I had a PCB board with 8 layers to be fabricated. I have used an opensource deign modified it a bit and want to get them fabricated. The PCB company asked me to provide layer stack and impedance requirements.

In order to make better PCB, please offer me the layer stack for every layer and the impedance requirements.

I am not sure what exactly to reply with specially regarding the impedance requirements

Here is my layers setting in eagle and regarding impedance control I have an A20 soc and DRAM.

enter image description here


The PCB manufacturer is asking for the stack-up because generally people include Power planes and Ground planes in between the layers. So how would the PCB manufacturer know where to put which layer?

Sophisticated PCB Manufacturers also have impedance control on signals. You should provide him the stack file. Like USB Differential Signals (D+ and D-) require impedance control on tracks. AFAIK, 90 ohm to be exact.

He requires these files for quality manufacturing.

  • 1
    \$\begingroup\$ USB is 90 ohm differential, most everything else is 100 ohm differential or 50 ohm single-ended. \$\endgroup\$ – alex.forencich Dec 16 '15 at 8:31
  • \$\begingroup\$ Yeah. I'll edit it. \$\endgroup\$ – ammar.cma Dec 16 '15 at 9:25

If you have a design with impedance controlled traces, you need to assume/define some PCB parameters to calculate the required trace width in the first place.

Prepreg material and thickness, copper thickness and layer-stack-up are most important from the manufacturing perspective.

Manufacturers have specific Prepregs, cores and foils available from stock. Exotic stack-ups will probably cost extra, so it is a good idea to base your layer-stack on the available materials.

Some manufacturers will suggest you a (more or less) suitable layer stack, if you provide information about which traces have what specific impedance requirements. You obviously get the best match, when you design your stack based on the manufacturers material specs and provide this information when you order the PCBs.


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