GDS-II and Cif Files Are Not Unitless
Linkcad
DXF files are unitless — a distance of 10 units may correspond to 10 microns, 10 inches, or even 10 meters. It is therefore very important that you specify the meaning of the DXF units. Select microns if you want a distance of 1 to represent 1 micron in the DXF file. This does not limit your drawing's resolution to one micron because DXF supports fractional units.
GDS-II and Cif files are not unitless.
Cadence
The units in the Cadence database are set by the technology file. If the units aren’t set in the technology file, the Cadence software default unit is microns.
SolidWorks units are set by the user. After opening a part or an assembly, under the Tools->Options->Units menu. The smallest units are mm. Using 0.002 mm, etc. works just fine. If you select the units of mm, part densities will be defined in terms of mm. For whatever units you choose in SolidWorks, you can’t enter a numerical value less than 0.001 or greater than 1,000,000. Assemblies do not have mass properties, mass properties must be assigned for each part. When a part window is open, the density can be assigned under Tools->Options->Material Density. After the geometry of that part is defined, the total mass can be viewed from Tools->Mass Properties. In an assembly window, mass properties can be found for individual parts or for the entire assembly. In the assembly window, use the Feature Manager Tree to select the top-level assembly, or an individual part, and select Tools->Mass Properties. This will print out the mass properties and also show the location and directions for the global coordinate system. Moments of inertia are also listed in the mass properties dialog box, with respect to the coordinate systems shown. Since a part’s local origin can be different that the global origin, the coordinate system for the moments of inertia for the selected part is also shown.
Dynamic Designer uses these masses and coordinate systems to calculate dynamic forces and reaction forces. Consequently, using 0.002mm to describe a length of 2 microns is the right thing to do. However, for COSMOSWorks, COSMOSWorks can’t work with numbers as small as 0.002, etc. In that case, using SolidWorks mm-unit scale and using 2 mm to represent a length of 2 microns can be useful. To get accurate modal frequencies, etc., from COSMOSWorks, just scale the density of the material and the Young’s modulus accordingly. There is also some possibility of loss of resolution when making masks with circles, if you use 0.002 mm to represent 2 microns.
To make masks, you can use either method of setting SolidWorks units, but scale appropriately further down the translator line. To make masks from SolidWorks, you need to cut the 3D model at the height of interest and create a 2D drawing, which can be saved as a DXF file. DXF files are unitless. However, when converting to GDS-II or Cif formats from Linkcad, units have to be reinserted. While .tap files for the Microlab’s pattern generator can be made directly from GDS-II files, some users may want to read their data into Cadence first, before making masks. From Cadence database files, the procedure to make masks is also to export to GDS-II format and then convert to .tap files.
Cadence can read in Cif or GDS-II formats and output Cif or GDS-II formats. Linkcad recommends using GDS-II to go between SolidWorks’ DXF and Cadence, as GDS-II is an industry standard and if Cadence doesn’t support it to the T, “They’re out of business. Cif is used mostly just by universities.”
Intermsoflayers,theyareonlyusedintheSolidWorks2Ddrawing environment.Ifyouhaveanassemblydrawing,thecomponentsthatmakeup theassemblycanbeputontodifferentlayers.Firstyourneedtospecifiy thelayers...name,color,etc.Thenright-clickoverapartinthedrawing andselect"ComponentLineFont...".Inthelowerrightcornerofthe dialogboxthereisadrop-downmenuwhichliststhelayersinthedrawing. Selectthelayeryouwantassignedtothepart.
SolidWorkscanalsoassignlayerstodimensionsandannotations.However,
itcannotassignlayerstoindividualfeatureslikecut-extrudesor
boss-extrudes (or assembly features).
Linkcad is a program that not only converts between various CAD packages, it also has a viewer that lets you look at a file in any of the formats. The viewer also contains a ruler for measuring, which lets you check distances.
Cadence Export
- The following settings convert the layout to a micron scale (i.e. 1.0 in the layout equals 1micron in the exported file).
Scale UU/DBU: 0.001
Units: micron