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RULES.md

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NOWAE - KiCad6 Footprint Design Rules

Ispired by KiCad Library Conventions. This document contains our rules to design footprint symbols and is more or less the same of KiCad Conventions.

Footprint libraries files

Footprints are grouped into directories with .pretty extension, based on their primary function. Library names must be defined based on the priority list below, with each element separated by the underscore character:

  • Function (e.g. Connector, Capacitor)
  • Sub-function (e.g. HDMI, USB)
  • Qualifier (e.g. RightAngle, SMD)
  • Manufacturer name (e.g. Wurth, ST)
  • Footprint series name (e.g. MicroFit)

Connector footprint libraries

Connector is very difficult to divide by function.

  • Connectors are grouped firstly by their primary function (e.g. USB, HDMI)
  • After that they can be split:
    • by sub-function or by manufacturer;
    • for connectors without a specific function, the connectors are grouped by their mechanical type (e.g. DSUB, DIN, Header, Socket). In this case, connector libraries must be split by another qualifier (e.g. 2.54mm, 1.27mm)
  • Connector libraries can also be split by manufacturer and series, for multi-purpose connectors.

Footprint name

  • General footprint naming conventions

    • Each footprint is a .kicad_mod file into a .pretty directory.
    • Specific package type is written first.
    • Package name and number of pins are separated by a hyphen (e.g. DIP-20).
    • Packages with special pads add an identifier to the pin count field separated by a hyphen.
      • The field includes the count of uniquely numbered pads of this type.
      • For exposed pads (large copper pad below the part) [count]EP.
      • For shield pads [count]SH (Unless such a pin is already expected for the part. An example would be a HDMI connector.).
      • For pads connecting pure mechanical mounting leads [count]MP.
    • Unique fields (parameters) in the footprint name are separated by _ character.
    • Package dimensions are specified as length x width (and optionally height).
    • Pin layout (e.g. 1x10, 2x15).
    • Orientation (e.g. Horizontal, Vertical).
    • Technology (e.g. THT, SMT).

    Not all of the fields defined above are strictly required for a particular footprint. For a product series, footprint name is manufacturer code (e.g. Wurth code).

  • Footprint naming field prefixes

    • A footprint name has to convey a lot of information to clearly specify the purpose and parameters of the footprint. Some fields in footprint names are common to many footprints and can be shortened using special abbreviations.
    • Not all footprints will require the use of these abbreviations - they are provided as a method of standardising the manner in which footprint parameters are called out when encountered.
    • In many cases, the major dimensions (x/y/z) of a footprint may be specified without a prefix, as the body dimensions are assumed to have the greatest priority in the footprint name.
    • In cases where potential conflicts exist, however, the body dimensions must be explicitly named with the prefix B. Refer to the list below for accepted prefix abbreviations.
      • B: body dimensions
        • Body size (XxYxZ)
        • Height parameter Z may be omitted
        • Prefix B may be omitted if the body size is the major dimension used to define the footprint
      • D: diameter
        • Diameter of major axis for cylindrical component (e.g. D10mm - 10mm diameter)
      • H: height
        • Height of component measured from PCB
        • Body size B should be used in preference, where possible (e.g. H1.1mm - component measures 1.1mm above PCB)
      • L: lenght
        • Length along major axis of component
        • Body size B should be used in preference, where possible (e.g. L15.3mm - 15mm length)
      • W: width
        • Width along minor axis of component
        • Body size B should be used in preference, where possible (e.g. W4.75mm - 4.75mm width)
      • EP: exposed pad dimensions
        • Packages that include a single exposed pad include the size of this pad (e.g. EP2.4x3.6mm - for a single 2.4mm x 3.6mm pad
      • P: pad pitch
        • Pitch (distance) between pins, pads or leads (e.g. P0.63mm - 0.63mm pitch between pads)
      • T: thickness
        • Component thickness, where appropriate

  • Footprint naming for non-standard pin numbering

    • In the majority of cases, the pin quantity is self explanatory and is sufficient to describe the number of pins on the symbol.
    • However there may be cases where this numbering is insufficient. Where the number of footprint pins does not match the number of package pins, exceptions must be made.
    • Exception: the numbers for the missing pins are skipped and the normal pin numbers are assigned to the remaining pins. To indicate this, the footprint should be named as PKG-- where:
      • xx = number of remaining pins
      • yy = number of remaining pins + number of removed pins

Layer Requirements

  • Silkscreen layer requirements:

    • Reference Designator must be drawn on F.SilkS layer, with text size equal to 0.8mm and text thickness equal to 0.15mm
    • Silkscreen line width is 0.15mm
    • Silkscreen must not be placed over pads or areas of exposed copper
    • For SMD footprints, silkscreen must be fully visible after boards assembly
    • Pin-1 designator is provided on the F.SilkS layer and must be visible after board assembly

  • Fabrication layer requirements:

    • The fabrication layers are used to display the simplified mechanical outline of components on the PCB.
    • Simplified component outline must be provided on F.Fab layer, utline line width must be 0.15mm, but for very small component can be 0.10mm.
    • Component value (footprint name) must be displayed on the F.Fab layer, but it is set not visible. Text size must be equal to 0.8mm and text thickness must be equal to 0.15mm.
    • A second copy of the reference designator (RefDes) must be provided on the F.Fab layer, by using %R on the field value. With text size must be equal to 0.8mm and text thickness must be equal to 0.15mm.

  • Courtyard layer requirements:

    • The component courtyard is defined as the smallest rectangular area that provides a minimum electrical and mechanical clearance around the combined component body and land pattern boundaries.
    • Courtyard uses 0.05mm line width.
    • All courtyard line elements are placed on a 0.05mm grid.
    • Unless otherwise specified, clearance is 0.25mm.
    • Components smaller than 0603 should have a clearance of 0.15mm.
    • Connectors should have a clearance of 0.5mm.
    • Crystals should have a clearance of 0.5mm.
    • BGA devices should have a clearance of 1.0mm (A middle way of IPC-7351B).