IDF Exporter

Try to make some information about the outline available in the filename to give the user a general idea of what the outline is. For example axial leaded cylindrical packages may represent some types of capacitors as well as some types of resistors, so it makes sense to identify an outline as a horizontal or vertical axial leaded device and to add some extra information on the relevant dimensions: diameter, length, and pitch are the most important. If a device has a unique outline, the manufacturer’s part number and a prefix to indicate the class of device are adequate.

Use comments in the IDF file to give users more information about the outline, for example a reference to the source used for dimensional information.

Think carefully about the values to give to the Geometry and Part Number entries. Taken together, these strings act as a unique identifier for the MCAD system. The values of the strings will ideally have some meaning to a user, but this is not necessary: the values are primarily intended for the MCAD system to use as a unique ID. Ideally the values chosen will be unique within any large collection of outlines; choosing values well will result in fewer clashes especially in complex boards.

For through-hole components there are no widely accepted schemes for determining the pin orientation and component center in 3D models. For consistency, if there are only 2 pins they must be in a horizontal arrangement (see figure 4) along the X axis and for 3 pins try to keep 2 in a horizontal arrangement on the X axis. Polarized devices such as electrolytic or tantalum capacitors must have the positive lead on Pin 1 and diodes must have the cathode on Pin 1; this is to maintain compatibility of the schematic symbols with the orientation defined for SMT devices; however, note that many existing KiCad schematics and footprints place the anode at Pin 1.

For DIP devices the center of the outline must be at the center of the rectangle described by the pin locations and Pin 1 is preferably at the top left corner; this will maintain some consistency with the standardized orientation of SMT components; however, such a model will be rotated -90 degrees relative to most existing KiCad component footprints and VRML models. For items such as a horizontal radial leaded capacitor or a horizontal TO-220 package, prefer to place the leads in a row on the X axis and with the body of the device extending upwards (see figure 4). Non-polarized vertical axial leaded components must have the wire on the right hand side; polarized vertical axial leaded components may have the wire on either side, depending on whether Pin 1 is on the lower end (wire on right) or on the upper end (wire on left).

For SMT components the orientation, package center, and outline are defined by various standards. Use the standard appropriate to your work. Also keep in mind that many devices do not conform to any standard; in such cases the offending device is probably best identified by using the manufacturer’s part number in the outline file name. In general, an SMT outline is a rectangle encompassing the component package and including the leads; the package is oriented such that Pin 1 is as close as possible to the top left corner and the top left corner is usually chamfered for visual reference.

From left to right are (a) vertical radial leaded cylinder, (b) vertical axial leaded cylinder with wire on left, (c) vertical axial leaded cylinder with wire on right, (d) horizontal axial leaded cylinder, (e) horizontal radial leaded cylinder, (f) square outline, plain, (g) square outline with chamfer, (h) square outline with axial lead on right. The top outlines were specified in units of millimeters while the bottom outlines were specified in units of inches.

The purpose served by the extruded outlines is to give the mechanical designer some idea of the location and physical space occupied by each component. In a typical scenario the mechanical designer will replace some of the crude outlines with more detailed mechanical models, for example when checking to ensure that a right-angle mounted LED will fit into a hole on a panel. In most situations the accuracy of an outline doesn’t matter, but it is good practice to create outlines which convey the best mechanical information possible. In a few instances a user may wish to fit the component into a case with very little excess space, for example in a portable music player. In such a situation, if most extruded outlines are a good enough representation of components then the mechanical designer may only have to replace very few models while designing the case. If the outlines are not a reliable reflection of reality then the mechanical designer will waste a lot of time replacing models to ensure a good fit. After all, if you put garbage in you can expect garbage to come out. If you put in good information, you can be confident of good results.

When idfcyl is invoked with no arguments it prints out a usage note and a summary of its inputs:

The notes can be suppressed by entering any arbitrary argument on the command line. A user can manually enter information at the command line or create scripts to generate outlines. The following script creates a single axial leaded outline with the lead on the right hand side:

When idfrect is invoked with no arguments it prints out a usage note and a summary of its inputs:

The notes can be suppressed by entering any arbitrary argument on the command line. A user can manually enter information at the command line or create scripts to generate outlines. The following script creates a chamfered rectangle and an axial leaded outline:

The DXF file used to specify the component outline can be prepared with the free software LibreCAD for best compatibility. When dxf2idf is invoked with no arguments it prints out a usage note and a summary of its inputs:

The notes can be suppressed by entering any arbitrary argument on the command line. A user can manually enter information at the command line or create scripts to generate outlines. The following script creates a 5mm high outline from a DXF file test.dxf: