Design007 Magazine

Design007-Jan2021

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JANUARY 2021 I DESIGN007 MAGAZINE 15 – Signal, plane (PWR/GND), or mixed copper density assignment for each layer – Controlled impedance requirements (with reference layers) per layer • Minimum pitch of BGA or other special components that will require fan-out and the drill structures • Drill structures, including start/stop layers for µvias – Minimum drill/pads/antipads for all layers – Verification of VIPPO (non-conductive epoxy via fill in pad, Cu plated over) ° Confirm laser microvias, offset or stacked (buried stacked microvias should be solid Cu-filled). Skip blind vias. – Backdrills (confirming starting and do-not-cut layers, drill/antipad diameter) • Minimum lines/spaces requested – Internal layers, etch only – Plated layers, whether internal or external • Any special dimensional requirements affecting etching, routing, drilling, and lamination For example, when we're trying to route a 0.5 mm pitch BGA, which we know auto- matically means it's a laser microvia board, we'll get on WebEx so they can share the BGA pad configuration. With knowledge of how many rows of balls or pads there are on the device, my customer can figure out how many layers they need, and then we try to optimize the fan-out to route all those rows of pads in the lowest number of lamination cycles as possible (Figure 3). Once my prelim stackup is approved by the customer, I have the factories (quick-turn pro- totype and volume site, if necessary) provide their site stackups and confirm the design rules, the minimum lines and spaces on each layer, the minimum drill and pad diameters, and the controlled impedance lines and spaces. We provide all that information so the customer has the design rules to put into their CAD pro- gram before they start. Figure 2: Single lam stackup with filled vias.

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