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OCTOBER 2022 I DESIGN007 MAGAZINE 23 aer processing. ese build up in a trapezoid formation depending upon the photoresist thicknesses. e A-SAP process does not build traces in a trapezoidal fashion. e thicker the base copper, the more of a trapezoid shape you'll have to start with. Both can start with typical foil. When they do, mSAP usually starts with a thicker copper foil and A-SAP starts with a much t h i n n e r c o p p e r b a s e . Av e r a t e k 's Steve Iketani and Mike Vinson wrote an informative article on this topic i n t h e Ju l y 2 0 1 9 i s s u e o f P C B 0 0 7 Magazine 1 . Optionally, both A-SAP and mSAP can use an additive process vs. a sub- tractive process at fabrication using LMI (liquid metal ink) for the starting copper thickness. When using LMI to apply the starting copper, as seen in Figure 1, the density at the interface with the laminate increases dramati- cally. The process f low now becomes ver y different. So does the shape of my traces, the copper thickness and width. Figure 2 shows an example of what this looks like. Figure 1: Liquid metal ink (LMI) can change your entire process flow. (Courtesy of Averatek Corporation) Figure 2: Examples of A-SAP and mSAP trace constructions. (Courtesy of Averatek Corporation) ness, and A-SAP starts with bare dielectric and adds 0.2 mm of thin electroless copper. Table 1 shows typical additive copper thicknesses