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44 I-CONNECT007 MAGAZINE I MARCH 2026 In Figure 1, implementation and validation can easily become a 10-step process when you include fine-pitch packaging (driving HDI) and vast BGA ar- rays (driving layer count). It has become a workflow requiring modeling, validation, and increasingly, automation. Basic Stackups/Best Practices in Stackup Design For a complex multilayer, selecting the materials matters as much as choosing the construction type and via structure. Modeling and simulation help reduce cost and risk by defining the number of lay- ers, design rules, impedance targets, and reliability expectations before fabrications begins. Most of this information results from understand- ing laminate datasheets and using stackup plan- ners like the Z-Zero and Polar resources. 1 Material systems must be compatible with HDI via struc- tures, especially in sequential lamination builds. 2 Once the material system and thickness ranges are understood, the designer can select the right dielectric thicknesses for frequency planning and impedance design. A good example of this ap- proach is illustrated in papers by Gerry Partida of Summit Interconnect. 3,4 Gerry's simulations (for example, Avishtech's Gauss Stack and Gause 2D 3 ) show that sequential lamination and stacked microvias are reliable when the proper material systems are selected and used correctly. This completes the design phase for implementation but now, as illustrated in Figure 2, the process must continue into validation with the fabricator. Material characteristics (Figure 3), documented in books published by I-Connect007, provide insight into selecting the proper material system and un- derstanding trade-offs. Validation with the fabricator (Figure 1, steps 6–10) provides the feedback loop confirming that the multilayer stackup will perform, meet imped- ance requirements, and be reliable over time. Additional DFM checks and signal integrity/imped- ance modeling help complete the validation phase. Hardware-Tooling and Equipment In complex multilayer fabrication, other critical processes include tooling, multilayer presses, and via filling. ML-PWB Tooling The current best practice is pinless lamination stackup. New automated equipment is now avail- able from several vendors to support this approach. Pin tooling plates have been used for lamination since the early 1960s. I first encountered multilayer stackup when I was assigned to increase capacity for our multilayer output in 1972. In those days, we used mechanical pins and tooling holes to align layers. It worked, but it introduced its own toler- ance stackups, and anyone who has fought multi- layer registration knows exactly what that means. Pinless systems, using optical alignment and inner-laying welding, offer a major improvement in both registration accuracy and process predict- ability. H A P PY'S T EC H TA L K # 47 Figure 2: The "Rule of 10" applied to the high-speed PCB design-to-validation flow. 2 Figure 3: Several material entries from the dielectric library include both an E-glass version of the laminate as well as a low-Dk glass version value with 50% resin content. 2