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96 I-CONNECT007 MAGAZINE I JUNE 2026 are completed while the die elements remain in the wafer-level format. Developers may prepare the original wire-bond sites for direct chip attachment or use an additive copper plating process to redis- tribute the edge-located wire-bond sites to a more uniform array pattern. The additive metallization process (Figure 3) provides an electrically conduc- tive interface from the wire-bond lands on the die element's perimeter to a wider spaced and more uniform array-configured terminal pattern. Fan-out Wafer Level Package Fan-out wafer-level BGA represents a major evo- lutionary direction in packaging technology when the die element is not capable of providing enough area to accommodate all the I/O terminals within the device outline. In preparation for the fan-out WLP, a silicon wafer is developed to redistribute the very fine-pitch bond sites of the die element outward to a wider-array terminal pattern that is more compat- ible with conventional circuit board fabrication. Mi- crovia through-holes are formed in the silicon (TSV) and Cu-plated to transfer the interconnect on the upper surface to an identical array pattern on the opposite surface. Individual die elements are then placed face- down onto and joined to the silicon wafer surface. While remaining in the wafer format, the devel- oper will often encapsulate the die with a molding compound to reinforce and protect the die elements, followed by the formation of terminals (solder balls, microbumps, or micropillars) on the wafer's bottom surface. Finally, marking is applied, and each section is separated (sawing, laser) from the wafer format. 2.5D Package Integration As semiconductor dies became more functionally complex, and the bump size and pitch continued to shrink, developers needed to adopt higher-density interconnections, moving from the traditional C4 solder ball or bumped terminal to a smaller solid- copper micro-pillar terminal that can support finer pitches and better electrical performance and me- chanical stability. A wide range of semiconductor package innovations has already been developed to meet the growing proliferation of ultra-fine-pitch multicore processors and related semiconductors. System-in-package developers have realized that, instead of the traditional monolithic integration used for earlier, less complex applications, adopting mature, high-yield miniature semiconductor chiplet- configured die to meet system-level criteria is more economical and can significantly reduce develop- ment time. "Chiplets" is where old-school flip-chip pack- aging reemerges to become new-school tech- nology. A chiplet is an integrated circuit block specifically designed to work with other similar chiplets. That is, by clustering and interconnecting two or more associated heterogeneous or homog- enous semiconductor dies within the confines of a single package outline, closer coupling and the potential for enhanced electrical performance are enabled. By positioning these smaller, less complex functional chiplets in close proximity to the more advanced core processor die, as shown in Figure 4, interconnect distance is minimized and power and ground distribution are optimized. Overall, the circuit density of the 2.5D interposer is significantly greater than that of the mainstream HDI circuit board. Commercial CAD tools are avail- able to support most very high density (VHD) inter- poser development. The key enabler for success in chiplet packaging is the interposer. Acting as an intermediary, it furnishes a bridge for electrical signals and thermal management. While the upper surface of the 2.5D interposer accommodates a majority of the semiconductor redistribution and/or Figure 3: Fan-in wafer-level package terminal array example. (Source: I-Connect007) D ES I G N E R 'S N OT E B O O K