A. Appendix

A.1. Example

A.1.1 Example footprint

A three pin SOT23 lihata footprint file has been generated using this guide, IPC7351 and the component drawing of a generic SOT23 datasheet from NXP. Copper pad sizes are computed using the method described in section 3.4.1.

The resulting footprint is very similar to the vendor recommended footprint with dimensions matching within the tenth of mms.

The generated footprint has all major features listed in this guide and passes all test of the checklist in the appendix A.3.

A.1.2 Template board for manual footprint drawing

A pcb-rnd template board is available for manual footprint drawing:

• load the template, draw footprint graphics then select and convert to subcricuit
• the template contains all layers normally used in a footprint
• the primary side of the footprint should be top side of the board
  • smd footprints should use only the top side
  • thru-hole footprints should normally use the bottom side only in padstacks, except for special components that really span physically to both sides
  • internal copper is relevant only in thru-hole padstacks
• keepout layers other than courtyard are not created; right click on an existing group in the layer selector to create a new keepout layer group
• predefined routing styles and objects:
  • use routing style silk-placement for drawing placement graphics on top silk
  • there is an 1*1 mm corner right angle drawn with silk-placement, often just copying and rotating this should be enough for all placement graphics of a footprint
  • there is a 0.3mm diameter circle (zero length line) placed on top silk for pin 1 mark; select it before moving it
  • use routing style assy-normal for drawing the assembly layer body and pin/lead outline
  • use routing style assy-thin for indicating pin/lead bends and other secondary (non-contour) features
  • there is a 0.25mm diameter circle (zero length line) placed on top assembly layer for pin 1 mark; select it before moving it
• make sure all layers are visible before selecting everything for the subcircuit conversion
• when converting selected object to subcircuit use the menu - that will run an extra step of querying for the centroid
• no need to remove unused layers and layer groups; subcircuit conversion will include only the relevant layers

A.1.3 Example centerpad paste pattern

Example centerpad-only footprint, with 0.3mm via hole, 0.3mm mesh separation, SMD (mask+paste mesh) over a large centerpad. This demonstrates paste pattern considerations discussed in 3.6.3.