Issue link: https://iconnect007.uberflip.com/i/1533085
52 DESIGN007 MAGAZINE I MARCH 2025 scrap boards. You can avoid these problems by understanding the manufacturer's sweet spots. Via aspect ratios (the ratio of the board thickness to the smallest hole diameter) mat- ter. Disappointment will probably result if you use a small-diameter drill for via holes in a thicker-than-average board and expect per- fect hole plating. As the aspect ratio increases, the ability to plate copper in these smallest holes becomes more difficult. e cost usually increases, as does the chance of yield loss and reliability. An aspect ratio of less than 10:1 is generally a rule of thumb for most fabricators. Above that threshold, fabricators must take special care to produce quality products. Another error is improper copper balanc- ing. Make sure the layer stackup is symmetrical about the center, and consider dielectric thick- nesses, copper weights, and the distribution of plane versus signal layers. e more balanced and symmetrical the design is along the Z-axis, the better. Uneven copper distribution (in the X or Y axis) across the individual layers can also create issues and lead to board warpage, which oen makes it difficult to assemble surface mount components accurately and reliably. Unnecessarily tight tolerances can drive up costs and increase yield loss. Designers love pushing the limits, specifying tolerances that are not required or that fabricators can't pro- duce reliably. I once saw a design with zero deviation from nominal called out as the toler- ance. When we asked the designer about devi- ating to a reasonable tolerance, he said, "It is not critical to have it so tight, but I thought. "What the heck? It takes out some of the varia- tion in my design." Specifying ultra-tight toler- ances when you don't need them is like driv- ing a Ferrari at top speed to the grocery store: unnecessary and risky. Please refer to our book, DFM Essentials, for an in-depth look at potential cost drivers and common design-related errors. How Oversights Cause Bottlenecks When small design issues pile up, the risk to the yield, board reliability, and your project's delivery timeline increases. Layer misalignment is one of the most common causes of non-conformance on high-den- sity projects. Materials shrink and expand during lamination. Sometimes, it is routine and predictable, but at other times, it can be design-specific. Working up front with your manufacturer when creating the layer stackup can help the first build be more successful. Using known material sets in known configurations can take some of the guesswork out of the build. Another potential design issue is miss- ing thermal relief on pads. Designers want to minimize resistance and maximize cur- rent flow, but connecting pads directly to large copper planes without thermal relief creates issues at assembly. Uneven heat distribution prevents proper solder wet- ting, resulting in weak or cold solder joints.