Box Header Keying: Notches, Pegs and Pin-1 Marks That Prevent Reverse Mating

Reverse mating is a power incident

Unkeyed dual-row headers can accept a plug 180° out. Pin 1 and the last pin swap; supplies may land on GPIO. Keying belongs in plastic, not only in the WI.

Three layers

• Shroud key: one-way entry. The cable plug must use the same key family.
• Locating pegs: stop the header itself being placed 180° on the PCB. Two identical pegs do not polarize.
• Silkscreen / triangle: for service. It does not replace a plastic key.

Keep one pin-1 rule

Put pin 1 on the key side in the schematic symbol, footprint and drawing. Mixing leftover keyed and unkeyed stock mid-project is how field returns start.

Junjia can supply keyed and pegged box headers. Freeze the key at first prototype and put the harness vendor on the same interface drawing.