Reference symbols and dimension examples

Terminology Reference Symbol Description
Nominal dimensions D x E
or
D x E
Largest dimension of the package length excluding terminals and width excluding terminals
Package length D or D Largest dimension of the package length excluding terminals
Package width E or E Largest dimension of the package width excluding terminals
Package center offset w Tolerance of package center offset defined by datum S , A and B
Seating plane S The surface determined when package is placed on a horizontal surface.
Datum surface A A Calculated by crossing 2 straight lines by the Least Squares Method from both lengthwise and then widthwise terminal center positions, then making the X axis (lengthwise) surface datum A.
Datum surface B B Calculate by crossing 2 straight lines by the Least Squares Method from both the widthwise and lengthwise terminal center positions, then making the Y axis (widthwise) surface datum B.
Mounting height A Height from the seating plane to the highest point of the package(including package warp)
Stand-off height A1 Distance from the seating plane to the base plane
Package height A2 Height from base plane to top edge of Package body
Terminal pitch e Terminal pitch. This represents theoretical reference dimension.
Tolerance of package lateral profile v Positional tolerance of the package outlines
Terminal diameter Φb Diameter of each terminal
Tolerance of terminal center Positional tolerance for center axis of the terminal defined by the datum S (seating plane) , A and B . Using the maximum material principle, show the tolerance for maximum terminal diameter. When terminal diameter is narrow, allowable tolerance is increased by the difference with the maximum diameter.
Terminal coplanarity y Uniformity of the bottom-most surface of the terminal relative to the datum S (seating plane).
Parallelism of package top surface y1 Parallelism of package top surface relative to the datum S (seating plane).
Lengthwise overhang SD Position of the closest terminal with respect to datum line A
Widthwise overhang SE Position of the closest terminal with respect to datum line B
Overhang in body direction D ZD
or
ZD
Distance from the true position of the outer-most terminal to the package edge
Overhang in body direction E ZE
or
ZE
Distance from the true position of the outer-most terminal to the package edge