Definition of seating plane

1. in plug-in type devices, such as dual inline packages (sidebrazed or cerdip) or pin grid arrays, the plane formed by the three lowest shoulders on the leads or pins as measured from the bottom of the package. The seating plane holds the package off the circuit board to which it is mounted. This gap allows solder flux and residues to be cleaned after soldering the leads and, in some cases, allows for sufficient cooling air flow around the device. A prescribed force is used to hold the device in the mounting holes when the seating plane is to be measured. [SEMI G61-94] Also see standoff.