Identification on bodies and properties of areas where solids overlap
Posted: 26 Jun 2023, 16:08
Hi,
I'm trying to simulate capacitance of copper plane on PCB. I've already got some results which looks ok but I'm not sure I do it right.
Below is description of what I did.
1. First step was to export gerber file to svg, then do some cleanup in inkscape (including saving as png and converting back to svg), then the svg file could be imported to FreeCAD.
2. In FreeCAD I created 3D structure which consist of:
- the piece of copper imported as above and extruded
- a second piece of copper - simplified ground plane below the described above (I want to know capacitance between these two)
- substrate - layer of dielectric between these two
- simulation box - I want the whole structure (2 copper parts separated by dielectric) to be simulated in some volume of air although so I placed a cube including the parts
3. I prepared geometry in Salome. First, I used function "Explode" to have all the parts separated. Then it was necessary to use "Shape Processing" on the more complicated copper plane with adjusted parameters to avoid further errors. Next I created "Partition" to have all the parts together to create mesh. Also I used "Create Group" to create boundary conditions on two inner surfaces of copper parts.
4. I created mesh in Salome from the partition using gmsh. With "Create Groups from Geometry" I added the boundary conditions.
5. When I opened unv file in ElmerGUI i noticed it's displayed incorrectly. I assigned materials (copper Er=1, Air from library, dielectric Er=4.5), boundary conditions (1V and 0V) and solver (electrostatics). Simulation seems to work ok.
My questions are:
1. As the bodies are not displayed correctly and names from Salome are not imported it's not clear how to assign materials. I opened the mesh in Salome to figure out what is what by looking at the numbers (assumed that Solid_1 is Body Property 1) but I'm not sure it's correct.
2. I'm not sure if I defined the air around my structure correctly. I've got the three parts (2 copper parts separated by dielectric) and the box which includes the structure. The problem is that the box is a solid which is overlapping the other parts and I'm not sure how to make sure the properties of the box have lower priority than properties of the structure. The dielectric has higher dielectric constant (4.5) and I'm not sure if/how elmer can determine if the area between copper parts has Er like air or like the dielectric. A solution maybe would be to add cavity inside the cube representing air around (by using boolean subtraction) but meshing tool failed to mesh that (unless the geometry is simple).
I'm trying to simulate capacitance of copper plane on PCB. I've already got some results which looks ok but I'm not sure I do it right.
Below is description of what I did.
1. First step was to export gerber file to svg, then do some cleanup in inkscape (including saving as png and converting back to svg), then the svg file could be imported to FreeCAD.
2. In FreeCAD I created 3D structure which consist of:
- the piece of copper imported as above and extruded
- a second piece of copper - simplified ground plane below the described above (I want to know capacitance between these two)
- substrate - layer of dielectric between these two
- simulation box - I want the whole structure (2 copper parts separated by dielectric) to be simulated in some volume of air although so I placed a cube including the parts
3. I prepared geometry in Salome. First, I used function "Explode" to have all the parts separated. Then it was necessary to use "Shape Processing" on the more complicated copper plane with adjusted parameters to avoid further errors. Next I created "Partition" to have all the parts together to create mesh. Also I used "Create Group" to create boundary conditions on two inner surfaces of copper parts.
4. I created mesh in Salome from the partition using gmsh. With "Create Groups from Geometry" I added the boundary conditions.
5. When I opened unv file in ElmerGUI i noticed it's displayed incorrectly. I assigned materials (copper Er=1, Air from library, dielectric Er=4.5), boundary conditions (1V and 0V) and solver (electrostatics). Simulation seems to work ok.
My questions are:
1. As the bodies are not displayed correctly and names from Salome are not imported it's not clear how to assign materials. I opened the mesh in Salome to figure out what is what by looking at the numbers (assumed that Solid_1 is Body Property 1) but I'm not sure it's correct.
2. I'm not sure if I defined the air around my structure correctly. I've got the three parts (2 copper parts separated by dielectric) and the box which includes the structure. The problem is that the box is a solid which is overlapping the other parts and I'm not sure how to make sure the properties of the box have lower priority than properties of the structure. The dielectric has higher dielectric constant (4.5) and I'm not sure if/how elmer can determine if the area between copper parts has Er like air or like the dielectric. A solution maybe would be to add cavity inside the cube representing air around (by using boolean subtraction) but meshing tool failed to mesh that (unless the geometry is simple).