Do you know how to Design PCB Stackup

2018-11-23 21:11Writer: qyadminReading:

There are two options:

  1 Leave your PCB manufacturer to design PCB stackup for you.

  You don’t need to spend your time by designing stackup. Leave it on PCB manufacturer-they are professionals. They do it every day. Also, by doing it this way, you can work on design in parallel of handling issues with PCB stackup.

  Many times PCB manufacturer is not able to build PCB stackup designed by other company or a person outside their company. The main reason is unavailability of material used in some PCB stackups. three basic materials: Copper foil, Prepreg, Core

  Standard Copper foil thickness: 5um, 12um, 18um, 35um, 70um

  Standard prepreg thickness: 65um, 100um, 180um

  Standard core thickness: 0.15mm, 0.20mm, 0.36mm, 0.46mm, 0.56mm, 0.71mm, 1mm, 1.2mm, 1.5mm, 2.0mm, 2.4mm, 3.2mm. Core is supplied with copper foil on both sides. For some cores you need to add copper foil thickness (18um or 35um) to the core thickness.

  PCB stackup examples

  Standard 4 Layer PCB stackup [mm] Standard 6 Layer PCB stackup [mm] Standard 8 Layer PCB stackup [mm]

  Copper foil

  0.18 prepreg

  0.18 prepreg

  0.71 core

  0.18 prepreg

  0.18 prepreg

  Copper foil Copper foil

  0.10 prepreg

  0.10 prepreg

  0.36 core

  0.10 prepreg

  0.10 prepreg

  0.10 prepreg

  0.36 core

  0.10 prepreg

  0.10 prepreg

  Copper foil Copper foil

  0.10 prepreg

  0.10 prepreg

  0.20 core

  0.10 prepreg

  0.10 prepreg

  0.20 core

  0.10 prepreg

  0.10 prepreg

  0.20 core

  0.10 prepreg

  0.10 prepreg

  Copper foil

  2.There are some rules how to build your stackup. Not every combination is possible. Check it out with your PCB manufacturer.

  Note: If you calculate impedances for your own stackup, don’t forget about PLATING. Plating process add an additional copper (e.g. 20um) to top and bottom layer (or if you use uVIAs and buried VIAs, then also to some of the inner layers).

  PCB impedance calculation and Track geometry design

  Example of Microstrip (the tracks on TOP and BOTTOM layers) impedance calculation

  90 Ohms Differential / 55 Ohm Single ended for:

  Track width: 11mil / Copper foil 18um (0.7mil) / Track Gap 8 mil / Dielectric thickness 2x 0.1 prepreg = 0.2mm (7.8mil) / material FR-4 (dielectric constant 4.8)

  PCB impedance calculator – Single ended / Differential pair

  Tip: It’s easy to convert between mm and mils. Use google and look for: “10mil to mm” or “0.2mm to mil”.

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