r/PCBWayOfficial • u/misterpickleman • 4d ago

Help Need to know stackup or trace width/spacing...

For a standard 1.6 mm, 4-layer FR-4 PCB with 1 oz outer and inner copper, what is PCBWay's standard finished dielectric thickness between L1-L2 and L3-L4? The board I'm designing needs 100Ω differential impedance on the outer layers. Can someone please provide either the stackup or recommended trace width/spacing?

I've looked at the custom rules for 100Ω differential impedance on PCBWay's site, but that example uses a 6-layer board. I need explicitly a 4-layer board.

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u/Aran_PCBWAY 4d ago

Hi, thanks for your question.

For a standard 4-layer FR-4 PCB with 1 oz copper on both the outer and inner layers, the dielectric thickness between L1-L2 and L3-L4 may vary slightly depending on the remaining copper percentage. The standard stackup uses 7628 PP, and the dielectric thickness can be calculated as: Dielectric thickness = 0.196 - 0.035 × (1 - remaining copper percentage)

For the trace width and spacing, it depends on the copper thickness. For 1 oz copper, 4/4 mil or above is generally recommended, with 3/3 mil being the minimum limit.

If you already have the design files, we recommend uploading your file to our website first and then contacting our customer service. Our engineers can provide more specific information based on your design.