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22 DESIGN007 MAGAZINE I OCTOBER 2022 Smaller Vias A variety of options are available here: Blind vias with through vias is is the optimal choice. It adds a little expense while giving you the ability to place components on both sides of the board with- out having to be confined by opposing pad with different nets. Blind and buried vias with through vias is option gives you the most routing con- trol; however, it also adds the most cost. Through vias only While this can cut fabrication costs, it lim- its breakout, routing, via size, and component placement. Smaller vias are dependent upon the aspect ratio of the board. Keep the board thin and most fabricators can produce smaller vias, down to 6 mils (1.5 mm) if your board measures 50 mils of thickness or less, without additional costs. Both the A-SAP and mSAP processes can be used to plate holes. Again, the aspect ratio will make a difference. How much plating do you need? Are you plugging the vias with conduc- tive or non-conductive material? Smaller Traces How small you go depends on the fabrication process you select and how small the compo- nent pin pitch is. It's important to understand the differences between A-SAP and mSAP before you commit to a process. Standard subtractive etch pro- cesses start with very thin copper foils, etch a pattern, and then add copper for the finished traces and copper features. Table 1 is a chart for starting copper thicknesses from the IPC-6012. When using basic core material, mSAP usu- ally starts at the quarter-ounce copper thick- Table 1: External conductor thickness after plating, according to IPC-6012.