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Step export: Copper Layer is added to nominal thickness

Description

When exporting STEP files with the new function "Export tracks, pads and vias" and "Export zones", the copper layers (top and bottom) are added to the nominal thickness specified in layer stackup. Is this intended behaviour?

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Admittedly, I do not know how I would propose to fix this issue, since KiCad does not also model the solder mask in STEP. Therefore, If base material would be reduced to effective size (0.71mm in this case) and and effective copper thickness modeled, overall thickness would be smaller that nominal since solder mask is missing. But if solder mask thickness is simply added to base material the exported model also does not really reflect the real mechanical facts. Maybe STEP export could be identical to how 3D Viever shows the part? There solder mask, tracks, vias, pads and zones get displayed and positioned correctly (even though i have no measurement function to verifly geometric accuracy)

However, what I can say is that the way the FreeCAD plugin creates STEP Models with tracks and pads suits my specific workflow, which focuses on transferring PCB measurements and position of blank copper to my mechanical engineering colleague, far better. I hope, though, that I can use the KiCAD internal exporter in future as it's much more streamlined to use.

Steps to reproduce

  1. Create PCB with some tracks, pads vias and zones. Set overall thickness to desired value in stackup editor.
  2. Export STEP with tracks, pads vias and zones
  3. Measure PCB thickness in external STEP viewer (e.g. FreeCAD)

KiCad Version

Application: KiCad x64 on x64

Version: 8.0.2, release build

Libraries:
	wxWidgets 3.2.4
	FreeType 2.12.1
	HarfBuzz 8.3.0
	FontConfig 2.14.2
	libcurl/8.5.0-DEV Schannel zlib/1.3

Platform: Windows 10 (build 19045), 64-bit edition, 64 bit, Little endian, wxMSW

Build Info:
	Date: Apr 27 2024 23:05:17
	wxWidgets: 3.2.4 (wchar_t,wx containers)
	Boost: 1.83.0
	OCC: 7.7.1
	Curl: 8.5.0-DEV
	ngspice: 42
	Compiler: Visual C++ 1936 without C++ ABI

Build settings:
Edited by Sven Wanzenried