Issue link: https://iconnect007.uberflip.com/i/1517130
42 DESIGN007 MAGAZINE I MARCH 2024 Consequently, we have seen numerous jobs culminate in resin-voiding. It is for this reason that we have established stackup testing pro- cedures as well as thickness calculators instru- mental to realizing maximum thickness allow- ance and properly filling etched spaces with resin during pressing (lamination). Since each design is unique and there is no standard for- mula for creating heavy copper multilayer PCB stackups, collaboration between fabrication and design is imperative. Design issue:Stackup dielectric thicknesses too thin Manufacturing pitfall: Inner layer misalignment Meeting the designer's maximum overall thickness requirements while still ensuring proper resin fill is another major contention between fabrication and design. In contrast, there is no dispute between copper weight and dielectric spacing as they are proportionally integral to one another (the heavier the cop- per, the more dielectric spacing required). For this reason, fabricators must assign sufficient prepreg plies to achieve the necessary resin volume, and the easiest way to compensate is by reducing the core material's thickness. Material handling issues are primarily gener- ated from older horizontal conveyorized lines not equipped for thinner materials. Materials are destroyed when dropped into the chemi- cal sumps or wrapped around conveyors, so shops counter this by attaching them to thicker panels that tow them down the line. Obviously, this extra step affects lead times and cost. Figure 3: Maximum fill requirement. Figure 4: Resin voiding. Table 4