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88 PCB007 MAGAZINE I JANUARY 2022 capabilities of various SAP processes includ- ing the SAP and pattern plating for the ABF process used for flip-chip and other IC packag- ing substrates. e trend is clear that organic (PCB) sub- strates are continuing to evolve down to less than five-micron trace/spaces. e most important characteristic is the surface smooth- ness and planarity of the dielectric. Figure 2 shows the reduction of trace/space as a func- tion of device pitch and SAP process technol- ogy, as portrayed in the 2019 IEEE Heteroge- neous Roadmap. 6 Direct Metallizations Considerable advances have been made in the direct metallization processes to replace elec- troless copper, introducing a simpler and less costly process for mSAP/amSAP. e proven direct metallization systems have added a new copper etch of 0.2–0.3 mm to eliminate carbon from the copper surfaces. e simplified metallization process (compared to electro- less copper) is shown in Table 3. While the direct metalliza- tion process is easier to control, it also has the advantage of one- third the space required and is environmentally friendly. Heterogeneous Integration e constant reduction in semiconductor transistor geometries have created a situa- tion where it appears less costly to break up very large, complex dies into smaller dies and com- bine them with "modular" dies, now named "chiplets" and tiny discretes on an organic sub- strate using these exceedingly small traces and spaces along with very tiny vias as a "system- in-package"—now referred to as Figure 2: Trace and space for 0.25 mm pitch BGA and evolving trace width reduction with new processes. (Source: IEEE Heterogeneous Integration Roadmap) Table 3: Process comparisons of metallization for SAP. 7