Issue link: https://iconnect007.uberflip.com/i/1327102
16 DESIGN007 MAGAZINE I JANUARY 2021 Shaughnessy: You're sort of like an intermedi- ary between the designer and the circuit board shop, in a way? Ellis: Yes, I'm the person who will translate information going both directions. I share fabrication knowledge with customers for their projects, so they can confidently make informed design decisions that align with fab- rication capabilities. The key manufacturability considerations and standard design guidelines (which can be improved upon engineering review) that all design engineers would benefit from under- standing are listed below. We have to take all of these into account if we are creating stackups in the vertical plane (microsection view) that accommodate the component and drill con- nection requirements in the horizontal plane (TOP or BOT view): 1) Aspect ratio: The ratio of thickness being drilled to the drill diameter to assure compliant Cu plating thickness inside the hole walls a. Plated through-hole (PTH), mechani- cal drill: <10:1 – thickness drilled should not be more than 10X the drill diameter b. Blind microvia, laser drill: <0.75:1 —the drill diameter is 33% larger than the thickness drilled 2) Pad diameter, tangency, no break-out (accommodates misregistration of drill and Cu etching): a. Mechanical drill, through-hole: = drill diameter + 10 mil b. Laser drill, blind hole: = drill diameter + 5 mil (note the space-saving potential here, but these are shallow, blind vias that can't go all the way through the board) 3) Etched lines: Increase in width as Cu thickness increases, refer to fabricator tables 4) Etched spaces: Increase in width as Cu thickness increases, best if larger than adjacent lines by 0.5–1mil in dense circuitry due to artwork compensation that increases the lines to achieve the designed line after etching 5) Etched line widths are slightly different for plated versus unplated layers, because plated layers include starting Cu foil + surface plating that occurs when plating the hole walls Figure 3: 0.5 mm and 0.4 mm BGA pitch with one line, for inner layer.