Design Rules

These design rules are derived from experiences of designing schematics and layouts.

• Schematic Design Rules
• PCB Layout Design Rules

Schematic Design Rules

ID	Description
SDR-001	Using libraries delivered with the schematic capturing tool is not allowed. The device libraries must be saved in (a) project specific file(s) and be used by all contributors. The device libraries can be found in the Code section of the project. Rationale: Different versions of the used schematic tool may deliver different versions of the device libraries. This will lead to errors when the schematic files are edited by multiple contributors or older schematic files are opened in a newer version of the schematic tool.
SDR-002	Standard symbols like for resistors or capacitors are implemented using the IEC 60617-2 ..-11 standard. http://de.wikipedia.org/wiki/Liste_der_Schaltzeichen_%28Elektrik/Elektronik%29
SDR-003	The pins of two devices must always be connected with a wire. It is not allowed to place two devices with their pins together without a wire. Rationale: There is no way to tell if the pins are connected when they are put on the same grid in the schematic tool. This may lead to open connections and hard to find errors.
SDR-004	Some design tools (e.g. KiCAD) allow hidden pins on symbols, especially for supply pins. Hidden pins are not allowed. If there are multiple supply rails or different ground nets there is no way to connect them properly to the symbols with hidden pins. Also pins that are not connected internally in the device are to be shown on the symbol. These pins will be terminated in the schematic using a "not connected" symbol.
SDR-005	Ceramic capacitors on DC signals should have at least two times the voltage rating of the highest applied DC voltage because of the capacity loss due to DC bias.
SDR-006	References on devices must be placed below or on the right side of the device. Rotated text must be oriented to be readable from the right edge of the page. Rationale: This prevents confusion in densely drawn schematics what reference belongs to which device.
SDR-007	If there are circuits where the tolerance of the parts is relevant for the performance of the circuit (e.g. filters or supervisor circuits) the tolerance must be displayed in the schematic for the respective part. Rationale: this makes it easier in reviews or redesigns to spot the parts where special care must be taken to ensure the correct behaviour of the circuit.
SDR-008

PCB Layout Design Rules

ID	Description
LDR-001	Similar through-hole devices should be placed in the same orientation whenever possible. Example: Big electrolyte capacitors should all have their polarity marking pointing in the same direction to prevent errors when mounting them on the board. A wrong mounted device is therefore much easier to spot and helps preventing damages.
LDR-002	Areas with high voltage potentials should always be oriented horizontally to each other due to possible shorts when condensation occurs.
LDR-003