment of theseadvancedpackaging technologieshas been leftbehind. [12] This sectiondiscusses the taxonomy of packaging technology from a security perspective. PACKAGING TECHNIQUES AND TAXONOMY Dual in-line packaging (DIP), a previously widely used packaging type, placed pins on two sides of the package. However, the limited space to place pins in a DIP package meant these samples could only contain 4-64 pins. In the 1980s to 1990s, the pin grid array (PGA) and ball grid array packaging (BGA) used surface mounting technology to place more pins at the bottom of the packaging. Surface mounting technology allows the chip to directly attach to the motherboard, increasing the thermal transfer and reducing mechanical stress, meeting the requirements of high-performance chips. SOC, the next improvement in the packaging approach, included different electronic circuits on a single die. SOCwas equally effective for both mixed analog and digital circuit packaging. In the same period, flip-chip technology such as flip-chip ball grid array (FCBGA) was used to further decrease the package thickness and enhance thermal transfer. While SOC packages had the benefit of consolidating several separate systems, they generally resulted in larger areas required for the die. This drastically decreased the process yield and increased design costs. [13] Multichip module (MCM) packaging was used to overcome this challenge. However, the excessive heat generation and the low yield of this technology limited its development. In 2000, new wafer fabrication and interconnection tech- nologies such as silicon interposer and micro-bump appeared as emerging solutions for the above-mentioned issues, leading to SIP as a more appropriate selection for high-performance chips. SIP includes homogeneous and heterogeneous integration that use an interposer or embedded bridges for communication. Heterogeneous packages combine the chips with different process nodes and technologies, and the die-to-die interconnect distances are so close that it mimics the functional block interconnect distances inside SIP. In summary, advanced ICpackaging has a complicated structure and involves a significant interplay between several distinct technologies. It not only uses traditional packaging technologies suchasDIP, PGA, etc., but includes advanced techniques such as SOC, 3D connections, and more in the process. INTERPOSER-BASED ADVANCED PACKAGING Interposers with fine pitch through-silicon vias (TSV) have become a broad solution for homogeneous and heterogeneous connectionofmultichips to formadvanced packaging, [14] as shown in Fig. 2. In traditional IC packag- ing, the chip is assembled face-up (transistor side down) to the substrate. The die is connected to the package using copper or aluminum wires bonded at both ends (wire bond). However, to keep up with the lower profiles and high-performance demand of modern memory applications, higher I/O counts and higher bandwidth are inevitable for the advanced packaging. Themost effective way to achieve this is to decrease the length of the inter- connection. Most of the interposer-based advanced pack- aging, for instance, 2.5D and 3D packaging, use flip-chip technology to meet the high bandwidth requirements. In interposer-based packaging, multiple chips are placed side-by-side in the closest proximity possible instead of a vertically stacked3D topology. The interposer forms abase for mounting the chips and also provides a high density Fig. 1 Packaging development trends. Fig. 2 Interposer-based advanced SIP packaging.