4-Layer HD PCB Stackup

Stackup for 4-Layer Boards

We use Panasonic Prepreg 1080, Peters coatings and Elga Copper foil.

The following track layouts can be used to realise defined impedances. Please note that these values only provide a basic orientation. Interference factors such as angles, meanders or vias in the routing of the tracks may have a negative effect on the intended impedances.

Type Impedance Signal- / Reference Layer width space width
Single Ended 50 Ω TOP / IN1, BOT / IN2 245 µm - -
Differential pairs 90 Ω TOP / IN1, BOT / IN2 230 µm 165 µm 230 µm
Differential pairs 100 Ω TOP / IN1, BOT / IN2 190 µm 180 µm 190 µm
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4 layer stackup was significantly changed between December 2021 and February 2022, but the stackup information has not yet been updated. After some conversation with Aisler, they promised to update these specs quickly.


Now the specs are updated. Unfortunately the changes are not visible. The latest and currently valid version is where the inner core is 710µm FR4 (not 1200µm as before).

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Looking at the 4L HD stack-up picture above I’m confused/concerned (accurate loss and trace-trace coupling calculations) about the true thickness of the outer copper layers. It says 18um copper foil, but a processed thickness of 40um. How does 18um become 40um? Surely your ENIG coating isn’t 22um thick.
Speaking of ENIG, Nickel is magnetic and causes considerable loss in high-speed/high-frequency signals. Is there a way to order WITHOUT ENIG coating?

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Hello @justatoms,

welcome to the community!

The final copper thickness of 40 µm is the result of the 18 µm base copper of the copper foil plus approx. 22 µm copper, which is applied by the electroplating process.


Thank you Manuel,

Pardon my ignorance on PCB manufacturing.
Am I correct then in assuming this 22um Cu plating being the result of the same (electroless) plating process that creates the PTH vias?

Will copper under the soldermask be ENIG plated?


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Hello Anne,

correct, this electroplating process is the key process step that leads to the formation of a conductive copper sleeve in the borehole of each PTH.

The ENIG coating is applied after the soldermask has been applied. Consequently, the copper structures below the soldermask are not coated.

Best regards,


Hello Aisler Team,

I have a question about your Soldermask: Why is it getting lighter on the outside? Is it getting thinner there due to surface tension?

The picture was taken from Plated and Non-Plated Slots and Cutouts, I have seen it on my boards I odered from you too in the past.

Thank you. :cowboy_hat_face:

Hello Aisler team,
do you have recommended W and W/S for the most popular transmission lines impedance, such as SE45, SE50, Diff85, Diff90, Diff100, possibly based on past experiences with this stackup or, even better, real world measurements?
Those numbers would be very helpful.

Many thanks!

Best regards,

Hello Andreas,

I am sorry for the late reply.

Correct, this effect is due to differences in the thickness of the solder resist. The electroplating process builds up tracks and surfaces with additional copper. However, this build-up does not occur completely evenly across the entire width of the track/surface. Thus, any copper structure has more a trapezoidal or dyke-like shape in cross-section rather than a rectangular shape. On the slopes, the solder resist has less adhesion and therefore forms thinner.

Best regards,

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Hi Giacomo,

welcome to the community and thank you for your request!

I will try to make this information available here as soon as possible.

Best regards,

Track layouts for SE50, Diff90 and Diff100 are now listed below the stackup information!