Read the layer sequence before entering values
A simple four-layer cross-section contains four copper layers and three dielectric regions. Enter dielectric dimensions in millimeters and copper dimensions in micrometers. One micrometer is 0.001 millimeter. The order follows the board from the top copper surface through the core to the bottom copper surface.
The default values are an arithmetic example, not a recommended manufacturing construction. They represent three dielectric regions of 0.2, 1.0 and 0.2 mm, plus four copper layers of 35 µm each.
Work through the thickness example
The dielectric sum is 0.2 + 1.0 + 0.2 = 1.4 mm. Converting 35 µm gives 0.035 mm; four such copper layers add 0.14 mm. The nominal total is therefore 1.54 mm. This value excludes solder mask, surface finish and any adjustment between nominal and finished layer construction.
Do not round that example into a guaranteed finished thickness. A fabrication specification should state the required finished dimension and tolerance, while the proposed stackup should describe how that requirement will be achieved.
Separate total thickness from impedance geometry
A trace on an outside layer responds strongly to its distance from the adjacent reference plane. Increasing the core thickness between the two inner layers can change the overall board thickness without producing the same effect as increasing the dielectric immediately below that trace. Use the actual trace-to-plane spacing when discussing impedance.
Also distinguish base copper from finished outer copper. Plating and processing can change the relevant finished geometry. Keep those assumptions explicit in the drawing and review them with engineering.
Prepare the stackup for release
Record the material designation, layer names, functional assignments, copper assumptions and thickness requirements. If impedance is controlled, attach the target values, tolerance and relevant layers. Ask for discrepancies between the proposed construction and layout assumptions to be resolved before production release.
The planner accepts positive dimensions only. It does not model resin flow, glass style, copper balance, warpage, dielectric variation or tolerance accumulation. A mechanically plausible sum is not a manufacturing approval.